There are sports such as weightlifting, marathon and 100 meter speed, in which performance depends almost exclusively on these variables ( strength, endurance and speed ). Other mixed sports depend on the optimal use of combinations between different capacities and even tactics, strategy and synergy with other athletes (soccer, tennis …).
Stand out in a sport, especially in those that require more pure capacities, is conditioned by the ability of our muscles to contract with more or less intensity at greater or lesser speed, using different metabolic substrates (‘gasoline vs. Diesel’ ). The muscle specializes by adapting to the stimulus in order to perform said stimulus in the future with greater efficiency (lower metabolic expenditure for the same effort) and efficacy (better performance). Another determinant of performance is anthropometry – study of the proportions and measurements of the human body -, which can be genetically conditioned.
A question of mitochondria
The ability to maintain a muscle contraction for a longer time –muscle resistance– is conditioned by the ability to use different metabolic substrates in the cellular motors, the mitochondria . Our muscles develop more force if they manage to generate extra protein structure (hypertrophy) that allows them to maintain greater tension, and they will be faster if the structures that allow muscle contraction, the sarcomeres, are capable of being shortened with sufficient efficiency. The biological mechanisms responsible for these adaptations are well known from sports physiology . However, relatively little is known about the genes that condition a person’s biology so that they are more likely to have resistant, strong or fast muscles.
There have been countless studies that sought to associate a gene (or a modification of a gene, known as a polymorphism) with a sport or physical ability. However, the conclusions are controversial and in few cases a consensus with sufficient scientific rigor has been reached. For example, the genes responsible for a person having a maximum oxygen consumption before starting a workout are not the same genes that determine the response capacity of that maximum oxygen consumption to a workout.
On the other hand, our anthropometry conditions the ability to excel in a sport. To be a good marathoner, you must have light legs and little weight, while the best basketball players tend to be very tall. Genome-wide studies (GWAS) have shown that the genes that make an African taller do not have to be the same genes that make a European taller.
An exception to the lack of correlation between a gene and a physical ability, in this case potency, is represented by the alpha-actinin 3 (ACTN3) gene. The protein that this gene encodes is required for explosive muscle contractions . A polymorphism of the ACTN3 gene, called R577X, has been identified that causes muscles to contract with less explosiveness, making us slower but more resistant to fatigue and metabolically more efficient.
This is a natural mutation that is estimated to have arisen approximately 50,000 years ago when our species migrated from Africa to Europe and Asia, thus favoring being more resistant to the detriment of explosiveness. Currently, approximately 1 billion people around the world are considered to have this genetic variation. In sports, the homozygous ‘null’ genotype (XX) is infrequent among Jamaicans and African Americans, the great protagonists of speed events; as well as elite footballers, a predominantly explosive sport. However, the existence of an association does not imply causality. There are athletes of reputed level who, being XX homozygous for the ACTN3 gene, have become elite in sports specialties where muscle power and explosiveness prevail, such as soccer.
Another, somewhat more controversial example is the gene for angiotensin converting enzyme (ACE). Its I allele has been associated with better endurance, while the D allele of this gene is common in sports of strength and muscular explosiveness. A recent study has analyzed 346 elite sprinters of whom only one athlete with a homozygous genotype for ACE II – and none for the XX variant of ACTN3 – recorded a better time in the 200-meter event than those classified for the final of this modality in the Olympic Games in London. In addition, sprinters with the ACE DD genotype made better times in the 400-meter race than those with the ACE II. Given the solid evidence found in animal research models, numerous studies have been carried out that have attempted to link the myostatin gene, whose protein limits muscle hypertrophy, with muscle strength. However, these studies are not conclusive enough.
Of the 20,000-25,000 genes that the Human Genome Project estimates a person has, only 2 have been associated with basic physical abilities, with sufficient scientific rigor. This fact shows the complexity in the interrelation of the different genes to generate a specific muscular ability that translates into performance for a sport modality.
So, is the athlete born or made?
To solve the classic dilemma of whether an athlete is ‘born or made’ (or ‘genetics vs. environment’), we have to resort to the branch of genetics known as epigenetics, which studies how certain genes are expressed and inhibited in a function of external factors such as training, diet, climate, exposure to pollutants and even a mother’s treatment of her child in its first years of life. Genes may determine our athletic performance, but we don’t yet know what genes they are.
Helios Pareja and Javier Morales Rojas are researchers at the Doctoral and Research School of the European University
