Book Review: The Sports Gene

The Sports Gene is by David Epstein. The subtitle is “Inside the Science of Extraordinary Athletic Performance”.

Body Shape

Different body types excel at different tasks — in football, wide receivers and linemen have different body shapes, and there’s a reason for that. And different genetic groups can have, on average, different body types:

In 1877, American zoologist Joel Asaph Allen published a seminal paper in which he noted that the extremities of animals get longer and thinner as one travels closer to the equator. African elephants can be distinguished from Asian elephants by their sail-like floppy ears.

A 1998 analysis…found that the higher the average annual temperature of a geographic region, the proportionally longer the legs of the people whose ancestors had historically resided there…Low-latitude Africans and Australian Aborigines had the proportionally longest legs and shortest torsos. So this is not strictly about ethnicity so much as geography. Or latitude and climate, to be more precise. Africans with ancestry in southern regions of the continent, farther from the equator, do not necessarily have especially long limbs.

And different types of physical activity are more or less efficient with different bodies, due purely to the mechanics/physics of how bodies move. Longer legs are usually better for running:

[R]esearchers...used engineering models of bodies moving through fluids—air or water—to determine that the 3 percent difference [in height of one’s center of gravity] translates into a 1.5 percent running speed advantage for athletes with the higher belly buttons and a 1.5 percent swimming speed advantage for athletes with a lower belly button…

Michael Phelps, at 6'4", reportedly buys pants with a 32-inch inseam, shorter than those worn by Hicham El Guerrouj, the Moroccan runner who is 5'9" and holds the world record in the mile.

The amount of weight at the end of the leg also has a big effect on running efficiency. Again, this is just due to the basic physics of moving bodies:

...the leg is akin to a pendulum, and the greater the weight at the end of the pendulum, the more energy is required to swing it…

Weight that is far out on the limbs is called “distal weight,” and the less of it a distance runner has, the better. A separate research team calculated that adding just one tenth of one pound to the ankle increases oxygen consumption during running by about 1 percent.

Epstein argues that this is one reason why distance runners from Eastern Africa are so dominant (The term “Kalenjin” below refers to the group of people who are most over-represented in Kenyan running. “The 4.9 million Kalenjin people represent about 12 percent of Kenya’s population, but more than three quarters of the country’s top runners.”):

The volume and average thickness of the lower legs of the Kalenjin boys was 15 to 17 percent less than in Danish boys…

Compared with the Danish runners, the Kalenjin runners tested by the Danish scientists had nearly a pound less weight in their lower legs. The scientists calculated the energy savings at 8 percent per kilometer.

A smaller lower leg is better for overall running efficiency. Continuing on with body shape differences in the lower leg, there’s the Achilles tendon, which is a “spring” — and a longer one can store more energy. Epstein recounts the story of Donald Thomas, a high jumper who was a natural prodigy. Quoting from Wikipedia:

He tried high jump for the first time when challenged by members of the track and field team, who were reacting to his claims about his ability to slam dunk. Thomas cleared 6'6" on his first attempt and 7' on his third ever jump. The athletes then sought the head track coach Lane Lohr, who entered Thomas in a meet two days later at Eastern Illinois University. At the meet he cleared 7'3.25", on his seventh-ever jump.

The above story happened in January 2006. He then won the 2007 world championship.

Whereas [the Achilles of another top high-jumper] was a more normal-sized, incredibly stiff spring, Thomas’s, at ten and a quarter inches, was uncharacteristically long for an athlete his height. The longer (and stiffer) the Achilles tendon, the more elastic energy it can store when compressed…

The Achilles tendon is very important in jumping, and not just in humans…For example, the tendon in the kangaroo that’s equivalent to our Achilles tendon is very, very long.

