Both stepping on a rotating platform and stepping while voluntarily turning around produce a post-effect consisting in inadvertent turning around while stepping-in-place eyes closed

Abstract

Turning around while stepping in place can be produced voluntarily. One way of producing involuntary turning around while stepping-in-place eyes closed is by training subjects onto a rotating platform while stepping-in-place and maintaining a fixed body orientation in space. This task produces a post-effect called “podokinetic after-rotation” (PKAR). Such training has been suggested for Parkinsonian patients. We tested the hypothesis that voluntary stepping-in-place and turning around also produces a post-effect similar to the PKAR. Sixteen subjects performed two different trials: 12 min of voluntary rotation around their vertical axes eyes closed and 12 min of stepping-in-place eyes open on the centre of a platform, rotating at of 60 °/s. Then, subjects were asked to continue stepping-in-place eyes closed for 10 min more. We recorded the body's segment positions. Subjects’ rotation velocity was the derivative of the angle described by the shoulders axis in the horizontal plane. The post-effect of stepping-in-place while voluntarily turning shares all features of the PKAR induced by the “podokinetic stimulation” of the platform rotation. In particular, stepping cadence, peak rotation velocity and its time decay are similar between the two conditions. Also, the ratio of the turning velocity pre (podokinetic stimulation or voluntary rotation) to the turning velocity of the PKAR is similar. Under both conditions, the post-rotation takes place without perception. We suggest that the post-effect of both protocols is induced by the repeated voluntary contraction of the leg and foot intra-rotating pelvic muscles, which are active when the trunk rotates over the stance foot for aligning these segments, a synergy common to both protocols. We propose that stepping-in-place while voluntarily turning can substitute the rotating platform for learning the rotating coordination in patients with impairment of turning synergies of various origin. This study was supported by the “Giovani Ricercatori 2009” grant (GR-2009-1471033) from the Italian Ministry of Health.