Jindrich, D. L.*; Full, R. J.: Dynamic Stabilization of Rapid Hexapodal Locomotion

Mechanical properties of muscles, connective tissues, and skeletal elements contribute to reducing energy costs, but can also simplify the control of rapid locomotion in animals. Passive mechanical behavior of the musculo-skeletal system may play a role in stability. Rapidly acting, musculo-skeletal ‘preflexes’ have been hypothesized to contribute to disturbance rejection during rapid movements and can augment the actions of a neural feedback controller. To assess the role of ‘preflexes’ in the stabilization of rapid locomotion, and to study the control strategies used by hexapods to stabilize locomotion, we subjected cockroaches (Blaberus discoidalis) to short-duration perturbations during rapid running. The perturbations were generated using a small device attached to the animal’s dorsal surface, positioned just above the animal’s center of mass. The device used black powder to propel a ball bearing laterally as the cockroach ran along a track. The reaction force from the explosion generated a perturbation to the animal’s lateral velocity with a force impulse of 60-70% of the forward momentum of a 2 gram cockroach running at its preferred speed of 25 cm/s. The duration of force was less than 10 milliseconds. Lateral velocity began to decrease 14 +/- 8 S.D. milliseconds from the onset of the perturbation. Cockroaches were able to recover from lateral perturbations (i.e. lateral velocity returns to within the range observed during unperturbed running) in 37 +/- 10 milliseconds. The rapid recovery of lateral velocity supports the hypothesis that fast-acting musculo-skeletal ‘preflexes’ may play a role in stabilizing insect locomotion. Supported by DARPA/ONR N00014-98-1-0747