In The Sports Gene, science and sports journalist David Epstein makes a science-based argument against the popular idea that enough practice can guarantee success in sports. As he argues in the book, practice cannot make you great at a sport unless you have the “right” genes to go with it. Epstein uses data to argue that some people are genetically hardwired to be better at certain sports than others, and he explores the complex interplay among genes, environment, culture, and training that produce the world’s greatest athletes.
In this guide, we have focused on Epstein’s four main themes:
The thesis of The Sports Gene is that our genes determine our potential in sports. In making this claim, Epstein offers a counterargument to the emphasis our culture places on hard work and determination. The media popularized the idea that enough practice can guarantee success; in particular, Malcolm Gladwell’s bestselling book Outliers, in which he coined the term “the 10,000-hour rule.” This “rule” claims that 10,000 hours is the amount of practice it takes to become an expert in a given field. Were the rule valid, it would mean that practicing any sport for 10,000 hours would be a virtual guarantee of success at the elite level.
Early Specialization in Sports
The attitude that more practice is better is common in American culture. As a result, parents encourage their children to specialize in sports from an early age. While this may work for some athletes (Tiger Woods would be a top-of-mind example for many people as he was hitting golf balls by 11 months old), research has shown that early specialization is not only unnecessary but potentially harmful in most sports.
A literature review of studies involving specialization in sports noted that early specialization carried risks of physical injuries, burnout, and psychological stress. The study concluded that, for most sports, waiting until late adolescence to focus on a single sport was the best strategy.
Interestingly, Tiger Woods (as noted in chapter 3 of The Sports Gene) maintains that he was never pushed to practice golf but was always the one asking to play.
As Epstein explains, practice does matter, but its power and potential vary by individual. He shares research findings to illustrate this point.
These findings highlight why the 10,000 hours rule should not be a guide for how much to practice. As Epstein explains, there are many more factors involved in success than hours logged.
A Meta-Analysis of Practice and Sports
A 2016 study called “The Relationship Between Deliberate Practice and Performance in Sports: A Meta-Analysis” (which included studies on endurance sports and weight lifting as well as games such as chess and darts) found that 18% percent of the difference in athletes’ performance could be explained by practice. While that may seem like a low number at first, 18% percent is a huge difference in sports. For example, the world record in the mile run is 3 minutes and 43 seconds. Eighteen percent slower (4 minutes 23 seconds) would be blown away by talented high school runners. The same study found that at the highest level, deliberate practice (practice aimed at improvement rather than enjoyment) explained just 1% percent of the difference in performance, a powerful testament to innate ability.
Even though practice is not equally effective for everyone, Epstein notes that it is still a vital piece of sports success. So, rather than focusing on the way practice impacts an athlete's strength, endurance, and physical skills, he focuses on the ways that practice gives elite athletes a mental edge.
Epstein explains that practice allows elite athletes to build a sophisticated mental model of their sport. The more time an athlete has spent practicing, the more extensive their mental database of sport-specific knowledge and the better they can quickly and accurately make sense of what they see on the field. Epstein cites studies showing that elite chess players, field hockey players, and basketball players can accurately recreate the setup of an entire board or field after looking at a photo for just a few seconds. This increased processing speed allows athletes to make better decisions during play.
Evidence of Improved Data Processing in Athletes
An article from Grantland shows that the brains of professional basketball players were better than basketball coaches and non-players at predicting whether the ball would go into the hoop while watching short video clips of a person shooting free throws. These findings support Epstein’s discussion of practice building mental models.
Even more intriguing was that the neurons of the non-players showed “generalized” activity, while the neurons of the professional players and coaches showed increased activity in areas of the brain associated with taking a shot. Only the professional players showed increased firing of neurons associated with hand muscles (specifically the muscles in their pinkie fingers). This last result suggests that the players have a sophisticated mental model of how taking a good shot feels.
No amount of practice can change that certain body types have a natural advantage in certain sports. Epstein gives several sport-specific examples of advantageous physical traits, including the difference in body proportions between elite runners and elite swimmers.
Sprinters have longer legs than the general population proportionally. Epstein cites a study that found that male sprinters were on average two inches taller than the average man, but all of the height difference came from having longer legs. Hurdlers and high jumpers also benefit from having long legs because a higher center of gravity means producing less vertical force with each jump.
Body Mass Index and Running Speed
In addition to leg length and height, one study found that elite runners’ body mass index (BMI) varied predictably according to their event. The study found that athletes became lighter and smaller as race distances increased, while sprinters benefitted from being taller and heavier.
Sprinters need muscle mass to generate enough power to cover short distances quickly. They use their mass to apply enough force to the ground with each step so that their muscles can rebound and propel them forward. If they were to sacrifice too much mass, they would lose their power and explosive speed. In contrast, distance runners do not need to be as explosively powerful as sprinters and benefit from being lighter. Being lean means that it takes less energy to propel their bodies forward. In addition, the forces of gravity and wind resistance decrease with decreased mass, and ground reaction forces are smaller for lighter runners, meaning their bodies don’t have to absorb so much energy from the shock of each step.
While long legs are an advantage in some running events, having a proportionally longer torso is advantageous in swimming. Epstein cites a study of Olympic athletes showing that male swimmers were 1.5 inches taller on average than Olympic sprinters, but the swimmers’ legs were half an inch shorter. All of the extra height was in their torso. Long torsos mean more surface area gliding through the water, which helps swimmers move at high speeds.
Michael Phelps: The Ideal Body Type for Swimming
Michael Phelps has been highlighted as the model of the ideal swimming physique. He has won more Olympic medals (28 Olympic medals, 23 gold) than any athlete in history and has set 39 world records. He is tall (6 feet 4 inches), with a large wingspan (6 feet 7 inches), and a long torso (his torso would fit someone who is 6 feet 8 inches). In addition to providing a larger surface area to glide through the water, long torsos benefit swimmers by putting their center of mass closer to their lungs, which is their center of flotation. Having their center of mass near their center of flotation allows athletes to float horizontally in the water more efficiently.
Some traits are less evident than height and torso length. For example, Epstein cites research showing that Kenyan distance runners’ calves were an average of 15-17% less thick than those of a control population. This difference translates to nearly a whole pound of mass per calf that Kenyan runners do not have to move, saving them 8% of their energy each kilometer compared to their peers. Thus, slight calves may help explain a piece of why Kenyan runners dominate the marathon.
(Shortform note: It takes more energy to move “extra” weight in the legs farther from the hips, which is why companies that make running shoes put so much effort and advertising into making the lightest shoes possible.)
Our body type and proportions are a product of our genes, but which gene(s) is hard to say. Epstein explains that almost all of our traits, even ones as seemingly straightforward as height, are determined by multiple genes. Advances in genetic research (notably the 2003 completion of the Human Genome Project, which successfully mapped the roughly 20,000 genes encoded in our DNA) have allowed researchers to hone in on some specific genes and how they relate to sports performance. Epstein highlights several of them in the book.
We All Have the Same Genes
There is a common misconception that people are different from each other because we all have different genes. If this were true, there could indeed be a “sports gene” that people simply would or would not have. However, the reality is that all people on Earth are over 99% genetically identical to one another.
When we say we have the “gene” for something, we are referring to alleles. (Epstein uses the term variant rather than allele.) Alleles are different versions of a gene that lead to differences in the way that gene is expressed. Even though they represent well under 1% of our DNA, different alleles account for the huge diversity we see in the human race. For example, we all have the ABO gene that determines our blood type. But there are different versions of the gene (alleles) that result in different blood types among people. Instead of saying that an athlete has the “right gene” for their sport, it is more accurate to say that they have the right version of a gene, or allele, for their sport.
Epstein uses studies highlighting people’s varying responses to exercise programs to illustrate the power of genes in shaping athletic careers. He discusses two studies that followed groups of people participating in cardiovascular fitness and strength-building exercise programs. The results showed that people’s genetic differences cause them to respond differently to training. Results from the cardiovascular exercise program showed that:
As Epstein explains, these results make it clear that there is a strong genetic component to how people’s bodies respond to cardiovascular training. The researchers were able to find 21 alleles (versions of a gene) that accounted for the diversity in responses to cardio training. Results from the strength training program were similar:
Along with these results, researchers again found that those who responded the most to the training program had pre-existing genetic differences from those who did not. Epstein explains that the participants who gained 50% more muscle had more active IFG-IEa, MGF, and Myogenin genes than those who did not respond to exercise.
Epstein suggests that elite athletes likely fall into the category of people whose bodies elicit a greater response to exercise and whose genes give them a naturally more athletic starting point.
There Are Benefits to Exercise Outside of Sports Performance
There is still reason to exercise even for people who do not see performance gains despite training. Epstein notes improvements in blood pressure, cholesterol, and insulin sensitivity as benefits of aerobic training outside of sports. There are also cognitive, social, and emotional benefits to exercise for athletes and nonathletes alike. An article from the University of California, Berkely outlines several benefits of exercise that have less to do with performance on the field and more to do with overall well-being. They include:
Greater happiness and overall satisfaction
Less loneliness and a lower risk of depression
A greater sense of purpose and more feelings of love, gratitude, and hope
As the article explains, this is because exercise has a powerful effect on our brains, even if we don’t see any gains in our muscles.
While researchers have only been able to identify groups of genes that influence some elements of our physiology (as seen in the examples above), the relationship between some specific genes and athletic performance is more apparent. Epstein highlights some of these genes in the book.
ACTN3 Gene: Our ratio of fast- to slow-twitch muscle fibers can determine our success in some sports. Epstein discusses two versions of the ACTN3 gene, which codes for a protein found in fast-twitch muscle fibers: the “R variant” and the “X” variant. While scientists do not know how this happens, there is a strong correlation between the R variant and sprinting speed. Tests on athletes from around the world have revealed that the X genotype is almost nowhere to be found in elite sprinters.
The SRY Gene: Epstein uses the performance difference between men and women to emphasize his assertion that genes matter in sports. Epstein explains that the Sex Determining Region Y (SRY) gene accounts for most sexual variation between men and women. It is on the Y chromosome (women have two X chromosomes). The SRY gene causes the formation of testicles, which release the testosterone that produces male characteristics in developing fetuses. Epstein credits this gene and the associated higher levels of testosterone in males as the reason male athletes are (on average) bigger, faster, and stronger than female athletes.
Epigenetics: Our environment acts on our genes
An athlete’s performance is a function of both her genes and her environment. Simply knowing the gene (or genes) that codes for a particular trait is just one piece of the puzzle in demystifying human genetics. Our internal and external environments impact the way our genetic code is expressed in the real world.
Chemical compounds and proteins within our cells attach to our genetic code and control the way our DNA is read (and thus which proteins are produced). These ‘DNA attachments’ are referred to as our epigenome. Elements of our epigenome are inherited from our parents, and some are acquired (and change) throughout our lifetime. Much of our epigenome is determined after birth. Our environment and lifestyle can change the expression of our genes. This is often called epigenetics. (The term “epigenome” falls under the epigenetics term.) A well-known example of epigenetics in daily life is the risk of skin cancer from our cells being damaged by UV radiation.
As this article from the National Library of Medicine notes, even if researchers are able to pin down the exact genes for certain athletic traits, unraveling which traits in sports have a purely genetic origin is an impossible task. Athletes will always be the product of genes and environment, or as Epstein calls it, nature and nurture.
Our environment has an impact on our genes. Since our genes play such a large role in our sports performance, Epstein argues that you cannot understand what makes an athlete successful without the context of their environment. He illustrates this point using Kenyan distance runners.
The dominance of Kenyan athletes in distance running events is one of the best-known stereotypes in sports. As Epstein explains, this well of talent mainly comes from one specific tribe within Kenya. Athletes from the Kalenjin tribe represent only 12% of the Kenyan population but 75% of its elite runners. At the time of The Sports Gene’s writing, only 17 men in the United States had ever run a marathon faster than two hours and 10 minutes. But 32 men from the Kalenjin tribe accomplished the same feat in October of 2011.
Epstein’s research suggests that the environment in which Kalenjin runners’ ancestors evolved helps to explain the tribe’s exceptional running ability. The Kalenjin tribe has what anthropologists call a “Nilotic” body type, characterized by long, thin limbs. Evidence from animal and human populations shows that limbs generally become longer and thinner as you move closer to the equator. Epstein explains that this is likely due to the higher temperatures in many low-latitude environments since long limbs create a greater surface area for cooling. During long-distance running events, becoming overheated will not only decrease performance but can be dangerous.
Evolution by Natural Selection Develops Human Traits
Traits that are an advantage on the sports field may also be helpful in survival situations. Evolution by natural selection, the accepted theory of evolution in modern times, posits that traits that boost an organism’s survival and (more importantly) reproductive success will become more common in a population over time.
Advantageous traits are specific to an organism’s environment. For example, while having long, thin limbs may confer a survival advantage near the equator, Epstein notes that populations that evolved in the arctic tend to have short legs (short legs conserve heat just as long legs allow it to dissipate). The traits that help certain athletes succeed in specific sports may have helped their ancestors better survive their natural environments.
Another environmental factor that likely enhances the Kalenjin’s running ability is altitude. Ancestors of the Kalenjin tribe evolved close to sea level but migrated to a higher elevation in recent evolutionary history. Today the Kalenjin live at altitude in the Rift Valley. Epstein presents research suggesting that the body’s initial response to a move to altitude is an increase in the production of hemoglobin.
Hemoglobin is the molecule that carries oxygen in our blood. Producing more hemoglobin is the body’s way of capitalizing on every molecule of available oxygen in the thinner air at altitude and is the reason athletes use altitude training to maximize aerobic capacity. The combination of sea-level ancestry and living and training in the altitude “sweet spot” for hemoglobin production (between 6,000 and 9,000 feet) likely contributes to the Kalenjin tribe’s running prowess.
Sherpas as Superathletes
Epstein reinforces the idea that no single factor, genetic or environmental, can account for an athlete’s success by pointing out that other populations living at altitude are not producing Olympic endurance athletes. Nepal has competed at the Summer Olympics since 1964 but has yet to take home a medal. If simply living or training at altitude could make someone a great endurance athlete, we would expect to see marathoners from Nepal running alongside Kenyan runners.
Natives of Nepal who work on Mount Everest as sherpas are widely regarded as superathletes in their own right. Not only have many of them made the ascent up Everest many times (a feat considered by many as a pinnacle of athletic achievement), but they do so while caring for groups of other climbers and carrying the extra weight of climbing gear on their backs. If mountaineering were to become an Olympic sport, Nepal would surely be raking in the gold medals, and Sherpas would be highlighted as athletes with a genetic makeup perfectly suited to their sport.
An athlete’s genes, practice, and environment all play an important role in her performance. But none of these explains why athletes from certain cultures choose to specialize in specific sporting events. Epstein argues that an athlete’s culture and socioeconomic status can help explain why sport-specific talent (such as the Kenyan marathon phenomenon) tends to cluster in certain areas. He focuses on Kenyan distance running and Jamaican sprinting to highlight this point.
Epstein highlights the following factors as reasons why so many Kenyans choose to pursue a running career:
Coupling these factors with physiology exceptionally well-suited to distance running creates a well-rounded view of why there are so many successful Kalenjin runners.
Kalenjin Runners and Exceptional Mental Toughness
An NPR article highlighting the success of Kalenjin runners offers an additional culturally-based explanation for why Kalenjin runners are so successful. The article proposes that in addition to physiological advantages, athletes from this tribe are conditioned to have an exceptionally high pain tolerance. According to the article, learning to tolerate pain is an important part of growing up in the Kalenjin tribe. The article describes pain ceremonies as a rite of passage where teenagers prove their mental toughness to the rest of the tribe. High pain tolerance is a clear advantage in a sport such as the marathon, where athletes push themselves through discomfort for hours.
Taking culture into account can paint a more well-rounded picture of why Jamaican athletes have such a strong presence in sprinting events.
Talented American Sprinters Choose Other Sports
According to a Gallup poll, the most popular sports (measured by viewership) in the United States are football, basketball, baseball, and soccer, in that order. Less than 0.5% of people chose track and field as their favorite sport to watch. This helps to explain why young American athletes would choose to focus on the four sports listed above instead of focusing on their speed on the track. In fact, in The Sports Gene, Epstein notes that some people worry that the growing popularity of basketball in Jamaica may draw promising athletes away from the track.
In the Afterword of The Sports Gene, Epstein invites us to explore our unique genome by trying new sports and experiencing personal growth and discovery through a training program. As his research findings and stories show, we never know what we may be good at unless we try!
(Shortform note: These invitations convey a tone of optimism and possibility. Our takeaway from The Sports Gene should not be that we don’t have the “right” genes to excel in sports. Instead, the book invites us to explore how our own genes, environment, culture, and training interact. Perhaps the most important takeaway from The Sports Gene is that we should be patient with ourselves and others along our sports journeys. If we are open to trying new things, we will likely find a sport that feels like a “natural” fit. While we may not end up in the Olympics, understanding that our bodies are programmed to have their own strengths and weaknesses can help us identify a sport that we find personally rewarding.)
The Sports Gene explores how our underlying genetic differences impact our performance on the sports field. As the title implies, author David Epstein suggests a strong genetic component to success in sports. However, the book also recognizes that as complex human beings, athletes cannot be defined by genes alone. An athlete’s culture, upbringing, environment, opportunities, and training all play decisive roles in athletic success. As Epstein phrases it, success in sports is always the product of both nature and nurture.
David Epstein has written multiple bestselling books: In addition to The Sports Gene being a New York Times bestseller, he also wrote the 2019 #1 NYT bestselling book Range: Why Generalists Triumph in a Specialized World. He has master’s degrees in environmental science and journalism. Epstein has experience in both the science and sports fields. He has worked as an ecology researcher and as a science reporter for ProPublica. His writing in the science field has received acclaim from the National Academies of Sciences, Engineering, and Medicine. He was a decorated collegiate athlete himself, and he went on to work as a senior science writer for Sports Illustrated.
Connect with David Epstein:
Publisher: The Sports Gene was published by the Penguin Group in 2014.
Sports have been important to human culture throughout history, as the tradition of the Olympic games attests. For as long as sports have entertained us, we have been captivated by athletes. The quest for athletes to become bigger, stronger, and faster is never-ending. Prevailing cultural views (particularly in the United States) favor grit, determination, and practice as the driving forces of improvement in sports. However, scientific advances (particularly in the field of genetics) are shedding light on what makes elite athletes great. The Sports Gene uses modern scientific research to enhance our understanding of human performance.
The Sports Gene is a research-based book. It includes discussions of race and sex from a scientific rather than a cultural perspective. Epstein acknowledges that some of the topics covered may be socially uncomfortable. He even notes that some researchers refrain from sharing their findings when they illuminate a racial divide. However, Epstein maintains that it is a disservice to both science and society to avoid discussing research findings for the sake of social comfort.
