INHERITANCE OF PHYSICAL-FITNESS IN 10-YR-OLD TWINS AND THEIR PARENTS

This study focuses on the quantification of genetic and environmental sources of variation in physical fitness components in 105 10-yr-old t win pairs and their parents. Nine motor tests and six skinfold measure s were administered. Motor tests can be divided into those that are pe rformance-related: static strength, explosive strength, running speed, speed of limb movement, and balance; and those that are health-relate d: trunk strength, functional strength, maximum oxygen uptake, and fle xibility. The significance and contribution of genetic and environment al factors to variation in physical fitness were tested with model fit ting. Performance-related fitness characteristics were moderately to h ighly heritable. The heritability estimates were slightly higher for h ealth-related fitness characteristics. For most variables a simple mod el including genetic and specific environmental factors fitted the obs erved phenotypic variance well. Common environmental factors explained a significant part of the variation in speed components and flexibili ty. Assortative mating was significant and positive for speed componen ts, balance, trunk strength, and cardiorespiratory fitness, but negati ve for adiposity. Static strength, explosive strength, functional stre ngth, and cardiorespiratory fitness showed evidence for reduced geneti c transmission or dominance. The hypothesis that performance-related f itness characteristics are more determined by genetic factors than hea lth-related fitness was not supported. At this prepubertal age, geneti c factors have the predominant effect on fitness.