Relative growth of thigh muscle size and running performance in children from 3 to 15 years / 体力科学

This study aimed to clarify the relative growth in thigh muscle size and sprint performance in children from 3 to 15 years. A total of 902 children performed a 30-m sprint test. Sprint time was measured by a photocell system. Muscle thicknesses of thigh anterior and posterior were determined by using a B-mode ultrasound. For 431 children, step frequency (SF) and step length (SL) during the sprint running were also analyzed with the films, and corrected by leg length. Using an allometry equation based on body height, relative growth of thigh muscle size and sprint performance was estimated. In both boys and girls, there was a breakpoint (BP) at which the rate of development in sprint velocity changes, and the rate of development was slower after the BP. On the other hand, the rate of growth in thigh muscle size after the BP was superior to that before the point, except of thigh posterior in boys. Regardless of sex, the rate of development in SL index after the BP became to be lower with increasing body height, whereas SF index relatively increased. These current findings indicate that in boys and girls, the rate of development in sprint velocity becomes to be lower above a certain body height, and the relative slow development may result from those in SF and SL.

Differences in cardiorespiratory and metabolic responses between body mass-based squat and lunge exercises with relation to muscular activity with relation to muscular activity level / 体力科学

<p>This study aimed to clarify the differences in cardiorespiratory and metabolic responses to body mass-based front lunge and squat exercises with relation to muscular activity. Seven healthy adult males performed 200 times body mass-based squat and front lunge exercises. During the exercises, oxygen uptake, heart rate (HR), blood lactate concentration (La), ground reaction force were measured. Oxygen uptake was divided by body mass (VO₂). VO₂ and HR was normalized to maximal VO₂ (%VO₂max) and maximal HR (%HRmax) obtained from an incremental load test. Electromyograms (EMGs) during the two exercises were recorded from the vastus lateralis (VL), rectus femoris, vastus medialis (VM), biceps femoris, gluteus maximus (GM). EMG amplitudes during both exercises were normalized to those during maximal voluntary contraction, and expressed as relative value (%EMG_MVC). Time that cardiorespiratory parameters became stable was 4-6 min in both exercises. VO₂, %VO₂max, metabolic equivalent, were higher in the front lunge than the squat. No significant differences in HR, %HRmax and La were found between both tasks. %EMG_MVC in VL, VM and GM were higher in the front lunge than the squat. These current findings indicate that 1) body mass-based squat and front lunge exercises are physiologically of more than moderate intensity, and 2) the cardiorespiratory responses to body mass-based front lunge are greater than those to body mass-based squat. This may be due to the difference in muscular activities of VL, VM and GM during the tasks.</p>

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.

DEVELOPMENT OF AN EQUATION FOR PREDICTING BODY SURFACE AREA BASED ON THREE-DIMENSIONAL PHOTONIC IMAGE SCANNING / 体力科学

This study was conducted to examine the reliability of three-dimensional photonic image scanning (3DPS) for measuring body surface area (BSA), and formulate equations for predicting BSA based on 3DPS. The surface area (SA) of a cylinder with known SA and BSA of 7 males were repeatedly measured by 3DPS. BSA was determined by 3DPS for 122 subjects (25–76 yrs). BSA prediction equations for both genders were developed for the validation group (16 males and 45 females) using body height and mass as independent variables, and were cross-validated for the cross-validation group (16 males and 45 females). The standard error of measurement was 2.2cm² (0.16%). The coefficients of variation (CV) for repeated measurements of SA were less than 0.2%. The BSA of subjects did not differ significantly on any given day nor between days, with a CV of less than 1%. The coefficient of determination and standard error of estimation of the prediction equations were 0.98 and 183cm² (1.1%), respectively, for males and 0.98 and 204cm² (1.3%), respectively, for females. There was no significant difference between the predicted and measured values. In the cross-validation group, there was no significant difference between the predicted and measured values without systematic errors. These findings indicate that 3DPS is reliable for measuring BSA, and the formulated equations are valid and applicable to individuals within a wide age-range.