Author(s): Mille ML, Rogers MW, Martinez K, Hedman LD, Johnson ME,
Abstract Share this page
Abstract Standing subjects were unexpectedly pulled forward to identify a threshold boundary that evokes stepping in terms of the size of the pull relative to the base of support (BoS). Performances in a range of sensorimotor tests were correlated with the threshold boundary parameters. Younger and older subjects were studied to identify age-related changes in stepping and the threshold boundaries. The threshold boundary had a forward limit (T(L)) that, when crossed, always made subjects step no matter how slowly they were pulled. As velocity increased, the threshold position that produced a step shifted nearer to the ankles. Eventually a pull velocity was reached above which velocity had no further effect and a position threshold (T(H)) was identified behind which subjects never stepped. Thus the position threshold boundary for stepping is a posterior-going sigmoidal function of perturbation velocity. Older subjects stepped more than the young (69\% vs. 40\% of trials). For the older subjects, T(L) (91\% vs. 107\% BoS) and T(H) (59\% vs. 72\% BoS) were closer to the ankles, and the transition between T(L) and T(H) occurred at lower velocities (96\% vs. 121\% BoS.s(-1)). Across the entire study population many sensorimotor factors were associated with T(L) and T(H). However, these associations were not present when age was removed as a factor. Thus, although the older subjects use protective stepping more often, this cannot be attributed directly to the sensorimotor factors tested here. It can be explained by stepping as a triggered response to the perturbation event rather than later sensory input about body movement.
This article was published in J Neurophysiol
and referenced in Journal of Novel Physiotherapies