Biomechanical Mechanisms of Improved Balance Recovery to Repeated Backward Slips Simulated by Treadmill Belt Accelerations in Young and Older Adults

Abstract

Aim: Exposure to repeated gait perturbations improves the balance of older adults (OAs) and decreases their risks of falling, but little is known about the underpinning mechanical adjustments. We aimed to quantify the changing temporo-spatial and kinetic characteristics of balance recovery following repeated backward slips to better understand the mechanical adjustments responsible for improved balance.Methods: We exposed 17 young adults (YAs) (25.2 ± 3.7 years) and 17 OAs (62.4 ± 6.6 years) to 10 backward slips simulated on an instrumented treadmill by unilateral backward belt accelerations. We measured the balance of the participants (margin of stability: MoS), balance recovery (nsteps: number of steps necessary to return to a steady gait for at least three consecutive steps), temporo-spatial (step length), and kinetics [ground reaction force (GRF) angle, lower limb joint moments] for 15 steps following each slip. The results were compared with baseline.Results: Participants in both groups improved their MoS and nsteps with repeated exposure to the slips, but no significant effect of age was detected. During the perturbed step, the GRF vector was directed more posteriorly during mid-stance and more anteriorly during push-off than baseline, which resulted in a longer step. These adjustments were maintained from the first (Slip01) to the last (Slip10) slip, and by Slip10 were correlated with better balance (MoS) on the second recovery step. During the first recovery step following Slip01, participants developed lower plantarflexor and larger knee extensor moments whilst taking a shorter step, these adjustments were correlated with poorer balance and were not maintained with repeated slips. Joint moments and step length of the first recovery step returned to normal levels by Slip10.Conclusion: Young adults and OAs improved their balance with repeated slips. The adjustments that were positively correlated with balance (changes in step length, GRF angle) were maintained whilst those that were not (changes in joint moments) were discarded. All the responses observed in Slip10 were observed in Slip01. The observed balance improvements were achieved by refining the initial strategy rather than by developing a new one. The underlying mechanics were correlated with step length of the first recovery steps, which was associated with balance and should be monitored in fall prevention interventions.

Compensatory Responses During Slip-Induced Perturbation in Patients With Knee Osteoarthritis Compared With Healthy Older Adults: An Increased Risk of Falls?

“…In line with previous studies ( Debi et al, 2012 ; Sun et al, 2017 ; Wiik et al, 2017 ), patients with KOA showed significantly shorter step lengths relative to older adults in Normal. In this regard, the step length of slip_Rec1 is considered to be a critical element for improving balance recovery after a perturbation, as sufficient step length may help restore balance and may be more effective in avoiding falls ( Debelle et al, 2021 ). In the current study, the step length of slip_Rec1 decreased slightly compared with Normal, even though statistical significance was not reached between Normal and slip_Rec1 in either group.…”

“…Subsequently, Inkol et al (2019) found that the first response of a slip perturbation has the largest effect on the gait variables compared with the subsequent perturbations of the same type ( Inkol et al, 2019 ), and the first step following the perturbation is the most important protective postural strategy ( Maki and McIlroy, 1997 ; Melzer et al, 2008 ). Further, the step length of the first recovery step after a slip perturbation determines the stability of the subsequent steps and is corrected with balance recovery mechanics ( Debelle et al, 2021 ). It has been found that the frequency of backward slip on the oiled surfaces is twice as high as that of the forward slip ( Nagano et al, 2013 ), implying a high risk of falls, yet this perturbation is also most prevalent in daily life ( Debelle et al, 2020 ).…”

Lower extremity joint compensatory effects during the first recovery step following slipping and stumbling perturbations in young and older subjects

“…The role of joint moments to balance recovery is task-dependent, as mechanical requirements vary considerably [ 8 , 14 , 51 ]. The slipping perturbation in our investigation triggered the right belt to accelerate backward, resulting in a forward loss of dynamic stability.…”

“…The first response of a slipping perturbation has the largest effect on the gait variables compared with the subsequent perturbations of the same type [ 5 , 11 ], and the first step following the perturbation is the most important protective strategy [ 12 , 13 ] . A longer length of the first recovery step following a backward slipping [ 14 ] or a larger distance between the center of mass (CoM) and the recovery step after stumbling [ 15 ] plays a critical role in balance regaining. Therefore, quantifying the gait performance of recovery steps is intuitively critical following an unexpected slipping or stumbling perturbation.…”

“…To date, only a small portion of research has assessed the patterns of changes in lower extremity joint moments following perturbations through time-series features of the entire gait cycle. Only two studies investigated the joint moment effects induced by backward slipping perturbation on the treadmill [ 8 , 14 ]; however, the role of lower extremity joint moments in response to perturbations was inconsistent in the results.…”