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.

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.

We aimed to elucidate the impact of the conducting state in exercise programs and the degree of improvement in sit-to-stand power index (STS-PI) on the continuation of Chokin exercise by participants one year from the completion of the intervention period. Subjects participated in a 12-week Chokin exercise class for the elderly, which consisted of 10 body mass-based exercises. As variables indicating exercise conditions, the number of exercise days weekly and the total number of sets performed during the intervention period were adopted. STS-PI was calculated using the time required to perform 10-times-repeated sit-to-stand task, and its relative change (%∆STS-PI) was used to represent the degree of improvement in physical function. Among 52 men and 129 women who responded to the inquiry about the continuation of Chokin exercise one year from the completion of the intervention period, 32 men and 93 women confirmed continuation of the exercise program. Logistic regression analysis showed that %∆STS-PI for men, as well as %∆STS-PI and the number of exercise days weekly for women, were factors associated with the decision of subjects to continue the Chokin exercise. These results indicate that the degree of improvement in STS-PI associated with the Chokin exercise class is a factor for continuing the exercise program one year from the completion of the intervention period, at least in elderly men and women. Furthermore, high exercise frequency during the intervention period may be associated with the decision to continue Chokin exercise after the completion of the intervention among women.

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.

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.

In this study, we examined applicability of existing equations to predicting the body surface area (BSA) of children, and newly developed prediction equations for the BSA of children. BSA of 87 children of both genders (7∼12 yr) was determined by the three-dimensional photonic image scanning (3DPS), which was used as reference. BSA predicted using existing equations yielded overestimation or underestimation and/or a systematic error with respect to the reference. BSA prediction equations for boys and girls were developed using height and body mass as independent variables for the validation group and cross-validated for another group. The standard errors of estimation of the prediction equations were 105 cm² (0.9 %) for boys and 158 cm²(1.4 %) for girls. In the cross-validation group, there was no significant difference between the predicted and measured values without systematic errors. These findings indicate that existing equations cannot accurately predict BSA of children, and that the newly developed prediction equations are capable of predicting BSA of children with adequate accuracy.

The present study aimed to investigate the profiles of activities of thigh muscles during 100 m sprint running in track and field athletes experienced hamstrings (muscle) strain injury, with specific emphasis on the difference between injured and non-inured legs. The subjects were 20 track and field athletes who were divided into muscle strain injury group (MS) and non muscle strain injury group (NMS). The electromyograms (EMGs) of five thigh muscles (the biceps femoris, semitendinosus, rectus femoris, vastus lateralis and vastus medialis) and knee joint angles were recorded during 100 m sprint running. For NMS, there were no significant differences between the right and left legs. For MS, the averaged EMG of every muscle,expressed as relative to that during maximum voluntary contraction (%mEMG_MVC), values of the biceps femoris and semitendinosus in the latter phases of takeoff and swing periods were significantly higher in the injured leg than in the non-injured leg. Also, the maximal flexed and extended angles of the knee joint during takeoff and swing period, respectively, for the injured leg were significantly greater than those for non-injured leg. Thus, the present results indicate that track and field athletes experienced hamstrings (muscle) strain injury show by higher EMG activities in the biceps femoiris and semitendinosus of the injured leg at the later phases of swing and takeoff periods during 100 m sprint running. This may be partially related to the running style with a greater extended position of knee joint angles at the corresponding phases.

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.

The aim of this study was to investigate the differences between male and female in the activity level of trunk and lower limb muscles during basic daily physical actions. Six young adult male and six female subjects performed 14 daily life actions, i. e. postural maintenance and change, and body weight transfer actions. The surface EMG of six muscles of the trunk and the lower limb was recorded using a portable electromyography apparatus. Maximal EMG response (EMG_max) during isometric maximal voluntary contraction for each muscle was used to normalize the EMG signal. In the performed actions, the average activity level of each muscle corresponded to 20% EMG_max or less in male and 30% EMG_max or less in female subjects, though there were some actions which exceeded 40% EMG_max in the soleus muscle. As a result of 3-way ANOVA, significant effects for each of the 3 factors (action, muscle and sex) for muscular activity level were recognized and there were significant interactions among each pair of factors. The mean activity level of leg muscles in actions which support and transfer body weight was significantly higher in females than males. In the case of identical actions, the total time taken to reach a high muscular activity level was longer in females than males. From these results, it can be assumed that the load on the lower limb muscles is larger for females than males in the case of supporting and transferring body weight in daily life.

The present study aimed to investigate the level of muscular activities such as postural mainte nance and change, and body weight transfer during daily physical activities, through electromyogram (EMG) recordings. In each of 27 prescribed movements, EMGs of a total of 8 muscles located in the upper arms, trunk and lower limbs were recorded in 12 young adult men and women using a port-able surface electromyograph apparatus. The percentage of integrated EMG per time (mEMG) to that during isometric maximum voluntary contraction (MVC) was calculated as an index by assessing the muscular activity level in each of the prescribed movements. In most of the prescribed movements, the muscular activity level of every muscle corresponded to about 20-30% of MVC, and tended to be higher in women than men. However, some actions induced an activity level of 40% and more of MVC in the soleus muscle. The activity levels of the lower limb muscles in going up and down stairs and a slope at a fast speed, and jogging were higher compared to other prescribed movements. Thus, the results indicate that body weight transfer actions in daily life raise the activities of the lower limb muscles to a level sufficient for maintaining and increasing their function.