The purpose of this study was to investigate growth changes in human plantar flexor muscle and tendons. In addition, we ascertained whether growth changes in muscle and tendon were more closely related to skeletal age than chronological age. 22 elementary school children (ESC), 19 junior high school students (JHS), and 23 young adults (ADT) men participated in this study. Maximal strain and hysteresis of tendon structures and cross-sectional area of Achilles tendon were measured using ultrasonography. In addition, skeletal age was assessed using Tanner-Whitehouse III method. Maximal strain of ESC was significantly greater than that of other groups, while no significant difference was observed between JHS and ADT. There was no difference in hysteresis among 3 groups. Relative cross-sectional area (to body mass(2/3)) of ADT was significantly smaller than that of other groups. For ESC and JHS, measured variables of muscle and tendon were significantly correlated to both chronological and skeletal ages. These results suggested that immature musculoskeletal system was protected by more extensible and larger tendon structures in ESC and only by larger tendon structures in JHS, respectively. Furthermore, there were no differences in correlation coefficient values between measured variables of muscle and tendon and chronological or skeletal ages.

The purpose of this study was to compare the morphological and mechanical properties of the human patellar tendon among elementary school children (prepubertal), junior high school students (pubertal), and adults. Twenty-one elementary school children, 18 junior high school students, and 22 adults participated in this study. The maximal strain, stiffness, Young's modulus, hysteresis, and cross-sectional area of the patellar tendon were measured using ultrasonography. No significant difference was observed in the relative length (to thigh length) or cross-sectional area (to body mass(2/3)) of the patellar tendon among the three groups. Stiffness and Young's modulus were significantly lower in elementary school children than in the other groups, while no significant differences were observed between junior high school students and adults. No significant differences were observed in maximal strain or hysteresis among the three groups. These results suggest that the material property (Young's modulus) of the patellar tendons of elementary school children was lower than that of the other groups, whereas that of junior high school students was already similar to that of adults. In addition, no significant differences were observed in the extensibility (maximal strain) or viscosity (hysteresis) of the patellar tendon among the three groups.

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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 a . 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.(Jpn. J. Phys. Fitness Sports Med. 2011, 60：195-205)