A pilot study of reactive balance training using trips and slips with increasing unpredictability in young and older adults: Biomechanical mechanisms, falls and clinical feasibility
Introduction
Falls in older age can result in fractures and fear and can trigger a decline in physical function and loss of independence (Centers for Disease Control and Prevention, 2006). Falls in the community setting are often caused by trips and slips during walking (Berg et al., 1997) and impaired reactive balance against trip and slip hazards have been identified as key risk factors for falls (Maki et al., 2003; Rogers et al., 1996; Woollacott and Tang, 1997; Young et al., 2013).
Earlier studies have shown that reactive balance can be modulated and improved by exposure to repeated perturbations (Nashner, 1980; Pavol et al., 2002; Pavol et al., 2004; Quintern et al., 1985). Thus, the use of mechanical postural perturbations in a safe environment has been proposed as a training method to prevent falls (Pai and Bhatt, 2007; Shimada et al., 2004). Preliminary systematic review evidence suggests that reactive balance training (also called “perturbation-based balance training”) can prevent falls by approximately 50% in older populations (Mansfield et al., 2015; Okubo et al., 2017). Previous studies have used a variety of methods to present postural perturbations and different methods are likely to yield different training effects, with most effective and feasible methodology yet to be determined (Gerards et al., 2017; McCrum et al., 2017).
Treadmills with abrupt belt accelerations (Shimada et al., 2004), ankle pulls (Karamanidis et al., 2011) or obstacles (Schillings et al., 1996) have been used to produce slip-like and trip-like simulations of balance loss. Over-ground walkways concealing hazards have higher ecological validity, but previous studies have often used a single hazard type (e.g. a sliding plate) in a detectable or known fixed location. Such prior knowledge of the hazard location and type can be used to make predictive (i.e. feedforward or proactive) changes in the approach (e.g. shorter step lengths) and anticipatory postural adjustments (e.g. anterior centre of mass [CoM] shift) prior to an expected slip or trip (Bhatt et al., 2006; Liu et al., 2017; Wang et al., 2011; Yang and Pai, 2013). These predictive changes to the approach may cause significant bias in the assessment of balance recovery reactions (i.e. feedback control of balance and stepping after hazard initiation) (Bohm et al., 2015). Changes in the approach may also reduce the need for a rapid response and therefore the efficacy of reactive balance training.
To address the issue of hazard predictability, we designed a perturbation system that can expose participants to unexpected slips and trips in various concealed locations while controlling for gait speed, step length and cadence (Brodie et al., 2018; Okubo et al., 2018). Since this perturbation system can generate repeated slips and trips while maintaining high unpredictability, it should enable specific training of rapid balance recovery reactions (Bierbaum et al., 2011; Bohm et al., 2015); however, it is not known if young and older adults can tolerate this high level of unpredictability. The purpose of this study was to examine and compare the effects of reactive balance training for young and older adults on: (i) the biomechanical parameters of a step immediately before and after a perturbation; (ii) falls; and (iii) clinical feasibility. We hypothesized that the reactive balance training protocol would be feasible and result in improved balance recovery responses and fewer falls with minimum predictive gait alterations.
Section snippets
Participants
A convenience sample was used for this pilot study. Ten young adults aged 20 to 40 years and ten older adults aged 65 to 90 years were recruited from the NeuRA Research Volunteer Registry (HC14320) and institute staff. Inclusion criteria were independent living community or retirement village residents, no osteoporosis or neurological impairment restricting activities of daily living, no history of fractures in the past 3 years, and able to stand or walk for 20 min without support. The above
Baseline characteristics
The demographic and usual gait characteristics of the young (4 females/6 males) and older (9 females/1 male) participants (mean [standard deviation]) are presented in Table 2. Compared to the young counterparts, older participants were significantly shorter in height and step length. No other characteristics showed a significant between-group difference (P > 0.05).
Normal walk trials
During the normal walks (unperturbed trials) the older participants walked significantly slower (1.13 [0.3] ms−1 vs 1.35 [0.08] ms−1
Biomechanical mechanisms
In the older participants, repeated exposure to unpredictable perturbations successfully induced large improvements in stability (MoS) during the first recovery step after slips. The participants managed to reduce the slip speed to the extent that it may be no longer hazardous (< 1.0 m/s) (Moyer et al., 2006) and was likely the major contributor to the smaller backward XCoM displacement and improved MoS during recovery. We assumed this increased stability was primarily related to improved
Conclusions
Reactive balance training using unexpected trip and slip hazards may provide an ecologically valid simulation of real life balance recovery biomechanics. The improved margin of stability and the non-significant reduction in fall rates (in absence of changes to approach kinematics) suggests that older adults can improve their balance recovery reactions in a single day. However, the high dropout rate and elevated anxiety during training suggests this protocol may not be suitable for all older
Contributions
YO, SRL, MAB and DLS contributed to the conception and design of the study. YO and CH recruited participants, conducted the experiments and collected data. YO and MAB processed and analysed the data. YO drafted the article. SRL, MAB, DLS and CH revised the article for important intellectual content. All authors approved the final version.
Declaration of Competing Interest
We declare we have no conflicting interest related to this manuscript.
Acknowledgements
We express our thanks to all the participants of this study. We especially thank Hilary Carter for developing and maintaining the slip and trip walkway. YO was supported by a Japan Society for the Promotion of Science fellowship. YO and MAB currently receive support from a National Health and Medical Research Council (NHMRC) Program Grant (#1055084). SRL holds an NHMRC research fellowship.
Funding
This work was supported by the National Health and Medical Research Council (Program Grant #1055084, 2014-2018). The funding source was not involved in the conduct of the research or preparation of the manuscript.
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