The Sports Gene contributes to the perennial nature vs. nurture debate by counterbalancing a widespread cultural belief that nurture (practice) can always trump nature. It stands as a challenge to assertions made about the power of practice in Malcolm Gladwell’s best-selling book Outliers. As a testament to the strength of Epstein's arguments, even Gladwell called The Sports Gene “fascinating” and “educational.”
The Sports Gene has received widespread acclaim and, as Epstein notes, was purchased by both President Barack Obama and former Secretary of State Condolezza Rice. A review in The Washington Post calls it “fascinating,” and one in The Guardian calls it “dazzling” and “illuminating.”
The Sports Gene argues that genes have a determining effect on sports performance by discussing findings from scientific research, explaining important biology concepts, highlighting results from athletic competitions, conducting interviews with athletes and researchers, and presenting individual stories as case studies. The combination of modalities gives the audience a well-rounded perspective on Epstein’s ideas. Some critics note that the book becomes dense and loses some of its flow during technical, scientific explanations. While this may be true, readers who persevere through the more technical sections will come away with a better understanding not just of genetics and sports but of human physiology in general.
Each chapter covers a general theme. However, Epstein frequently bounces from one idea to another within the chapters, often introducing an idea in one chapter and then referring back to it or presenting evidence in another. Epstein also varies his style from chapter to chapter, with some chapters being full of technical, scientific content and research findings. In contrast, others have a more narrative style and focus mainly on the story of a single person or group.
As a general flow, Epstein begins by explaining why the idea that practice alone can determine success in sports is flawed. He then presents evidence on specific genes and their impact on sports performance to support this claim. In later chapters, he applies these principles to explain why certain groups of people (specifically Kenyan and Jamaican runners) excel in certain sports.
To streamline Epstein’s argument and avoid repetition, we have reorganized the content by Epstein’s major themes. For brevity, we have left out much of the narrative Epstein includes about specific people and the stories of their lives and work, instead pulling the main takeaways from these stories.
In The Sports Gene, a New York Times bestseller published in 2013, science and sports writer David Epstein makes an evidence-based argument against the popular idea that enough practice can guarantee success in sports. Rather, he argues, some people are genetically hardwired to be better at certain sports than others. His research covers the complex interplay among genes, environment, culture, and training, and he paints a well-rounded picture of why elite athletes excel in their field.
The idea that anyone can become an expert in anything if they practice enough is ingrained in popular culture. In the perennial nature vs. nurture debate, the idea that nurture (practice) can overcome nature (innate ability) has obvious appeal, especially in sports. The Sports Gene takes a scientific approach to this assertion and has a decisive rebuttal: Practice is not an equalizer in sports, and hours of hard work are no substitute for innate ability. Instead, the combination of innate ability (that comes from genes) and practice creates elite athletes. Part 1 will explore Epstein’s research on practice and sports performance by:
Meritocracy in Society and Sports
We like to think that the athletes who work the hardest are the ones who will succeed. Meritocracy is a social belief system that sees success (particularly wealth and power) as the outcome of skill and hard work. This idea is popular worldwide, but it is most popular in the UK and US, where most people believe that hard work is more important than luck or heredity. While this idea has obvious appeal, some argue that it is dangerous and unhealthy for society and individuals.
Believing that people end up in the social standing that they “deserve” can make people behave more selfishly, make them less likely to critique their behavior, and can even be used to justify discrimination (in part because it conveniently explains away present circumstances). In contrast, acknowledging the importance of luck can make people behave more generously.
Since meritocratic views are so prevalent in popular culture, it makes sense that they are also popular in sports. We love the story of the gritty underdog making it to the top. But failure to recognize differences in innate ability (genes) can lead people to believe that they are simply not working hard enough when they don’t meet their goals. The reality may be that no amount of hard work will propel them past athletes whose natural abilities are better suited to their sport. It is easy to see how meritocracy could be a particularly detrimental idea in youth sports as children are forming their beliefs about themselves and building their self-esteem.
The phrase “the 10,000-hour rule” has become a popular way to express the idea that enough practice is a virtual guarantee of expertise. It epitomizes the idea that practice (nurture) can overcome nature (innate ability). The phrase is based on a 1993 study entitled The Role of Deliberate Practice in the Acquisition of Expert Performance, which examined the number of hours violin players at a prestigious music academy practiced. The study found that:
(Shortform note: For the rest of the summary, we will refer to The Role of Deliberate Practice in the Acquisition of Expert Performance study as “The 10,000-hours study.”)
Practice vs. Deliberate Practice
Not all practice is equally productive. The authors of the 10,000-hours study use the term “deliberate practice” instead of “practice” to reinforce this idea. Deliberate practice is time put aside to improve one’s skills. By definition, it is structured and requires effort and engagement. It also requires attention to strategies that best suit an individual’s learning style or needs.
The authors make it a point to note that deliberate practice is not necessarily enjoyable. Simply participating in a sport or activity does not necessarily count toward hours of “deliberate practice.” The seemingly endless drills run during sports practice (often not inherently enjoyable) are an example of deliberate practice (if players are actively engaged).
While well-known and heavily referenced, we should be cautious when applying findings from the 10,000-hours study to other disciplines and situations. The study has been cited by other researchers more than 12,000 times, and it has become one of the most well-known studies in the field of psychology. However, Epstein notes that it has significant limitations that are unfortunately overlooked in popular interpretation. Some of these include:
The authors of the 10,000-hours study did not use the phrase “the 10,000-hour rule,” nor did they propose 10,000 hours as a guarantee of expertise. Epstein notes that the catchy term was a product of the media reporting on the study. It was pushed further into the mainstream by Malcolm Gladwell’s bestselling book Outliers (where he coins the term “the 10,000-hour rule” and asserts that the ability and luxury to dedicate thousands of hours to practice is what truly sets elites in their fields apart). The lead author of the study himself has stated that the phrase the “10,000-hour rule” misconstrues the study’s findings.
Follow-up Research Does Not Support the Study’s Findings
A 2019 study sought to replicate the findings of the original 10,000-hours study while addressing gaps in experimental design. Similar to the original study, the researchers found that a large amount of the difference in violinists' performance was explained by practice. However, the follow-up study found that practice had less of a determining effect on overall skill level than the original study. In fact, the newer study found that the “best” violinists had practiced for fewer hours (on average) than the “good” violin players by the time they were 18.
The popularity of the “10,000-hour rule” phrase has conferred a disproportionate emphasis on practice as the defining variable in success. Findings from several other research studies support a more well-rounded view of the power of practice. For some, practice provides the medium for innate (genetic) ability to flourish. Given the same amount of practice, others may have a more difficult time learning a particular skill. Next, we will look at evidence that Epstein has collected from sports and beyond that suggests each of us responds to practice and learns skills to varying degrees and in varying timeframes.
Education researchers have been studying the effects of practice for decades. In the early 1900s, Edward Thorndike (who Epstein notes is considered to be the founder of educational psychology) studied adults who were given the opportunity to practice a task. He found that:
A Different Perspective on The Matthew Effect
The Matthew effect shows how underlying differences between people (differences that come from our genes and experiences) lead to both different starting points and different results when learning a skill. It helps to explain why the 10,000-hour “rule” cannot be applied broadly. If we all learn at different rates and have different starting points, then a set number of hours cannot account for individual differences.
When viewed from a different perspective, however, The Matthew Effect can also be used to support the 10,000-hour rule. In that case, the logic could look like this: Those young athletes who showed more promise at the start of their athletic careers, in gym class, for instance, were recruited onto teams younger and received more attention from coaches. By the start of high school, their head start amounted to hundreds of more and or better hours of practice than their peers with a “lower” starting point.
The Matthew Effect is also a common concern in early literacy. Educators stress the importance of building literacy early in the hopes of avoiding gaps in academic performance from delayed reading skills. The idea is that the students who have early access to and an early affinity for reading will learn to read younger. Since they are able and (presumably) enjoy reading, they will read more often and build their literacy skills further. By the time students are reading for content knowledge in school (as opposed to for enjoyment), the early readers will have a clear academic advantage.
Thorndike’s assertion that people respond differently to practice has been born out countless times on the sports field and beyond and has been substantiated by several studies. Epstein gives these examples:
The “85% Rule” for Learning
While we all learn new skills differently, there does seem to be a “sweet spot” when it comes to learning something new. Things that are “too easy” can quickly become boring. Things that are too difficult can cause us to abandon our learning and become disheartened. An article in the journal Nature used computer programs to determine that the “sweet spot” for learning a new skill is to be successful 85% of the time and fail 15% of the time. While the study measured computer learning, the authors suggest that the results can also be applied to human learning. Optimizing the success-to-failure ratio does not eliminate underlying differences in ability, but it could help us optimize our individual pace of learning.
The article does not discuss an extension to sports, but it would make sense that athletes should neither feel under-challenged nor overly discouraged when training for their sport.
Epstein uses the story of two elite high jumpers to illustrate how athletes can reach the highest level of their sport with startlingly different amounts of practice.
Stefan Holm won an Olympic gold medal in the high jump in 2004. He was a paragon of dedication to his craft. He completed twelve workouts per week, moved to live next to his training facility, and dedicated his life to the high jump for 20 years.
At the 2007 World Championships, Holm was beaten by Donald Thomas, who had taken up high jump eight months prior on a friendly bet with his friend. Thomas was known for skipping practice and admitting that he found the high jump boring compared to his passion (basketball). Moreover, Thomas’ technique was so different from other jumpers as to be comical. Still, his long legs and his abnormally long Achilles tendon (which acts like a spring when jumping) seem to have conferred an innate high jump ability that all of Holm’s practice couldn’t best.
As Epstein notes, Thomas’s career clearly does not support the idea of the 10,000-hours rule in multiple ways. He was successful from the very beginning of his career (which he started “late”). Additionally, his 2007 World Championships-winning jump is the highest in Thomas’ career to date at 7 feet 8 inches. He has gone on to win several other elite competitions and has competed in three Olympic games. But he has never jumped as high as he did that day in 2007, despite, presumably, many more hours of practice.
Non-Sport Specific Practice Matters
Thomas may not have had much training before becoming a world champion high jumper, but that does not mean he did not have any relevant practice. Thomas was already an athlete before trying his hand at the high jump. Epstein shares that Thomas’s athletic passion was basketball, a sport where jumping high is a clear advantage. Presumably, Thomas already knew that he was a good jumper, or he wouldn’t have made the friendly bet that launched his high jump career. A more nuanced view may be that he transferred his athletic skills from basketball to the high jump with startling results.
As evidenced by Donald Thomas’ high jump success, naturally gifted athletes can frequently rise to the elite level of their sport with far less practice than their peers. This calls into question the strategy of amassing as many sport-specific practice hours as possible.
In a study of athletes in “cgs” sports (“centimeters, grams, and seconds” sports such as rowing, jumping, and weight lifting), the elite athletes actually logged fewer hours of training than their peers until their late teenage years. Epstein notes that this could be because their natural athletic ability allowed them to “coast” until then. Another study on sprinters showed that starting intense training too young could hinder long-term success because athletes reach a “speed plateau” that they cannot train past.
Early Specialization in Sports
As we have seen, the attitude that more practice is better is very common in American culture. As a result, parents are increasingly encouraging their children to specialize in sports from a very early age.
While early specialization may work for some athletes (Tiger Woods would be a top-of-mind example for many people as he was hitting golf balls by 11 months old), research has shown that early specialization is not only unnecessary but potentially harmful in most sports. A literature review of studies involving specialization in sports noted that early specialization carried risks of physical injuries, burnout, and psychological stress. The study concluded that, for most sports, waiting until late adolescence to focus on a single sport was the best strategy.
Interestingly, Tiger Woods (as noted in Chapter Three of The Sports Gene) maintains that he was never pushed to practice golf but was always the one asking to play. His seems to be a fortuitous case of early passion, the opportunity for early practice, and success.
In Australia, later specialization in a specific sport is part of the strategy for identifying athletes who will compete on the world stage. Coaches and recruiters have found success searching for athletes (like Thomas) who are ‘natural fits’ in specific sports regardless of their experience. This involves switching some athletes out of their current sports and assigning them to new ones (called “talent transfer”). As Australia took home ten times more medals per citizen than the United States in Sydney, the strategy seems to work. Epstein uses the following examples of Australian athletes to highlight talent transfer:
Accessibility of Sports
Without a doubt, Alisa Camplin, Michelle Steele, and Melissa Hoar are incredible athletes, and their success stories are evidence of natural ability being just as, if not more important than, years of training even at an elite level. However, the relative obscurity of the aerial skiing and skeleton events is worth noting. There are plenty of examples of naturally gifted athletes rocketing to the top of their field across the sports world. But the popularity and accessibility of the sport in question certainly have an impact on the chances of success.
Some sports are clearly more accessible than others. For a high school to have a rowing program, for example, athletes need access to a safe and navigable body of water, transportation to the water, a huge amount of expensive equipment, and a well-equipped coaching staff to keep athletes safe. For snowsports, accessibility is even more limited; by equipment, geography, transportation, seasonality, cost, and so on.
Athletes who rocket to the top of less accessible sports have the advantage of a much smaller pool of competitors. Here is a graphic showing the chances of high school athletes making it to the summer Olympics by sport. It estimates the chance of a high school female basketball player (a popular and accessible sport) making it to the Olympics to be approximately one in 45,500. The chance of becoming an Olympian in equestrian events (far less accessible) is estimated to be one in 198.
While research may indicate that early training is not a prerequisite for success in many sports, there are also arguments for training at a young age. Epstein offers the concept of neuron pruning as a possible counterargument to late specialization. Neuron pruning refers to the idea that humans are born with an abundance of neurons that are selectively “pruned” based on what our brains focus on. This is a “use it or lose it” view of neurons and our opportunity to prime our brain for certain skills.
Epstein cites a study suggesting that if children did not take up serious chess by 12, they were much less likely to become an international grandmaster. One explanation may be that children who started “late” missed the opportunity to strengthen the connections needed to play chess at the elite level, and critical neurons were pruned.
(Shortform note: According to an article from the National Academy of Sciences, infants have 100 billion neurons at birth, which continue to form rapidly until the age of two. At this age, they may have double the neurons that adults will have. The article notes that, in a sense, infants are born with brains that are “ready” to adapt to various circumstances. As we age and learn, the connections that become the most relevant to our lives and environments get stronger, and those that we do not use are “pruned.”)
Knowing that there isn’t a direct correlation between practice time and mastery can help us to be more patient with ourselves (and others) when we struggle to learn a new skill, and more humble when we are able to master a new skill quickly.
What is a skill that you have tried to pick up recently, but have found frustrating to learn?
Taking a mental inventory of your strengths, weaknesses, and related experience—what are some factors that you think make this skill more difficult for you?
Now think of a skill that you have recently learned that seemed to come more naturally.
Taking a mental inventory of your strengths, weaknesses, and related experience—what are some factors that you think helped you pick up this skill?
We have reviewed theories and evidence for why practice alone cannot determine outcomes in sports. In this section, we will look at how Epstein highlights practice as a way for naturally gifted athletes to develop their skills.
By the time they reach the elite level, Epstein notes that most athletes have spent so much time playing and practicing that they know their sport backward and forward. Because they know the sport so well, elite athletes can make sense of the information they see on the field more quickly than the average player. Studies have shown that experts’ eyes move faster through visual information from their field of expertise than the average persons’.
This is not because every professional chess, volleyball, and baseball player has a photographic memory. In fact, when chess pieces were set up randomly, the elite players’ ability to recreate the board was no better than anyone else’s. It is because rather than trying to memorize individual pieces of information, experts focus on the relationships between those pieces to make their next move. This strategy is called “chunking.” By breaking the information into meaningful chunks, and having enough experience to know how chunks fit together, athletes are able to predict what is coming next and react accordingly.
“Mirror Neurons”
An article from Grantland shows how the brains of experienced athletes process information differently than the brains of novices. It describes a study testing “mirror neuron” activity (neurons that fire when we see someone perform a familiar action) in professional basketball players, basketball coaches and journalists (“experienced watchers”), and people who had never played the game. The three groups watched video clips of people shooting free throws. The video was stopped several times throughout the shot, and the participants made a prediction about whether the ball would go into the hoop. The results showed that:
The players made the most accurate predictions overall.
The difference in frequency of players’ correct predictions versus correct predictions from the other groups was greatest when the video was stopped before the shooter’s hands released the ball.
These results support Epstein’s discussion of practice building mental models. The player’s mental model of what a successful shot should look like allowed them to make more accurate predictions. Even more intriguing: only the professional players showed increased firing of neurons associated with hand muscles (specifically the muscles in their pinkie fingers). This response was greatest when they watched missed shots, suggesting that the players were unconsciously trying to correct the technique they were watching on the screen.
Epstein explains that the reaction times of elite athletes are about the same as the rest of the population. But at the elite level, most sports are played fast. In a sense, elite athletes can predict the future when it comes to their sport because they can read the field well enough to anticipate what is coming next. The more experience (practice) an athlete has, the more extensive their mental database of sport-specific knowledge, and the more meaning they can quickly make from what they see. As Epstein notes, this sport-specific wisdom cannot be replaced by raw athleticism.
Epstein illustrates the idea of natural ability needing the wisdom of practice with Jennie Finch’s (Olympic gold medalist in softball) ability to strike out Barry Bonds, Albert Pujols, and other famous MLB players with her softball pitches. Even though her pitches are slower and thrown closer to home plate than baseball pitches, the difference between a baseball pitch and a softball pitch is enough to stump even the best baseball players. Her pitches are not part of baseball players’ mental databases. They cannot forecast how her pitches will travel, and their athleticism does not stop them from striking out.
What About “Straightforward” Sports?
Epstein discusses practice in sports in general terms, but sports have vastly different levels of complexity, physicality, and strategy. Football can be likened to a game of chess much more readily than running can. Not only do football players have to train their bodies, but they need to learn all of the rules and study the strategy of their game. Not to mention, on game day, football players have another team of equally well-trained players trying to stop them from doing the exact thing they are trained to do. On the other hand, the marathon is a much more straightforward event (not to say that there is no strategy involved).
Adding a ball to a sport adds a level of complexity and unpredictability. Playing on a team also adds confounding elements of anticipation, awareness, and collaboration not found in endurance sports. Sports like rowing and cycling are complex in their own right, but athletes in these sports are able to focus on their technique without many of the variables present in “ball sports.” Sports like weightlifting are even more straightforward, with each athlete having their own equipment, space, and time to execute their craft.
The complexity of a sport adds another layer to the debate around the 10,000-hour rule. Perhaps, in certain sports, the amount of time spent thinking about and studying the sport does have more impact on eventual success than in others. After all, the study which originally sparked the 10,000- hour-rule debate was based on musicians, a largely cerebral discipline.
As Epstein notes, athletes are building and utilizing their sport-specific wisdom largely unconsciously. In fact, at an elite level, thinking too much during play can hinder an athlete’s performance (a phenomenon widely known as paralysis by analysis). With enough practice, sport-specific wisdom becomes so ingrained that elite athletes’ brain activity shifts from the frontal lobe (the area of more conscious thought) back towards the more “automated” sections of the brain when they are playing their sport.
