A well written primer of our understanding of specific genes and their impact on sports performance—from natural physical traits (height, strength, achilles, calf size, etc) to training ability to pain thresholds and more. David tries to balance the nature (genes) vs nurture (environmental) factors. He also points out, repeatedly, that our understanding of impact of specific genes, specially in combinations, is still very incomplete.
Another takeaway, for me, is that much of what our understanding of these genes reveals is what separates the (say) Olympians from everyday people. The performance differences amongst the people at the top is too small to be explained by our current understanding of genes.
Finally, even at the very top, there are multiple paths to get there. The story of two high jumpers illustrated this well.

Beat by an underhand girl

… for the 1980 Olympics, she was dismayed to find that the national coaches were relying on outdated ideas to choose and arrange the team. “They thought everybody saw the team the same way. They were using simple reaction time tests for selection, and they thought it would be a good determinant of who would be the best goalies or strikers.…”

In her (Starkes) occlusion tests of field hockey players, she found that not only were elite field hockey players able to tell faster than the blink of an eye whether a ball was in the frame, they could accurately reconstruct the playing field after just a fleeting glance.
This held true from basketball to soccer. It was as if every elite athlete miraculously had a photographic memory when it came to her sport.


Top tennis players could discern from the minuscule pre-serve shifts of an opponent’s torso whether a shot was going to their forehand or backhand, whereas average players had to wait to see the motion of the racket, costing invaluable response time.

Pro cricket teams have been moving away from using bowling machines, because they don’t train the body recognition skills that hitters need for anticipation.

A tale of two high jumpers

Deliberate practice

“According to the tenets of deliberate practice, you have to be cognitively engaged,” McLaughlin explains.

Dan McLaughlin, undergoing the 10,000 hours scientific experiment to go from a non-golfer to a PGA player.

Just going to the driving range and swatting balls for a few hours without an eye toward improvement and error correction doesn’t cut it.
So, six days a week, McLaughlin puts in six hours of deliberate practice, a workday that consumes eight hours because he takes frequent breaks to think about what he did well and what can be improved—like closing the club face on impact—and because it is exhausting to maintain strict focus for hours on end.


The renowned 10,000 hours violin study only reports the average number of hours of practice. It doesn’t report the range of hours required for the attainment of expertise, so it is impossible to tell whether any individual in the study actually became an elite violinist in 10,000 hours, or whether that was just an average of disparate individual differences.

Matthew effect — from the gospel of Matthew

For to all those who have, more will be given, and they will have an abundance; but from those who have nothing, even what they have will be taken away.

… the larger individual differences increase with equal training, showing a positive correlation with high initial ability with ability to profit by training.
… every subject improved, but the rich got relatively richer. Everyone learned, but the learning rates were consistently different.


Phillip Ackerman on skill acquisition.

In simple tasks, practice brings people closer together, but in complex ones, it often pulls them apart.

Major league vision and the greatest child athlete sample ever

If a player has better visual skills, he can pick up the pitch while it’s five feet or ten feet closer to the pitcher. If he doesn’t, his mechanics might be outstanding but he reacts so late that he breaks his bat because the ball is in on his hands. It’s not the bad speed, it’s the visual skills.

This was researched for baseball batsmen. It is also the story behind my abysmal batting in cricket. Once I saw the ball, I played it well, but I usually saw it very late. This also explains why I played better against slower spinners and non-swinging fast bowlers, and suffered against medium pace that swung a lot.

German tennis study

… the children’s tennis-specific skill scores predicted 60-70 percent of the variance in their eventual adult tennis ranking. But..

The tests of general athleticism—for example, a thirty meter sprint and start and stop agility drills—influenced which children would acquire the tennis-specific skills most rapidly.

Steffi Graf

We called Steffi Graf (under 12yo at the time) the perfect tennis talent. She outperformed the others in tennis specific skills and basic motor skills, and we also predicted from her lung capacity that she could have ended up as the European champion in the 1500-meters.

Graf was at the top of every single test, from measures of her competitive desire to her ability to sustain concentration to her running speed. Years later, when Graf was the best tennis player in the world, she would train for endurance alongside Germany’s Olympic track runners.


It was once thought that as we grow and learn our brain forms neurons. But it now appears that we are born overflowing with neurons and that the ones we don’t use early on are pruned away, and those that we do use are strengthened and interconnected. The brain becomes less broadly flexible but more narrowly efficient.

Why men have nipples

We all begin life as females. Every human embryo is female for the first six weeks of existence. Because mammal fetuses are exposed to a hefty dose of female hormones from the mother, it is more economical to have the default sex be female. In males, in six weeks, the SRY gene cues the formation of testicles and, inside them, the Leydig cells that synthesize testosterone. Within a month, testosterone is gushing and triggering specific genes to turn on and others off.

