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Jpn J Biomechanics Sports Exercise 8(1):2-11, 2004

Support of the lower extremity by joint moments during drop landings

Yasuyuki YOSHIDA, Takeo MARUYAMA

Graduate School of Decision Science and Technology, Tokyo Institute of Technology

Abstract

    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 e3ltremity 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, Northem 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 boB1. 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 thehorizontal GRF (r = 0.699, p < 0.001). In the sensitivity analysis, whenthe horizontal GRF was changed, the hip joint moment changed moremarkedly than the others. Thus, these findings indicate that decreasing thehorizontal GRF is an important factor in decreasing the support moment.

Key Words: support moment, joint moment, drop landing, sensitivity analysis

Submittted for Publication : June 6, 2003,

Accepted for Publication : November 12, 2003

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