The Sports Gene: Inside the Science of Extraordinary Athletic Performance

The ACTN3 gene, discovered by geneticist Kathryn North, is often referred to as a “gene for speed” (155). In the body, ACTN3 codes for the alpha-actinin-3 structural protein that’s found in fast-twitch muscle fibers. North found that one variant of that gene, called the X variant, stopped production of alpha-actinin-3 structural protein. Her research found that the X variant “had been favored by natural selection only in non-African environments” (154), almost no elite sprinters had two X variants, and “nearly all of the control subjects from African populations” had the protein in their fast-twitch muscles (155).

This is the term coined by Australian sports scientists Kevin Norton and Tim Olds to describe the explosive shift in the late 20th century away from an “average” and presumably ideal athletic body type. As Epstein describes the researchers’ findings, “Early in the twentieth century, the top athletes from every sport clustered around that ‘average’ physique […], but they had since blasted apart in all directions” (116). Epstein cites female gymnastics and male basketball as highly visible examples of this specialization of body types.

First introduced in “Beat by an Underhand Girl,” “chunking theory” holds that “experts unconsciously group information into a smaller number of meaningful chunks based on patterns that they have seen before” (10). Epstein explains that athletes chunk information to process information “without thinking,” leading to quick reaction times in sports like baseball and tennis.

Human muscles contain two major types of fibers: slow-twitch and fast-twitch. Generally speaking, athletes with more fast-twitch fibers do better at sprinting sports, whereas athletes with more slow-twitch fibers do better at endurance sports. Epstein introduces these terms in Chapter 6, and he refers to them repeatedly as they emerge in discussions about genetic mutations, evolution, and genetic profiles of ethnic groups.

A York University study in the late 1990s, led by kinesiology professor Norman Gledhill and his colleague Veronica Jamnik, tested the aerobic capacity of 1,900 young men and found that six had the aerobic capacity of collegiate runners despite having “no history of training whatsoever” (91). The data of the “naturally fit six,” if extrapolated, would suggest that “there are more than 100,000 naturally fit people in the United States between the ages of twenty and sixty-five” (95). This information appears in “The Talent of Trainability,” which explores genetic advantages in trainability and the existence of people who begin that training with a naturally higher baseline fitness, also determined by genetics.

The HERITAGE (HEalth, RIsk factors, exercise Training And GEnetics) Family Study was a 1992 project that combined the forces of five universities in the United States and Canada to test how five months of stationary-bicycle training would affect two-generation families (79-80). The inclusion of family members allowed researchers to look at responses to training within groups of people with similar DNA and between groups with different DNA. Researchers used a metric of aerobic capacity to monitor a person’s aerobic improvement. In 2011, the HERITAGE group identified 21 gene variants that “predict the inherited component of an individual subject’s aerobic improvement” (82). Researchers found that “subjects who had at least nineteen of the ‘favorable’ versions of the genes improved their VO2 max nearly three times as much as subjects who had fewer than ten” (82). Epstein uses HERITAGE, and the studies it inspired, to explain the genetic components in trainability.

Hypertrophic Cardiomyopathy is a “genetic disease that causes the walls of the left ventricle of the heart to thicken, such that it does not relax completely between beats and can impede blood flow into the heart itself” (245). Epstein introduces this term after telling the story of his former high school track teammate who dropped dead on the finish line, absent any warning signs or a history of unhealthiness; Epstein adds, “HCM is the most common cause of natural sudden death in young people. And it’s easily the most common cause of sudden death in young athletes” (245). Scientists now know (as of 2012) that “18 different genes and 1,452 different mutations” can cause HCM, and that families can pass down the mutation, or “mutations can occur randomly in someone with no family history of the disease” (247). Athletes can screen their genes for known HCM mutations, giving them knowledge that may influence their decision about whether to pursue a life in sports.

The Kalenjins are an ethnic group living in and around Kenya’s Rift Valley, known in the sports world for producing elite long- and middle-distance runners. Theories about the overrepresentation of Kalenjins on the world running stage include one that describes “a reproductive advantage that favored men with superior distance running genes” in "traditionally pastoralist cultures that once practiced cattle raiding” (190), as well as about physiological advantages like the “volume and average thickness of the lower legs” and the “running economy” thereby gained (197). Kalenjin ancestry finds its origins in the Nile Valley, where “the Nilotic body type evolved in low latitude environments that are both hot and dry, and because the long, thin proportions are better for cooling” (199).

The myostatin gene and its protein, also called myostatin, signal the stoppage of muscle growth. In the absence of that gene, animals (including humans) continue to grow muscle past the point of people who possess the gene. Myostatin was discovered as the “gene that produced ‘double muscle’ in mice” (101), and researchers develop myostatin therapies for people with muscle-wasting diseases, as well as to combat aging. Cows, whippets (racing dogs), and thoroughbred racehorses all benefit from a myostatin mutation that gives them more muscle. Epstein introduces the discovery of myostatin as part of a discussion of genetically influenced sports advantages.

The recent African origin model is a theory that “every modern human outside of African can trace his or her ancestry to a single population that resided in sub-Saharan East Africa as recently as ninety thousand years ago” (144). Epstein refers to this model in tracing genetic diversity between and within ethnic groups in his search to identify genetic traits that may confer athletic advantages.