Sexual selection and muscle mass

If you want to know whether the male or female of a given species is bigger and stronger, one piece of information is particularly useful: which sex has the higher potential reproductive rate.

Because of a long gestation and breastfeeding period, a female gorilla can produce only one offspring about every four years. Male gorillas collect and defend harems of females and have a much higher potential reproductive rate. But for each male gorilla that has a harem, several other males are frozen out of breeding altogether. The result is that male gorillas compete fiercely for access to multiple females, and this “male-male competition” takes the form of fighting and natural selection accentuates traits that make male gorillas better fighters.

In species where females have a higher potential reproductive rate, like seahorses, the situation is reversed, and the females are bigger and more aggressive. Not surprisingly, male seahorses, which care for eggs, prefer larger, stronger females.


This made me feel obese with my 21-22% body fat:

Even the very leanest of adult female marathoners get down to around 6 to 8 percent body fat, double that of their male counterparts.


You can’t program males and females totally separately. Our basic biology is mostly the same, with a little difference. If women didn’t need to run, you could argue that they don’t need the Achilles tendon for springs in their legs. But how would you do that? You would have to have a sex-specific loss of the Achilles.
Instead, nature has left humans with a system whereby—instead of great numbers of genes changing—hormones can selectively activate genes to different effect.

The talent of trainability


Aerobic capacity is a measure of the amount of oxygen a person’s body can use when he or she is running or cycling all out. It is determined by how much blood the heart pumps, how much oxygen the lungs impart to that blood, and how efficient the muscles are at snatching and using the oxygen from the blood as it hurtles past. The more oxygen one can use, the better one’s endurance.

To be fair, VO2Max is not the sole predictor of endurance, but it is important. While knowing the VO2Max of runners in a marathon will not nearly tell you the finishing order, it may tell you which runners are professionals, which are collegians, which are weekend warriors, and which will still be running when the cleanup crews arrive.
In other sports, aerobic capacity might be even more predictive. … data from 1970s showed VO2Max to be a decent predictor of Olympic medals in cross-country skiing.

Endurance exercise effect

Endurance exercise has a profound impact on the human body. More blood is produced and it flows through new capillaries that sprout like roots into muscle. The heart and lungs strengthen, and energy-generating mitochondria proliferate in the cells.


An athlete who stops training can within weeks lose more than 15 percent of the VO2Max he built up.

Superbaby, bully whippets, and the trainability of muscle


The rodents without GDF-8 gene had double muscle.
The researchers named it myostatin. The latin myo-, meaning muscle, and -statin, to halt. Something that myostatin does signals muscles to cease growing. In the absence of myostatin, muscle growth explodes.


Slow-twitch muscle fibers require abundant oxygen, and thus are surrounded by blood vessels, which makes them appear dark.
At Thanksgiving dinner, you can tell that turkeys are primarily walkers, not fliers, because dark meat is in the legs, and white, fast-twitch meat is in the breast. The slow-twitch fibers are iron-rich, so if you’re looking to add iron to your diet, go for turkey legs.


… aerobic training can make fast-twitch fibers more endurant and strength training can make slow-twitch fibers stronger, but they don’t completely flip. Save for extreme circumstances, like if one’s spinal cord is severed, in which case all fibers revert to fast twitch.


Muscle type and training

The guys who have the very fast muscles can’t really tolerate as much training as the others. The guys with a log of fast-twitch fibers that can contract their muscles very fast have much more risk of a hamstring injury, than the guys who cannot do the same type of explosive contraction but who never get injured.

In American football, the big fat guy becomes one position and the fast guy becomes a wide receiver and they train differently. But the soccer players are trained all alike. I hear coaches say all the time, “We can’t use him because he’s always injured.” If he gets injured all the time, it’s probably because we do something wrong to him and we need to change that. We shouldn’t lose the fastest players.

The big bang of body types

Top athletes in jumping sports—basketball, volleyball—not have short torsos and comparatively long legs, better for accelerating the lower limbs to get a more powerful liftoff. Professional boxers come in an array of shapes and sizes, but many have the combination of long arms and short legs, giving greater reach but a lower and more stable center of gravity.
The height of a sprinter is often critical to his best event. The world’s top competitors in the 60 meter sprint are almost always shorter than those in the 100, 200 and 400 meter sprints, because shorter legs and lower mass are advantageous for acceleration.


In other cases, body types have more nuanced effects. While smallness is generally a boon for endurance runners, Paula Radcliffe, at 5’8” is literally head and shoulders above most of her world-class competitors. It didn’t keep iconically tough Brit from winning eight marathons in the prime of her career, 2002 to 2008. But her size may have helped confine her victories to autumn.
One reason that marathon runners tend to be diminutive is because small humans have a larger skin surface area compared with the volume of their body, so more quickly the body unloads heat. (Hence, short, skinny people get cold more easily than tall, hefty people.)


