The form and function of the human body is determined by numerous environmental and genetic factors. Characteristics associated with physical performance are ultimately an expression of our genetic blueprint under particular environmental conditions.
If a sportsman has an “ideal” genetic profile and the environment is optimal then we would expect performance to be of a high level. If the environment is less than favorable we can predict that performance would suffer. The following is meant as an introduction to the influence of human gene variation on physical performance.
Heritability 
Heritability is the proportion of observed variation in a particular trait that can be attributed to inherited genetic factors in contrast to environmental.1
Scientists calculate heritability as a value between 0.0 (no contribution of genes to the variation of a trait) to 1.0 (genes are the only reason for the variation in a trait).
As an example, the heritability of height is estimated to be 0.8 or 80%.2 The other 20% would be attributed to variation in environmental factors such as the availability of adequate nutrition.
Inheritance and Endurance
Maximum aerobic capacity is a measure of aerobic fitness and is associated with success in endurance sports.1
Heritability of maximum aerobic capacity has been estimated to be between 4o and 71% percent.4,5 This demonstrates that our genes have a significant effect on our aerobic capacity and in turn potential success in endurance sports.
Inheritance and Muscular Strength
Maximum strength is the maximum amount of force that can be generated during a voluntary muscular contraction. This is an important fitness quality because we know maximum strength is associated with markers of sport performance such as sprint speed.6
Heritability of maximum strength is estimated to be between 29-82%.7,8 This indicates that our genes have a significant effect on the expression of physical strength and in turn potential success in strength sports.
As a side note, the eccentric component involved in maximum strength may be more heritable than the concentric element. This has potential implications for the relation between genetics and eccentric activities such as those involved in downhill skiing.
The list goes on…
Contributions from our genes are numerable and associated with all fitness qualities including susceptibility to injury and response to training. The overall effect of our genes is thought to be responsible for 66% of the difference in athletic status while the remaining 44% is thought to be environmental.11
In addition to the form and function of our bodies genes are also significantly associated with psychological determinants of physical performance such as the motivation to train.8
Bottom Line (TL;DR)
Variation in human performance is greatly influenced by our genes.
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