title: Stability-maneuverability trade-offs during lateral steps.
abstract: Selecting a specific foot placement strategy to perform walking maneuvers requires the management of several competing factors, including: maintaining stability, positioning oneself to actively generate impulses, and minimizing mechanical energy requirements. These requirements are unlikely to be independent. Our purpose was to determine the impact of lateral foot placement on stability, maneuverability, and energetics during walking maneuvers. Ten able-bodied adults performed laterally-directed walking maneuvers. Mediolateral placement of the "Push-off" foot during the maneuvers was varied, ranging from a cross-over step to a side-step. We hypothesized that as mediolateral foot placement became wider, passive stability in the direction of the maneuver, the lateral impulse generated to create the maneuver, and mechanical energy cost would all increase. We also hypothesized that subjects would prefer an intermediate step width reflective of trade-offs between stability vs. both maneuverability and energy. In support of our first hypothesis, we found that as Push-off step width increased, lateral margin of stability, peak lateral impulse, and total joint work all increased. In support of our second hypothesis, we found that when subjects had no restrictions on their mediolateral foot placement, they chose a foot placement between the two extreme positions. We found a significant relationship (p<0.05) between lateral margin of stability and peak lateral impulse (r=0.773), indicating a trade-off between passive stability and the force input required to maneuver. These findings suggest that during anticipated maneuvers people select foot placement strategies that balance competing costs to maintain stability, actively generate impulses, and minimize mechanical energy costs.
authors.affiliation: Department of Biomedical Engineering, Northwestern University, Evanston, IL, USA.
authors.forename: Julian
authors.initials: J
authors.lastname: Acasio
authors.affiliation: Physical Therapy and Human Movement Sciences, Northwestern University, Chicago, IL, USA.
authors.forename: Mengnan/Mary
authors.initials: M
authors.lastname: Wu
authors.affiliation: Center for Bionic Medicine, Rehabilitation Institute of Chicago, Chicago, IL, USA.
authors.forename: Nicholas P
authors.initials: NP
authors.lastname: Fey
authors.affiliation: Physical Therapy and Human Movement Sciences, Northwestern University, Chicago, IL, USA; Research Service, Edward Hines Jr. VA Hospital, Hines, Illinois, USA. Electronic address: keith-gordon@northwestern.edu.
authors.forename: Keith E
authors.initials: KE
authors.lastname: Gordon
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D005528:Foot / Q000502:physiology*; D005684:Gait; D006801:Humans; D008297:Male; D056888:Patient Positioning; D004856:Postural Balance; D012016:Reference Values; D016138:Walking
keywords: Energy; Gait; Maneuver; Margin of stability; Work