Fig. 3. A representative trace of joint moments (A) and forces (B,C) developed by the MG (blue lines) and LG (red lines) for the right limb of a turkey running at 2 m s^–1. A positive then negative joint moment is required at the ankle joint during swing as the joint flexes and extends. The black line (B,C) is the force required from the gastrocnemius, calculated from the moment measured by inverse dynamics and the muscle moment arm. Only forces during swing phase were calculated from inverse dymanics (required force). The muscular force required to produce the measured joint extension moment is closely matched by the force produced by the lateral head of the gastrocnemius, while the medial head produces almost no force. The exclusive force production by the LG ends at the beginning of stance (gray shaded region in C).