In basketball, there’s a specialization towards long arms:

In NBA predraft measurements for active players, the average white American NBA player was 6'7½" with a wingspan of 6'10". The average African American NBA player was 6'5½" with a 6'11" wingspan; shorter but longer. Both white and black players in the NBA have wingspan-to-height ratios much greater than the population average, but there’s a sizable gap between white and black players. The average ratio for a white American NBA player is 1.035, and for an African American NBA player 1.071.

One last note on body shape: it can sometimes lead to differences between in-game performance and the fitness tests that are intended to predict that performance:

Bench press is much easier for men with shorter arms, but longer arms are better for everything on the actual football field.

On a personal level, I’m not an especially tall person, and I have short legs for my height. But at the same time, reading The Sports Gene didn’t leave me with a negative outlook on my athletic potential. Although I may not have the body type to be an NBA player, at the same time I know that I’m limited by my training much more than I’m limited by my body shape. The main reason I’m not more athletic is because I’m not training more, not because I have the wrong body shape. Epstein interviews an employee at a rugby training facility who says, “We’ve tested over ten thousand boys, and I’ve never seen a boy who was slow become fast.” But it seems that he’s talking about (1) truly world-class elite speed and (2) athletes who were already training hard. An average athlete like me can become a lot faster through training — even if an elite athlete without elite speed has no hope of ever gaining truly elite speed.

Some other interesting genes

Some genetic factors are discussed in detail over a number of chapters; others get less time on the page. Here are a few other genetic differences that influence athletic ability:

1. Naturally having more blood:

In the late nineties, [researchers] set out to see whether they could identify and study such naturally fit folk…Over two years, the team gave VO2max tests to 1,900 young men.

Among them were six men with absolutely no history of training whatsoever who nonetheless had aerobic capacities on par with collegiate runners…the naturally fit men had a crucial gift, through no discipline or effort of their own: massive helpings of blood.

One family is discussed that has a genetic mutation to a single “letter” of their DNA. This came from a later chapter and it wasn’t clear if the mutation in this family was the same as the six men discussed above. To me, that is pretty crazy. One single changed letter in our multi-billion letter genetic code can turn a family of otherwise average folks to a group that’s capable of Olympic greatness (with the right training!). It really can come down to differences that are that small:

…But at position 6,002 in only one copy of each affected family member’s two EPOR genes, there was an adenine molecule instead of a guanine molecule. A minuscule alteration, but the impact was immense... In the affected Mäntyrantas, the production of red blood cells runs amok.

2. There’s a protein called myostatin whose function is, essentially, to stop muscle growth (The image search results for “mysotatin” are a bunch of unimaginably buff people and animals). Some animals and people have genetic mutations that cause their bodies to produce less or no myostatin. And as a result...they grow lots of muscle. The book tells the story of a baby who was born looking super buff:

Superbaby’s mother had one typical myostatin gene and one mutant myostatin gene, leaving her with more myostatin than her son but less than the average person. She was the only adult with a documented myostatin mutation, and she was a professional sprinter.

3. Wanting to train. Studies in lab animals and sled dog breeding experience have proved that wanting to be active is partly due to specific genetic factors (Epstein says in a footnote, “Anything that can be bred for must have a genetic component, or else the breeding would not work”). One study of twins found that:

The largest study, of 37,051 twin pairs from six European countries and Australia, concluded that about half to three quarters of the variation in the amount of exercise people undertook was attributable to their genetic inheritance

4. Sometimes abilities are, surprisingly, not genetic. Baseball players are not necessarily endowed with amazing reaction time (but they do often have excellent vision). Instead, they’ve just spent years learning the subtle signals that can be seen as a pitcher gets ready to throw (and thus they’ll be unable to hit a pitch requiring the same reaction time but thrown underhand, softball style – they haven’t trained to recognize those cues):

When scientists at Washington University in St. Louis tested him, Pujols, the greatest hitter of an era, was in the sixty-sixth percentile for simple reaction time compared with a random sample of college students.