The Hierarchy of Competence
Elite athletes become so competent in their sport that they can perform the skills involved with little conscious thought. This expertise is often called “unconscious competence,” and is part of a learning trajectory model known as The Hierarchy of Competence. Noel Burch developed the model in the 1970s to track progression when learning a new skill.
In the model, we start in the “unconscious incompetence” zone in which we do not even realize that we do not know how to perform the skill. We can think of this as the naive or ignorant zone.
As we learn, we move into the “conscious incompetence” zone, where we realize that we have a lot to learn.
As we start to pick up the skill, we become “consciously competent.” We can perform the skill, but we still have to think about it. A novice playing a sport would likely be in the conscious competence zone.
As we master the skill we move into the “unconscious competence” zone, where we can perform the task without even thinking.
We have all had the experience of letting our minds wander while we do something else. For example: trying to plan your weekend while out for a run, talking on the phone while cooking dinner, or even (not advisably) letting our minds wander while driving. We can do this because we are unconsciously competent at many tasks in our lives. For elite athletes who have amassed hours of practice, their sport becomes one of these automated tasks.
Epstein gives a powerful example of the interplay between practice and talent by citing a longitudinal study following German tennis players throughout their careers.
In 1978, the German Tennis Federation tracked over 100 eight-to-12-year-old tennis players. They wanted to predict which kids might become elite players later in their careers. The study looked at tennis-specific skills and general athleticism. Epstein highlights the following results:
The lesson of these results is that both practice (the tennis-specific skills) and innate ability (general athleticism) were integral to the future elite tennis players’ success. As the Matthew Effect predicts, the already gifted natural athletes benefited from the tennis-specific practice and reached the top of their sport.
A Meta-Analysis of Deliberate Practice and Sports
The results of the tennis study discussed above are supported by several other studies of practice and success in sports. A 2016 study called “The Relationship Between Deliberate Practice and Performance in Sports: A Meta-Analysis” found that 18% of the difference in athletes’ performance could be explained by deliberate practice. While that may seem like a low number at first, 18% is a huge difference in sports. The world record in the mile run is three minutes and 43 seconds. Eighteen percent slower (four minutes 23 seconds) would be blown away by talented high school runners. The same study found that at the highest level, deliberate practice explained just 1% of the difference in performance—a powerful testament to innate ability.
We have seen that 10,000 hours of practice is not a magic number when mastering a new skill. But chances are there are several skills we have spent so much time on that we can do them well without even thinking. Sometimes we may not even realize that we have “mastered” a skill.
What is a skill or activity that you feel you are an expert at? What makes you feel you’re an expert?
When you picture yourself doing that activity, how would you describe your thought process? (Do you have to think hard about what you are doing? Do you do periodic mental check-ins to make sure you are on point? Can you do this activity without even thinking, maybe even while multitasking?)
How long have you been working on this skill? (You don’t need a specific number of hours, but think about how much you have practiced and for how long.)
Given your answer above, do you feel like this is an activity you are naturally good at, something you have worked very hard to be good at, or a combination of both?
Are there any aspects of how you either learned or currently perform this task that you can apply to another task that you find more challenging?
We have examined the relationship between practice and expertise, and we have reviewed evidence for why practice alone cannot guarantee success in sports. We have seen that the combination of practice and innate ability (or talent) creates elite athletes. Next, we will look at where this innate ability comes from.
Different sports place different demands on the human body. Sprinters need to be fast. Soccer players need to be coordinated. Most people’s mental model of a female gymnast would be of someone small in stature, while our mental model of a basketball player is likely tall. We are all born with a unique body type. We can train our bodies to be the best they can be at a sport, but no amount of training can change the fact that another athlete’s body may be a better fit.
Epstein notes that as sports become more competitive, athletes often start to look more and more similar to each other in regard to certain traits. At the most elite level, athletes competing in the same event often share remarkably similar body types. In the next section, we will:
We All Have the Same Genes
There is a common misconception that people are different from each other because we all have different genes. If this were true, there could indeed be a “sports gene” that people simply would or would not have. The reality is that all people on Earth are over 99% genetically identical to one another. This may come as a surprise, as we look, sound, and act so differently from each other. It also runs counter to the way that many people speak about genetics. People will often use phrases like “she has the gene for freckles” or, sadly, “she has the cancer gene.”
When we say we have the “gene” for something, we are really referring to alleles. Alleles are different versions of a gene that lead to differences in the way that gene is expressed. Even though they account for well under one percent of our DNA, different alleles account for the huge diversity we see in the human race. For example, we all have the ABO gene, which determines our blood type, but different versions of the gene (alleles) result in different blood types between people.
What we can see and observe about each other; our physical traits, our behavior, and our development is called our phenotype (this includes things like blood type, hormone levels, etc). Our phenotype is produced by the combination of our genes and our environment. When we discuss the huge diversity among athletes, we are talking about different phenotypes. (Check out Shortform’s summary of The Selfish Gene for a more in-depth discussion about how our genes influence everything about us, from our hair color to our aggressive or altruistic behaviors.)
Epstein notes that athletes competing in the same event at the elite level often look strikingly similar to each other. Though they may come from different corners of the globe, they often look more like each other than many siblings do in terms of body type and proportions. This is because physical features provide sport-specific advantages. The more competitive sports become, the more difficult it becomes to excel without those specific traits.
(Shortform note: This is not to say that anything is impossible. Muggsy Bogues is famous for playing 14 seasons in the NBA at only 5 feet 3 inches.)
Next, we will explore some of the traits that Epstein highlights as being shared by athletes in the same sport and discuss how these traits provide a sport-specific advantage.
Basketball players in the NBA are generally much taller than the average man. Only 5% of men in the US are taller than 6 feet 3 inches. The average height of an NBA player is 6 feet 7 inches. Height is a clear advantage in basketball. It puts you nearer the hoop for both shooting and rebounding and allows you to block shots more effectively while being harder to block.
A man’s chances of playing professional basketball correlate strongly with his height.
In addition to height, having long arms is an advantage in basketball. Basketball players generally have a very large wingspan, far outside the norm for the general population. Epstein explains that arm span is a pretty good approximation of height for most of us. (For context, an arm span to height ratio greater than 1.05 is abnormal and can be a sign of a disorder called Marfan syndrome, characterized by elongated arms and legs). The average ratio for NBA players is 1.063. This means that a 6 feet 7 inches tall player can have arms that would fit a seven-foot frame.
Epstein notes that a large wingspan is an advantage in basketball, especially when blocking shots. “Shorter” players usually have an even greater wingspan to height ratio than their taller teammates, which balances out their lack of height.
Advantageous Traits in Sports May Not Be an Advantage Off the Court
Multiple studies from both human and animal populations have shown that smaller individuals live longer than larger ones. A study of nearly 4,000 basketball players showed a correlation between height and mortality, with the tallest players dying younger than the shortest players.
Science has not unraveled the mechanism by which height seems to shorten lifespans. As the study on basketball players explains, one idea is that taller and larger people simply have more mass to maintain into old age. Bigger bodies have more cells, which means that their bodies constantly need to generate more new cells. As we age, our body’s ability to generate new cells decreases. This means that larger bodies are at a greater risk of disease in old age because they are less able to replace diseased and damaged cells.
While basketball players’ height is a genetic attribute (although our environment does influence our height to some degree), some athletes intentionally make themselves larger for sports performance.
Linemen in the NFL need to be large to be effective players. But the weight they maintain or put on for the sake of the game can damage their long-term health. Linemen have hypertension, obesity, and sleep apnea at higher rates than both the general population and other football players. They may also be more at risk for severe heart conditions, particularly after they retire. All of these conditions can have an impact on players’ quality of life, and even their life expectancy, off the field.
One size does not fit all for runners. Epstein explains that different leg lengths, leg proportions, and height have such an impact on performance that runners’ measurements often differ by event. We will look at a few examples.
Female sprinters generally have very narrow hips. While the average woman has wider hips than most men, Epstein explains that female sprinters’ hips tend to be more narrow than the average mans’.
Epstein cites wide hips as a biomechanical disadvantage because it creates a greater angle from the hip to the knee. Energy that could be used for forward motion is lost to compression in the hips.
Are Wide Hips Really a Disadvantage in Running?
The idea that women are less efficient runners because of their hip width stems in part from long-standing ideas about runners’ “Q-angle.” The Q-angle refers to the angle between the quadriceps muscle and the patella. We can think of it as a measure of how well the quad lines up with the knee. A Q-angle can be made larger by having larger hips. Epstein cites wider hips as part of why female runners are more prone to injury than male runners, but this idea is contested in the literature.
One study found that a larger Q angle was not associated with a higher incidence of running injury. An additional research study found that men and women of a similar height had similar Q angles and suggests that the differences seen in Q angles between men and women are explained by differences in average height rather than physiology.
The idea that women’s hip width impacts their running efficiency is a long-standing and, according to a study from Harvard University, often unexamined assumption about female locomotion. The study found that hip width could not predict energy expenditure. The authors cite long-held cultural ideas about female roles in early society (staying closer to home and performing less “athletic” tasks) as a potential reason for the permanence of this idea. But these ideas are flawed. The authors note that our female ancestors likely worked just as physically hard as men and were under evolutionary pressure to be efficient athletes.
Body Mass Index and Running Speed
In addition to leg length, height, and proportions, one study found that elite runners’ body mass index (BMI) varied predictably according to their event. The study found that athletes became lighter and smaller as race distances increased. Sprinters benefited from being taller and heavier, with some variation between athletes. In longer events, there was a more narrow range of measurements that correlated with speed, and the athletes were smaller and leaner.
Sprinters’ muscle mass allows them to apply enough force to the ground with each step so that their muscles can rebound and propel them forward. If they were to sacrifice too much mass, they would lose their power and explosive speed. In contrast, distance runners do not need to be as explosively powerful as sprinters. Being lean means that it takes less energy to propel their bodies forward. In addition, the forces of gravity and wind resistance decrease with decreased mass. Ground reaction forces are also less for lighter runners, meaning their bodies don’t have to absorb so much energy from the shock of each step, translating to less force on their joints.
While there may be performance benefits to being lean in distance running (and other sports), trying to be as lean as possible can be a detriment to both physical and mental health. Excessive calorie restriction can lead to unhealthy relationships with food, poor body image, and even problems with athletes’ metabolism, bone health, immune system function, heart health, and more. Finding the right balance for each athlete’s individual needs is more complex than a single BMI measurement can show.
In a sport where athletes are often airborne and rotating, Epstein explains that the laws of physics make being small in stature an advantage. Watching the opening ceremony of the Olympic games, it is clear how small female gymnasts are compared to other athletes. The average height of a female gymnast is about 4 feet 9 inches, much shorter than the average American woman at 5 feet 4 inches, and certainly much shorter than athletes from other sports.
(Shortform note: Smaller athletes have smaller moments of inertia than larger athletes. This means that it takes less force for them to get their bodies moving into a flip, rotation, or spin than it would take a larger athlete. Larger gymnasts have to generate more force to complete the same movements. Larger athletes also have more mass farther away from their axis of rotation, which means that any rotation will require more force to initiate and will slow down faster (This is why figure skaters spin faster when they pull their arms into their bodies.))
Female gymnasts also have very narrow hips. Epstein cites the benefits of having a small, linear build as a primary reason female gymnasts are generally much younger than other Olympic athletes. Many elite female gymnasts peak in their teens and are considered “old” by the time they reach their twenties. Epstein notes that growth spurts and changes to a young athlete’s figure during puberty can be detrimental to a gymnast’s career.
(Shortform note: A study found that smaller gymnasts who had larger strength to weight ratios were better able to perform whole-body rotation skills than larger athletes. The study also found that as an athlete grew, her ability to perform specific skills (particularly back rotations) was negatively affected, while her ability to perform others was unchanged. (This may be because as athletes grow, they become more powerful, which can be an advantage for specific skills).
Epstein notes that female divers also have narrow hips, presumably for the same reason as gymnasts (their dives are entirely airborne and often include multiple rotations and flips).
Does Gymnastics Stunt Growth?
There is a long-standing belief that the years of intense training during a career in elite gymnastics both stunts athletes’ growth and delays puberty. Research on the topic is mixed but suggests more nuance than the idea that gymnastics “makes” athletes short.
One study found that participating in gymnastics did not affect height or proportions in adulthood. This study also found no measurable ill effects on athletes’ endocrine system and found that the timing of puberty in gymnasts was on the late side of normal. Another study found that gymnastics did not affect leg length but may temporarily stunt “sitting height” (the length from trunk to head). But this change did not last into adulthood.
A third study found that intense training of 18 hours per week did delay both growth and puberty, but that, while delayed, maturation still progressed typically. This study found that the delay was largely a function of energy output during training, with more intense training leading to more growth delays. (One of the main reasons that puberty is delayed is likely that hormones involved in puberty are regulated by fat tissue. Gymnasts train so hard and keep so lean that they don’t have much fat.)
A meta-analysis involving gymnasts’ physiology suggested that it is likely that many young athletes gravitate to and continue to train in gymnastics because they found it to be a good fit for their naturally small body type. While there may be a component of training affecting physiology, the study suggests an element of self-selection that produces teams of smaller athletes.
While the exact interplay of stature and training may remain mysterious, there is also an element of culture that affects gymnasts’ size. The sport of gymnastics has come under intense criticism in recent years for subjecting young athletes to both mentally and physically unhealthy conditions. There is a growing call to shift the culture of the sport away from pushing athletes to peak so young and keep so lean. The new scoring system in gymnastics (which opens the potential for earning higher scores based on the difficulty of the skills performed) is allowing athletes with a less “linear” and more powerful and muscular build to shine, whereas in the past, the lightweight athletes with slim hips had often received higher
In contrast to long legs in running, longer torsos relative to height are an advantage in swimming. Epstein cites a study of Olympic athletes that found that male swimmers were 1.5 inches taller on average than Olympic sprinters, but the swimmers’ legs were half an inch shorter. All of the extra height was in their torso. Long torsos mean more surface area gliding through the water, which helps swimmers move at high speeds. Epstein highlights Michael Phelps, who is 6 feet 4 inches tall but only has a 32-inch inseam, as an example.
(Shortform note: In contrast to running events, one study of Olympic athletes found that the same body type was beneficial across all swimming events. Swimmers did not become leaner with increasing race distances as runners did.)
Michael Phelps: The Ideal Body Type for Swimming
Michael Phelps is an excellent example of the “nature and nurture” model of sports success proposed in The Sports Gene. He has won more Olympic medals (28 Olympic medals, 23 of them gold) than any athlete in history and has set 39 world records. His success is a product of a colossal amount of training and physical and mental effort as well as a body type perfectly suited for his sport.
Michael Phelps has been highlighted as the model of the ideal swimming physique. He is tall (6 feet 4 inches), with a large wingspan (6 feet 7 inches), and a long torso (his torso would fit someone who is 6 feet 8 inches). In addition to providing a larger surface area to glide through the water, long torsos benefit swimmers by putting their center of mass closer to their lungs, which is their center of flotation. This allows athletes to float horizontally in the water more easily.
Michael Phelps also has very flexible joints, which he can hyperextend. Shoulder flexibility allows swimmers to lengthen their strokes by holding onto the water longer while their bodies rotate (freestyle and backstroke) and pressing their chests further into their strokes (breaststroke and butterfly). He also has large hands and feet and very flexible ankles, which allow his feet to act like flippers.
Weight lifters and water polo players share the trait of having disproportionate forearms compared to the general population. Water polo players tend to have long forearms relative to their total arm length. Epstein notes that this allows them to better “whip” the ball during play.
(Shortform note: The length of forearms in ball sports is an example of just how specific different advantageous traits can be in different sports. While a longer forearm may be useful in water polo, the opposite may be true for baseball pitchers. A pitcher’s arm forms a lever that applies force to the ball. Having a shorter forearm means less inertia at the end of the lever and allows the pitcher to release the ball at a higher speed.)
In contrast to water polo players, weight lifters often have relatively short forearms. Just as in throwing a baseball, weightlifters’ arms act as a lever to apply force to the bar. Having a shorter forearm means that the weight does not have to travel as far during lifts. Because of this, Epstein notes that the bench press may be a misleading test when it comes to selecting the most promising football players. A heavy bench press could be aided by short arms, which is not necessarily a desirable trait on the field.
(Shortform note: Short limbs provide a mechanical advantage to lifters by reducing torque as well as the total distance that the weight must be moved. (Torque can be thought of as force around an axis of rotation. The farther away the force is from the axis of rotation, the greater the torque.))
The traits discussed above may be obvious, such as a basketball player’s height, or more subtle, such as a relatively long torso. But all of them are visible to the naked eye. Next, we will look at a few traits that Epstein highlights that are not as readily apparent.
Testimony and measurements from optometrists and ophthalmologists reveals that professional baseball players have eyesight that far exceeds the average person’s.
(Shortform note: When we visit an optometrist or ophthalmologist, we hope that they will tell us that we have “20/20 vision.” This ratio has become a colloquialism for “perfect eyesight.” It means that from 20 feet away, we can clearly and accurately see what we should be able to see from 20 feet away. If we could stand 20 feet away to see what most people see from 10 feet away, then our vision would be 20/10.)
Epstein includes testimony from an ophthalmologist working with major league baseball teams who found that the visual acuity of the average MLB player was 20/11 or 20/12 (Most charts available for the general population only go to 20/15). Half of the players on the Dodgers between 1992 and 1995 had 20/10 vision (the theoretical maximum is thought to be 20/8). As Epstein highlights with two large studies from India and China, this level of visual acuity is very rare.
(Shortform note: While these studies give a sense of how rare the eyesight of professional baseball players is, it is worth noting that India is one of the countries with the highest rates of vision impairment worldwide. There are likely more individuals with exceptional eyesight in other countries.)
Epstein suggests that the general decline in hitters’ statistics around the age of 29 may in part be because visual acuity begins to decline around that same age.
In addition to literal “off the charts” visual acuity, Epstein adds that measures of baseball players’ depth-perception were also far better than average. Fifty-eight percent of MLB players had “excellent” depth perception, compared to 18 percent of the general population. The same trends held true when Olympic softball players were tested. Olympic archers had visual acuity comparable to baseball and softball players, but their depth perception was not as good. Epstein suggests that this is because archers are aiming for a flat, immobile target.
Olympic athletes who have to track a moving ball through the air (baseball and softball players, soccer players, and volleyball players) were all found to have better than average contrast sensitivity. This makes sense as keeping track of the ball is an integral part of the game.
(Shortform note: Advances in eye care, including contact lenses, Lasik surgery, and glasses, may provide some leveling of the playing field for athletes who do not have 20/20 (or better) vision. Novak Djokovic (ranked as the number one tennis player in the world in 2021) wears contact lenses to correct his vision during games. It seems likely that the earlier vision problems are identified and corrected (such as in childhood vision screenings), the greater the chances that athletes with less than perfect vision will have the opportunity to excel. Vision problems that go uncorrected may cause a talented young athlete to either self-select out of or be cut from their favorite sports team.)
