FAMILIAL DETERMINANTS OF MODERATE AND INTENSE PHYSICAL-ACTIVITY - A TWIN STUDY

This twin study estimates familial clustering of moderate and intense leisure-time physical activity and investigates quantitatively its gen etic and environmental components. Study subjects are 3,344 male twin pairs aged 33-51 yr. Moderate activity levels were assessed with six q uestions about discretionary walking or stair climbing for exercise. F ive questions assessed regular participation in specific, intense athl etic activities (running, bicycling, swimming, racquet, and other spor ts). Familial aggregation is estimated by odds ratios of one twin enga ging in an activity when his co-twin does. Monozygotic and dizygotic t win correlations were compared to estimate genetic and nongenetic sour ces of phenotypic variation. For each activity, the familial aggregati on odds ratio was statistically significant with values between 2.9 to 4.6 for intense activities and between 1.4 and 1.9 for all moderate a ctivities but one. Monozygotic twin correlations were higher than dizy gotic, suggesting genes play a role in the observed phenotypic variati on. For four questions, and a composite scale of moderate activity, th e difference between correlations was statistically significant (P < 0 .05). In this cohort, much of the phenotypic variability for both mode rate and intense activities is a result of familial effects. Genes may influence regular participation in specific intense exercises more th an moderate activity, such as walking for exercise.