Adaptation of the Compensatory Stepping Response Following Predictable and Unpredictable Perturbation Training.

Naoya Hasegawa,Yun Wang,Kazuhiko Watanabe,Hiroki Mani,Takahiro Inoue,Shintaro Tanaka,Tadayoshi Asaka

doi:10.3389/fnhum.2021.674960

Abstract

BackgroundEffective training of the backward step response could be beneficial to improve postural stability and prevent falls. Unpredicted perturbation-based balance training (PBT), widely known as compensatory-step training, may enhance the fear of falling and the patterns of postural muscle co-contraction. Contrastingly, PBT with predictable direction or both direction and timing would suppress the fear and the co-contraction patterns during training, but the efficacy of predictable PBT for unpredictable perturbations is still unknown.ObjectiveTo compare the adaptation effects of compensatory-step training with and without predictable perturbations on backward stepping against unpredictable perturbations.MethodsThirty-three healthy young adults were randomly assigned to one of the following step training groups: Unpredicted, Predicted, and Self-initiated. In training sessions, participants were perturbed to induce a compensatory step with (Predicted group) or without (Unpredicted group) knowledge of the perturbation’s direction or while knowing both the direction and timing of the perturbation (Self-initiated group). In test sessions (pre- and post-training), participants were instructed to recover their postural stability in response to an unpredicted perturbation. The margin of stability (MOS), center of mass (COM) shift, and step characteristics were measured during a backward step in both test and training sessions.ResultsAll three groups showed a significant increase in the step length and velocity in the post-training sessions compared to those in the pre-training sessions. Moreover, in the Unpredicted and Predicted groups, but not in the Self-initiated group, the MOS at step contact was significantly increased following the training session. In addition, the Self-initiated group showed a significant increase in COM shift at 50 ms after slip onset during training compared to the Unpredicted and Predicted groups.ConclusionUnpredicted and predicted PBT improve step characteristics during backward stepping against unpredictable perturbations. Moreover, the unpredictable PBT and PBT with direction-predictable perturbations enhance the feedback postural control reflected as the postural stability at step contact.

Highlights

Over 30% of people aged 65 and older experience falls each year, and the frequency of falls increases with age (Kalache et al, 2007)
The margin of stability (MOS) at step contact was increased by perturbation-based balance training (PBT) with unpredictable or direction-predictable perturbations, and the increase in the MOS was correlated with a longer step length and faster step velocity
Our findings firstly revealed that PBT against a perturbation of predictable direction improved the postural stability at backward step contact against an unpredictable perturbation

Summary

Introduction

Over 30% of people aged 65 and older experience falls each year, and the frequency of falls increases with age (Kalache et al, 2007). Older adults have a shorter step length and lower step velocity than young adults (McIlroy and Maki, 1996; Carty et al, 2011; Kilby et al, 2014; Lee et al, 2014). Considering their inefficient compensatory backward stepping and the importance of compensatory stepping for fall prevention (Carty et al, 2015), effective training of the backward step response is essential to improve postural stability and prevent falls. PBT with predictable direction or both direction and timing would suppress the fear and the cocontraction patterns during training, but the efficacy of predictable PBT for unpredictable perturbations is still unknown

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Results

Conclusion