An athlete’s ratio of fast to slow-twitch muscles can also provide sport-specific advantages. Epstein explains that most of us have a roughly equal percentage of fast-twitch to slow-twitch muscle fibers. Fast-twitch muscle fibers are more explosive than slow-twitch and allow us to sprint for short distances and lift heavy objects just a couple of times. Slow-twitch muscle fibers are not as explosively powerful as fast-twitch, but they can fire for much longer; think distance running. Epstein explains that, to some degree, we can train our fast-twitch muscles to have more endurance and our slow-twitch muscles to become stronger, but we cannot actually change the ratio of slow-twitch to fast-twitch fibers that we are born with.
Athletes who compete in explosive sports tend to have a higher percentage of fast-twitch muscle fibers than the general population. And athletes who compete in endurance events tend to have proportionally more slow-twitch muscle fibers. Epstein includes data showing that some sprinters have 75% fast-twitch fibers in their calves, while marathon runners can have up to 80% slow-twitch muscle fibers in their legs.
Epstein notes that since we can test samples of muscle fibers to learn athletes’ ratios, some athletes have been able to change their training programs and events to suit their physiology better. For example:
Creatine Supplements
Many athletes take creatine supplements to boost the performance of their type 2 (fast-twitch) muscles. Creatine is found naturally in our bodies. It is synthesized in the liver and kidneys and we also ingest it in our food. Almost all of the creatine in our bodies is stored in our muscles.
Creatine helps our body produce ATP. ATP is a molecule that stores the energy that we use during short periods of powerful movement. ATP stores in our muscles are depleted within roughly 10 seconds of explosive exercise. Creatine supplements give athletes just a few more seconds of extra power by increasing ATP stores. In explosive sports, a few seconds can make a huge difference. Since the power-boost is so short-lived, creatine supplements are mainly used by athletes who participate in sports that rely on type 2 muscle fibers.
Creatine is generally considered to be a safe supplement and is allowed by the NCAA and Olympic Committee. However, research has shown that responses to creatine vary by athlete. While some athletes may see significant gains following creatine supplementation, some may see only minor gains, and some may see no gains at all. This is an example of how our underlying genetic differences affect our response to training.
Some athletes’ advantage in their sport comes from their bones. Research on skeletons from around the world suggests that some people are born predisposed to be strong. Epstein explains that one kilogram of bone can support five kilograms of muscle in men, and about 4.2 in women. Having a heavier skeleton can be a benefit to athletes, particularly in sports where packing on muscle is an advantage. For example, Olympic shot putters and discus throwers have skeletons that are about 6.5 pounds heavier than average, but on those 6.5 pounds, they can pack on 30 extra pounds of muscle.
The five to one (or 4.2 to one in women) ratio of muscle to bone is of particular interest to athletes looking to maximize their weight to power ratio. Beyond this ratio, the skeletal scaffold for muscle will be full, and extra weight gain is likely to be fat. Epstein notes that athletes who need to be lean and strong, such as javelin throwers, may do well to adhere to this ratio as closely as possible. They need to be strong enough to throw (which means having as much muscle as possible) but lean enough to sprint (meaning not having extra mass beyond this ratio). Athletes for whom force output is more important, such as shot putters, sumo wrestlers, or NFL linemen, may gain weight (as fat) beyond this ratio in an attempt to make their bodies more massive.
Exercise Builds Bone Density
It is easy to think of our skeletons as the static scaffolding for the rest of our body, but bone is living tissue that can respond to exercise. According to the National Institutes of Health, roughly 75% of our bone mass is genetically based, while our lifestyle can influence 25%.
Participating in sports is one of the best ways to build bone density and help reduce the risk of osteoporosis later in life. (Osteoporosis is a disease that occurs when bone breaks down faster than it is replaced, leading to weaker bones that are more susceptible to breaking.) Weight-bearing and resistance exercises are some of the best ways to build bone density, but the timing of exercise is important. Bone density in women generally peaks around 18 years of age (with men peaking a little later). We can build bone density until around age 30, at which point it begins to decline (but we can slow this decline with exercise).
While we have discussed common traits shared by sprinters above, sports and science have yet to determine the exact recipe that makes an athlete fast. Speed seems to be a talent that can be cultivated but not taught. While it is not a physical trait in the same sense as those discussed above, speed is a necessary trait shared by athletes in many sports.
Epstein cites a manager at the Sports Sciences Institute in South Africa who has tested over 10,000 young athletes looking for speed. He attests that he has never seen an athlete who started out slow learn to become fast. Similarly, 2,000 12-year-old boys in the Netherlands were followed as part of a study tracking future professional soccer players. As they grew up, those who went on to play at the highest level were always in the fastest group during shuttle sprints.
Epstein cites a study of collegiate football players in the book’s afterword, which showed that four years of weight training in college made athletes much stronger but did not increase their speed. These studies suggest that there is a genetic component to speed.
In an interesting counterargument to the “10,000-hour rule,” Epstein notes that trying too hard to cultivate speed at a young age can actually be detrimental. Athletes who train too hard too early can get stuck in a rhythm while running that results in a “speed plateau,” a top speed that they cannot train past.
Corroborating Research on Sprinting Performance
An article on sprint performance discusses research findings supporting ideas on sprinting presented in The Sports Gene. A few of these include:
While there may be an optimal technique in sprinting, athletes whose bodies are not “predisposed” to execute those techniques will not be able to benefit from technique-specific training. This may be part of the reason for the idea that speed cannot be taught.
The article also discusses how people are born predisposed to be fast, and notes that speed seems to be a polygenetic trait (meaning that no single gene confers a speed advantage).
Data on the top 100 sprinters in the world in their early 20s showed that the runners only improved by 0.1% to 0.2% a year. While there was a range in improvement, and improvement rates varied by age and experience level, these statistics support the idea that sprinters are naturally fast.
The study also noted that the 10,000-hour rule does not seem to apply to sprinting and that athletes can reach an elite level in five to six years if they have natural talent.
Our genes help dictate which sports we are naturally best at. So being aware of our traits can help us choose the sports where we have the best chances for success.
Think of a sport or activity you either participate in now or have tried in the past that did not feel like a good fit. Why wasn’t it (or isn’t it) a good fit?
Now think of a sport or activity that you either participate in now or have tried in the past that did feel like a good fit. Why was it (or is it) a good fit?
Given your physical traits, what other activities might be rewarding for you to try and why?
Athletic people with an average build have the potential to perform well in several different sports. Epstein notes that experts in the field of anthropometry (the study of human form and function) used to be convinced that the best athletes would be those that fell right in the center of a bell curve of human form; or, the most average person possible. This logic does make sense in the context of finding the best all-around athletes. Athletes who are too big and heavy will likely have a harder time running long distances. Athletes who are too small will likely have a harder time lifting or throwing heavy objects. It stood to reason, then, that an average person should be able to compete in any sport with some degree of success.
Until relatively recently, this was the case. Epstein notes that in 1925, elite volleyball players were the same size as discus throwers, and high jumpers were the same size as shot putters. Put someone with an “average” build into any event at the Olympics today, and they would likely look quite out of place. Today, athletes in many sports represent some of the extremes of human proportions.
Epstein cites a survey that looked at body measurements of elite athletes from the early 1900s through the modern day. Results showed that athletes in different sports have become radically physically dissimilar from one another in recent decades. The survey authors call this explosive appearance in diversity “The Big Bang of Body Types.” Epstein notes that the increasing frequency of “extreme” physical traits in sports is a product of changes in sports culture facilitated by technology. We will look at this idea next.
Decathlon: The Best Athletes in the World?
Most athletes in high-profile sports are specialists, competing exclusively in one event. Decathletes compete in 10 and are often applauded as the best athletes in the world (the NBC Olympic website even lists the 2021 decathlon winner as “the most athletic man in Tokyo”). Yet the winner of the Olympic decathlon would not necessarily place if they were to compete in each corresponding Olympic event. Decathletes and triathletes are considered to be “generalists'' in sports. In a way, they represent the “ideal athlete” envisioned by the anthropometrists discussed above.
Decathletes have to be powerful enough to throw a shot put, but not so massive (an advantage in shot put) that they cannot race in the 1,500 meters. While data on the morphology of elite decathletes and triathletes compared to corresponding specialists is difficult to find, the results of the 2021 Olympic decathlon illustrate this compromise.
Damian Warner won the 2021 Olympic decathlon and set an Olympic record for the event in the process. He is 6 feet 1 inch and 183 pounds. In the shot put, Warner’s best throw was 14.8m. The winner in the shot put event was Ryan Crouser, whose best throw was 23.3m (also an Olympic record). Crouser is 6 feet 7 inches tall and roughly 320 pounds. Every one of the top 12 shot put competitors threw over 20 meters. Clearly, athletes who are generalists must make compromises in their training. Being great at a single event can preclude being great at another, due to both body type limitations and practice constraints (if you only compete in one event you can focus all of your training there).
Technology and cultural enthusiasm for watching elite sports have facilitated the concentration of “extreme” body types into various athletic disciplines. Epstein notes that sports culture used to center around local clubs. Players, fans, and the events themselves were local (or regional). Today popular sports are widely televised and recorded, and the audience has shifted from local to global. As Epstein explains, the increasing visibility and popularity of many sports has created a “winner take all” sports culture. Elite athletes are no longer local heroes but global superstars, with a corresponding increase in earning potential.
In 1975, professional athletes made, on average, five times more money in a given year than the average American. Today, Epstein notes, professional athletes’ salaries are 40-100 times higher than average. At the very top of the most popular sports, an average person would have to work for over a century to match some athletes’ wages.
(Shortform note: In 2021, 10 NFL players signed contracts for annual salaries of $30 million or more (with the highest being Patrick Mahomes at $45 million). In contrast, the real median earnings in 2020 for full-time work in the US was $61,417 for men and $50,982 for women.)
Of course, not all athletes sign multimillion-dollar contracts, even in the world’s most popular sports. But being a professional athlete in the modern-day does hold unprecedented potential for fortune and fame. Sports superstars are famous on and off the field. Epstein notes that in 1983, the NBA entered into a collective bargaining agreement with its athletes that allowed the players to collect royalties, portions of ticket sales, and profit from their fame (Michael Jordan’s sneakers were an early and famous example). This decision reflects the shift in sports culture toward superstardom for the most elite athletes.
With the greater potential for glory comes greater interest from potential athletes around the world. Within three years of the new collective bargaining agreement, Epstein notes that the NBA had doubled its number of seven-foot players. The NBA now draws players from countries like Croatia and Lithuania, among the world’s tallest populations.
(Shortform note: Viewership (and revenue) for major sporting events is huge. While numbers vary by year, Super Bowl viewership hovers at around 100 million people. About 150 million Americans watched the Tokyo Olympics, down from 198 million for Rio in 2016. According to FIFA, more than 3.5 billion people watched part of the 2018 World Cup.)
The powerful appeal of fame and fortune in some sports may explain why the WNBA lags behind the NBA in attracting the tallest female athletes. Female basketball players make far less money than men. Players in the WNBA are only 10% taller than the average woman, while NBA players are, on average, 15% taller than the average man.
(Shortform note: In 2020, the WNBA signed a collective bargaining agreement that increased players’ base salary to an average of about $130,000, as well as increased their potential for total earnings. While this is an improvement, it does not come close to the $7.7 million average NBA salary in 2019. A similar discrepancy in soccer has been the source of much media coverage in recent years. In September 2021, after a long and highly publicized legal struggle, the US Soccer Federation announced that it would offer the same contracts to the men’s and women’s national soccer teams.)
The Increase in “Extreme” Traits in Sports Is Not Evolution
Epstein states that body proportions in athletes are changing more quickly than in the general population. For example, he notes that within eight years of the Fosbury Flop technique (in which athletes clear the bar backward by arching their backs) taking over the high jump world, the height of jumpers increased by several inches. He also notes that Croatian water polo players’ arms “grew” five times longer than the rest of the population in a 20-year time frame. Epstein is speaking about groups of athletes as their own populations to illustrate the increase in certain traits by sport. It should be made clear that Epstein does not suggest that these athletes are somehow “evolving” more quickly in a biological sense.
Evolution by natural selection, the accepted theory of evolution in modern times, posits that traits that boost an organism’s survival and (more importantly) reproductive success will become more common in a population over time. For evolution by natural selection to account for longer arms in water polo, the athletes' lives and reproductive opportunities would have to hinge on their winning the game. Then those traits that helped them win, if they were heritable, would have to be passed to their offspring and help them survive and reproduce. Over the course of several generations, the trait would have to become common enough to change the overall frequency of longer arms in the general population. Even if all of these stipulations were met, lasting evolutionary change in a species often takes one million years!
Epstein notes that the frequency of athletes breaking records in their sports has slowed in recent years. It may be that, for now, sports has reached the bulk of the global talent pool. However, it may also be that when sports such as women’s basketball produce a significant enough incentive, we will see another surge of highly specialized athletes emerge to claim their place.
We have reviewed how both physiology and practice contribute to athletes’ success, and we know that our anatomy and physiology is a function of our genes. As we have seen, traits such as long legs and off-the-charts eyesight give some athletes a natural genetic advantage in their sport. While we may know that these traits are encoded for in our DNA, finding the exact genes that produce these characteristics remains elusive. However, science has made great strides in finding specific genes that impact sports performance. This section will review Epstein’s research on how genetic differences determine people’s response to training.
Genes and the Central Dogma of Biology*
Before we dive into a discussion of genes and sports, we have included a basic refresher on genes.
DNA is housed within the nucleus of our cells. We inherit our DNA from our parents. When cells divide, our DNA is condensed into structures called chromosomes. Each of our cells (except sex cells) has 23 pairs of chromosomes (46 total). One set of chromosomes comes from our mother, and one set comes from our father. The two sets of each chromosome that we inherit from our parents make up our genome.
Certain sections of our DNA, called coding regions, contain instructions for building proteins. These sections are called genes. (Interestingly, the coding sections total only about 1% of our entire genome. Scientists are still trying to figure out what the other 99% does!) Our genes contain the blueprints to make proteins, used to build, run, and protect our bodies. The flow of information from DNA to proteins (via RNA) is commonly referred to as the Central Dogma of Biology. Basically, our genes contain the instructions necessary to build and run a human body (or an onion, a bat, a bacteria, and so on).
*Molecular biology is moving at a rapid pace, and this idea is quickly being shown to be an oversimplification both of what constitutes a “gene” and of the flow of information from genes to proteins. Here is an article from Nature about how the very concept of a “gene” has become less fixed as knowledge advances.
Epstein notes that most of our traits are not produced by a single gene but by the combination of many genes and our environment. To unravel which talents in sports are a product of genes, training, or circumstances, is an impossible task. This is partly why scientists and sports researchers are often hesitant to share ideas and findings that place genes at the forefront of outcomes. To suggest that our potential for success in sports is predetermined runs counter to our cultural values of hard work and determination. It can also lead into socially and culturally problematic territory as certain genetic traits are often distributed along geographic and racial lines.
Since human beings are so complex and sports so diverse, no single genetic trait can be said to determine outcomes in sports. But in recent decades, science has made great progress in demystifying the human genome and identifying individual genes and their roles. In 2003, scientists from around the world completed The Human Genome Project, a massive undertaking that mapped the over 20,000 genes encoded in our DNA. Epstein emphasizes that completion of the project and the information that it has made available has huge implications for technology, medicine, sports, and society.
Epigenetics: Our Environment Acting on Our Genes
Simply knowing the genetic code for a particular trait is just one piece of the puzzle in demystifying human genetics. Our internal and external environments impact the way our genetic code is expressed in the real world.
Chemical compounds and proteins within our cells attach to our genetic code and control how our DNA is read (and thus which proteins are produced). These ‘DNA attachments’ are referred to as our epigenome. Our environment and lifestyle can also change the expression of our genes. This is often called epigenetics. (The term “epigenome” falls under the epigenetics term.)
Epstein introduces epigenetics, though not by that name, in his discussion of height. He notes that 80% of height seems to have a genetic basis, while the remaining 20% is a product of our environment. If people grow up without proper nutrition, they are less likely to reach the full height their genes “allow.” He highlights rapid, population-wide increases in height following a country’s economic growth as an example of how greater access to nutritious food allows more individuals to reach their full height potential.
Another well-known example of epigenetics in daily life is the risk of skin cancer from our cells being damaged by UV radiation. Exposure to UV radiation can cause acute damage to our skin in the form of a sunburn, and can also damage a tumor suppressor gene in our skin cells, increasing the risk of cancer.
As an article from the National Library of Medicine notes, even if researchers can pin down the exact genes for certain athletic traits, unraveling which traits in sports have a purely genetic origin is an impossible task. Athletes will always be the product of genes and environment, or as Epstein calls it, nature and nurture.
Scientists’ ability to analyze DNA samples from study participants has allowed researchers to better understand the role of our genes in our response to exercise programs. While we may not yet know the exact genes involved, Epstein cites research showing that our genes play a determining role in how our cardiovascular and muscular systems respond to exercise.
A 1992 collaborative study between universities in the US and Canada known as the HERITAGE study (HEalth, RIsk factors, exercise Training, and GEnetics) showed that participants on the same training plan showed varying degrees of improvement in response to cardiovascular exercise. The researchers were particularly interested in the effect of the training program on participants’ VO2 max values (which is a measure of how much oxygen our bodies can use while we are exercising). The study followed nearly 100 families (two generations of each family participated, for nearly 500 total participants) over a five-month period. Participants did a prescribed workout three times per week on a stationary bike. Epstein highlights the following results:
As Epstein explains, these results make it clear that there is a strong genetic component to how people’s bodies respond to cardiovascular training. The researchers were able to find 21 alleles (alleles are versions of a gene) that accounted for the response to training that we inherit from our parents.
High-Intensity Interval Training for VO2 Max
HIIT (High-Intensity Interval Training) is a popular way to improve VO2 max. It involves performing repeated short bursts of intense exercise followed by short periods of rest. HIIT has been a popular fitness trend over the last several years. In the annual American College of Sports Medicine survey of over 2,000 fitness professionals, HIIT was ranked as the number one fitness trend in 2014 and 2018, number three in 2019, and number five in 2021.
HIIT gives both recreational and elite athletes a big ‘bang for their buck’.
Research suggests that, for the same amount of total work, HIIT training is more effective at improving VO2 max than cardiovascular training performed at lower intensities.
Research has also shown that gains can be made in VO2 max values from participating in HIIT workouts just twice a week (less than many workout programs using other modalities call for).
HIIT allows participants to burn more calories in a shorter amount of time than other forms of exercise and continue to burn extra calories for a few hours after the workout is over (although these effects are not necessarily as large as some proponents of HIIT advertise).