In sports like swimming, kayaking, and lacrosse, athletes tend to have a very high “brachial index”. That is, the forearm is relatively long compared to the upper arm, which makes the arm better suited to propulsion. Weight lifters and wrestlers, who need stability and strength, have very low brachial indices.


Adults with a high proportion of fast-twitch fibers can pack on muscle, they have a more difficult time losing fat. Fat is primarily burned as part of the energy-making process that occurs in slow-twitch muscle fibers. The fewer slow-twitch muscle fibers an individual has, the lower his capacity to burn fat—one possible reason that sprint and power athletes tend to be stockier than endurance athletes, even before and after their competitive years.

Bone to mass ratio

In measurements of thousands of elite athletes from soccer to weight-lifting, wrestling, boxing, judo, rugby, and more, Holway has found that each kilogram of bone supports a maximum of five kilograms of muscle. Five-to-one, then, is a general limit of the human muscle bookcase.

The documented limit for women is closer to 4.2 to 1. And both limits are sans steroids. On steroids, athletes have been able to surpass the 5:1 upper bound.

The vitruvian NBA player

Inhabitants of the industrialised world grew taller over much of the twentieth century at a rate of about one centimeter per decade—at least partly because of increased protein intake and the decline of growth—stunting childhood infections, and perhaps because people are mixing genes more widely, with “tall” genes dominating “short” genes.

Michael Gladwell’s IQ threshold hypothesis

There is a threshold above which more dos not really matter. Above an IQ of 120—which already eliminates most of humanity—one is already smart enough to consider the most difficult intellectual problems, and more IQ does not translate into real-world success.


The permutations of size-determining interactions between nature and nurture are fathomless. Consider that children grow more quickly in spring and summer than in fall and winter, and that this is apparently due to sunlight signals that enter through the eyeballs, since the growth of totally bling children consists of similar fluctuations but are not synchronised with the seasons.


The height that inhabitants of urban societies gained over the twentieth century came principally from increased leg length. Legs got longer faster than torsos. In developing countries that have gaping nutritional and infection-prevention disparities between the middle class and poor, the difference in height between the comfortable and the afflicted is all in the legs.

Malaria and muscle fibers

Using data from nearly 30,000 people in ten different stats, with ages ranging from the first year to the ninth decade, it reported that African Americans have lower hemoglobin levels at every stage of life than white Americans, even when socioeconomic status and diet are matched.


In 2011, scientists from the U of Copenhagen proposed that a high proportion of fast-twitch muscle fibers could account for several physical traits that have been documented in African American and Afro Caribbeans, including low resting and sleeping metabolism, and less metabolism of fat for energy and more of carbohydrates as compared with Europeans.


The concept that physical superiority could somehow be a symptom of intellectual inferiority only developed when physical superiority became associated with African Americans. That association did not begin until about 1936.

Can every Kalenjin run?

Thin calfs = more efficient running

The scientists’s most unique finding was not the length of the legs, but their girth. The volume and average thickness of the lower legs of the Kalenjin boys was 15 to 17 percent less than in the Danish boys.

The finding is substantial because the leg is akin to a pendulum, 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.
… adding just one tenth of one pound to the ankle increases oxygen consumption during running by about 1 percent.

“Running economy” is the measure of how much oxygen a runner utilises to run at a given pace. Elite distance runners have both high VO2Max and good running economy.
Or, to use the car analogy, the rare mix of a big engine and good fuel economy.


This section connected to the Bantu expansion I learnt about in Guns, Germs and Steel.

“Nilotic” refers to a set of related ethnic groups residing in the Nile Valley. And it so happens, the Kalenjin are a Nilotic people.
The nilotic body type evolved in low latitude environments that are both hot and dry, because the long, thin proportions are better for cooling. (Conversely, the extreme of short, stocky build was historically known as the Eskimo type.)


“The genes didn’t go away in Finland, the culture did” — Father Colm O’Connell, coach to elite runners in Iten

“In these days of computer games, sedentary pursuits, and driving our children to school—it is the ‘hungry’ fighter or the poor peasant who has the endurance background and the incentive to work on it, who makes the top distance runner.

The world’s greatest accidental (altitudinous) talent sieve

The similarity (of Kenyan distance running talent) to Jamaican sprinting—or to Canadian hockey, or to Brazilian soccer—is that there is a large number of athletes put in the top of funnel, and a smaller number who display talent and survive the rigorous training and come out the bottom as world beaters.


Mock charity drive on a online track-and-field message board:

Help Americans compete in distance running by donating school buses to Kenyan children.


