COP-AV is assumed to decrease with exactly improved balance ability (Winter, 1990). The children completed the PAQ-C (Crocker et al., 1997), a physical activity (PA) level questionnaire designed to quantify their daily activity level, which is a guided self-administered 7-day recall measure for children. It provides a summary PA score derived from nine items, each scored on a 5-point scale. A score of 5 indicates high PA level, whereas a score of 1 indicates low PA. The PAQ-C has been suggested as one of the most reliable and valid self-administered recall instruments (Crocker et al., 1997). Data are described as means ��SD. An independent sample t-test was used to examine the gender difference in postural stability parameters, whereas one-way ANOVA was used to examine the differences between conditions.

Effect sizes (Cohen��s d) were calculated to determine the practical difference between girls and boys. Effect size values of 0�C0.19, 0.20�C0.49, 0.50�C0.79 and 0.8 and above were considered to represent trivial, small, medium and large differences, respectively (Cohen, 1988). Pearson product moment correlation coefficient was used to assess the relationship between COP parameters and other variables. The magnitude of the correlations was determined using the modified scale by Hopkins (2000): trivial: r < 0.1; low: 0.1�C0.3; moderate: 0.3�C0.5; high: 0.5�C0.7; very high: 0.7�C0.9; nearly perfect > 0.9; and perfect: 1. Significance level was defined as p < 0.05. Results Significant gender differences (p < 0.05) were observed in COP-PV, COP-RD and COP-AV when the three conditions were pooled (Table 1).

Specifically, boys had significantly higher COPPV (p < 0.05, medium effect), longer COP-RD (p < 0.05, medium effect), and higher COP-AV (p < 0.05, medium effect), as compared to girls. Furthermore, COP-RD (p < 0.05, large effect) and COP-AV (p < 0.05, large effect) were significantly different between genders in CONTROL condition (Table 1), indicating the sensitivity of these two parameters in differentiating postural stability between genders in this age group. Table 1 Gender difference in postural stability performance and percentage change from CONTROL in postural stability performance for girls and boys with effect sizes, effect size magnitudes and 95% confidence intervals The data in Table 1 include the analysis of the percentage change from the CONTROL condition and these data are presented in Figure 1.

While there were no significant gender differences in the percentage change in COP-PV for either ECHB or EOCS, there was a significant gender difference (p > 0.05) in COP-RD for the ECHB condition with a medium gender effect for EOCS. There were medium gender effects in COP-AV Cilengitide in both ECHB and EOCS conditions. Figure 1 Percentage change (with reference to CONTROL) in postural stability performance for boys and girls (* indicate significant gender difference: p<0.