This study was conducted to investigate the kinematic characteristics of javelin throw for further comprehension of the techniques and mechanics of the javelin throw. Forty-nine male javelin throwers were videotaped, using two 200 fps high-speed video cameras in three athletic competitions.

The results revealed the significant positive correlation between the initial velocity of javelin and the throw distance (r = 0.797, p < 0.001). The throwers showing the higher initial velocity of javelin showed the higher forward rotation angular velocity of trunk at the moment of javelin release (r = 0.484, p < 0.001). The elbow joint angle and shoulder abduction angle at the moment of javelin release showed the significant negative correlations with the initial velocity of javelin (r = -0.437, p < 0.01 and r = -0.454, p < 0.01, respectively). The velocity calculated by taking the shoulder velocity from the grip velocity at the moment of javelin release showed the significant positive correlation with the initial velocity of javelin (r = 0.819, p < 0.001). These results suggested that both extension and internal rotation of the shoulder contributed to the enhanced relative arm velocity for the elite throwers, while the internal rotation of the shoulder for the novice throwers limitedly contributed to it.

The effectiveness index of mechanical energy utilization (EI) is defined by the following equation;

EI =

　　Performance and / or Effective energy (and / or Work)

　　　　　　 Mechanical energy (and / or Work) 　　　　

The generic definition of EI is useful for evaluating skilled motion in human movement from the viewpoint of effective usage of mechanical energy and/or work.

Certain correlations between EI and locomotion speed were observed in several locomotion studies using EI. If the EI has correlations with locomotion speed, however, interpretation of the EI is complicated. In the present study, EI was applied to the evaluation of walking and running motion in order to examine if EI correlates with locomotion speed.

Two subjects were asked to perform 15 walks and runs at several speed levels. The trials in each speed level were measured using an automatic coordinate acquisition system and a force platform. Then the EIs with several numerators representing performance and/or effective energy utilization were calculated. The numerators were P_E (= 0.5 x body mass x (locomotion speed)²), P_V (= body mass x locomotion speed)_, P_D (= body mass x step length) and P_DV (= body mass x step length x locomotion speed). W_JP (absolute work in a cycle obtained based on joint torque power) was used as the denominators of EI.

The all EIs examined in this study have significant correlations with locomotion speed. In these cases, correlation coefficients as well as regression coefficients were different among subjects, movements and the numerators of EI. Based on these results, in order to appropriately examine EI of the target locomotion, firstly we need to confirm correlation between EI and the locomotion speed. Then, if EI correlates with locomotion speed, it may be necessary to consider the effect of locomotion speed in the interpretation of EI.

Purpose of this study was to estimate the moment arm of human Achilles tendon by application of gravity. Eight male subjects were requested to perform passively plantar-and dorsiflexion movements by a dynamometer with two different leg positions, i.e. one was the horizontal position of leg and thigh with the knee joint fully extended (setA), and the other was the supine horizontal position with 60° leg up (setB). Excursion of myotendinous junction (MTJ) was determined by ultrasonography during passive ankle movement. Moment arm was calculated by dividing the MTJ excursion (mm) by the angle change (rad). At the plantarflexed position (60°), the moment arm in the setB (35.1 ± 5.6 mm) was significantly higher (p < 0.05) than that in the setA (26.0 ± 10.0 mm). The moment arms obtained in the setB were within a range of reference data reported in previous studies, suggesting that the application of gravitation is useful to estimate Achilles tendon moment arm.