Fig. 7. Velocity, force and power output of the simulated muscle contractile element (thin red line), tendon (green line) and muscle–tendon unit (thick black line) for simulated jumps under the same four configurations as for Fig. 6: (A) no series elastic element, constant effective mechanical advantage (EMA), (B) no series elastic element, decreasing EMA, (C) compliant series elastic element, constant EMA and (D) compliant series elastic element, increasing EMA. All values are expressed relative to the maximum for the modeled muscle. When the muscle operates with a series elastic element (tendon), muscle velocity peaks early in the contraction due to stretch of the elastic element (top panels, C,D). Muscle–tendon power output can exceed peak isotonic power late in the jump due to high power outputs of the recoiling spring (bottom panels, C,D). When EMA is varied to maintain a constant muscle shortening velocity (B), power output is maintained at peak isotonic power until a small decline in force due to length–tension effects.

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