The purpose of this project was to clarify the angular momentum of Asian top discus athletes during the single support phase by right foot and the delivery phase, by using a three-dimensional (3 D) cinematography. Top six finalists of the discus competition for the 12th Asian games in Hiroshima 1994 were filmed with two high-speed video cameras at 200 frames/s. The average distance of the top six was 56.44 ± 1.84 m. 3 D landmark coordinates of 15 body segments were obtained by using the DLT method. The angular momentum (L) of the thrower and the velocity of the discus were calculated. We confirmed that there are two different patterns in the angular momentum of the thrower-plus-discus system during the delivery phase. One was the pattern of the gold-medalist, with rapid increase of the positive L_Z with the negative L_X and the negative L_Y decreasing. The other was that of the bronze-medalist, with marked increase of the negative L_X and the negative L_Y with the positive L_Z dropping. And also, time used from the instant of the ground contact by right foot to the release of discus was short in the gold-medalist (0.31 s) than in the bronze-medalist (0.42 s). Therefore, the pattern of the gold-medalist could be called the motion of “high-speed type”. On the other hand, the bronze-medalist called “low-speed type”. The most important conclusion of this project was that “high-speed type” generates the horizontal speed of discus more than the vertical speed of discus during the second single support phase to the delivery phase. On the other hand, “low-speed type” continue increasing the vertical speed of discus more than the horizontal speed of discus during those phases.

The purpose of this study is to investigate the behavior of the triceps surae muscle-tendon complex during repetitive ankle extension-flexion bending exercises (with knee and hip joints fixed) at various frequencies. During the exercises, ground reaction forces, ankle angles, and electromyograms of gastrocnemius, soleus and tibialis anterior were measured. Using inverse dynamics, triceps surae forces were calculated, and these were used to calculate the series elastic component (SEC) elongation ΔL_SEC. In combination with ankle angle changes (from which total length changes of the muscle-tendon complex (ΔL_OI) was calculated), this allowed for calculation of the contractile component (ΔL_CC). At low frequencies, ΔL_OI and ΔL_CC were calculated to be in phase, and EMG was high when the force was high. At high frequencies, however, ΔL_OI and ΔL_CC were calculated to be in the opposite phase. The CC was shortening in the dorsiflexion phase against increasing tension. This suggests the muscles were very active in this phase as was confirmed by the high EMG activities. On the contrary, in the plantarflexion phase the total length of the muscle-tendon complex of the triceps surae became shorter, but the CC was elongating with the tension decreasing. The EMG activities disappeared in this phase. At intermediate frequencies, the CC acted almost isometrically, although the total length changed about the same as at the other two frequencies. Using a model of an externally forced mass-spring system, the phase reversal between CC and SEC behavior is explained: the low frequencies are below the natural frequency of the subject, and the high frequencies are above it. This assumption suggests that a strong relationship must exist between the natural frequency (ω₀) and the frequency at which large phase shift occurs between the joint movements and EMG activities (ω₀′). Ankle bending exercises were done with two legs and with one leg. For both exercises ω₀ and ω₀′ were calculated and no significant differences were observed between the two values, which support the assumption.

The relationship between skinfold thickness (SF) and body density (BD) was investigated in female collegiate athletes. The highest correlation was found between BD and SF in Umbilicus. The equation using SF of Scapula plus Triceps that has been used to estimate BD for Japanese females overestimated percent body fat of female athletes in this study. Linear equation showed similar results to estimate BD from SF comparing with quadratic equation, logarithmic equation and with equation using body surface area.