Fig. 7. Viscous 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 (k) of the fixed coxa. (B) Stiffness of the free-coxa leg. (C) Viscous damping coefficient (c) of the fixed-coxa leg decreased with oscillation frequency and amplitude. (D) Viscous damping coefficient of the free-coxa leg also decreased with frequency and amplitude. Viscous damping in the free-coxa leg was 40–50% less than in the fixed-coxa leg.