Influences of body composition, force-generating capacity and jump performance on 50-m sprint velocity in circumpubertal boys / 体力科学

This study aimed to elucidate how body composition, force-generating capacity and jump performances are associated with 50-m sprint velocity in circumpubertal boys, in relation to sprint phases and maturation. One hundred thirty four circumpubertal boys were allocated to preadolescent or adolescent group on basis of the height at the peak height velocity of Japanese boys (154 cm) reported in literature: those with body heights over 154 cm as adolescent group and others as preadolescent group. Body composition was determined by bioelectrical impedance analysis. In addition to maximal voluntary isometric knee extension torque, the performances of counter movement jump (CMJ), rebound jump (RJ), standing long jump (SLJ) and standing 5-step jump (SFJ) were also measured. RJ-index was calculated by dividing height by contact time. The time of 50-m sprint was determined at 10-m intervals. Multiple regression analysis showed that in preadolescent boys, SFJ become a predictor for the sprint speed during acceleration phases, and SFJ, RJ-index and CMJ as predictors for the sprint speeds during maximal speed and deceleration phases. In the adolescent boys, age, CMJ, SLJ, and SFJ become a predictor for the sprint speed during acceleration phases, and torque relative to body mass, CMJ and SFJ were selected as predictors for the sprint speeds during maximal speed and deceleration phases. Thus, the current results indicate that force-generating capacity and jumping ability are determinants for sprint performance in circumpubertal boys, but the relative contribution of each of the two factors differs between preadolescent and adolescent stages and among the sprint phases.

Influence of the torque generating capacity of the lower extremity muscles on the running and jump performance in primary and junior high school boys / 体力科学

This study aimed to determine the relationships between the torque generating capacity of the lower extremity muscles and either running or jump performance in primary and junior high school boys. A total of 102 primary and junior high school boys participated in this study. Muscle thicknesses (MTs) of the knee extensors and plantar flexors were determined using ultrasonography. Muscle volumes (MVs) of the knee extensors and plantar flexors were estimated using MTs and limb lengths. The isometric joint torques (TQs) for knee extensors and ankle plantar flexors were measured using myometer. MV and TQ were divided by body mass (MV/BM and TQ/BM, respectively). Running velocity was measured using a non-motorized treadmill. The counter movement jump (CMJ) and squat jump (SJ) were performed on a matswitch system. The flight time was measured and used to calculate the heights of CMJ and SJ using the following equation; height (cm) = g × (flight time)² /8/10. As the result of multiple regression analysis, age, MV/BM and TQ/BM were selected as predictors of running velocity in the primary school boys, whereas TQ and lean body mass in junior high school boys. In the primary school boys, TQ/BM and body fat mass was selected as significant contributors for SJ and CMJ performances, whereas, in the junior high school boys, TQ and the percent of body fat for SJ performance and MV/BM and TQ for CMJ performance. Thus, the present results indicate that the relationships between torque generating capacity of the lower extremity muscles and either running or jump performance differ between primary and junior high school boys. It may be assumed that, for running and jump performances, muscle mass and strength become determinant factors in junior high school boys, whereas their values relative to body mass in primary school boys.

LONGITUDINAL HEIGHT VELOCITY DURING ADOLESCENCE AND ITS RELATIONSHIP TO SPORTS INJURY / 体力科学

Purpose: We compared longitudinal height velocity between subjects with Osgood Schlatter Disease (OSD) and those with other chronic lower leg diseases (LD) group involving the knee in order to examine the utility of this velocity as an indicator of bone axis development.Method: Subjects included 92 adult men who have played organized sports. Height values at 9 to 15 years of age were individually approximated by fitting 6-degree polynomial functions. Each polynomial function was differentiated to be led the height velocity curve. Timing of growth spurt and values of height velocity in the OSD and LD group were compared to those in a normal (N) group.Results: Peak height velocity (PHV) was accelerated in the OSD group compared to the LD group. When individual velocity curves were aligned by age of peak height velocity (PHA), the average height velocity in the OSD group was higher than that in the N group at 0.8 years after PHA. Furthermore, when the averaged velocity curve of each group was shifted based on the average PHA, the height velocity in the OSD group was significantly greater than that in the N group at ages 11.6–12.5 years. However the height velocity in the LD group was greater at ages 10.6–10.8 years and 13.3–14.0 years, smaller at ages 11.8–12.3 years than that in the N group.Conclusion: Subjects with OSD may possess higher height velocity than normal individuals before PHA. Conversely, subjects with LD seem to be related to other complicated factors.