Dynamic characteristics of muscle in preadolescent boys

Abstract

　The purposes of this study were to determine dynamic characteristics of muscle in preadolescent boys from relationship of isometric, concentric and eccentric torque, and effects of growth and development in dynamic characteristics of muscle. Thirteen healthy boys performed maximal efforts of elbow flexion to obtain maximal torque during isometric, concentric and eccentric action. Electromyographic activities of biceps brachii and brachioradialis were also recorded to measure motor unit activation (MUA) during maximal efforts. To determine the dynamic characteristics of muscle in preadolescent boys, maximal isometric (P₀), concentric (P_CON) and eccentric torque (P_ECC) were analyzed by Hill equation and repeated one-way ANOVA. As a result, relative eccentric torque (P_ECC /P₀), which showed 1.19±0.23, was obviously lower than that of adults, and it appeared to stem from the fact that the boys showed less than 1.0 P_ECC/P₀. To determine the individuality of P_ECC/P₀, subjects were divided into two groups by P_ECC/P₀ above 1.0 (high group) or under 1.0 (low group) and then MUA of both groups were compared by repeated two-way ANOVA (group × region of muscle). Consequently the activation level in both regions of muscles of the low group was significantly lower than the high group, and there was no significant interaction. Therefore, it is suggested that the dynamic characteristics of muscle in preadolescent boys are similar to those of adults during isometric and concentric action, and there are effects of growth and development on characteristics of muscle in boys during eccentric action.