Purpose The purpose of this study was to investigate the differences in physique and physical fitness according to maturity between primary and middle school baseball players. Methods Participants were 112 elite youth baseball players (49 primary school; 63 middle school). Skeletal age estimated maturity. Physique (height, arm span, thigh volume), body composition (weight, muscle mass and body fat), physical fitness (strength, power, agility, flexibility, coordination, anaerobic power and aerobic power) were measured. An independent sample t-test was used to conduct verify the difference between physique and physical fitness according to maturity. Results The results of analyzing physical and physical fitness according to maturity showed that there was a significant difference (p<.05) between the early maturation group and on-time group in primary school baseball players, body fat percentage, muscle mass percentage, sit-up, anaerobic power and reaction time. There was a significant difference between the early maturation group and the on-time group in the middle school baseball players, weight (p<.05), thigh volume (p<.05), fat mass (p<.05), muscle strength (p<.01), power (p<.05) and coordination (p<.05). Conclusions In conclusion, the maturity of a growing baseball player may be influenced by the performance, so maturity status should be considered when judging the performance of a growing baseball player, especially a middle school baseball player.
