Seven high school boys (16.4 +/- 0.5 y, mean +/- SD) and 7 girls (16.4 +/- 0.5 y), who specialized in track and field events, performed ten 5-s maximal sprint runs with an interval of 10s between each sprint on a non-motorized running ergometer. In each sprint, the mean mechanical power (MP) from the start until the belt velocity of the ergometer (i. e., running velocity) peaked was calculated. The boys showed significantly higher MP than the girls in all sprints. However, when MP was expressed as the ratio to the total volume of muscles located in the right lower limb (MP x MV(-1)), estimated using a bioelectrical impedance analysis, significant gender effect was limited to the values at the 1 st and 2 nd sprints. The decline of MP over the ten sprints, expressed as a relative value to that at the 1 st sprint, was greater in boys (46.2 +/- 7.6 %) than in girls (33.9 +/- 8.6 %), and significantly correlated with MP x MV(-1) at the 1st sprint (r = 0.568, p < 0.05). However, no significant difference between the boys and girls was found in the relative difference between MP values at the 3rd and 10th sprints, where the gender difference in MP x MV(-1) at every sprint was insignificant. The findings here indicate that, for trained teenage boys and girls, (1) significant gender difference in mechanical power developed during repeated bouts of maximal running exists only in the initial phase of the task, when the difference in the volume of the lower limb muscles is normalized, and (2) it may be a reason for a greater decline of mechanical power developed during the bout in boys compared to girls.

In this study, the relationship between the physical fitness of college baseball players found from 6 field tests and a performance evaluation by coaches was investigated. The purpose was to ascertain whether the results would be similar to those obtained in a previous study. The subjects of the study were 43 college baseball players (mean age, 20.7 +/- 1.4 years; mean athletic career, 10.9 +/- 2.6 years). Referring to the previous study, the field tests of physical fitness were composed of 6 items: throwing distance, back strength, medicine ball throwing, standing long jump, T-test, and base running. For capabilities in batting, fielding, and running, the coach's evaluation was expressed by T scores. The results of the analysis indicated that those players with high evaluation scores had significantly better test results in comparison with those players who were rated low in the evaluation. Although the multiple regression models of the previous study were associated with a middle goodness of fit, a significant correlation was found between physical fitness found in the field tests and performance. The results from a partial correlation analysis indicated a significant correlation between the following: batting evaluation with back strength (p < 0.01) and medicine ball throwing (p <0.01); fielding evaluation with throwing distance (p < 0.05); and running evaluation with medicine ball throwing (p < 0.01), standing long jump (p < 0.05), T-test (p < 0.01), and base running (p < 0.01). It is certain that the performance of college baseball players is related to their physical fitness.

An evaluation of mechanical power during walking and running in humans was undertaken after developing a specially designed running ergometer (RE) in which the subjects gripped the handlebar in front of them keeping both arms straight and in a horizontal position. Ten subjects participated in comparisons of the mean horizontal pushing force (MFam) on the handlebar with the mean horizontal ground reaction force (MFfp) recorded by force platform under the RE during five different constant speeds of walking or running and sprint running with maximal effort. Mechanical power developed during sprint running on the RE was compared with a 50 m sprint. Mean linear velocity (Mv) of the RE belt was recorded by the rotary encoder attached to the axis of the belt. Mean mechanical power calculated from the handlebar setting (MPam = MFam x Mv) was compared to that calculated from force platform recordings (MPfp = MFfp x Mv). A high test-retest reproducibility was observed for both MFfp (r = 0.889) and MFam (r = 0.783). Larger values for the coefficient of variation for MFam (11.3%-15.8%) were observed than for MFfp (3.3%-8.2%). The MPam, which were obtained from five different constant speeds of walking, running and sprint running were closely correlated to those of MPfp (y = 0.98x - 19.10, r = 0.982, P < 0.001). In sprint running, MPam was 521.7 W (7.67 W.kg-1) and was correlated to the 50 m sprint time (r = -0.683, P < 0.01). It is concluded that the newly developed RE was useful in the estimation of mechanical power output during human locomotion such as when walking, jogging and sprinting.

Ground reaction force is often used to predict the potential risk of injuries but may not coincide with the forces applied to commonly injured regions of the foot. This study examined the forces applied to the foot, and the associated moment arms made by three foot strike patterns. 10 male runners ran barefoot along a runway at 3.3 m/s using forefoot, midfoot, and rearfoot strikes. The Achilles tendon and ground reaction force moment arms represented the shortest distance between the ankle joint axis and the line of action of each force. The Achilles tendon and joint reaction forces were calculated by solving equations of foot motion. The Achilles tendon and joint reaction forces were greatest for the forefoot strike (2 194 and 3 137 N), followed by the midfoot strike (1 929 and 2 853 N), and the rearfoot strike (1 526 and 2 394 N). The ground reaction force moment arm was greater for the forefoot strike than for the other foot strikes, and was greater for the midfoot strike than for the rearfoot strike. Meanwhile, there were no differences in the Achilles tendon moment arm among all foot strikes. These differences were attributed mainly to differences in the ground reaction force moment arm among the three foot strike patterns.

The moment arm of muscle‐tendon force is a key parameter for calculating muscle and tendon properties. The tendon excursion method was used for determining the Achilles tendon moment arm (ATMA). However, the accuracy of this method remains unclear. This study aimed to investigate the magnitude of error introduced in determining the ATMA using the tendon excursion method by comparing it with the reference three‐dimensional (3D) method. The tendon excursion method determined the ATMA as the ratio between the Achilles tendon displacement during foot rotation from 15° of dorsiflexion to 15° of plantarflexion and the joint rotation angle. A series of foot images was obtained at 15° of dorsiflexion, the neutral position, and 15° of plantarflexion. The 3D value of the ATMA was determined as the shortest distance between the talocrural joint axis and the line of action of the Achilles tendon force. The ATMA determined by the tendon excursion method was smaller by 3.8 mm than that determined using the 3D method. This error may be explained mainly by the length change in the Achilles tendon due to the change in the force applied to it, as passive plantarflexion torque was different by 11 Nm between 15° of dorsiflexion and 15° of plantarflexion. Furthermore, the ATMAs determined using the 3D and tendon excursion methods were significantly correlated but the coefficient of determination was not large (R 2 = 0.352). This result suggests that the tendon excursion method may not be feasible to evaluate the individual variability of the ATMA.