Abstract
Stride durations in gait exhibit long-range correlation (LRC) which tends to disappear with certain movement disorders. The loss of LRC has been hypothesized to result from a reduction of functional degrees of freedom of the neuromuscular apparatus. A consequence of this theory is that environmental constraints such as the ones induced during constant steering may also reduce LRC. Furthermore, obstacles may perturb control of the gait cycle and also reduce LRC. To test these predictions, seven healthy participants walked freely overground in three conditions: unconstrained, constrained (constant steering), and perturbed (frequent 90° turns). Both steering and sharp turning reduced LRC with the latter having a stronger effect. Competing theories explain LRC in gait by positing fractal CPGs or a biomechanical process of kinetic energy reuse. Mediation analysis showed that the effect of the experimental manipulation in the current experiment depends partly on a reduction in walking speed. This supports the biomechanical theory. We also found that the local Hurst exponent did not reflect the frequent changes of heading direction. This suggests that the recovery from the sharp turn perturbation, a kind of relaxation time, takes longer than the four to seven meters between successive turns in the present study.
Highlights
Control is extended beyond the requirements of a specific task
The first objective of the present study is to test whether an indirect constraint on gait cycle timing would result in a drop of long-range correlation (LRC)
It is expected that constant steering as a form of constant constraint on performance will lead to a decrease in LRC
Summary
Control is extended beyond the requirements of a specific task. For example, one might hypothesize that the timing mechanism for finger taps covers other supporting aspects of the task such as maintaining arm posture and paying attention to the stimulus. Increasing the difficulty of the task or using a secondary task executed in a different modality tends to be associated with a drop of LRC15 To this end, the first objective of the present study is to test whether an indirect constraint on gait cycle timing would result in a drop of LRC. Gait regulation for steering is one such factor that does not directly determine step timing in the same way that instructed synchronization with a cueing stimulus would[13] In this way it complements previous studies such as ones involving treadmill walking where the constant constraint of keeping fixed velocity and a limited stepping range results in reduced LRC in stride velocities. Several muscles become engaged in order to reduce forward speed[16] and contribute to medio-lateral center of mass acceleration during sharp turns[23]
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