Elsevier

Clinical Biomechanics

Volume 88, August 2021, 105448
Clinical Biomechanics

Change in ‘first-trial’ performance after protective step practice in people with multiple sclerosis

https://doi.org/10.1016/j.clinbiomech.2021.105448Get rights and content

Highlights

  • Reactive stepping is relevant to falls & altered in people with multiple sclerosis.

  • The 1st trial after training is highly clinically relevant but often not assessed.

  • We show that performance on the 1st reactive step trial after practice was improved.

  • This provides preliminary evidence that reactive step practice could reduce falls.

Abstract

Background

Multiple sclerosis (MS) is a debilitating, neurodegenerative disorder causing considerable gait and balance dysfunction. Reactive balance (i.e., quick movements in response to a loss of balance) is particularly important for fall risk and is impaired in people with MS compared to neurotypical peers. Therefore, improving reactive balance among those with MS is critical. However, for maximum ecological validity, improvements in reactive balance through training would be demonstrable upon first loss-of-balance, rather than an average of several trials as is typically reported. This study evaluated changes in performance on the first stepping trial in people with MS after one day of practice.

Methods

Fourteen people with MS underwent two, consecutive days of support-surface perturbations from stance. On day 1, participants underwent a single backward-stepping trial, followed by 35 practice trails (forward and backward). Approximately 24 h later, participants were again exposed to a single backward stepping perturbation. Protective stepping outcomes were step length, step latency, and margin of stability at first foot contact. The backward step performance on the first trial of days one and two were compared, and difference scores were evaluated for relationships with correlates based on theoretical considerations.

Findings

First-trial margin of stability increased (improved) from day 1 to day 2 (P = .016). Steps were also faster on average by approximately 5 ms on day 2, although this improvement was not significant (P = .062).

Interpretations

Although preliminary, these findings provide evidence that individuals with MS may be able to experience first-trial improvements after a low dose of perturbation training.

Introduction

Multiple sclerosis (MS) is a chronic, debilitating, neurodegenerative disorder that affects approximately one million people in the United States and over two million people worldwide (Wallin et al., 2019). It is usually diagnosed in young adulthood and is the most common, non-traumatic cause of disability in young adults in the U.S. and Europe (Tullman, 2013). Although MS can cause manifold symptoms, chief among these are gait, balance, and mobility problems (Heesen et al., 2008; Zwibel, 2009). These concerns mean that falling, and suffering injury and even death as a result (Brønnum-Hansen et al., 2006), are problems that affects those with MS frequently—with studies showing that over 50% of those with MS are fallers (Gunn et al., 2014; Nilsagård et al., 2015) and 37% are classified as frequent fallers (Nilsagård et al., 2015). Further, 50% of those with MS have reported an injurious fall (Bazelier et al., 2012) and over half of falls are injurious (Peterson et al., 2008). These facts make gait and balance dysfunction and the risk of falling important targets for intervention in this population.

One aspect of gait and balance dysfunction that may be particularly important with respect to fall risk is impaired reactive balance (Cameron and Lord, 2010; Sturnieks et al., 2013). Reactive balance is a construct that evaluates one's ability to regain their balance following postural perturbations. Individuals with MS have been shown to have notable deficits in reactive balance (Peterson et al., 2016) and gait and balance deficits in general have been shown to manifest before clinical disability (Benedetti et al., 1999; Comber et al., 2017, Comber et al., 2018). A recent meta-analysis found that individuals with MS can experience acute improvements in reactive balance through training (Mohamed Suhaimy et al., 2020). Further, there is evidence that interventions aiming to improve reactive balance can decrease fall risk in other neurological populations—such as in individuals recovering from stroke (Mansfield et al., 2015), as well as older adults (Carty et al., 2015; Gerards et al., 2017; Lurie et al., 2020). Early evidence also exists suggesting aspects of protective steps—quick steps to regain balance after a loss of balance—can be modified through exposure in those with MS from static stance (Van Liew et al., 2019) and during gait (Yang et al., 2019).

Many of these previous studies assess reactive stepping as the average performance on several trials. However, in terms of fall risk, a patient's performance on the first exposure to a slip may be particularly meaningful (Nanhoe-Mahabier et al., 2012). Although any improvements in reactive balance performance likely bode well for decreasing fall risk, in everyday life, there is only one “trial” or slip that may result in a fall. Therefore, the ability of an individual to respond effectively the first time their balance is perturbed following exposure to reactive balance practice may suggest a smaller likelihood that an individual would fall if they experienced a loss of balance in the real world. Said differently, a single, ineffective protective step in the real world can be the difference between a non-injurious trip or slip and a potentially injurious fall. Although first-trial responses have not been evaluated in MS, previous work in people with PD suggests that such first-trial responses may be adaptable to change (Barajas and Peterson, 2018).

Among those with MS, individual responsiveness to physical activity and exercise interventions varies (Baird and Motl, 2019), but understanding which patients are more likely to receive benefit from such interventions could improve efficiency of care. It is likely that such considerations would apply in reactive balance training as well, but no studies have investigated variables related to responsiveness to reactive stepping practice. Identifying factors that predict responsiveness to training is particularly important for people with MS given the high degree of heterogeneity in this population (Baird and Motl, 2019). Thus, the aims of the present study are 1) to explore changes in first-trial performance after 1 day of repeated reactive balance challenges and 2) to evaluate the correlates of changes experienced in first-trial performance to evaluate factors that may predict who may be most likely to respond to such training.

Section snippets

Method

Data reported here are from a larger collection that has been published on previously (Van Liew et al., 2019). Although participants are the same across the previous and current study, the “first-trial” data reported here have not been reported previously.

Results

Participant characteristic data are shown in Table 1. Although data were collected on 14 participants, two individuals were excluded from analyses because they required harness support on day 1 which made obtaining reliable outcomes untenable. Therefore, all data reported below (including in Table 1) is from the 12 remaining participants. It is worth noting that no participants used harness support on the first trial on day 2.

Participants were mild to moderate in MS disease severity, but with

Discussion

In this study, we sought to determine 1) the change in first-trial stepping performance in individuals with MS and 2) whether these changes related to a variety of possible clinical correlates. Our previous analyses of this dataset (Van Liew et al., 2019) indicates that, on average, people with MS can improve average (of 5 trials) on reactive stepping performance. While identifying average or aggregate effects of training is promising, knowing whether exposures to perturbations result in

Declaration of Competing Interest

There are no conflicts of interest to support. This study was support by National Multiple Sclerosis Society Pilot Award (PP-1512-07101).

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