ABSTRACT
The purpose of this study was to investigate the relative growth of thigh muscle thickness and development of ball kicking performance in junior male soccer players.The study participants included 235 Japanese male soccer players aged between 10 and 18 years. Subjects were classified into 10 groups on the basis of their body height every 5 cm. The thickness of the anterior and posterior thigh muscles (MTA and MTP, respectively) were measured using B-mode ultrasonography. The ball distance (BD) and ball velocity (BV) were measured using a tape measure and a speed gun, respectively. By using a custom-made speed meter, we measured the maximal swing velocity of the lower limb (SV) while the players were kicking the ball. These parameters, along with the height, were plotted on a logarithmic graph to obtain the allometric equation y = bx<sup>a</sup>.There was a sharp bend in the graph showing the relationships between MTA, MTP, BV, SV, and body height. The growth indexes "a" of MTA and MTP were increased at 157.3 cm and 159.9 cm, respectively. The development indexes "a" of BV and SV were increased at 144.3 cm and 146.1 cm, respectively. However, there were 2 sharp bends in the graph showing the relationships between BD and body height. The development index "a" of BD showed the highest value from 150.5 to 171.2 cm.These results suggested that the developmental spurt in ball kicking performance was faster than the growth spurt in muscle thickness of the thigh.