2013 Volume 62 Issue 5 Pages 365-373
The purpose of this study was to determine the relationship in prepubertal children between lower limb muscle thickness, a quantitative index of lower limb muscle, and sprint motion, in order to clarify the effects of muscle mass development on sprint motion as well as differences in these effects due to sex and muscle location. Participants comprised 41 children in 8year-old (21 boys, 20 girls) in good health attending an elementary school in the city of Kitakyushu. Muscle thickness of the anterior thigh (MTa), posterior thigh (MTp), and calf (MTC) were measured using B-mode ultrasonography. Sprint abilities (sprint speed, stride length, and step frequency), kinematic indices relating to sprint motion and ground reaction force were also measured. Pearson product-moment correlation coefficients were calculated to determine relationships between measured variables. Effects of height and weight were eliminated, and stepwise multiple linear regression analysis was performed, using stride length and step frequency as dependent variables, and kinematic indices and ground reaction force as independent variables. In boys, posterior thigh muscle thickness and calf muscle thickness showed significant simple correlations with flying time/support time (FT/ST), which was selected as an explanatory variable for step frequency. However, no significant relationship was found between step frequency and sprint speed. The conclusion of these findings is that developing lower limb muscle mass affects sprint motion in 8-year-old boys, but does not directly lead to improved sprint speed. In girls, a significant relationship was found between posterior thigh muscle thickness and maximal leg swing velocity during the support phase (ωL), which was selected as an explanatory variable for step frequency, and a significant relationship was found between step frequency and sprint speed. Unlike boys, developing lower limb muscle mass in 8-year-old girls influences step frequency and is closely connected to sprint speed.