Abstract
Training subjects to step in place on a rotating platform while maintaining a fixed body orientation in space produces a posteffect consisting in inadvertent turning around while stepping in place eyes closed (podokinetic after-rotation, PKAR). We tested the hypothesis that voluntary turning around while stepping in place also produces a posteffect similar to PKAR. Sixteen subjects performed 12 min of voluntary turning while stepping around their vertical axis eyes closed and 12 min of stepping in place eyes open on the center of a platform rotating at 60°/s (pretests). Then, subjects continued stepping in place eyes closed for at least 10 min (posteffect). We recorded the positions of markers fixed to head, shoulder, and feet. The posteffect of voluntary turning shared all features of PKAR. Time decay of angular velocity, stepping cadence, head acceleration, and ratio of angular velocity after to angular velocity before were similar between both protocols. Both postrotations took place inadvertently. The posteffects are possibly dependent on the repeated voluntary contraction of leg and foot intrarotating pelvic muscles that rotate the trunk over the stance foot, a synergy common to both protocols. We propose that stepping in place and voluntary turning can be a scheme ancillary to the rotating platform for training body segment coordination in patients with impairment of turning synergies of various origin.
Highlights
When walking in everyday environments, subjects frequently change direction to negotiate corners and avoid obstacles
Training subjects to step in place on a rotating platform while maintaining a fixed body orientation in space produces a posteffect consisting in inadvertent turning around while stepping in place eyes closed
One elegant way of producing inadvertent turning around while stepping in place eyes closed is to “induce” this behavior by having subjects stepping on a rotating platform while maintaining fixed heading by referencing body orientation to the seen environment [14, 20, 34]
Summary
When walking in everyday environments, subjects frequently change direction to negotiate corners and avoid obstacles. The ability to change direction and the ability to accurately control the curved trajectory while walking are essential components of successful navigation. Under the curved walking condition, the control of the muscle synergies takes into account the obligatory propulsion and the equilibrium constraints connected to body rotation. Given the complex coordination and multisensory integration underlying curved walking [8], studies requiring subjects to travel both linear and circular pathways have detected abnormalities in patients with neurological disorders [9,10,11,12,13]
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