The effect of body size on countermovement jump kinetics in children aged 7-11 years.

The purpose this study was to examine the effect of body size on countermovement jump (CMJ) kinetics in children. Participants (n = 160) aged 7-11 years, divided equally by sex and into primary school year groups (years 3, 4, 5 and 6), each performed one CMJ on a force platform. The variables bodyweight (BW), peak force (Fmax), in-jump minimum force (IMF), in-jump vertical force range (IFR) and basic rate of force development (BRFD) were attained from the force-time history and then subsequently scaled to account for body size. A significant age, sex and interaction effect were found for the absolute variables BW, IMF, Fmax and IFR (P < 0.05) between school year groups 3 and 4 against year's 5 and 6. Simple main effects highlighted no significant sex differences between the boys and girls for all variables (P > 0.05). No significant age or sex differences were observed for normalised or allometrically scaled values (P > 0.05). The results indicate that girls and boys can be grouped together but that body size must be accounted for to enable accurate conclusions to be drawn independent of growth. Body size significantly effects the representation of CMJ kinetic results and therefore, future studies should report both absolute and scaled values. Future research should develop an age-appropriate criterion method for children in order to determine processed CMJ variables to further investigate the neuromuscular performance of children.