Similar age-related changes in running performance and growth in adolescent monozygotic twins

The purpose of this study was to assess the similarities in the pattern of age-related change in the running performance and physical growth in adolescent monozygotic (MZ) twins. The total sample was 70 boys and 100 girls, including 14 pairs of male and 25 pairs of female MZ twins. Performance of the 50 m dash and endurance run (1,500 m for boys and 1,000 m for girls), and stature and body mass were measured longitudinally at yearly intervals from 12 to 17 years of age. The within-pair resemblance was compared between MZ twin pairs (MZ) and control pairs (CP), which were selected from the other subjects matched with each member of MZ for the initial values. The within-pair similarity in performance and growth curves was quantified by an average Euclidean distance coefficient (d(jk)) and a coefficient of shape differences (z(jk)) and a graphical analysis on the d(jk)-z(jk) coordinate. The time relationship between two curves was assessed by the arrangement of the sign of within-pair differences (number of runs, NR). Within-pair differences of measured value at the first and the last measurements were also examined. MZ generally showed smaller d(jk) and z(jk), clustering around the origin on the d(jk)-z(jk) coordinate. Frequency of observation of NR = 1, which means one member of a pair had consistently larger values than the other, tended to be lower in MZ in performance items. Within-pair differences in the last measurements were generally greater in CP. It was concluded that MZ twins have meaningful similarities in the pattern of age-related changes in running performances and physical growth during adolescence. (C) 2000 Wiley-Liss, Inc.