Men and Women

Men and women are undoubtedly different physically, on average:

Men are twice as likely to be left-handed as women…Men have less fat, denser bones, more oxygen-carrying red blood cells, heavier skeletons that can support more muscle, and narrower hips, which makes running more efficient and decreases the chance of injury—like ACL tears, which are epidemic in female athletes—while running and jumping.

Epstein notes in a footnote that the popular belief that women can tolerate pain better than men is a myth:

The idea that women are more pain tolerant than men because they go through childbirth is a myth contradicted by every study done on the topic. Women are more sensitive to pain and much more likely to be chronic pain patients. Women do, however, become less sensitive to pain as they approach childbirth.

I did a search on this topic, and found that the results generally agree with Epstein’s comment, although I think he goes too far when he says “every study” — here’s one where women come out as better able to handle pain. It also makes me extra curious what the deal is with this story about the period cramp simulator.

The most enlightening part of the discussion of men and women in this book is the few people who are born with bodies that are somewhere between the stereotypical “male” and “female” — and prove that there really is no hard and fast difference between male and female that every human on earth can be separated into:

Doctors ultimately decided that Martínez-Patiño had been treated unfairly. She was, they determined, a woman for competitive purposes. A woman with both a vagina and internal testes, breasts but no ovaries or uterus, and male doses of testosterone that circulated inertly through her body.

Neither body parts nor the chromosomes within them unequivocally differentiate male from female athletes.

Having XY chromosomes with androgen insensitivity is surprisingly common in women’s athletics. It seems there’s a benefit in terms of body shape that makes up for the drawback that their bodies can’t use testosterone at all:

The typical rate of androgen insensitivity is estimated to be between 1 in 20,000 and 1 in 64,000. Over five Olympic Games, an average of 1 in every 421 female competitors was determined to have a Y chromosome…

Women with androgen insensitivity tend to have limb proportions more typical of men. Their arms and legs are longer relative to their bodies, and their average height is several inches taller than that of typical women.

Top Marathoners

In the section “Body Shape” above, I discussed some elements of why some East Africans are so dominant in distance running (long legs and light ankles/feet, on average). I’ll add a bit more here.

1. One study ruled out a few possibilities:

Overall, the findings did not support any of the long-standing but uninvestigated theories. Elite runners from the Kalenjin tribe and from Europe did not differ on average in their proportion of slow-twitch muscle fibers, nor did Danish boys differ from Kalenjin boys who lived in cities or those who lived in rural villages. Kalenjin boys from villages did have higher VO2max than Kalenjin boys from cities, who were much less active, but it was similar to the VO2max of the active Danish boys. And Kalenjin boys, as a group, did not on average respond to three months of endurance training—as measured by aerobic capacity—to a greater degree than did Danish boys.

2. There’s something to be said for the “they just want it more” theory. Kenya is a poor country, and distance running is a way out of poverty. Many of these top runners grew up running to school every day (however, many others did not run to school). One thing seems clear, Americans “want it” less than they used to:

Between 1983 and 1998, the number of U.S. men who ran under 2:20 in the marathon for the year declined from 267 to 35.

But that being said, the differences are too big to just be explained by wanting it more:

five American high-schoolers have run under four minutes in the mile in history; St. Patrick’s High School, in the Kalenjin training town of Iten, once had four sub–four milers in school at the same time.

3. There are differences that come from living/growing up at altitude:

Altitude natives who are born and go through childhood at elevation tend to have proportionally larger lungs than sea-level natives, and large lungs have large surface areas that permit more oxygen to pass from the lungs into the blood. This cannot be the result of altitude ancestry that has altered genes over generations, because it occurs not only in natives of the Himalayas, but also among American children who do not have altitude ancestry but who grow up high in the Rockies. Once childhood is gone, though, so too is the chance for this adaptation. It is not genetic, but neither is it alterable after adolescence.

