ABSTRACT
This chapter summarizes published work that quantifies genetic contributions to endurance-related traits both in the intrinsic state (i.e., in the sedentary state at baseline) and following exercise training using traditional family and twin study approaches in humans. There are large interindividual differences in endurance-related phenotypes, which may be affected by age, sex, physical activity, and fitness levels. Additionally, numerous twin and family studies have provided evidence that endurance-related traits clearly aggregate in families and have a significant genetic component in the intrinsic state. Both animal and human studies provide strong evidence that there is a significant genetic component to endurance-related traits. Importantly, the genetic component is thought to affect both the intrinsic level of endurance in the untrained state and responsiveness to endurance training. In general, the heritability estimates tend to be lower for endurance response phenotypes as compared to intrinsic phenotypes.
