Lower limb muscle thickness in relation to sprinting abilities in children aged between 3 and 8 years old

The purpose of this study was to clarify the effects of lower limb muscle mass growth on sprinting ability in children aged 3 to 8 years. The subjects were 514 unimpaired children (266 boys and 248 girls). We measured their lower limb muscle thickness (anterior thigh: MTa, posterior thigh: MTp, and calf: MTC) and 25 meter sprinting time. Muscle thickness was measured using a B-mode ultrasound diagnostic imaging unit. From the 25 meter sprint, we measured the following characteristics in relation to sprinting ability: results, maximum velocity, stride and pitch. The results revealed that sprinting ability significantly correlated with MTp and MTC in both boys and girls. This suggests that, in addition to morphological development, lower limb muscle mass growth contributes to an increase in stride (m/step) and affects sprinting ability during the period from infancy to early childhood. However, no relationship was seen between sprinting ability and anthropometric characteristics (body height and mass) or lower limb muscle thickness among 8-year-old boys. It is possible that lower limb muscle quality and power as well as improvement in elements such as sprinting movement have a stronger influence on sprinting ability than morphological elements such as physique and muscle mass in boys around that age. In contrast, a significant relationship was seen between lower limb muscle thickness and sprinting ability in girls of all age groups, suggesting that, unlike boys, innate lower limb muscle mass influences sprinting ability for girls.