1st INTERNATIONAL SCIENTIFIC CONGRESS ORGANIZED BY SLOVENIAN GYMNASTICS FEDERATION Statistical analysis All data are expressed as means ± standard deviation. For all variables the hypothesis of a normal distribution was tested with visual inspection and the Shapiro-Wilk’s test. Muscle differences were tested using one-way analysis of variance (ANOVA) with Bonferroni post-hoc analysis. Age, gender and muscle effect on Tc were tested with three-way ANOVA, with age (6) and muscle (4) as within factors and gender (2) as between factor. If age was a significant factor then the Bonferroni post-hoc was used to precisely identify significant differences in Tc. If there was a significant age x gender interaction, indicating that age does have different effects in boys and girls, a one-way ANOVA was used to identify those differences. To evaluate the effect of sport effect on the Tc of the VL and BF a three-way RM ANOVA was used, with age (6) and muscle (4) as within factors and sport (3) as between factor. Eta-squared (η2) was used to estimate the effect size; Cohen’s (1988) interpretation was used for the qualitative description of η2 (where 0.0099 constitutes a small effect, 0.0588 a medium effect and 0.1379 a large effect). Statistical significance was accepted at P < .05 level. RESULTS Child anthropometric growth could be classified as normal, following general trends reported by Rogol, Clark & Roemmich (2000). Both boys and girls showed a progressive increase in body height (P < .001) and body mass (P < .001). The age x gender interactions for body height (P < .001) and body mass (P = .028) are reflected by a larger increase in body height and body mass in boys than girls in the 5-year period (Table 1). Figure 1. Age trends with gender effect on contraction time (Tc) for both skeletal muscles. * P < .05: statistical gender differences. Figure 1 presents pooled Tc data for boys and girls in both muscles. Tc in VL was consistently lower from BF (P < .001). A three-way ANOVA revealed significant age effect (P < .001; η2 = .050) on Tc; significant muscle effect on Tc (P < .001; η2 = .850); significant muscle x gender interaction effect on Tc (P < .001; η2 = .111); significant age x muscle interaction effect on Tc (P < .001; η2 = .123); and significant age x muscle x gender effect on Tc (P = .002; η2 = .035). As evident from Figure 1, a significant gender effect was found in VL (P = .027; η2 = .046) and also in BF (P = .004; η2 = .077). An age x gender interaction was found only in VL (P = .006) with small effect size (η2 = .031). These effects were seen as a lower Tc in VL and longer Tc in BF after the age of 12.9 years in girls than boys. 89