Walking through the looking glass: Adapting gait patterns with mirror feedback
Introduction
The ability to adopt and learn new walking patterns is critical for safe and efficient mobility in complex and dynamic environments; still, optimal methods for promoting skill acquisition in walking are not resolved. Learning novel gait mechanics is crucial for gait rehabilitation in patient populations, such as those with hemiplegic gait after a stroke, who need to relearn normal walking. As a result, efforts in locomotor rehabilitation research have focused on understanding factors that facilitate gait adaptation and learning (Balasubramanian et al., 2014, Eng and Tang, 2007, Hollands et al., 2013, Timmermans et al., 2016). Providing feedback is one such factor with the potential to improve the gait rehabilitation process (Eng and Tang, 2007, Hollands et al., 2013, Timmermans et al., 2016).
Models of motor adaptation and learning suggest providing additional feedback of behavior could influence adaptation and retention of a movement (Malone and Bastian, 2010, Newell et al., 2003, Roemmich et al., 2016, Sharma et al., 2016, Willy et al., 2012). For instance, individuals with patellofemoral pain were able to improve their running mechanics when provided a frontal plane mirror image of their body and given verbal cues about their running (Willy et al., 2012). Examining gait adaptability, the split-belt treadmill is an ideal tool for testing the effects of feedback on gait adaptation as it elicits the adjustment of an already learned walking pattern to accommodate novel demands and has demonstrated efficacy in improving walking symmetry after stroke (Reisman et al., 2013, Reisman et al., 2010b, Reisman et al., 2009, Reisman et al., 2007). Previous split-belt treadmill walking studies that manipulated corrective feedback have shown visual feedback (e.g. video projection of the sagittal view of a participant’s lower limbs or visual representation of step lengths) results in faster step length adaptation (Malone and Bastian, 2010, Roemmich et al., 2016), but has no impact on retention (Roemmich et al., 2016). Visual feedback of the sagittal plane provides an indication that an error has occurred (e.g. step lengths are different between legs), but may influence only certain aspects of gait adaptation.
Corrective/instructive feedback is a critical component of motor learning paradigms with the nature of feedback lying within the continuum between explicit and implicit motor learning. Explicit motor learning generates verbal knowledge of movement performance, involves cognitive processes and is dependent on working memory, whereas implicit learning progresses with no or minimal increase in verbal knowledge of movement performance and without awareness (Kleynen et al., 2015). Explicit cueing (Won and Jiang, 2015) with direct representation of error likely engages cognitive processes in a way that fails to promote motor learning (Fitts and Posner, 1967), whereas motor skills learned under more implicit conditions (i.e. without declarative knowledge gained from corrective performance feedback) are more stable and resilient to perturbation, such as stress (Hardy et al., 1996, Masters, 1992) and fatigue (Masters et al., 2008, Poolton et al., 2007). Indeed, motor learning protocols that do not rely on cognitive functions may facilitate rehabilitative benefits in populations with gait and cognitive comorbidity, such as individuals post-stroke (Hochstenbach et al., 1998, Lee et al., 1994). Thus, feedback that indirectly provides information about the walking pattern without providing corrective feedback or verbal instruction may facilitate both adaptation and retention of gait patterns.
Mirror feedback in the absence of explicit verbal instruction represents a more implicit motor learning design, capable of providing real-time visual information about locomotor kinematics. Yet there is a gap in evidence regarding the effect of frontal plane mirror feedback on adaptation and retention of outcomes related to gait symmetry and variability. Therefore in this study, we sought to investigate the effects of a real-time clinically feasible form of feedback that gives less direct perception of error during split-belt treadmill walking, but still provides relevant information about gait mechanics (e.g. general coordination) during a primarily sagittal plane perturbation. To accomplish this, we used mirror-based frontal plane visual feedback to provide participants a view of their body mechanics during adaptation to the novel walking paradigm. We hypothesized mirror feedback would reduce the number of steps needed to adapt and mitigate the magnitude of initial asymmetry in response to the perturbation. Additionally, because this visual plane provides less overt representation of error while still enhancing sensory information, we hypothesized feedback would also enhance retention and reduce the variability of the adapted pattern on the split-belt treadmill.
Section snippets
Subjects
Forty healthy young adults [18 males, 22 females, age (mean ± SD) 21 ± 3 years, height 1.7 ± 0.1 m, mass 67.3 ± 11.6 kg, 5 ± 2 h/week physical activity] naïve to the split-belt treadmill volunteered to participate. At the time of recruitment, all subjects were physically active as defined by participation in a minimum of 30 min of physical activity at least two times per week. Participants were excluded if they were currently injured or suffered an injury within the last six months that limited
Results
Demographic data (age, mass, height, and physical activity level) were not statistically different between groups (P > 0.60).
Discussion
Corrective feedback can vary in degree of implicit or explicit information provided to the individual (i.e. overtness of the indication that an error exists). The impact of this distinction has been investigated in many domains, such as dynamic balance (Orrell et al., 2006, Shea et al., 2001) and visuomotor adaptation (McDougle et al., 2015, Taylor et al., 2014). Within the realm of split-belt treadmill walking, feedback that directly represents error has been shown to accelerate adaptation (
Acknowledgements
The authors would like to thank all laboratory students, particularly Devan Ludden, for their help with data collection and processing and all volunteers for their participation in this study. The authors would also like to thank Dr. Michael Marsiske for his expertise and assistance with statistical analysis. The authors declare no funding sources.
Conflict of interest statement
The authors declare no conflicts of interest.
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