Meeting Abstract

122.2  Tuesday, Jan. 7 13:45  Ground-bird running in non-rigid terrain: deducing task-level priorities in locomotion HUBICKI, C*; SPROEWITZ, A; HURST, J; DALEY, M; Oregon State University; Royal Veterinary College; Oregon State University; Royal Veterinary College hubickic@onid.orst.edu

Terrestrial animals including ground birds regularly traverse terrain of irregular geometry and rigidity. We postulate that these diverse behaviors are unified at their foundation by task-level priorities based on the fundamental mechanical demands and functional limits of locomotion. We refer to these as task-level goals or control priorities. In prior work, behavior of ground birds in uneven rigid terrain suggested musculoskeletal injury avoidance and energy minimization as key task-level priorities. We also discovered a simple leg model that fits data across species. Building on these findings, we aim to quantitatively predict animal locomotor behavior in novel terrain scenarios. We probe the control priorities of running birds by leveraging both animal experiments and model analysis via optimal control. We run birds over a plannable perturbation, i.e. non-rigid ground, challenging hypothesized task-level priorities by provoking potential tradeoffs. To test for a stability-economy tradeoff, we collect motion-capture, force-plate, and high-speed video data of helmeted guinea fowl (Numida meleagris) running over non-rigid surfaces (sand, elastic foam, damped foam). We assess hypothesized priorities by comparing observed behavior to computed optimal trajectories. Our ongoing analysis aims to reveal deviations in strategy with differing ground properties, signaling tradeoffs between energy economy and stability (and not injury). Preliminary optimizations predict that work-optimal running on elastic terrain prolongs stance time, but maximally stable gaits do not. This work, combined with our prior analyses, will help reveal if steady and unsteady locomotion are governed by the same task-level priorities.