4. Finally, there are genetic adaptations found in groups of people who have been living in altitude for thousands of years. This was one of the most interesting parts of the book for me. There are a few groups of people who have been living at high altitudes (say, 8,000+ feet) for thousands of years: they include people in the area of Tibet, people in South America’s Andes, and the Kalenjin and related groups in the Great Rift Valley area. And all of these groups have adapted to altitude in different ways. As Epstein puts it, “why, then, aren’t runners coming down from the Andes and the Himalayas and smoking the rest of the world, as the Ethiopians and Kenyans have done? ”

Andeans:

At that altitude, there are only around 60 percent as many oxygen molecules in each breath of air as at sea level. In order to compensate for the scarce oxygen, Andeans have profuse portions of red blood cells and, within them, oxygen-carrying hemoglobin.

The amount of oxygen in the blood is determined by two factors: how much hemoglobin one has and its “oxygen saturation,” or how much oxygen that hemoglobin is carrying. Because there is so little oxygen in their air, many of the hemoglobin molecules in the blood of the Andean highlanders rush through the body without a full load of oxygen—like roller coaster cars with few passengers. But the Andeans make up for it by having many more cars. This is not necessarily good from an athletic standpoint. Andeans have so much hemoglobin that their blood can become viscous and unable to circulate well, and some Andeans develop chronic mountain sickness.

Tibetans:

...Tibetans survive by having extremely high levels of nitric oxide in their blood. Nitric oxide cues blood vessels in the lungs to relax and widen for blood flow. “The Tibetans have 240 times as much nitric oxide in the blood as we do,” Beall says. “That’s more than in people at sea level who have sepsis,” a life-threatening medical condition. So Tibetans adapted by having very high blood flow in their lungs, and they also breathe deeper and faster than native lowlanders, as if they’re in a constant state of hyperventilation.

And Ethiopians/Kenyans:

The Amhara people [another group living near the Kalenjin] had normal, sea-level allotments of hemoglobin and normal, sea-level oxygen saturation. The same number of roller coaster cars as sea-level natives and nearly all of them were filled, just as in sea-level natives. “If we didn’t know we were at altitude, I would’ve said we were looking at sea-level people,” Beall says. It’s not entirely clear how the Amhara pull this trick off. But Beall has preliminary data on Amhara Ethiopians that shows they move oxygen unusually rapidly from the tiny air sacs in their lungs into their blood.

Top Sprinters

While Epstein offers a few convincing reasons why East African peoples are so good at distance running, the question of why many top sprinters have West African ancestry is less settled. We know that the sickle-cell trait (along with lower average levels of hemoglobin in the blood) is prevalent in West Africa because it protects against malaria: “sub-Saharan Africans with sickle-cell trait have far fewer malaria parasites in their blood than inhabitants of the same region who do not have sickle-cell trait.” And people with sickle-cell trait are over-represented in explosive athletic events (at least in some studies):

About 12 percent of Ivorian citizens are sickle-cell carriers… [but] nearly 30 percent of 122 Ivorian national champions in explosive jumping and throwing events were sickle-cell trait carriers.

The chapter ends inconclusively:

And that is all the science there is. A single mouse study and a single rat study demonstrating in rodents that low hemoglobin can induce a switch to more explosive muscle fibers. No scientist has attempted to test Cooper and Morrison’s idea in humans, so there are simply no human studies at all.

But fast-twitch muscle fibers can have their downsides, even in sports that require explosiveness:

Soccer coaches all want the fastest athletes, so Andersen wondered how it could be that many of the Danish pros have fewer fast-twitch fibers than an average person on the street. He turned to F.C. Copenhagen’s development academy, where he found that the swiftest players are lost to chronic injuries before they ever reach the top level. “The guys that have the very fast muscles can’t really tolerate as much training as the others,” he says. “The guys with a lot of [fast-twitch fibers] that can contract their muscles very fast have much more risk of a hamstring injury…”

Epstein suggests that this can be worked around by using a training program that is unique to each individual’s needs (i.e. people who respond more quickly to training or have a high ratio of fast-twitch fibers should train less).