A small study showed that even though HIIT workouts are inherently difficult, participants enjoyed them more than moderate cardio training. While this study used a small number of participants and only compared two forms of training, the sustained popularity of HIIT supports these results.
A popular and research-backed form of HIIT is Tabata training. Tabata consists of performing 20-second intervals of all-out effort followed by 10 seconds of rest eight times, for a total of four minutes. After one minute of rest, the cycle can be repeated. This workout, in particular, has been shown to increase the VO2 max of exercisers on a stationary bicycle, but the results have been widely applied to other exercise modalities (sprinting, burpees, thrusters, and so on).
Epstein cautions that we should not take these results to mean that exercise is futile for 15% of people. Even the participants whose aerobic capacity remained unchanged saw improvements in other health parameters such as blood pressure and cholesterol. (While most exercisers saw improvements in insulin sensitivity, the HERITAGE study did find that some people may be genetically predisposed to become more insensitive to insulin in response to exercise.)
The Benefits of Exercise Extend to Our Mental and Emotional Health
There are plenty of reasons to exercise beyond gains in cardiovascular fitness. An article from the University of California, Berkely outlines several benefits of exercise that have less to do with performance on the field and more to do with overall well-being. The author cites the effects of exercise on our brains as the reason for these benefits. For example:
Exercise releases endocannabinoids (think: “runner’s high”-cannabis mimics this chemical). The increase in these chemicals in our bloodstream, and thus in our brains, make us feel less anxious, more optimistic, and more social (thus improving our relationships with other people).
Exercise leads to higher levels of dopamine (a neurotransmitter involved in our brain’s reward system) and prompts our bodies to create more dopamine receptors. This can increase our brain’s capacity to experience joy.
When we exercise, our muscles release lactate. Many people blame lactate for muscle soreness, though this article cites that this is not the case. Instead, lactate decreases feelings of anxiety and depression, to the point, according to the author, where regular exercise can help rebalance our brain’s “default” fight, flight, or fright state.
Group exercise can help people bond. Moving in sync with other people releases endorphins and can help forge a sense of connection to the people we are exercising with.
Exercise changes the way we perceive our bodies. When our nervous system registers that our body is performing in a “powerful” or “graceful” way, it can help us see ourselves as being powerful or graceful.
Similar to our cardiovascular system, our muscles also respond to exercise to varying degrees. Epstein highlights a study of 66 participants in a four-month program involving various strength training exercises that found similar results to the HERITAGE study.
Also similar to the HERITAGE study was that those who responded the most to the training program had pre-existing genetic differences from those who did not. Epstein notes that the participants who gained 50% more muscle had more active IFG-IEa, MGF, and Myogenin genes than those who did not respond to exercise. Additionally, those who responded the most to exercise had more muscle satellite cells (stem cells that sit outside the muscle fibers and help muscles become bigger and stronger in response to training). While these results do not provide a clear reason why some people gain strength more readily than others, they show that genes play a determining role.
(Shortform note: It is important to keep in mind that all participants had the same genes. Differences did not result from which genes were present but from the degree that participants’ bodies used those genes to make proteins.)
Epstein highlights two other studies to support the idea that genes determine training responses.
Increasing Strength With Steroids
Some athletes use anabolic steroids to force greater muscle gains than can be accomplished with training alone. Our bodies naturally produce steroid hormones in the adrenal glands, the testes, and the ovaries. The male sex hormone testosterone is one of the main steroids produced by the testes (and the ovaries, but in much smaller amounts). Testosterone stimulates muscle and red blood cell production. Anabolic steroids are synthetic versions of testosterone developed for medical purposes but abused by some athletes looking to boost their performance. Beyond being banned in sports, misusing anabolic steroids can have serious health consequences, including high blood pressure, heart problems, liver disease, kidney damage, and many others.
Anabolic steroids are banned by the NCAA, IOC (International Olympic Committee), the NBA, NFL, and the NHL. They are also listed in the Controlled Substances Act and are illegal to possess without a prescription. Nevertheless, there is a long history of using substances to increase performance, dating back to the ancient Greeks and Egyptians, who used figs and mushrooms and ground-up mule hooves, respectively, to boost their athletic performance.
One of the most famous doping scandals in the Olympics came during the 1976 games when East German athletes ran away from the field and took home 40 medals. However, many athletes were stripped of their medals (and left with long-term health problems) when it was discovered that the East German government had given 9,000 athletes steroids. More recently, Russian athletes were banned from the Olympics for two years when evidence was uncovered of an elaborate state-run doping program. (Some athletes were able to compete in the 2021 Olympics but could not represent their country or use their national anthem.
Epstein uses the results of these studies to provide two important insights into how people respond to exercise and training.
According to Epstein, many elite athletes likely fall into both the naturally fit and high response to exercise categories.
Other Measures of Success in Training Programs
Exercise can help us perform better in our daily lives. Epstein’s research highlights two ways that people can “respond” to exercise training programs. However, as noted in our comment on exercise and changes to our brain and mood, there are many other ways we can benefit from a training program beyond strength and VO2 max. According to the CDC, regular exercise can help reduce the risk of falls, especially in older adults. It can also reduce pain caused by conditions such as arthritis and joint problems and reduce mortality (from all causes) by 33% (based on 150 minutes of exercise per week).
We would all love to see impressive gains in fitness when we invest time and effort at the gym. But being able to walk up stairs, pick up a child, or even get dressed without pain or fear of falling are all ways that our bodies can “respond” to exercise that a single metric cannot measure.
As we have seen, people respond differently to identical training plans. We might work hard at something and still not get the results we want, or, we might be pleasantly surprised by our body’s response to training.
Has there been a time when you trained or practiced for something and were surprised by your results? Compare your expectations to your results.
In the above instance, how did you structure your expectations? (Did you create your goal by comparing yourself to other people on a similar training plan? Did you create your goal based on your past performance and experience?)
Given the above discussion of genes and response to training, does the experience you described above give you any insight into your natural strengths or challenges?
What are some ways that you benefited from your training that were not related to your initial goals?
How can you use this insight in setting future goals?
There is no single gene that can account for an athlete’s success. Epstein notes that at our current level of understanding, investigating the effects of a single gene can tell us more about why someone is not an elite athlete than about why they are. He notes that even given how far our knowledge of specific genes has come, the most powerful piece of technology in determining whether someone will be an Olympic runner is still a stopwatch. In making this point, Epstein conveys a message of optimism to the vast majority of us who are not elite athletes. We should not let research on a single gene or trait discourage us.
It will be a long time before science unravels the genetic basis of even seemingly basic traits. For example, Epstein explains that it took a study of nearly 4,000 people and nearly 300,000 gene variants to determine just 45% of the genetic basis for height! However, for some genes, scientists have developed a decent idea of their role and effect on our physiology. We will look at a few examples that Epstein highlights next.
As discussed above, our ratio of fast- to slow-twitch muscle fibers can determine our success in certain sports. Alpha-actinin-3 is a protein found in fast-twitch muscle fibers. The code for making this protein is found in the ACTN3 gene. The “R variant” of the gene results in normal production of the protein, but the “X” variant prevents the protein from being synthesized. While scientists do not know how this happens, there is a strong correlation between the R genotype and sprinting speed. Tests on athletes from around the world have revealed that the XX genotype is almost nowhere to be found in elite sprinters.
The lack of a scientific explanation for why the XX variant is virtually absent in elite sprinters has not stopped for-profit genetic testing companies from selling genetic tests for ACTN3 gene variants to interested athletes and parents. As Epstein points out, since we do not know why some athletes are naturally fast, these tests can only really serve to add further evidence to the fact that most people with the XX genotype will not become elite sprinters; a fact that most people can ascertain without genetic testing.
Heterozygosity: Getting Different Versions of a Gene From Our Parents
It is possible for a parent who possesses an athletically advantageous version of a gene to not pass this advantage on to their children. Inherited genes from our parents are a product of chance. All of the cells in our body (except for sex cells) are called diploid cells. We inherit one of our father’s versions of a gene and one of our mother’s versions of the same gene.
Since we have two versions of each gene, two letters are often used to describe a person’s genotype when discussing a particular trait. The two letters (or an uppercase and lowercase letter) refer to the two versions of the gene we inherited from our parents. A person who inherits two different versions is said to be heterozygous for that trait. (In his discussion of the ACTN 3 gene, Epstein is discussing heterozygosity, though not by that name.) Two of the same letter indicates that the person is homozygous for that trait.
Versions of genes are generally thought of as dominant or recessive (although inheritance often does not break down as cleanly as this). This means that we can carry a recessive version of a gene that we do not express. In some cases, being heterozygous for a gene can have a protective effect. For example, cystic fibrosis is a genetic disease caused by a mutation in the CFTR gene. The disease is recessive, which means that if a person inherits a normal copy of the CFTR gene from one parent and a mutated copy from the other, they will not have cystic fibrosis. Instead, they are said to be carriers of the disease. The child of two carriers of the mutation will have a 25% chance of having cystic fibrosis.
Researchers have discovered that the CREB 1 gene (a gene that influences the pace of our heartbeat) can help determine how much a person’s resting heart rate may drop in response to fitness training. This can help explain why some athletes’ resting heart rates can drop into the 40 beats per minute range, while some very fit people’s resting heart rates will remain higher.
(Shortform note: An article from the American Heart Association explains that this gene has a strong impact on how our heart rate responds to exercise, but that there are also “at least five” other alleles that also contribute to this response.)
Resting Heart Rate as a Measure of Fitness
Epstein does not go into detail about the relationship between resting heart rate and fitness. Generally speaking, a lower resting heart rate indicates a more efficient heart muscle. Most adults have a resting heart rate between 60 and 100 beats per minute. Athletes with a high degree of cardiovascular fitness may have a much lower resting heart rate (down to around 40 beats per minute). A lower resting heart rate is an indicator that, with each beat, the heart muscle can provide oxygenated blood to the rest of the body efficiently. Our hearts, like any muscle, respond to exercise. Participating in cardiovascular fitness training can strengthen our heart and thus lower our resting heart rate.
While most of us are aware that our resting heart rate is a proxy for our fitness level, our heart rate variability (a heart’s ability to quickly vary its rhythm in response to changing demands) is also an important indicator of our overall heart health. Low heart rate variability has been associated with depression, anxiety, and increased mortality from cardiovascular disease. When we are relaxed, our heart rates are more variable, indicating a heart that is both fit and able to respond to the demands (on or off the field) that we place on it.
Being heftier can be an advantage in sports like football and shot put while having a slighter frame can be an advantage in sports such as distance running. While athletes will intentionally put on or take off weight as part of their training strategy, our heft is, at least in part, determined by our genes. Epstein cites a study called the GIANT (Genetic Investigation of Anthropometric Traits) Consortium Study, which looked at the genetic makeup of 100,000 adults. They were able to identify six gene variants that affected individual heft. One of the genes identified was the FTO gene, which can cause a person to have a stronger or weaker preference for fatty foods.
(Shortform note: In 2007, the FTO gene became the first gene that research definitively linked to obesity. Several studies have shown a strong link between genes and obesity, with an estimated range of 40-90% of a person’s obesity being genetically determined.)
Other genetic factors, such as a person’s ratio of fast- to slow-twitch muscle fibers, can also make losing weight easier or more difficult. Fat is largely burned in the slow-twitch muscle fibers. Epstein notes that this may explain, in part, why people who put on muscle easily can have a hard time losing fat. It can also explain why athletes who excel in power sports often have a naturally “stockier” build than endurance athletes.
The Myth of the “Fat Burning Zone”
While some athletes put on weight for the sake of their sport, many exercisers are looking to lose fat. Both fat and carbohydrates can fuel exercise. When we perform cardiovascular exercise at a low intensity, a greater percentage of our body’s fuel comes from fat than from carbohydrates. The ratio of fats to carbohydrates burned at low intensity has led to a persistent idea in the fitness industry that exercisers looking to lose fat should stay in the low-intensity “fat-burning zone” (think a fast walk or light jog) during cardio.
This idea is so ingrained in the fitness industry that many pieces of cardio equipment list low target heart rates as “fat-burning zones.'' However, while low-intensity exercise may mean a greater percentage of fat is used for fuel, this does not mean that “light” cardio is better for weight loss. When the intensity of exercise is increased over the same period of time, our bodies burn more calories overall. Shifting the intensity to a higher level may decrease the ratio of fat to carbohydrates used, but the overall increase in calories burned will still result in more fat being utilized. Exercisers who adhere to the “fat-burning zones'' listed on the treadmill or other pieces of equipment may be unintentionally burning fewer calories (and thus less fat) than they would if they were to increase their effort level.
Source: National Academy of Sports Medicine. (2014). NASM Essentials of Personal Fitness Training (Fourth Edition Revised ed.). Jones & Bartlett Learning.
The Apolipoprotein E gene influences inflammation in our brains following head trauma. This gene is of particular interest for athletes such as football players for whom head trauma is a constant possibility during play. As Epstein notes, the Apolipoprotein E gene has three variants: APOE2, APOE3, and APOE4. A person’s variant of the gene can influence how they recover from a brain injury. People with the APOE4 variant can experience more complications during the healing process and seem to be more at risk for dementia and cognitive impairment years down the road. (The APOE4 variant is also associated with Alzheimer’s disease.)
Studies on boxers and football players have shown that having the APOE4 variant and being hit in the head during play can result in cognitive impairment. Data shows that of the athletes who suffered severe complications from head trauma, many more had two copies of APOE4 than occurs in the general population. Epstein cites one researcher who compares the risk of getting dementia for someone with one copy of APOE4 to the risk of brain damage from playing in the NFL. Having two copies (one from each parent) increases the risks.
In a possible direction for future policies in sports, Epstein notes that the elevated risk for athletes in contact sports with one or more copies of the APOE4 variant may warrant genetic testing. This would give players more information about their personal risk.
CTE
A 2017 article in The New York Times looked at the rates of CTE in NFL football players. CTE, or chronic traumatic encephalopathy, is associated with confusion and memory loss, depression, and dementia. It is likely caused by the accumulated damage of multiple blows to the head over time. The article notes that it likely does not take repeated game-stopping/concussion-causing blows to cause CTE. The article cites a study from Stanford showing that one lineman received 62 blows to the head during a single game, and each one carried the equivalent force of driving a car into a wall at 30 mph. These smaller hits happen more frequently and do not cause players to take time out to heal, which may contribute to CTE.
The NYT article discusses research findings from postmortem brain studies of 111 NFL players. One hundred and ten of them had CTE. While the article acknowledges that the results are skewed toward finding CTE (because many of the brains were donated by family members who suspected that their loved ones had CTE), these findings are far too decisive to be explained by bias alone. The evidence of long-term damage from playing football has led to calls for major changes in the sport, including a shift toward flag football for children.
Our genes influence our experience of pain. As Epstein notes, pain is inevitable in most sports, and managing pain is an important part of being an elite athlete. Having a version of a gene that makes us better able to manage pain could give some athletes an advantage on the field and during training. Research from a professor of psychology showed that collegiate student-athletes were less sensitive to pain than their peers.
Epstein cites a few genes that have been implicated in our response to pain:
While some athletes may have a genetic advantage when processing pain, intense athletic competition can make anyone less sensitive to pain. Epstein notes that sports can activate our fight or flight response. Under stressful or dangerous conditions, our brains are able to block out pain signals so that we can run or fight. This explains how athletes can sometimes play through injuries or may not even notice injuries sustained during play until later.
Can Pain Tolerance Be Learned?
Many athletes may be tougher than the average person when it comes to physical discomfort because of their genes. But it would also make sense for pain tolerance to be something that can be learned through practice, much like other sports-related skills.
A Scandinavian Journal of Pain study asks whether athletes who play contact sports are more tolerant of pain at the outset of their sports season or whether their tolerance is acquired through play. Just over 100 athletes from rugby, American football, and martial arts were tested for their pain tolerance and coping strategies at the start, middle, and end of their seasons. The study found that athletes who participated through the entire season had higher pain tolerances through the season (including before it began) than “non-participating athletes.” Additionally, athletes who participated through the entire season became more tolerant of some types of pain.
The authors hypothesize that athletes who “stick with” contact sports may better manage pain because they are less emotionally bothered by it than other people. While they realize that part of the sports experience is painful, they “catastrophized less” when they were injured or in pain. Thus, the authors suggest that participating in sports can help build pain tolerance and pain management skills.
In addition to the genes discussed above, Epstein discusses a few specific genetic mutations and their impact on athletic performance.
Genetic Mutations
Genetic mutations can have a major impact on any person, including athletes. Our DNA is made up of several molecules, but most of us think of our DNA as a series of letters: specifically, A, T, G, C. These four letters stand for Adenine, Thymine Cytosine, and Guanine. These are the four nitrogen bases found in nucleotides, the building blocks of DNA. The order of the nucleotides is “read” like a book of instructions to make living things. Every series of three “letters” codes for a specific amino acid. Amino acids are put together to build proteins.
Changing a letter in the sequence can change the way the genetic code ‘reads’ and can alter the instructions for making proteins. Some of these changes will not affect the organism, and some can have large effects. For example, sickle cell anemia (a disease in which red blood cells take on a sickle shape and are less able to travel through blood vessels) is caused by a single A being changed to a T. Other ways that mutations can change the reading of our genetic code include adding a letter (nucleotide), deleting a letter, deleting an entire series of genes, attaching parts of one chromosome to another (like a misplaced copy-paste), and more. Mutations can be inherited, acquired through environmental exposure (like skin cancer from UV radiation), or can happen spontaneously.
The word mutation has a colloquially negative connotation, but mutations can be harmful, neutral, or even helpful to an organism. In fact, genetic mutations are largely the reason we have so much diversity among living organisms. When a mutation leads to a new trait found in 1% or more of the population, it is often no longer called a mutation but simply another “trait” (or allele, or variant) like the ones we have discussed in this guide. The term “mutation” is often used when traits are very uncommon and/or lead to disease.
Epstein recounts a trip he took to Finland to interview famous cross-country skier Eero Antero Mäntyranta, who won seven Olympic medals (three gold) from 1960 to 1968 (Eero passed away in 2013). His achievements included a decisive win in the 15km race at the 1964 winter Olympics, with 40 seconds separating him and the second-place finisher (this is the greatest margin of victory in this Olympic event ever). Epstein describes Eero’s dedication to his sport, with long hours of practice during the dark Scandinavian winters. However, Eero also had a genetic mutation that may have conferred an athletic advantage.
Eero had a mutation in his erythropoietin (EPO) receptor gene, a gene that codes for a molecule involved in producing red blood cells. The mutation results in an overproduction of red blood cells (Eero had up to 65% more red blood cells than other men) and very high levels of hemoglobin (the molecule on red blood cells that carries oxygen). A high volume of red blood cells is an advantage in sports, as it indicates a greater capacity to carry oxygen to hard-working muscles.
