An isolated insect leg's passive recovery from dorso-ventral perturbations.

Cockroaches recover rapidly from perturbations during high-speed running that allows them to cross unstructured terrains with no change in gait. Characterization of the exoskeletal material properties of the legs suggests that passive mechanical feedback could contribute to the self-stabilizing behavior. We imposed large, dorsal-ventrally directed impulsive perturbations to isolated hind legs having both a fixed and free body-coxa joint and measured their recovery. We tested a frequency-independent hysteretic damping model that effectively predicted the behavior of sinusoidal oscillations of isolated legs. Leg position reached its peak amplitude within 4-6 ms following an impulse. Position was 99% recovered within 16+/-3.3 ms for the stiffest possible leg configuration and within 46+/-6.6 ms for the most compliant leg configuration. The rapid recovery supports the hypothesis that passive musculo-skeletal properties play an important role in simplifying the control of high-speed locomotion.