The influence of genetic factors on physical functioning and exercise in second half of life.

During the past decades, a number of studies of families and twins in particular have assessed the relative contribution of genetic and environmental factors to traits reflecting various aspects of physical functioning: maximal O2 uptake, muscular endurance, muscular strength, muscle cross sectional area, flexibility, and trainability. Although the estimate of the size of the genetic component differs between the various studies, they point towards a moderate to substantial genetic influence on these phenotypes. Most of the studies have used only young and healthy study subjects, although in recent years phenotypes of particular importance to the elderly and the oldest-old (e.g., activities-of-daily living abilities) have also been shown to have substantial genetic component. Furthermore, behavioural studies have also revealed a genetic contribution to the disposition to level of leisure time physical activity. At present, there is still a few association studies on specific genetic variants, and the results have either been inconsistent or failed to show an association with physical functioning. Therefore, the mechanisms through which the genetic influence is expressed, is still an enigma. Here, we summarise the evidence currently available for a genetic influence on physical functioning and disposition to leisure time physical activity with a focus on recent Danish twin data.