Epstein notes that Eero disagreed that his mutation gave him a natural advantage in skiing, but evidence suggests otherwise. There have been cases of other elite athletes in skiing and cycling (both of which place intense demand on the cardiovascular system) who have had abnormally high levels of hemoglobin and red blood cells and have been very successful at the elite level. Some athletes will even inject themselves with synthetic hormones in an attempt to get their bodies to produce more red blood cells. This is considered cheating and Epstein notes that in endurance sports, athletes may be required to provide documentation that their high hemoglobin and red blood cell counts are natural to compete.
Eero’s mutation was hereditary, and evidence from his family adds to the idea that the mutation provides an advantage in sports. He had a niece and nephew who also race (the only other family members who do). His nephew has won two Olympic medals (one gold) in cross-country ski racing, and his niece was a two-time junior world champion in cross-country skiing relay events.
Gene Doping
“Gene doping” is a term used to describe athletes injecting pieces of DNA into their bodies to enhance performance. Gene doping remains largely theoretical in sports. But as gene therapy for medical purposes advances, the World Anti Doping Agency cautions that gene doping is likely to become a new frontier of cheating in sports (whether gene doping should be allowed is a current and interesting debate that we will not cover here). An article in Nature identifies the EPO gene as a “candidate” for doping in the future.
Currently, EPO is given as a hormone to patients with anemia, kidney failure, or undergoing chemotherapy. As Epstein notes, these hormones can also be abused by athletes. However, the article notes that scientists hope to develop a gene therapy technique for EPO in the future, which will likely also be attractive to athletes looking to boost their performance. Eager athletes may be tempted to use EPO gene therapy before research is complete. This would be a dangerous situation, as the article notes that early experiments of EPO gene therapy in monkeys caused the monkeys’ blood to become as thick as “sludge.”
Eero Mäntyranta’s mutation seems to either give carriers an athletic advantage or, should the carrier not be an athlete, have no effect on overall health. But this is not the case for many mutations.
Sickle cell anemia, as we’ve mentioned, is a disease in which red blood cells have a sickle rather than a round shape. This shape impairs their ability to travel through blood vessels and deliver oxygen to the body. The sickle-shaped cells also die much more quickly than normal red blood cells, leading to anemia. People can either be carriers of the sickle cell trait with a single copy of the mutation, or, if they inherit two copies of the mutated gene from their parents, they will have the disease.
Even though sickle cell anemia can shorten a person’s life, the mutation seems to have persisted in the human population for so long because being a carrier of the trait has a protective effect against malaria. The mutation is very common in parts of Africa where malaria is prevalent and in African-Americans whose ancestors came from areas with a high incidence of malaria. (Research suggests that having low hemoglobin levels in these populations also protects against malaria.)
While carriers of the sickle cell mutation are relatively common in certain populations, they are underrepresented in endurance events. This is because low oxygen environments, such as those created during heavy aerobic exertion, can cause the red blood cells in sickle cell carriers to curl up into the sickle shape, which can impede blood flow. As a result, there are virtually no athletes carrying the sickle cell trait in elite running events longer than 800 meters. More than a disadvantage, being a carrier of the sickle trait in endurance events can be dangerous. Since 2000, Epstein notes that nine collegiate football players who were carriers of the trait have died, prompting the NCAA to provide genetic screenings to athletes.
“Gene Therapy” as a Cure for Sickle Cell Anemia
Sickle Cell Anemia affects 100,000 Americans, making it the most common hereditary blood disorder in the country. One in 12 African-Americans and one in 100 Hispanic Americans carry the trait. The National Institutes of Health notes that, until recent medical advances, most people with the disease did not live past childhood. Today, only 50% of people live past 50 years old.
The only current cure for sickle cell anemia is a bone marrow transplant. However, since we know that the disease is caused by a mutation on chromosome 11, scientists are working on a cure using gene-editing technology. Research on mice has shown promise for a technique in which some mutated bone marrow cells could be removed from a patient, corrected using technology, and then inserted back into the patient’s bone marrow; where they should start producing healthy red blood cells. This is an example of how findings from the Human Genome Project and other research into the human genome give the medical field much more power in fighting diseases.
Hypertrophic cardiomyopathy, or HCM, is another mutation that has proven to be deadly on the sports field. HCM is a disease caused by a mutation in which the walls of the heart’s left ventricle become thicker. This means that the heart does not relax as it should after each heartbeat, and the heart muscle itself can be deprived of oxygen. The mutation is relatively common. One in 500 people have it, but many people will never show any symptoms.
Hypertrophic cardiomyopathy is the most common cause of death in young athletes. Epstein notes that a high school, collegiate, or professional athlete will die from the condition every two weeks. During intense exercise, electric signals in an athlete with HCM’s heart can misfire. In the excitement of competition, athletes may not recognize that anything is wrong, making getting prompt medical attention more difficult. In addition to dangerous cardiac events being unpredictable, the condition can be difficult to diagnose. A symptom that doctors look for to determine whether someone has HCM is an enlarged heart. But the heart muscle can grow as a result of athletic training, adding an additional degree of difficulty in diagnosing the disease in young athletes.
Heart Murmurs in Sports
Epstein explains that another reason diagnosing heart problems in athletes may be difficult is that heart murmurs are common in athletes; particularly athletes in sports with high cardiovascular fitness demands. According to the Cleveland Clinic, most heart murmurs in athletes result from the heart becoming enlarged through exercise and pose no health risk. The clinic also notes that the timing and pitch of the murmur can help distinguish an “innocent” murmur from something more serious, like HCM.
An article from the National Institutes of Health notes the extra burden that this difficult diagnosis places on health care providers. Of course, no provider wants to be responsible for dismissing a life-threatening problem as an “innocent” heart murmur. But a doctor would also not want to give a young person a diagnosis that unnecessarily keeps them off the field.
Some people are more prone to injury than others. Knowing whether your genes make you more likely to sustain certain types of injuries can allow athletes to use “prehabilitation” exercises to strengthen at-risk body parts and modify training plans. Epstein highlights two of these “injury genes.”
(Shortform note: Brittle bone disease is also called Osteogenesis Imperfecta (OI). Children are born with the disease. OI can cause soft bones, malformed bones, and other types of bone problems that can be mild or severe. The National Institutes of Health notes that people once believed children with the condition should be “protected” as much as possible by avoiding many activities. However, it is now recommended that children with the condition participate in sports to the extent that they are able, as strong muscles can support weak bones. However, the NIH does note that the choice of sport is important; for example, no contact sports).
(Shortform note: An article from the American College of Sports Medicine notes that Ehlers-Danlos syndrome (EDS) affects roughly one in 5,000 people, but as it is present in different people to different degrees it is difficult to determine an exact number. In athletes, common issues from EDS may include “tissue fragility,” joint pain, joint instability, and joint dislocation.)
While human athletes self-select into their sports, often based on inherited advantageous physical traits, canine and equine athletes are bred for their events. The power of genetics in athletic performance has long been known to breeders looking for the fastest dogs and horses. Whippets and Alaskan Huskies are breeds whose genes are especially well-suited to their respective races. In this section, we will look at Epstein’s research on athletic traits from animal athletes and the insight they provide for humans.
Racing whippets are bred for speed. In the most competitive category of whippet racing (grade A), 40% of the dogs have a copy of what is usually a very rare mutated version of the gene that produces myostatin, a protein coded for by the GDF-8 gene, which acts as a stop signal for muscle growth. At less elite levels of racing, the frequency of the mutation decreases. Epstein notes that 14% of the dogs in grade B racing carry the mutation, and there are almost no carriers in grade C.
It seems clear that having one mutated copy of the GDF-8 gene is beneficial for speed. But if a puppy inherits two copies of the mutated gene (which will happen 25% of the time if two carriers are mated), they grow so much muscle that they are too bulky to race and are often killed off by breeders. These heavily muscled dogs with two copies of the mutation are called “bully whippets.”
The relationship between myostatin and muscle holds across species.
Artificial Selection
When breeders purposefully select for desirable traits, such as extra muscle and extra speed, they are practicing artificial selection. Artificial selection mirrors the mechanism of evolution by natural selection, except that humans act as the driving force rather than the environment.
In evolution by natural selection, individuals with genetic traits that help them survive and reproduce will pass their genes to the next generation. Over the course of many generations, the traits that help individuals survive (and reproduce) in their specific environment will become more common. In artificial selection, humans act as the environment by choosing the traits they want and selectively breeding for them. By intentionally pairing two animals with desirable traits as well as culling (either literally or by removing them from breeding) individuals who do not possess those traits, humans are able to accelerate the process of genetic change in a population of animals (or plants).
Epstein notes that interest in the myostatin gene extends beyond sports to medical research on muscle-wasting diseases such as muscular dystrophy and the universal experience of muscle loss with old age. At the time of writing, Epstein notes that clinical trials were underway on a molecule that researchers had successfully used to bind to myostatin and thus promote muscle growth in mice.
(Shortform note: A 2020 article from the journal Current Opinion in Neurology notes that clinical trials using myostatin inhibitors in humans, such as the one mentioned by Epstein, have yet to produce promising results for muscular dystrophy patients.)
Alaskan Huskies are impressive athletes specifically bred to excel in endurance events in cold environments. Some of their most racing-relevant traits highlighted by Epstein include:
Perhaps more important than all of these physical traits is the work ethic that Alaskan Husky breeders select for. Alaskan Huskies are used as sled dogs in 1,000-mile races over snow and ice. (Famous sled dog races include the Iditarod and Yukon Quest.) In a race that takes roughly 10 days to complete, having a dog that wants to run can make the difference between winning and losing. Epstein highlights the importance of breeding for personality with the story of Lance Mackey, who won both the Yukon Quest and Iditarod in 2007 and 2008 and has won the Iditarod a total of four times.
Mackey began his career as a sled dog breeder without the financial resources to purchase “elite” dogs. He took in street dogs and dogs that other breeders did not want. Rather than looking for speed, Mackey looked for dogs who wanted to run. His dogs were not fast in comparison to other sled dogs, but they would happily run forever with no motivation other than intrinsic desire. Over many generations, Mackey’s approach to breeding changed the culture of sled dog racing from a style in which dogs sprinted between checkpoints to a “marathon” style. He and his dogs became celebrities in the sled-dog world, with one of his dogs even being shipped to Europe where people paid thousands of dollars per breeding.
Animal Athletes or Animal Abuse?
While people generally play sports because they want to, animal athletes are not given a choice. There have been growing calls to end what animal rights activists characterize as animal abuse in the dog racing industries in recent years. The 2016 movie Sled Dogs is thought to have severely tarnished the image of the sled dog industry, and the Iditarod has been denounced by the Humane Society of the United States and lost lucrative sponsors in recent years. Enthusiasm for greyhound racing is also waning. An article in National Geographic notes that by the end of 2022, there will only be two commercial greyhound racetracks left, both in West Virginia.
One of the main reasons activists cite for shutting down dog racing is the killing of dogs who are either too slow or at the end of their racing careers. According to an article in the Washington Post, sled dogs that do not show racing promise may be culled from the pack. Epstein touches on this reality when he explains that Mackey got his first dogs as “castaways” from other breeders. The greyhound racing industry faces similar allegations, with an article in National Geographic describing instances where dogs were either shot or left to die at the end of their racing careers.
Horse racing has faced a similar decline in popularity and public approval. An article in the New Yorker notes that 35 horses died at one racing track (Santa Anita) in less than a year in 2019, prompting animal rights demonstrations and calls for legal action. Animal rights activists cite doping, forcing horses to train and race while injured, and the killing of “retired” racehorses as reasons to shut down the industry. PETA estimates 10,000 racing horses are slaughtered every year, and one activist cited in the article estimates that 2,000 racehorses die every year in the process of racing and training.
Sled dogs are not the only creatures with a desire to run. Epstein cites research on mice and humans that suggests a genetic component to our desire to exercise.
Further research on mice suggests that the way we process dopamine (which is a function of our genes) may play a determining role in exercise motivation. In a follow-up experiment with the mice discussed above, when the group of mice who were bred to love running were given dopamine, there was no change to their running habits. However, when the group of mice who had been forced to run were given dopamine, they began to voluntarily run more, presumably because they began to enjoy it.
(Shortform note: Dopamine is a chemical that carries messages between our neurons. It is part of our brain’s “reward system” and helps us feel happy and satisfied. According to Psychology Today, dopamine improves our mood and increases our attention and motivation. Since dopamine makes us feel ‘good,’ we tend to seek out activities that release dopamine. (This may be why people with low levels of dopamine may be more susceptible to addiction). Having high levels of dopamine can make people more resilient and optimistic in the face of challenges. Exercise is one way to naturally increase dopamine production.)
Epstein cites testimony from several highly successful athletes (Herschel Walker, Floyd Mayweather, Haile Gebrselassie, and Pam Reed) who identify as having a relentless drive, or need, to exercise. Epstein notes that differences in the way our bodies process dopamine can make some people more susceptible to drug addiction, and suggests that there may be similar genetic reasons for why some people have an extra powerful motivation to exercise. The findings of several research studies support exercise motivation being a function of our genes. A large study of nearly 40,000 sets of twins estimated that between half and three-quarters of exercise motivation was genetic.
Exercise Addiction
An article in Psychology Today discussing exercise addiction estimates that 3% of the general population and 25-52% of “long-term endurance athletes” may be addicted to exercise, with the highest rates of addiction occurring in triathletes, runners, and those who have an eating disorder. The article defines exercise addiction as feeling compelled to exercise even when it causes negative social, emotional, or physical consequences. The author cites seven symptoms of exercise addiction, but notes that most exercisers can relate to some of these, and this does not necessarily constitute an addiction:
Tolerance: constantly increasing the amount of exercise needed to feel satisfied
Withdrawal: negative experiences when someone is not able to exercise
Intention effect: constantly exercising more than we planned to
Lack of control: feeling compelled to exercise even when it interferes with other needs and obligations
Time: exercise taking up more time than is recommended by medical professionals or is healthy for each person
Interference with other activities
Continuance: continuing to exercise even while injured, sick, or experiencing other negative outcomes from exercise.
The takeaway from the article is that while exercise is an important part of a healthy lifestyle, it, like most things, should be practiced in moderation. The article even cites research suggesting that engaging in intense exercise for more than 17 hours a week may be just as unhealthy as not exercising at all!
All of the genes discussed so far can have an impact on an athlete’s success. But Epstein argues that no single gene has as much of an impact on an athlete's performance as the SRY gene found on the Y chromosome. He even goes so far as to say that, should there be a single gene to be labeled “the sports gene,” it would be the SRY gene. We will look at his argument for why next.
Epstein cites differences in athletic performance between men and women as a decisive testament to the power of genes in sports. Differences in performance between men and women are well documented, largely predictable, and can, at least in part, be traced to the SRY gene. In this section we will:
Until very recently, women’s records in running events were gaining rapidly on men's, and Epstein notes that it looked to some like male/female differences in running performance might disappear. He discusses a 2002 article in the science journal Nature, and another in 2005 from the British Journal of Sports Medicine proposing that women would soon close the performance gap in running events. This was a logical projection based on side-by-side comparisons of men’s and women’s records. Women’s world records were getting faster at a much greater rate than men’s. If the rates were assumed to be relatively constant, then female runners would eventually catch up to and surpass men.
Looking at running data alone, however, does not tell the whole story. Epstein explains that cultural factors can likely account for a great deal of the steep improvement in women’s performance. Men and women did not even have the same track and field events until 2008, and historically women have certainly not been given the same training opportunities as men. After the surge of the last few decades, women’s running records today have hardly advanced at all, while men’s are still advancing slowly. (Another factor that may account for some of the women’s records in sprint and power events from the 1980s was the illegal use of testosterone (steroids) in female athletes from Eastern Bloc countries during that time period).
The reality is that many female world record holders would not even qualify to compete in the same Olympic events against men. And some of the top female athletes in their sport can be bested by high school boys. Statistically, those women, of whom there are many, who can outperform the average man in sports are the exception. Epstein cites innate physiological differences between men and women as the reason women are unlikely to surpass men in most sports. We will look at some of these differences next.
Women Best Men in Other Measures of Strength
Research has shown that from birth to death, women are ‘tougher’ than men in ways that science has yet to explain. Even at birth female babies have higher survival rates than males. As adults, women better survive 12 of the 15 leading causes of death and are older than men at the onset of common diseases such as cardiovascular disease and hypertension. Women also survive longer than men. In 2017, 42 out of 43 supercentenarians (people who live past 110) were women. Women also survive infections better than men.
Evolution may explain much of this toughness. Epstein suggests that our female evolutionary ancestors were not as likely as men to participate in the most physically demanding or intense aspects of society. But this may not be true. As we learn more about ancient humans, anthropologists are discovering that the notion of women tending to the home while men hunted, gathered, and traveled long distances is flawed. It appears that women not only hunted and worked alongside men, but they had to do so while pregnant, nursing, and physically carrying young children. In this more modern vision of our female ancestors, it makes sense that natural selection would have developed an extra level of ‘toughness’ in women.
In general, men throw harder, run faster, and jump higher than women.
(Shortform note: This is not to suggest that if you were to line up a man and a woman the man would always outperform the woman. These differences occur on the level of a population and are based on statistical averages.)
Epstein concedes that cultural expectations and stereotypes may account for some of the difference in throwing ability, but in aboriginal populations where both sexes grow up throwing for hunting and combat, researchers found that boys were still able to out-throw girls. Additionally, 87% of boys were better than girls at tracking and catching flying objects.
Across running events, men are about 11% faster than women. And, on average, men are able to jump 19% farther than women in the long jump. Differences between male and female physiology largely explain these differences.
Swimming: The Smallest Performance Gap
Epstein notes that the smallest gap in Olympic events between men and women is in distance swimming events, with women coming within 6% of men in the 800m swim. In long open water swims, the gap between women closes and even reverses. Studies of finishing times from the English Channel, Catalina Channel, and Marathon Island Swim over several years found that women were as fast as, and more often faster, than men in these events.
One possible reason for these findings is that women generally have a higher body fat percentage than men, and they are better able to utilize that fat as a fuel source over long distances. More body fat can also mean more buoyancy for women in the water, as well as more insulation during cold open water swims.
The same trend seems to hold in ultra-running. An article in The New York Times discusses how in extremely long races, male physiological advantages become less relevant. In ultramarathons, in which athletes run up to 200 miles over multiple days, it seems that mental toughness and psychological fortitude allows women to run alongside and even beat their male counterparts. The article highlights Courtney Dauwalter, who has become a celebrity in this sports niche and frequently bests the entire field of male athletes.
The differences between men and women have their roots in our species’ evolution. Humans are a sexually dimorphic species. This means that males and females of the same species display different characteristics. Epstein notes that the difference in strength between men and women is similar to the difference in strength between male and female gorillas. While we may think of ourselves as ‘more evolved’ than our primate ancestors, it has not been very long since our species’ behavior looked very similar to the behavior we see in wild animals.
