For decades, athletes have run, jumped, skated, and skied their way into Olympic history. The rest of us watch with wonder, stunned by their unbelievable achievements, left struggling to grasp the reality of their physical feats. To us, many Olympians seem like anomalies in the human continuum, superfast, superstrong superathletes—clearly different from the type of person who prefers the couch to the gym.
The recipe for Olympic success is far more complicated than simply owning athletic genes, but genetics can have an influence and possibly enough to make the difference between silver and gold when it comes to the Olympic Games. Genetic variations, changes in DNA sequences that produce different forms of genes, can translate to phenotypic, or observable, traits, such as increased muscle mass. Together with the right combination of environmental influences—such as diet, exercise, and training—certain genetic variations could help propel an athlete to a higher level of performance.
Variations on Elite Performance
Examples of genes containing variations associated with athletic ability are ADRA2A (alpha-2A adrenergic receptor), ACE (angiotensin-converting enzyme), NOS3 (nitric oxide synthase 3), and ACTN3 (alpha-actinin-3). Of these, the ACE gene has received the most attention. This gene produces an enzyme that regulates blood pressure, and two different forms of the ACE gene, known as the D allele and the I allele, have been identified in elite athletes.
Olympic-caliber distance runners typically possess the I allele, which reduces circulating levels and activity of ACE. Those reductions are associated with increased relaxation of blood vessels. The gene also uses an indirect mechanism, namely the activation of other genes, to influence glucose uptake by skeletal muscle and to optimize oxygen utilization and energy production.
In contrast, elite swimmers and sprinters typically have the D allele, which is believed to result in increased muscle power via ACE’s ability to induce cell growth. In general these athletes rely more heavily on power than endurance athletes. Although it is not known for certain, the D allele appears to facilitate increased growth of the types of muscle fibers that power athletes rely on for explosive speed.
Genes and Training
The other half of the elite athlete equation relies on discipline and training, which takes advantage of the fact that genes are dynamic, able to switch between inactive and active states in reaction to what we eat and do. Several genes, including PPAR delta (peroxisome proliferator-activated receptor delta) and PGC-1 alpha (PPAR gamma coactivator 1 alpha), represent the impact that physical training has on altering gene activity. Activation of these genes is stimulated by exercise and is linked with higher production of type 1 (slow twitch) muscle fibers, which are the dominant fiber type in endurance athletes.
Two other genes, IL-6 (interleukin-6) and IL-6R (IL-6 receptor), have also been studied in athletes. The IL-6 gene produces an anti-inflammatory protein (IL-6) that is released by immune cells and binds to the IL-6 receptor to regulate immune response. High levels of both IL-6 and its receptor have been associated with chronic fatigue syndrome. In athletes, IL-6 receptor production increases with increasing exertion, and having more receptors raises sensitivity to IL-6 and triggers fatigue. Some athletes are resistant to IL-6, but whether there are precise gene variations or whether training gives rise to this resistance is not known.
There are many other genes able to adapt to exercise and training in athletes, including genes involved in increasing cardiac output (volume of blood pumped by the heart per minute), maximal oxygen uptake, and oxygen delivery to muscles. A well-known gene that influences blood oxygen levels is EPO (erythropoietin), activity of which is increased in athletes who train at high altitudes.
The Kenyan Question
The great success of many Kenyan endurance athletes has drawn attention to their genetics. Studies have shown that African distance runners have reduced lactic acid accumulation in muscles, increased resistance to fatigue, and increased oxidative enzyme activity, which equates with high levels of aerobic energy production. Several genetic variations have been proposed to play a role in giving African athletes a possible advantage in endurance sports. Among the implicated genes are ACE and ACTN3.