Physical and motor fitness in twins.

Thirty pairs of monozygotic (MZ) and 20 pairs of dizygotic (DZ) twins, of both sexes, were studied to estimate the role of genetic and environmental factors determining fitness measurements comprising vital capacity (VC), vertical jump, flexibility, agility, and PFI score. Intra-pair variances for VC, vertical jump, and heart rate were significantly smaller (p < 0.05-0.01) in MZ than in DZ twins, where values for flexibility, agility, and PFI were insignificant. Intra-pair correlations for VC, vertical jump, and heart rate were higher (p < 0.01) in MZ than in DZ twins where the opposite was found in the case of flexibility and agility. The correlation value for PFI was higher in both MZ and DZ twins. Following adjustment for physical characteristics including age, weight, and height, none of the results of all the residual fitness measurements were similar to the unadjusted values. Both unadjusted and residual variables with smaller intra-pair variances showed higher heritability estimates. These results suggest that VC, vertical jump, and heart rate are influenced more by genetic factors than environmental factors where the inverse is true of flexibility, agility, and PFI. Thus, the genetic and environmental influence of all the fitness measurements, except VC, more or less depend upon physical characteristics in this study.