Data and Code from: Humans prioritize walking efficiency or walking stability based on environmental risk

<p>This work demonstrates how humans exploit the mechanics of their bodies to achieve specific movement goals. While this phenomenon is well-known in sports (e.g., modulation of body postures to increase jump height or length in high jump or long jump, or to control the number of twists and somersaults while diving), we demonstrate that the same principle is applicable in an activity of daily living – walking and stepping over an obstacle. Our results motivate the investigation of the effects of aging and pathology on this ability, and how any decrements could underlie mobility issues in these populations.</p>

<p>Humans reuse the body’s mechanical energy at the end of one step to achieve forward progression during the subsequent step, thereby reducing the energy required for walking. This is achieved by harnessing the passive instability of the upright human posture. Here we test the novel hypothesis that humans manipulate passive anterior-posterior (AP) stability by actively modulating the placement of each foot for each step to either achieve energy-efficient gait or to improve stability when balance is threatened.</p>

<p>We computed the AP margin of stability, which quantifies the passive dynamic stability of gait, for multiple steps as healthy young adults (N=20) walked on a clear and on an obstructed walkway. Participants used passive dynamics to achieve energy-efficient gait for all but one step; when crossing the obstacle with the leading limb, AP margin of stability was increased and indicated cautious gait, reflecting the greater threat to balance arising from a potential trip. Furthermore, AP margin of stability increased while approaching the obstacle, indicating that humans proactively manipulated the passive dynamics to meet the demands of the locomotor task. Finally, the step length and the center of mass motion co-varied to maintain the AP margin of stability for all steps in both tasks at the specific values for each step. We conclude that humans actively regulate step length to maintain specific levels of passive stability for each step during unobstructed and obstructed gait.</p>