Fig. 8. Hysteretic damping model stiffness and damping coefficients as a function of frequency at amplitudes of 0.1 (circles), 0.5 (squares) and 1.0 mm (triangles). (A) Stiffness of the fixed-coxa leg increased with frequency from 0.05 to 25 Hz. The slopes and intercepts of the 0.3–1.0 mm amplitude oscillations were not significantly different from each other but were significantly lower than the 0.1 mm oscillations. (B) Stiffness of the free-coxa leg increased linearly with increasing frequency. As in the fixed-coxa preparation, the slopes and intercepts of the 0.3–1.0 mm amplitude oscillations were not significantly different from each other but were significantly lower than the 0.1 mm oscillations. The slopes and intercepts were 50–60% lower for the free-coxa leg than for the fixed-coxa leg. (C) Structural damping factor of the fixed-coxa leg was independent of oscillation frequency and amplitude. (D) Structural damping factor of the free-coxa leg also was independent of frequency and amplitude. Hysteretic damping in the fixed-coxa leg was 30% less than in the free-coxa leg.