Meeting Abstract

66.1  Thursday, Jan. 6  Active Muscle Enhances Rapid Perturbation Recovery in an Insect Limb. LIBBY, T.*; FULL, R. J.; Univ. of California, Berkeley

Passive, intact limbs of cockroaches recover from large impulses in less than 40 ms, sufficient for complete recovery from a perturbation at the onset of swing phase. Such capability could insure stable foot fall positions independent of perturbations at the stance-swing transition during running at the animal’s preferred speed, but would not be capable of recovering from perturbations later in swing or at higher stride frequencies. The stiffness and damping of active muscle varies with activation, allowing animals to modulate limb impedance over a wide parameter space. We studied Blaberus discoidalis limbs with added muscle activation, using a modification of the work-loop technique in which the animal and limb are kept intact, all muscles spanning the joint are denervated, and forces are applied to the limb instead of a single muscle. Using a servo and a stimulator, we enforced cyclic kinematics and muscle activation consistent with in vivo conditions of fast running. We then applied large impulse perturbations to the limb at various phases of limb flexion. By changing the phase of perturbation, number of elicited muscle action potentials, and frequency of oscillation, we tested active muscle’s ability to increase limb stability over the range observed in running cockroaches. Adding activation to muscles increased stability to perturbations, decreasing recovery time to as brief as 10 ms with typical stimulation patterns in both muscles. In the stimulated limb, tracking error at swing’s end was independent of phase for the first three quarters of the cycle, whereas error in the passive limb increased to over 50%. Nonlinear properties of both active and passive muscle decreased the limb’s sensitivity to perturbations as phase and frequency increased, enhancing stability as the task became more demanding.