A human gene, the tiny unit of matter made up of a sequence of deoxyribonucleic acid (DNA), is the fundamental item in the determination of heredity. Genetics is the science of genes, heredity, and the variation of all organisms. How much athletic ability present in a particular person is attributable to genetics, and how much is determined by training and other adaptations made by the athlete.
Genetics has long played a role in the understanding of sports performance. Certain body types are well suited to particular types of athletic functions and movements. The Rift Valley of Africa, which includes countries such as Kenya and Ethiopia, has produced more world- and Olympic-champion distance runners than any other place on Earth, due to the slender, relatively long-striding people of that district, who live at altitudes in excess of 6,562 ft (2,000 m). These physical attributes have created a superlative human form for distance running. The people who live near the Baltic Sea in northeast Europe, including Lithuanians and Russians, possess tall, lean, muscular frames, ideally suited to sports such as basketball. These two examples are based on a broad range of experience and athletic success that these groups have enjoyed in the stated sports; genetics research seeks to uncover the scientific foundation in support of these observations.
Genetics is a science distinct from considerations of race or ethnicity. Since 1990, there have been intense research undertakings that have delved into the issues surrounding human genetics, the most comprehensive of them the Human Genome Project. It is now understood that 99.9% of the human DNA sequence is common to all of the world population. The 0.1% remainder is the source of all genetic differences between people. With the intermingling of different populations over the centuries, it may be no exaggeration that while there are certain clear genetic traits that are common to broad groupings of people, individual uniqueness is so profound that every person of the world's population of almost seven billion could be described as being their own race.
The conflict between how much athletic ability is rooted in individual genetics as opposed to the influence of training and other factors is often expressed as "nature versus nurture." Genetic makeup will never be determinative in the success of an athlete in a particular sport; gene structure will be a very useful indicator by potential success that must be weighed with the nurturing that athletes receive in their chosen disciplines. Although precise attribution between athletic nature and nurture are impossible, it is a generally accepted sport science proposition that genes represent approximately 50% of athletic variation in performance, with 50% attributable to both the individual athlete's response to training, as well as social factors, such as the support provided to the athlete in pursuit of his or her goals.
An example is the very tall northern European male, who at a height of 7 ft (2 m) would seem to be a far more attractive recruit to the sport of basketball than a person 5 ft 10 in (1.7 m). The gene-governing height present in the taller male represents a potential dominant physical factor, but never a determinative one, as height is but one component of basketball success. Coordination, agility, spatial sense, determination, resilience, and intelligence are all traits that are essential; each is one that may not be capable of development in an athlete, irrespective of height. The fact that a runner comes from the Rift Valley area of Africa, with the genetic makeup that has been a basis for the multitude of successes for similar athletes in middle distances and the marathon, does not guarantee elite athletic status, as training and the determination to compete against similarly endowed and talented runners will spell the difference. Genetics provides certain indications, but not crystal clear predictions, of future success in any sport. An identified genetic trait, coupled with specific training adaptations, will generally create the desired sport result.
There are a number of critical training factors constructed upon the inherent individual physical traits that will influence athletic success. The ability to increase one's maximum oxygen uptake, expressed as VO2 max, is one such factor. A greater VO2 max represents a correspondingly enhanced ability to convert the bodily fuel sources into energy. VO2 max is a genetic characteristic that may be typically increased through training between 10% and 15%; exceptional athletes have experienced VO2 max gains of 30%.
As a further example of the interrelationship between genetic makeup and training determination, studies with elite endurance athletes such as cyclist Lance Armstrong confirm that intense, long-term endurance training will modify the ratio of fast-twitch, explosive muscle fibers and slow-twitch, endurance fibers present in the musculoskeletal structure, producing more useful sport-specific muscles.
It is also apparent that the importance of genetics in the prediction of athletic performance is less pronounced when the sport requires the development of a specific set of technical skills, placing primary emphasis upon efficient technique and error-free
The mental toughness or determination of the individual athlete is also a potential equalizing factor when balanced against apparently superior genetics. It has been said that sport success represents a combination of preparation, training, determination, and genetic makeup.