Abstract
The minimum toe clearance (MTC) results from the coordination of all bilateral lower limb body segments, i.e., a redundant kinematic chain. We tested the hypothesis that repeated exposure to trip-like perturbations induces a more effective covariation of limb segments during steady walking, in accordance with the uncontrolled manifold (UCM) theory, to minimize the MTC across strides. Twelve healthy young adults (mean age 26.2 ± 3.3 years) were enrolled. The experimental protocol consisted of three identical trials, each involving three phases carried outin succession: steady walking (baseline), managing trip-like perturbations, and steady walking (post-perturbation). Lower limb kinematics collected during both steady walking phases wereanalyzed in the framework of the UCM theory to test the hypothesis that the reduced MTC variability following the perturbation can occur, in conjunction with more effective organization of the redundant lower limb segments. Results revealed that, after the perturbation, the synergy underlying lower limb coordination becomes stronger. Accordingly, the short-term effects of the repeated exposure to perturbations modify the organization of the redundant lower limb-related movements. In addition, results confirm that the UCM theory is a promising tool for exploring the effectiveness of interventions aimed at purposely modifying motor behaviors.
Highlights
The minimum toe clearance (MTC) is the distance between toe and ground, as assessed when the time course of the toe’s vertical displacement reaches the relative minimum during the mid-swing phase of a gait cycle [1]
In one of our recent works, we extended previous findings to reveal that repeated exposure to a series of trip-like perturbations modifies MTC average and variability towards a more conservative and more precise neuro-muscular control strategy [9]
When the variability of elemental variables is mostly confined to the former domain, namely the uncontrolled manifold, it is possible to conclude that the orientation of lower limb segments is functionally organized across strides to minimize the MTC inter-stride variability (i.e., MTCSD)
Summary
The minimum toe clearance (MTC) is the distance between toe and ground, as assessed when the time course of the toe’s vertical displacement reaches the relative minimum during the mid-swing phase of a gait cycle [1] At this critical time, if the trajectory of the swinging foot is abruptly interrupted by an obstacle (i.e., tripping), the overall dynamic is challenged and the consequent lack of balance can result in a fall. In one of our recent works, we extended previous findings to reveal that repeated exposure to a series of trip-like perturbations modifies MTC average and variability towards a more conservative (i.e., lower MTC average) and more precise (i.e., lower MTC variability) neuro-muscular control strategy [9].
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