In our very recent evolutionary past, men were violently competing against each other to earn the ‘rights’ to women. Males that were stronger and better able to physically fight off other males had more access to breeding opportunities. Anthropology tells us that in hunter-gatherer societies, 30% of men were killed by other men. There is also evidence that we have fewer male ancestors than female ancestors. As Epstein explains, this suggests that the most physically imposing men were able to establish dominance and ‘claim the rights’ to multiple women.
Sports as a Platform for Male vs. Male Competition
As Epstein discusses, it was not long ago in evolutionary terms that our male ancestors engaged in hand-to-hand combat and violent competition (both one-on-one and with a tribe) on a regular basis. While outright violence may be less prevalent, and at least less socially acceptable, in modern culture, some researchers suggest that organized sports offers an outlet for men to express an innate proclivity for physical competition.
The authors of a three-part study on male and female participation in organized sports highlight three theories for why sports (with particular emphasis on team sports and sports where skills can be seen as combat-related) may hold special appeal for men.
Sports serve as a modern counterpart to courtship rituals in nature and offer men a way to display their physical attributes.
Sports allow men to compete for social status in a safer and more controlled way than outright combat.
Sports serve as a way for men to “train” for physical activities such as hunting and combat (in modern society the need to use this training may never arise, but the innate desire to train may still be present.)
The authors found a difference in participation rates between men and women in organized sports, and team sports in particular, with men choosing to participate more than women. They note that these findings should be viewed in the context of other cultural factors such as male/female gender norms and the encouragement and access to sports that girls receive.
The above study’s findings are supported by another study of 50 societies around the world, that also found universally more male than female participation in sports. However, the cross-cultural study did find that the gender gap was smaller in non-patriarchal societies, supporting the idea that culture plays an important role.
Epstein explains that the Sex Determining Region Y (SRY) gene accounts for most sexual variation between men and women. It is found on the Y chromosome. (Most women have two X chromosomes, and most men have an X and a Y chromosome.) At six weeks gestation, the SRY gene causes the formation of testicles, which release the testosterone that produces male characteristics in developing fetuses.
(Shortform note: Testosterone is a steroid hormone that is produced in both men and women, although men generally have much higher levels. In men, the testes produce testosterone, and in women, it is produced in the ovaries. In men, testosterone regulates sperm production, sex drive, fat distribution, bone mass, muscle size, and red blood cell production. In women, testosterone impacts sex drive, muscle strength, and bone density.)
Testosterone levels may be one of the most powerful factors in athletic performance. Epstein explains that performance differences between boys and girls are almost non-existent in many sports before puberty. Once boys hit puberty their bodies produce extra testosterone and the athletic gap widens quickly. (This is one reason why it makes sense to have co-ed sports teams for young children). Testosterone has such a defining impact on athletic performance that in 2012 the Olympic Committee decided that an athlete’s sex should be determined by how much testosterone their body is able to use.
Sex-Linked Traits
Traits that are produced by genes found only on the X or Y chromosome are called sex-linked traits. Off the field, genes found on one chromosome or another can help explain why some diseases are more common in men than in women.
Women have a greater degree of protection from diseases known as X-linked recessive diseases. These diseases are caused by a recessive gene on the X chromosome. Since women have two X chromosomes they can have the recessive version of the gene on one chromosome and the dominant version on the other and be carriers of the disease. Since men only have one X chromosome, if they inherit a disease-causing version of a gene on their X chromosome, they will have the disease.
Sex-linked traits also explain why red-green color blindness is more common in men than in women. The gene that causes red-green color blindness is located on the X chromosome. Women can carry one “faulty” gene but still see color normally, but if a man inherits that single “faulty” gene, he will be color blind.
The biological distinction between male and female is not black and white. Sports divide men’s and women’s events into two distinct categories for good reason, yet on the level of the individual athlete, the distinction between the sexes is not so easy to define. Epstein highlights a few scenarios:
There are some women who have an X and a Y chromosome, testes, and male levels of testosterone. Some of these women have androgen insensitivity. This means that, while they have male levels of testosterone in their bodies, they are not able to use it. In the general population, this happens in one out of 20,000 to 64,000 women. However, it is much more common in sports. From data taken over five Olympic games (the last time this data was collected was in 1996), one in 421 women had XY chromosomes and androgen insensitivity.
Epstein explains that “XY androgen insensitive” women are overrepresented in sports due to their body type rather than testosterone. Even though these women are unable to utilize the testosterone their bodies produce, their build is more “masculine” than that of other athletes. They are generally taller than most women, with longer arms and legs. For this same reason, it is likely that this genotype is also overrepresented in the modeling industry.
While women with XY chromosomes and androgen insensitivity cannot use any of the testosterone their bodies produce, another condition called partial 21-hydroxylase deficiency causes women to produce extra testosterone. This likely gives these women a significant advantage in sports. One study found that elite female athletes across several sports had twice as much testosterone as non-elite female athletes.
In yet another condition called De La Chapelle syndrome, people who have two X chromosomes (characteristic of women) develop as if they had an X and a Y chromosome (characteristic of men). This is because during recombination (the process in which chromosomes from our mothers and fathers “mix” their information), some of the genes from the father’s Y chromosome end up on an X chromosome.
Testosterone as a Basis for Discrimination
An article questioning the efficacy and ethics of testing for hyperandrogenism (high levels of testosterone) in female athletes asserts that there is no evidence of high testosterone levels boosting female athletes’ performance. The authors go so far as to state that, in women, naturally occurring testosterone levels are “not related” to sports performance. Therefore, the authors assert, tests conducted at elite sporting events looking for “intersex” women can only serve to damage the lives and careers of these athletes.
The article notes that the main impetus for conducting “verification” tests is to ensure that men do not masquerade as women during competition. However, the authors note that since testing began in 1966, this situation has never been documented (with a notable exception of an unproven incident in women’s volleyball in 1972).
Like The Sports Gene, the article’s authors suggest that it is the increased height of “XY” women that gives them an advantage. They argue that to test for intersex conditions in sports is discriminatory, as it falls into a large category of naturally occurring, genetically based differences between athletes. If athletes are not being screened out for other advantageous traits, they argue, neither should XY women or other athletes who would be considered “intersex.”
Women and Men Are Both Fierce Competitors
Epstein makes a reasonable, evidence-based argument for why women will never catch up to men in terms of sports performance, with the implication being that men are better at sports than women. It may be true that women will never, on average, jump farther, lift heavier, or run faster than men. But the book is not titled The Power Gene or The Speed Gene, the book is titled The Sports Gene. And just because men may be able to outperform women in measures of speed and strength does not mean they are inherently better at sports.
The main feature of sports is the competition. This is what viewers tune in for. We love to watch athletes at the top of their form test their limits against other athletes. In this respect, men hold no advantage over women. Female athletes are fierce competitors in their own right, who test their athleticism against other female competitors in the same way that men do.
An article in the Columbia Journalism Review notes that for fans, there is a connection between self-esteem and the success of their favorite sports teams. This is because when we feel connected to something, our brain adopts some of that person or team’s success as our own. This can happen while watching women represent their country at the Olympics or World Cup just as much as it can while watching men.
An article from Grantland discusses research on mirror neurons. The research shows that when we watch someone perform an action, approximately one-fifth of our own neurons for the same action fire. (If we watch someone do something strenuous, our own respiration and heart rate increase!) The more experience we have in a sport, the more our brains can “fire along with it” while we watch. The article cites an interview with one of the researchers who says that, while it is “very hard to prove,” watching sports makes us feel good in part because our mirror neurons are playing along with the players on the field. This happens whether the players are men or women.
If sports simply boiled down to statistics measured in meters jumped, seconds run, or points scored, there would be no need to tune in to watch the events. We don’t love sports for the final numbers, we love sports for the competition, the heart, and the story. These qualities are just as present in women’s sports as they are in men’s.
Elite athletes are a product of their heritage long before they are a product of their training. In exploring how genetic diversity impacts sports performance Epstein goes all the way back to the very beginnings of our species. Looking at humans over evolutionary time can help us understand why the genetic diversity that we see on the playing field exists.
Epstein notes that up until around the 1970s, many anthropologists believed that modern man had evolved independently in different populations around the world. However, extensive DNA sampling from populations all over the globe suggests otherwise. DNA samples show a greater variety of traits represented in the collective genome of African populations than populations from other parts of the world. For some traits the difference in diversity between DNA of African origin and DNA from the rest of the world is immense. For example, Epstein notes that for one set of genes, an African Pygmy population had more diversity than the rest of the world put together.
DNA sampling helped change the way anthropologists construct the story of modern man. The fact that there is so much genetic diversity in Africa and comparatively little elsewhere (particularly in Europe) suggests that humans originated in sub-Saharan East Africa and migrated around the world from there. This theory is called the “Recent African Origin Model.” (The term “recent” should be taken in evolutionary terms. Humans are estimated to have migrated out of Africa 90,000 years ago.)
The Recent African Origin Model also suggests that the reason genetic diversity in a population decreases the farther populations migrated from Africa (with Native Americans being the least diverse) is that only a relatively small group of people set off each time, taking a comparatively small amount of the gene pool with them.
Equity in Genetics Research Would Further Our Understanding of Genes and Sports
Understanding how genes impact athletic performance or any other trait requires a well-rounded sample. A 2020 article in Nature discusses the underrepresentation of people with African Ancestry in genetics research. Although African people represent the majority of the human population’s genetic diversity, the article notes that most research on genetics has focused on European populations. This lack of equity in research not only hinders scientific knowledge but further exacerbates inequities in medical research and health care.
The article notes that while there has been a recent push to increase equity in genetics research, people with European ancestry are overrepresented in research on polygenic risk scores (which can help identify an individual's risk of certain diseases) by a factor of 460%. This means that the results of research on diseases are not as applicable to non-European populations, leading to fewer reliable diagnostic tools for non-white patients.
The article also notes that insight into a population’s genes helps to predict how individuals in that group will respond to different medicines. If drug research is focused on people with European ancestry, then non-white patients may be more at risk of adverse side effects. For example, the article notes that individuals with African ancestry are more likely to experience dangerous bleeding when taking warfarin (a common blood thinner).
A sports-related example of how knowledge of genetic differences can lead to improved health care is the NCAA’s decision to test athletes for the sickle cell trait discussed in the section on genetic mutations. Epstein notes that white athletes can opt out of the screening, as they have a very low chance of being carriers of the trait. But the knowledge that the trait is relatively common in African-American athletes, and subsequent testing, has the potential to save young athletes’ lives.
Having a specific variant of a gene can tell researchers about a person’s ancestry. When small groups of people left the larger human population to colonize a new area they carried a small subset of the population’s genome with them. Their more narrow set of traits propagated through the new population as it grew. Epstein illustrates the principle that certain traits cluster in populations with a few examples:
These findings relate to sports in that they shed light on the dominance of African athletes (and athletes with recent African ancestry) in many sports. Epstein notes that, since there is so much more diversity in Africa than in other parts of the world, it makes sense that for a given athletic skill, there will be more individuals in and recently from Africa who will excel at that skill.
Founder Mutations as Evidence for the Recent African Origins Model
Founder mutations are a specific subset of gene clusters that can be used to help track human populations over time. (Skier Eero Antero Mäntyranta’s erythropoietin receptor gene mutation is a Founder Mutation.) Founder mutations are genetic mutations that arise in a single person, the “founder,” and are passed down unchanged from generation to generation.
As an article from Scientific American explains, founder mutations are especially useful for anthropologists because they are passed down as a section of a chromosome rather than as a single segment of DNA. This allows anthropologists to tell how long ago the mutation originated. The segment is shortened with each generation (as the chromosome with the mutation is recombined with the corresponding chromosome from the other parent). A longer stretch indicates a younger mutation and a very short segment can indicate an ancient one.
A particular founder mutation on the gene that codes for PTC tasting added important evidence to the Recent African Origins Model. PTC is a compound found in plants that most of us perceive as tasting very bitter. This serves as a warning so that we don’t eat plants that are poisonous. A mutation that stops people from tasting PTC arose in the human population roughly 100,000 years ago.
Researchers found seven versions of the gene in sub-Saharan Africa with four versions being endemic to Africa. One version is found on rare occasions outside of Africa but has not been found in the Americas, and the other two versions are found throughout the world (one of which is the “non-taster” gene). These results support the idea that humans originated in Africa, and that genetic diversity decreased as people migrated outward.
As we have discussed, our genes are influenced by our environment. But the interplay between genes and environment does not begin when we are born. Our genome is a product of thousands of years of evolutionary history. Our genes can help to tell the story of the environment that our ancestors evolved in. Next, we will look at Epstein’s discussion of how evolutionary environments developed the traits that give modern-day athletes a competitive advantage. Specifically, Epstein uses ancestral environments to help explain why many elite runners come from very specific populations.
(Shortform note: We use the term “adaptation” to refer to a specific trait that humans have developed over time in response to environmental pressure. This section deals with general adaptations and their relevance to endurance athletes. However, Epstein’s discussion of these principles in the book mainly focuses on explaining why Kenyan runners so heavily dominate the world of distance running. We will do the same.)
People with recent African ancestry have long arms and legs relative to the rest of their bodies. A trend that holds true in animal and human populations from around the world is that, as you move closer to the equator, limbs generally become longer and thinner. In contrast, cultures like the Inuit people who live in cold environments often have short legs. Epstein notes that this is likely due to the higher temperatures in many low-latitude environments. Short limbs conserve heat, while long limbs create a greater surface area for cooling. During long-distance running events, becoming overheated will not only decrease performance but can be dangerous.
Body Temperature Regulation During Exercise
Our ability to control our body temperature influences our sports performance. Our body releases heat to our environment via our skin. When we need to lose heat the blood vessels in our skin dilate. This allows more blood to pass through, where it can release heat to the air. This is called vasodilation. The larger the surface area of the skin, the more blood that can be nearer to the air, and the greater the potential for cooling (this is one reason why jackrabbits’ ears are so large and full of blood vessels.)
The other way our skin allows us to lose heat is through evaporative cooling (sweating). During intense exercise, our muscles produce a large amount of heat that our body needs to release. When we sweat, the energy that we perceive as heat is transferred to the water molecules on our skin. This energy causes the water molecules to evaporate, carrying away the energy (heat) from our bodies. This process happens continuously while we exercise so that we do not overheat. The larger the surface area of our skin, the greater the potential for evaporation and heat loss.
The adaptation of maximizing surface area is especially important for distance events such as the marathon, where runners are exerting themselves for hours at a time.
Populations from the Nile Valley in Africa evolved in hot low-latitude environments and tend to have long, thin legs. Anthropologists refer to this as a “Nilotic” body type for populations from the Nile Valley. A Nilotic body type may help to explain a piece of why Kenyan runners dominate in distance running events.
Kenyan superiority in distance running is one of the most well-known and consistent examples of athletes from a specific community dominating a sport. Epstein includes a few race results for illustration:
Epstein notes that even more striking than the fact that all of these athletes are from the same country is that most of them are from the same tribe, the Kalenjin tribe from the Kenyan Rift Valley. Kenyan athletes from the Kalenjin tribe represent only 12% of the country’s population but 75% of its elite runners. At the time of The Sports Gene’s writing, only 17 men in the United States had ever run a marathon faster than 2 hours and 10 minutes. But 32 men from the Kalenjin tribe did it in just the month of October in 2011!
The Tarahumara: A Tribe of Ultrarunners
The Kalenjin are not the only tribe where nature and nurture forged elite athletes. In his national bestseller Born to Run, Christopher McDougall highlights the Tarahumara tribe of the Sierra Madre mountain region in Mexico. This tribe lives deep in the wilderness, in cliffside caves and camouflaged dwellings. They are notoriously mysterious and elusive. McDougall describes the Tarahumara as “superathletes” and “the greatest runners of all time.” As he describes it, members of the Tarahumara tribe can run 300 miles through rugged mountain wilderness without stopping. A historian once documented a champion runner from the tribe covering 435 miles in a single run.
An article from The University of Chicago Press Journals corroborates McDougall’s description of the Tarahumara’s almost superhuman athleticism, and it discusses the impact of culture on the tribe’s running. The article notes that the Tarahumara do not “train” to run in the sense that Western cultures think of training for sports. Instead, running in the Tarahumara culture is practical (the Tarahumara have been said to run after deer until the animals simply collapse from exhaustion), cultural (the article notes that some long-distance running events are considered a form of dance), and spiritual (the culture views running in endurance races as a type of prayer).
Mcdougall notes that the Tarahumara are able to run incredibly long distances over their entire lives without sustaining common overuse injuries that plague most runners. This suggests a genetic predisposition to distance running. However, if running were not so integral to their culture, it is unlikely that so many Tarahumara people would run as much as they do.
The Tarahumara are also a counterpoint to Epstein’s discussion of globalization in sports. Epstein credits the incredible physiological diversity on the elite sports stage to the fact that modern sports have “drawn out” supremely gifted athletes from around the world. He suggests that part of the reason that athletic records are being broken at a slower rate in modern times is that much of the athletic potential from around the world has already been reached. However, the Tarahumara seem to represent an anomalous well of athletic talent that remains largely absent from the world sports stage.
Epstein notes that the different limb proportions between people with recent African ancestry and other athletes helps to explain a piece of why athletes of different races tend to be over or underrepresented in different sports. Research shows that long limbs give athletes a 1.5% advantage in running and a 1.5% disadvantage in swimming. In sports where races are often won by a fraction of a second, 1.5% is a big difference. Epstein notes that this says more about why African athletes and athletes with recent African ancestry dominate running events than it does about why there are far more white swimmers. There are significantly more barriers to entry into swimming, which prevents a true comparison.
Lack of Pool Access Led to Overrepresentation of White Swimmers
The historic lack of minority access to public pools helps explain the overrepresentation of white athletes in swimming events. In the United States, black swimmers have been systematically excluded from recreational swimming, both by policy and by outright intimidation.
An article from NPR notes that in the 1920s and ‘30s, during the largest boom of public pool construction, black swimmers were either officially banned from swimming pools or were intimidated and physically assaulted by white swimmers when they tried to participate. When official discriminatory policies were lifted, white swimmers “abandoned” public pools in favor of private clubs where they could still discriminate against black swimmers, leaving public pools to struggle and close. Today there are even fewer public pools in the US than there were in the 1920s and ‘30s, especially in low-income areas. This lack of access has created a dangerous situation today in which roughly 60% of black children do not know how to swim, and they drown at a much higher rate than white children.
A Nilotic body type, combined with the narrow lower legs found in Kenyan runners (discussed In the Body Types and Success in Sports section), creates a definitive advantage when it comes to running long distances. As we will see, there are additional environmental and cultural factors that combine to help explain why Kenyan (and specifically Kalenjin) runners dominate the world of distance running.
