ABSTRACT
This chapter focuses on voluntary exercise activities in leisure time such as jogging, swimming, exercising at fitness clubs, and participation in recreational or competitive team and individual sports. Such voluntary exercise activities are often specifically aimed at improving skills, fitness, and health and are rapidly becoming the major source of physical activity of moderate-to-vigorous intensity in many industrialized countries. The chapter reviews the evidence from twin and family studies that genetic factors play an important role too. The heritability of exercise behavior has been well established, but less is known about the genetic variants that are associated with this trait. Candidate gene studies in single small-sized cohort studies are widely distrusted as a reliable source of replicable association, because most complex behavioral traits are highly polygenic, with only a very low percentage of the variance in the trait explained by a single genetic variant.
