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Fig. 3. Mechanics of leg swinging as a function of frequency f, in terms of torque, work, and force/time, were modeled reasonably well by a forced pendulum (Equations 9, 10, 11). (a.) Hip torque amplitude, T0, increased approximately with f2 above natural frequency fn (R2=0.96). (b.) Rate of mechanical work, (+), increased approximately with f3 (R2=0.93). (c.) Rate of force/time, {tau}, increased approximately with f 4 (R2=0.95). Metabolic cost is hypothesized to increase with both rate of work and force/time, for frequencies above the natural frequency fn=0.64 Hz. Data fits were performed using dimensionless variables (right-hand axis) with body mass, gravitational constant, and leg length serving as base units; conventional units are shown (left-hand axis) for convenience. Data shown are mean ± S.D.





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