Fig. 7. Comparison of the effective mechanical advantage for horizontal versus vertical force production in crouched and upright postures. Biewener (1989) defines effective mechanical advantage as the ratio of the muscle moment arm (r) to the moment arm of the ground reaction force (R). For a crouched posture, the horizontal moment arm (R_hor) is smaller relative to the vertical moment arm (R_vert) than for an upright posture. This means that for a crouched posture the effective mechanical advantage for horizontal force production is greater relative to that for vertical force production than for a more upright posture.

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