Fig. 5. Energy storage, returned and lost as a function of frequency at amplitudes of 0.1 (circles), 0.5 (squares) and 1.0 mm (triangles). (A) Loading energy in fixed coxa increased with increasing amplitude and as oscillation frequency increased from 0.05 to 25 Hz. (B) Loading energy in free coxa required 45–60% less energy than the fixed leg. (C) Unloading energy in the fixed coxa increased with increasing amplitude and as oscillation frequency increased to 25 Hz. (D) Unloading energy in the free coxa returned 50–70% less energy than the fixed leg. (E) Hysteresis (or lost energy) in the fixed-coxa preparation decreased as frequency increased, but was only significant at 1.0 mm oscillations. (F) Hysteresis in the free-coxa preparation increased as frequency increased significantly for 0.5 and 1.0 mm oscillations and was only about 30% less than the fixed-coxa legs.