One way that athletes use their training environment to improve aerobic capacity is to train at altitude. Epstein notes that many athletes in the United States travel to Mammoth Lakes, California, or Flagstaff, Arizona to train at altitude (both of these cities sit at between 7,000 and 8,000 feet in elevation). The goal of training at altitude is to force the body to generate more red blood cells in response to lower levels of oxygen in the air (more red blood cells means more hemoglobin, which is the molecule in red blood cells that carries oxygen). However, In another example of how our genes affect our response to training, not everyone who trains at altitude will reap the same benefits.
Based on these studies, it seems that training at altitude does not guarantee improvement. But being born at altitude does seem to be an athletic advantage. As Epstein explains, people who are born or grow up at altitude develop larger-than-average lungs. This is an advantage in endurance sports because larger lungs create a greater surface area for oxygen exchange. This adaptation happens even in children whose parents were not born at altitude, indicating that the trait does not need to be inherited. However, Epstein notes that this adaptation only occurs in children. (He notes that at the time of writing, the fastest male and female American marathoners were both born and/or raised at altitude.)
Training for Race-Specific Conditions: Heat Training
While Epstein discusses the power of the environment on an athlete’s physiology, he does not discuss the importance of preparing for the environment athletes can expect on “game day.” As elite athletic competitions such as the Olympics happen all around the world, at varying altitudes and in varying temperatures, being physiologically prepared for environmental conditions can serve as a non-genetically based competitive advantage.
An article in the International Journal of Sport Nutrition and Exercise Metabolism discusses how “heat training” can allow athletes to prepare for competitions in hot environments, and may even improve performance in cooler environments. Some of the highlighted benefits of training in heat include:
An increase in VO2 max (aerobic capacity)
An increased ability to tolerate heat via improved blood flow to the skin and increased sweating
A decrease in heart rate and core temperature while exercising
An increase in “thermal tolerance” (which we can assume would decrease discomfort during a race on a hot day)
A potential increase in the time it takes to reach “exhaustion” during exercise
A potential reduction in blood viscosity (allowing blood to circulate more easily during exercise)
The article notes that these adaptations are maximized with 10-14 days of heat training, but that the training should occur as close to race day as possible as the benefits “decay” at a rate of 2.5% per day upon completion of the training.
As evidence of the impact of race-day conditions, Epstein notes that in the 2004 Athens Olympics Paula Radcliffe, the world record holder in the women’s marathon at the time, was unable to finish the race because the temperature was 95 degrees. If an extremely hot day can cause the world record holder in an event to not finish her race, clearly race day conditions can have an enormous impact on performance; in extreme circumstances, enough to negate genetic talents.
Studies of the three major human civilizations that have evolved at altitude show that different populations have adapted to altitude differently, and shed further light on why distance runners from Kenya in particular may have an extra athletic advantage.
(Shortform note: Bolivia has regularly participated in the Olympic games since 1964, but has yet to take home a medal.)
From these studies Epstein shares the following preliminary findings about altitude and sports:
Sherpas as Superathletes
Nepal has competed at the summer Olympics since 1964 but has yet to take home a medal. However, their lack of representation on the podium does not mean that Nepal does not produce some of the world’s toughest athletes. Natives of Nepal who work on Mount Everest as sherpas are widely regarded as superathletes. Not only have many of them made the ascent up Everest many times (a feat considered by many as a pinnacle of athletic achievement), but they do so while caring for groups of other climbers and carrying the extra weight of climbing gear on their backs.
If mountaineering were to become an Olympic sport, Nepal would surely be raking in the medals and sherpas would be highlighted as athletes with genes perfectly suited to their sport.
Epstein suggests that an ideal scenario for an endurance athlete would be to have a genotype that evolved at sea level (at least until relatively recently), and to be born and train at an altitude of between 6,000 and 9,000 feet. He notes that this is the exact scenario of the Kalenjin runners from Kenya and the Oromo runners from Ethiopia (he notes that Ethiopia often comes in second to Kenya in distance races), who both live in the Rift Valley.
The concept of the environment shaping the athlete over evolutionary history also adds a piece to the puzzle of why athletes with West African heritage dominate sprint events in track and field. Epstein notes that at the writing of The Sports Gene, every finalist in the men’s (and all but one in the women’s) 100 meters at an Olympic games since 1980 has had recent West African ancestry. This phenomenon has not yet been explained, but genetic research suggests that populations in West Africa evolved certain traits in response to their environment that happen to confer an advantage in explosive sports.
Research has shown that athletes with West African ancestors tend to have a high ratio of fast-twitch (type 2) muscle fibers. Fast-twitch muscle fibers are used for short bursts of explosive movements, such as sprinting. One evidence-based theory suggests that this muscle fiber composition evolved in response to high rates of malaria in West Africa.
A high ratio of type-two muscle fibers co-occurs with low levels of hemoglobin. Data from nearly 750,000 people shows that African American people (many of whom have West African ancestry) generally have lower hemoglobin levels than white Americans. For reasons not well understood, having low hemoglobin levels seems to provide a degree of protection against malaria.
According to the theory presented by Epstein, having low hemoglobin levels led to an evolutionary trade-off between endurance and speed. Low hemoglobin levels mean less capacity to oxygenate muscles during endurance exercise (hemoglobin is the molecule in red blood cells that carries oxygen), and so is a disadvantage in endurance events. Type 2 muscles are able to produce energy without using oxygen, but can only do so in short bursts. Having more type 2 muscle fibers would allow people living in high-malaria areas to maintain lower hemoglobin levels with the side effect of making them more powerful sprinters.
(Shortform note: We often hear muscle fibers being referred to as “fast twitch” and “slow twitch” or “type 1” and “type 2.” This is how Epstein refers to muscles throughout The Sports Gene. But we actually have three types of muscle fibers: type 1, type 2A, and type 2B. Type 2A muscle fibers are an intermediate muscle type, with characteristics of both type 1 and type 2B. They are larger than type 1 fibers, can produce a greater amount of force more quickly than type 1 fibers, are quicker to fatigue than type 1 fibers, and can use both oxygen and ATP (an anaerobic energy pathway) to produce energy. Type 2B muscle fibers produce energy anaerobically, and are very quick to fatigue.)
In addition to low hemoglobin, being a carrier of the sickle cell trait seems to have a protective effect against malaria. As we discussed earlier, carriers of the sickle cell trait have red blood cells that adopt the sickle shape when infected with malaria, which prevents the cells from traveling as easily through their bodies. As discussed in the section on genetic mutations and sports, being a carrier of the trait is a disadvantage in endurance events, as low oxygen environments can cause red blood cells to “sickle.” Conversely, for reasons not well understood, Epstein explains that this trait seems to be an advantage in explosive events that require low endurance but high power, such as sprinting and jumping.
(Shortform note: It is not clear whether Epstein is making the argument that the sickle cell trait itself confers a sprinting advantage, or whether the sickle cell trait merely tends to be seen alongside the adaptation of low hemoglobin levels. As Epstein discusses, this is an area of research that is still not well understood, and so for now we can only note that these two traits seem to be correlated with speed.)
The Black Sprinting Stereotype
In his discussion of the higher degree of genetic diversity between people with recent African ancestry and people with ancestors from other parts of the world, Epstein notes that two African or African-American athletes are likely to be more genetically different from each other than two athletes from a different population. This diversity is lost in the way that our culture often stereotypes black athletes as being universally fast.
An article from the BBC adds to Epstein's comment that every winner of the 100 meters in the history of the Olympics has been black. The article adds that every winner of the Athletic World Championships 100 meter dash has been black, as has every finalist (with one single exception) over the last 10 events. However, the article cautions against interpreting these results to mean that all African people, or all African-American people, are fast.
The article uses the example of Kalenjin running success to illustrate this point, noting that just because members of the Kalenjin tribe dominate the marathon, this does not mean that all African and African-American people are incredible distance runners. Rather, what both the marathon and 100-meter results can tell us is that there are two incredible pockets of talent —Kalenjin and a subset of runners with West-African heritage (largely Jamaican)—that dominate two running events. In fact, in The Sports Gene Epstein makes the argument that the high degree of genetic diversity in Africa suggests that both the fastest and the slowest runners in the world may have recent African origins.
The purpose of the article is to highlight the flawed logic and societal risk of characterizing a group of people with broad generalizations. This discussion also highlights the value of the conversations started in The Sports Gene, as a deeper understanding of genetic differences may lead to a more thoughtful society in general.
Epstein argues that an athlete's dedication to their sport is, at least in part, a product of socioeconomic factors and culture. He notes that even the genetic advantages of a Nilotic body type, the ideal altitude circumstances, and the narrow lower legs of Kenyan runners still do not completely explain their running dominance. These traits certainly give Kenyan runners who decide to train an advantage, but to run a marathon in under two hours 10 minutes takes an incredible amount of dedication. So too does being able to run the 100-meter dash in under 10 seconds. Athletes whose ancestors hail from West Africa may have a genetic edge in sprinting, but that does not explain why so many Jamaican athletes have the desire to train for sprint events. We will look at the interplay between culture and sports success next.
Just as Kenya is known for producing talented distance runners, Jamaica has a reputation for producing talented sprinters. Epstein notes that the national 100m dash record-holders in Canada and Great Britain are both originally from Jamaica, and many of the top sprinters in the US have Jamaican roots.
(Shortform note: Most Jamaicans have West African heritage due to the slave trade, and so will share the characteristic high ratio of type 2 muscle fibers discussed in the previous section.)
In a similar pattern to Kenyan runners being heavily represented by the Kalenjin tribe, many top Jamaican sprinters come from Trelawny, a smaller community in the Northwest of the country. Both Usain Bolt and Veronica Campbell-Brown (who won gold in the 100 and 200 and 100m sprints respectively at the 2008 Olympics) are from Trelawny.
Just as scientists have yet to pin down why athletes in the Rift Valley seem to have adapted to altitude in a uniquely athletic way, researchers are not yet able to explain why more sprinters come from Jamaica. Since Jamaicans have largely West African ancestry, a high ratio of fast twitch muscle fibers may provide an initial advantage, but this does not explain how Jamaica continues to produce a disproportionately large number of elite sprinters. Epstein notes that Jamaican culture can help explain why so many talented Jamaican athletes focus on sprinting.
Reason #1: As Epstein describes it, youth track is to Jamaica what football is to the United States. Epstein describes the Jamaican running event CHAMPS (the national high school track and field championships) as an event akin to the American Super Bowl. One hundred high schools compete over four days, with a stadium full of fans as well as talent scouts from American colleges. The event is even more popular than professional sports in Jamaica.
Championship track meets can certainly draw large crowds in the United States, but they do not carry the excitement, fan base, and potential for celebrity found in important football or basketball games. Epstein notes that there are likely many talented young athletes in the United States who could be very successful in track and field but chose to focus on more popular sports instead. (Another example of nature and nurture, these athletes may have the nature for sprinting but chose football based on nurture.)
(Shortform note: According to a Gallup poll, the most popular sports (measured by viewership) in the United States are football, basketball, baseball, and soccer, in that order. Less than 0.5% of people chose track and field as their favorite sport to watch. This helps to explain why young American athletes would choose to focus on the four sports listed above instead of focusing their speed on the track. In fact, in The Sports Gene, Epstein notes that some people worry that the growing popularity of basketball in Jamaica may draw some promising athletes away from the track.)
Reason #2: Jamaican coaches do not overtrain athletes: Like the Kalenjin, who believe that runners can take up the sport at any age if they have the will and ability, Jamaican coaches are not in a rush to get promising young athletes into rigorous training programs. Epstein notes that, until athletes are 15 or 16, they do not run every day or lift weights, and coaches cautiously avoid overtraining. Epstein also notes that Jamaican coaches believe that the NCAA over-races track and field athletes.
(Shortform note: It is worth noting that the two cultures that arguably produce the world’s top runners both display a different mentality toward age and sports than is common in the United States. Epstein notes that there is a general rush to get promising young athletes in the US into training programs as young as possible, before it is “too late,” Both Kenyan and Jamaican cultures have a more relaxed idea about talent, believing that innate talent will emerge when the athletes are ready.)
Reason #3: While children are not pushed into early hard training, children in Jamaica are pushed to try sprinting from a young age. Young children who show potential are recruited to high schools with competitive track teams, and high school students are even sponsored by local retailers. That such an interest is taken in runners at such a young age is a testament to the cultural importance of sprinting events in Jamaica.
In Jamaican sprinting, we see a similar scenario to Kenyan running. A naturally talented pool of athletes choose to focus on a particular sport in part because of cultural encouragement. Jamaican sprinters may possess a natural talent in sprinting due to their naturally high ratio of type 2 muscle fibers, but they choose to put those gifts to use in sprinting because it is part of the culture that they grew up in. Again, we see that nature and nurture create elite athletes. Epstein suggests that if these naturally gifted athletes were raised in the United States, many of them would likely focus on football (or other popular sports) instead of sprinting, since football holds a special place in American culture.
Other Sports Dynasties
Kenya and Jamaica are not the only countries that have developed a “dynasty” in certain sports. Epstein notes that German athletes have taken first place in dressage events at every Olympic games held between 1984 and 2008. He adds that rather than German people having genes well suited to dressage, this likely has to do with the cultural value placed on the sport. Other well-known sports dynasties listed in a Washington Post article include:
The United States in women’s basketball (winning nine out of 10 Olympic gold medals since 1984)
Great Britain in the men’s coxless 4x rowing event (winning five straight gold medals)
Chinese women in singles table tennis (who have taken every Olympic gold medal since 1988)
Perhaps the most impressive of these dynasties is the South Korean women in the Olympic three-person archery event. They have won every possible gold medal since the event was added to the Olympics in 1988. An article from the BBC provides insight into how South Korea consistently produces the world’s best archers. Once again, culture plays a large role.
The article notes that South Korean children begin archery lessons in primary school. Young children who show talent receive up to two hours of training a day (proponents of the 10,000-hour rule would likely cite this as the primary reason for their success). The best archers go on to be employed by private companies that fund their own archery teams. This means that there is a large pool of professional archers in South Korea who are paid to continue to hone their skills. The article also cites innovative, science-based training programs and huge amounts of money spent on training venues and equipment as reasons for South Korean success.
The statistics on Kenyan running dominance are impressive, and they certainly suggest a naturally superior running ability in Kenyan marathoners. However, Kenyans are not the only runners with body types ideally suited for distance running. While traits such as long slender legs, thin lower legs, and altitude adaptations are more common in the Rift Valley than in other parts of the world, that does not mean that they are unique to Kenya. Epstein cites a paper in the European Journal of Applied Physiology comparing running economies (a measure of how biomechanically efficient runners are) between elite Kalenjin runners and elite European marathoners with the same finishing time (2:08). The study found that the running economies between groups were too similar to explain Kenyan running dominance.
Epstein cites this study as an example of how both nature and nurture together create elite athletes. He notes that, although they would be the exception rather than the rule, there are plenty of people with similar body types to Kenyan runners in other countries. However, there are far fewer athletes with the combination of the “ideal” body type and Herculean motivation to train outside of Kenya. Epstein cites three reasons for this exceptional motivation:
Age and Endurance
Up to age 50, non-elite marathon runners often do not slow down, and may even continue to speed up. An article in The Guardian cites statistics showing that non-elite male and female marathoners in their 40s ran faster than marathoners in their 20s. The article cites a different mentality that comes with age as part of the explanation, noting that older runners are more patient, more relaxed, and more experienced than younger athletes. That age-related wisdom can trump physical prowess is another reason to take findings of specific genes and sports performance as simply a small piece of a large puzzle.
Kalenjin Runners and Exceptional Mental Toughness
An NPR article highlighting the success of Kalenjin runners offers an additional culturally-based explanation for why Kalenjin runners are so successful. The article proposes that in addition to physiological advantages, athletes from this tribe are conditioned to have an exceptionally high pain tolerance. According to the article, learning to tolerate pain is an important part of growing up in the Kalenjin tribe. The article describes pain ceremonies as a rite of passage where teenagers prove their mental toughness to the rest of the tribe.
Highlighted elements of the ceremony include crawling through a tunnel of stinging nettles, being beaten, and being circumcised with a sharp stick. During some of these proceedings, participants wear a mask of dried mud on their faces. They are expected to remain stoic throughout, and if the mud cracks from wincing they are labeled as a “coward” by their communities. After the ceremony and before wounds are healed, participants are expected to run instead of walk wherever they go, with the idea being that they need to learn to run through the pain. In a sport such as the marathon, where athletes push themselves through discomfort for hours, high pain tolerance is a clear advantage.
The article notes that pain ceremonies are likely to become far less common as the tribe becomes more modernized. However, the cultural value of toughness in the face of pain can still be passed down without these rituals.
While the answer to why Kenyans dominate distance running to such a degree is neither finalized nor simple, we can say that the combination of an “ideal” body type for their sport, the ideal altitude scenario for an athlete, a training regimen that began in childhood (whether or not it was recognized as such), a culture which normalizes running aspirations regardless of age or experience, and exceptional motivation can all help to explain Kenyan dominance in distance running events. Since none of these factors alone can account for their success, Epstein uses Kenyan runners as a perfect example of a combination of nature and nurture creates elite athletes.
Just as culture can help explain why certain people become elite athletes, it can also help explain why others do not. Epstein notes that since athletes from Kenya and Ethiopia have had such success on the world stage, it would make sense to expect to see successful runners from adjacent Southern Sudan. However, he notes that at the time of writing, it was a rarity to see a Sudanese runner in international competitions. This is because Sudan had been embroiled in a violent conflict that has prevented athletes from training and competing.
Since data was unavailable, Epstein used the “Lost Boys of Sudan” (a group of 3,600 boys who fled violence in their country and were ultimately housed with foster families around the US) as a case study. Many of the “Lost Boys” found running success shortly after arriving in the United States, becoming some of the top school-age runners in their respective states. Epstein notes that 22 of 3,600 were successful enough to have articles published about them. While 22 might seem like a small number, he notes that this would be like 22 exceptional runners coming out of the same big high school at roughly the same time—an unlikely scenario. Two notable members of this group include Lopez Lomong (who made two Olympic teams and was the US flag bearer in Beijing) and Guor Maria (who made the Olympic marathon team in 2011).
(Shortform note: South Sudan competed as a country in the 2016 and 2021 summer Olympics. While they have not won any medals yet, the country has only sent five athletes to the Olympic games so far. All of them have been runners.)
In the Afterword of The Sports Gene, Epstein invites us to explore our unique genome by trying new sports and experiencing personal growth and discovery through a training program. As his research findings and stories show, we never know what we may be good at unless we try!
(Shortform note: These invitations convey a tone of optimism and possibility. Our takeaway from The Sports Gene should not be that we don’t have the “right” genes to excel in sports. Instead, the book invites us to explore how our own genes, environment, culture, and training interact. Perhaps the most important takeaway from The Sports Gene is that we should be patient with ourselves and others along our sports journeys. If we are open to trying new things, we will likely find a sport that feels like a “natural” fit. While we may not end up in the Olympics, understanding that our bodies are programmed to have their own strengths and weaknesses can help us identify a sport that we find personally rewarding.)