In previous drop landing studies, support of the lower extremity was investigated by independent examination of the ankle, knee, and hip joint moments. Support of the lower extremity based on the net effect of the three joint moments has not been previously investigated. In addition, in those studies the horizontal ground reaction force was not examined. On the other hand, Winter (1980) proposed a support moment calculated from the summation of the ankle, knee and hip joint moments in a walking study. The purpose of the present study was to investigate correlation between the support moment and the lower extremity joint moments, as well as the effects of the joint moments on the horizontal ground reaction force, via sensitivity analysis.

Eight healthy male subjects (age; 25.30±2.71 yr, body mass; 67.52±6.25 kg, and height; 175.60±3.07 cm) participated. A force platform (Kistler type 9281 B, Kistler Instruments, Switzerland) was used to measure ground reaction forces (GRF) at 1 kHz. An imaging system (3D OPTTRACK, Northern Digital Inc, Canada) was positioned 5 m from the force platform at 0.2 kHz. Each subject performed drop landings from two platforms; 0.38 m (LOW) and 0.61 m (HIGH) from the floor. Subjects placed their hands on their hips while stretching out one leg above a target landing position on the force platform, and pushed off from the box with their leg on the box. Then, the legs were closed in the air, subjects landed on the force platform with both feet simultaneously. Joint moments were calculated using an inverse dynamic analysis. In addition, the sensitivity of the joints moments and the support moment to changes in the horizontal GRF were analyzed.

Significant positive correlation was observed between the hip joint moment and the support moment at the maximum peak of the support moment (r=0.838, p<0.001). The support moment also showed significant positive correlation with the vertical GRF (r=0.865, p<0.001) and the horizontal GRF (r=0.699, p<0.001). In the sensitivity analysis, when the horizontal GRF was changed, the hip joint moment changed more markedly than the others. Thus, these findings indicate that decreasing the horizontal GRF is an important factor in decreasing the support moment.

The purpose of this study was to analyze the mechanical energy during baseball pitching for 22 varsity baseball players by using three-dimensional motion analysis technique with two force platforms. Joint torque powers, joint force powers, and segment torque powers of the joints were computed using an inverse dynamics approach.

In the energy increasing phase of upper torso, a great deal of mechanical energy flowed into the torso. The mechanical energy transferred to the upper torso due to the segment torque power significantly related to the ball velocity at the release (r=0.480, p<0.05). In the late cocking and accelerating phase, great mechanical energy flowed into the distal segment and the ball due to the joint force power were observed at the throwing arm joints. There were significant relationships between the ball velocity at the release and mechanical energy flows due to the elbow and the wrist joint force powers (r=0.775, p<0.001 and r=0.827, p<0.001). These results suggested that the mechanical energy flows to the upper torso in the energy increasing phase of upper torso and to the throwing arm and ball in the late cocking phase are important to increase the ball release velocity.