Stability control during the double support phase of adaptive locomotion: Effect of age and environmental demands
Falls mostly occur when people are walking. Investigations of control of gait stability have focused primarily on the single stance phase. My dissertation focused on the double support phase of gait because (1) responses to perturbations occur during the double support (2) the portion of the gait cycle spent in double support is increased with old age, and, more importantly, (3) since both feet can push off the ground simultaneously, there are more kinetic degrees of freedom (DoF) and therefore greater control authority over body motion during this phase. However, how these kinetic DoFs are coordinated during the double support phase is not fully understood. Thus, the goal of this dissertation was to identify the inter-leg coordination to stabilize whole-body motion and quantify how the inter-leg coordination is affected by intrinsic and extrinsic factors. Specifically, Study 1 focused on healthy aging (an intrinsic factor) and varying task demands (an extrinsic factor that changed while curb ascent versus curb descent). Study 2 investigated another extrinsic factor of future uncertain environmental demands (fixed versus uncertain foot targeting demand for the step after descending a curb). Using the uncontrolled manifold analysis, I identified ground reaction variable (GRV) synergies, i.e., synergistic covariations between the ground reaction forces and moments under the two feet that stabilize whole-body linear and angular motions. Furthermore, I found that GRV synergies were modulated by extrinsic factors: GRV synergies were sensitive to current fixed environmental demands (Study 1), whereas they were robust to future environmental demands on foot placement (Study 2). Lastly, I found that GRV synergies were not changed by the intrinsic factor of age, despite the physiological declines with aging (Study 1). The absence of an age effect on GRV synergies indicates that older adults have the preserved ability to exploit the control authority during the double support phase to maintain stability while negotiating a curb. The work extends the current body of literature on gait stability mechanisms and improves our understanding of changes in stability control as a function of different environmental demands.
- Doctor of Philosophy
- Health and Kinesiology
- West Lafayette