Effects of unilateral real-time biofeedback on propulsive forces during gait

Schenck and Kesar Journal of NeuroEngineering and Rehabilitation (2017) 14:52 DOI 10.1186/s12984-017-0252-z RESEARCH Open Access Effects of unilateral real-time biofeedback on propulsive forces during gait Christopher Schenck1 and Trisha M. Kesar2* Abstract Background: In individuals with post-stroke hemiparesis, reduced push-off force generation in the paretic leg negatively impacts walking function. Gait training interventions that increase paretic push-off can improve walking function in individuals with neurologic impairment. During normal locomotion, push-off forces are modulated with variations in gait speed and slope. However, it is unknown whether able-bodied individuals can selectively modulate push-off forces from one leg in response to biofeedback. Here, in a group of young, neurologically-unimpaired individuals, we determined the effects of a real-time visual and auditory biofeedback gait training paradigm aimed at unilaterally increasing anteriorly-directed ground reaction force (AGRF) in the targeted leg. Methods: Ground reaction force data during were collected from 7 able-bodied individuals as they walked at a self-selected pace on a dual-belt treadmill instrumented with force platforms. During 11-min of gait training, study participants were provided real-time AGRF biofeedback encouraging a 20–30% increase in peak AGRF generated by their right (targeted) leg compared to their baseline (pre-training) AGRF. AGRF data were collected before, during, and after the biofeedback training period, as well as during two retention tests performed without biofeedback and after standing breaks. Results: Compared to AGRFs generated during the pre-training gait trials, participants demonstrated a significantly greater AGRF in the targeted leg during and immediately after training, indicating that biofeedback training was successful at inducing increased AGRF production in the targeted leg. Additionally, participants continued to demonstrate greater AGRF production in the targeted leg after two standing breaks, showing short-term recall of the gait pattern learned during the biofeedback training. No significant effects of training were observed on the AGRF in the non-targeted limb, showing the specificity of the effects of biofeedback toward the targeted limb. Conclusions: These results demonstrate the short-term effects of using unilateral AGRF biofeedback to target propulsion in a specific leg, which may have utility as a training tool for individuals with gait deficits such as post-stroke hemiparesis. Future studies are needed to investigate the effects of real-time AGRF biofeedback as a gait training tool in neurologically-impaired individuals. Keywords: Gait training, Real-time biofeedback, Ground reaction forces, Unilateral, Motor learning, Retention, Propulsion Background Individuals with post-stroke hemiparesis demonstrate reduced push-off force generation in the paretic leg during terminal stance phase, which can negatively impact gait speed, inter-limb symmetry, and walking function [1–5]. Restoration of normal push-off force generation is the focus of gait rehabilitation treatments such as fast treadmill walking [6–8] and functional * Correspondence: 2 Division of Physical Therapy, Department of Rehabilitation Medicine, Emory University, 1441 Clifton Rd NE, Atlanta, GA 30322, USA Full list of author information is available at the end of the article electrical stimulation [9–11]. Push-off forces can be quantified by measuring anteriorly-directed ground reaction forces (AGRF) recorded from a force platform [1, 12]. Here, we test a unilateral AGRF biofeedback gait training tool that has potential for application in individuals with unilateral gait deficits such as poststroke hemiparesis. Real-time gait biofeedback is a potent tool that can enhance patient awareness of the impairment targeted during a gait retraining session, enabling self-correction of aberrant gait patterns [13]. Although there is a paucity © The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Schenck and Kesar Journal of NeuroEngineering and Rehabilitation (2017) 14:52 of systematic investigations on the use of real-time biofeedback during post-stroke gait training, biofeedback during gait has been shown to be effective at modulating step asymmetry in post-stroke individuals [14, 15], trunk lean in able-bodied individuals [16], and knee adduction moment in individuals with varus knee alignment [17]. Force platform biofeedback during gait has been studied for improving limb loading symmetry following total hip arthroplasty [18] and gait asymmetry in trans-tibial amputees [19]. Previous investigations also used limb load monitors inserted within shoes to provide audio feedback about stance duration asymmetry post-stroke, but these monitors were not reliable for measuring GRFs [20, 21]. Recently, the advent and increasing popularity of instrumented treadmills has made it more feasible and convenient to provide real-time AGRF feedback during treadmill walking. Real-time AGRF biofeedback was recently shown to be effective at increasing propulsion bilaterally in older adults [22]. For AGRF feedback to have utility in the rehabilitation of individuals with unilateral gait deficits, it would be beneficial to target propulsion symmetry, i.e., specifically target the reduced AGRF in the affected leg without proportionally increasing AGRF in the contralateral leg. During normal locomotion, push-off is known to modulate with gait speed and slope [23–27]. Previous investigations on able-bodied individuals used verbal instruction to increase pushoff bilaterally [28, 29]. However, it is not known whether AGRF feedback can induce increases in propulsion unilaterally in one limb, instead of bilateral improvements in push-off force generation. We posit that the feasibility of using AGRF biofeedback to specifically target propulsion in the targeted leg should be demonstrated before AGRF biofeedback is used in the rehabilitation of individuals with unilateral gait deficits such as post-stroke hemiparesis. The objective of this study, therefore, was to investigate the use of AGRF biofeedback to unilaterally modulate propulsion during walking in able-bodied individuals. We hypothesized that a single session of unilateral AGRF biofeedback would lead to increased AGRF production in the targeted leg without increasing AGRF production in the contralateral leg. (...truncated)