Meeting Abstract

138.2  Monday, Jan. 7  Differentiating slip perturbation recoveries from falls in bipedally-running lizards. MARA, K.R.*; HSIEH, S.T.; Temple University kylemara@temple.edu

In nature, animals often encounter unsteady or unpredictable surfaces that they must counteract to maintain locomotor stability. Yet, the recovery mechanisms aiding restabilization remain under studied. The goal of this study was to describe the recovery kinematics that lead to successful slip recoveries compared to falls in the bipedally-running frilled lizard (Chlamydosaurus kingii). Lizards were run along a 2.5 m trackway and filmed with a six-camera auto tracking system (Motion Analysis Corp). Each lizard was run on a full-traction surface, as well as one in which we embedded an obscured low-friction surface. Trials were divided into three groups for analysis: steady-state unperturbed, successful recoveries, and falls. When lizards successfully recovered from a slip, perturbation compensation occurred rapidly and locomotor kinematics returned to unperturbed, steady-state values within one stride. Successful recoveries differ from falls by the proportion of ground contact time (duty factor), absolute slip surface contact time, and total displacement of the perturbed foot. In all perturbed trials, stride frequency increased relative to steady-state running, independent of the outcome. When lizards fell, the duty factor of the unperturbed foot (0.50 ± 0.058 SD) was significantly greater than that during steady-state (0.43 ± 0.10) or recovery (0.34 ± 0.19) trials. However, the duty factor of the perturbed foot was greater during falls (0.41 ± 0.12) than recoveries (0.32 ± 0.07) but no different than steady-state trials. Total translation distance of the perturbed foot appears to be an important factor determining perturbation outcome as falls coincided with the perturbed foot slipping significantly further (56.89 ± 4.82 mm) and for longer (0.067 ± 0.026 s) than in recovery trials(38.55 ± 16.48 mm; 0.053 ± 0.010 s).