The optimal altitude

There seems to be a rough “sweet spot for training, an altitude where red blood cell production increases, but not too much. Where the air is thin, but not too thin.
Andeans and Himalayans live far above it. Anecdotally, the sweet spot is around six to nine thousand feet (1800 - 2700m), high enough to cause physiological changes, but not so high that the air is too thin for hard training.

As it happens, the ridges of the Rift Valley in Ethiopia and Kenya are plumb in the sweet spot. The foremost training bases in Kenya: Eldoret, 6890 feet. Iten: 7575 feet. Kapsabet: 6395 feet. Kaptagat: 7870 feet. Nyahururu: 7215 feet. The major training cities in Ethiopia, Addis Ababa and Bekoji, both have running sites around 8000 to 9000 feet. In the US, pro endurance athletes hunting for the sweet sport train in Mammoth Lakes, California: 7800 feet. Or Flagstaff, Arizone: 7000 feet.


Preferable to moving to altitude to train is being born there. 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.


A helpful combination, perhaps, is to have sea-level ancestry—so that hemoglobin can elevate quickly upon training at altitude—but to be born at altitude, in order to develop larger lung surface area, and then to live and train in the sweet spot.
This is exactly the story of legions of Kalenjin Kenyans and Oromo Ethiopians.

Sled dogs, ultra-runners, and couch potato genes

A seemingly compulsive drive to exercise is hardly unique among distinguished athletes. Haile Gebrselassi says: “A day I don’t run, I don’t feel good. Floyd Mayweather Jr has been known to jolt awake in the middle of the night and force his bloated entourage to meet him at the gym for a workout. Steve Mesler, a member of the 2010 Olympic four-man bobsled team says he “feels anxious” when he takes a break from working out even now after retiring. Chrissie Wellington and high jumper Stefan holm, both claim addictive personalities that they channeled to their training.


“One of the issues is when we’ve looked at activity and what controls activity, we’ve forgotten that we know very clearly there are biological mechanisms that actually influence people to be active or not. You can have a predisposition to be a couch potato.”

“Maybe it wasn’t talent the Lord gave me, maybe it was the passion.” —Wayne Gretzky, the greatest ice hockey player in history.

The heartbreak gene

HCM gene causes sudden collapse and death in highly trained athletes. This is due to abnormal enlargement of heart. The grey zone is that without genetic testing, it’s hard to know if the enlargement is due to athletic training or due to the genetic disorder.

APOE4 gene has high correlation with Alzheimers.

The gene comes in three common variants: ApoE2, ApoE3, and ApoE4. Everyone has two copies of the gene, one from mom and one from dad. A single copy of ApoE4 increases the risk of Alzheimer’s threefold. Two copies increases the risk eightfold.

The importance of ApoE gene extends beyond Alzheimer’s to how well an individual can recover from any type of brain injury. Carriers of ApoE4 gene variants who hit their heads in car accidents, for example, have longer comas, more bleeding and bruising in the brain, more post-injury seizures, less success with rehabilitation, and re more likely to suffer permanent damage or to die.

The dementia risk of having a single ApoE4 copy is roughly similar to the risk from playing in the NFL, and the two together are even more dangerous.

MC1R and SCN9A genes - the pain inhibitor genes.
(Melanocortin 1 receptor)

It’s (MC1R) the same gene mutation that is responsible for the ginger locks of most human redheads. Mogil found that people with the redhead mutation have higher tolerance for certain types of pain, and require less morphine for relief.

People born with congenital insensitivity to pain tend not to live very long. They don’t shift their weight when sitting, sleeping, or standing as the rest of us do instinctively, and the die from the joint infections that result.

The perfect athlete

Alun Williams and Jonathan Folland combed though scientific literature for the twenty-three gene variants that have (so far) been most strongly linked to endurance talent, and then they compiled information about how frequently those gene variants occur in humans.

… the odds of any single human possessing the perfect set of gene variants was less than one in a quadrillion.

Yao Ming

Two generations of his forebears had been singled out by authorities or their hulking physiques, and his mother and father were both drafted into the sports system against their will.

“Regression to mean” means that even that the child of two gifted parents will likely be less better than them.

The child of two seven-footers is very likely to be taller than average, but not likely to be as significant of an outlier as his parents.

I loved this paragraph:

Amid the pageantry of the Opening Ceremony at the 2016 Olympics in Rio de Janeiro, make sure to look for the extremes of the human physique. The 4’9: gymnast beside the 310 pound shot putter who is looking up to the 6’10” basketball player whose arms are seven and a half feet from fingertip to fingertip. Or the 6’4” swimmer who strides into the Olympic stadium beside his countryman, the 5’9” miler, both men wearing the same length pants*.

* Earlier in the book he had mentioned how proportionally longer legs are advantageous for runners, and proportionally longer upper bodies are advantageous for swimmers. Hence despite the total height difference, the runner and swimmer have similar leg lengths, and thus similar pant lengths.