ABSTRACT
This study aimed to clarify the relative growth in thigh muscle size and sprint performance in children from 3 to 15 years. A total of 902 children performed a 30-m sprint test. Sprint time was measured by a photocell system. Muscle thicknesses of thigh anterior and posterior were determined by using a B-mode ultrasound. For 431 children, step frequency (SF) and step length (SL) during the sprint running were also analyzed with the films, and corrected by leg length. Using an allometry equation based on body height, relative growth of thigh muscle size and sprint performance was estimated. In both boys and girls, there was a breakpoint (BP) at which the rate of development in sprint velocity changes, and the rate of development was slower after the BP. On the other hand, the rate of growth in thigh muscle size after the BP was superior to that before the point, except of thigh posterior in boys. Regardless of sex, the rate of development in SL index after the BP became to be lower with increasing body height, whereas SF index relatively increased. These current findings indicate that in boys and girls, the rate of development in sprint velocity becomes to be lower above a certain body height, and the relative slow development may result from those in SF and SL.