Meeting Abstract
44.1 Wednesday, Jan. 5 Comparing stride local stability during walking and running QIAO, Mu*; JINDRICH, Devin; Arizona State University mqiao1@asu.edu
Morphology, musculoskeletal physiology, and active control could all potentially contribute to within-stride stability during locomotion. However, to what extent are within-stride movements actually stabilized during unperturbed locomotion? This study sought to characterize within-stride local stability by analyzing individual joints and the center of mass (COM). Specifically, we hypothesized that 1) different joints should show similar stability properties within the same gait; 2) constant speed walking or running is more stable than acceleration or deceleration; 3) walking is more stable than running. We recorded 6 locomotion tasks, running and walking at constant speed, acceleration, and deceleration. In each trial we calculated Lyapunov exponent on individual joint angle and COM histories to determine local stability within a stride. Positive Lyapunov exponents indicating an unstable system were found for within-stride dynamics in both gaits. A two-factor (gait; speed) repeated measure ANOVA showed a significant main effect: running is more unstable than walking (p < .01). We found in vertical COM and most joints, except left and right knee, running is more unstable than walking (p < .01). The main effect of speed on local stability shows that constant speed is less unstable than acceleration (p < .05). However, using only data from selected individual joint angles (left elbow (interaction, p < .05), left knee (no main effect)) can result in conflicting conclusions and may only reflect joint dynamic behavior. These conflicts show that individual degrees of freedom may not effectively represent the whole system’s dynamic behavior. Whereas stability is maintained over multiple strides, this does not appear to result from the maintenance of stable joint or COM movements within strides. Maneuvers such as acceleration and deceleration may exhibit less within-stride stability and require greater stride-to-stride control effort.
