Perturbation Training for Fall-Risk Reduction in Healthy Older Adults: Interference and Generalization to Opposing Novel Perturbations Post Intervention

Abstract

This study examined the effects of perturbation training on the contextual interference and generalization of encountering a novel opposing perturbation. One hundred and sixty-nine community-dwelling healthy older adults (69.6 ± 6.4 years) were randomly assigned to one of the three groups: slip-perturbation training (St, n = 67) group received 24 slips, trip-perturbation training (Tt, n = 67) group received 24 trips, and control (Ctrl: n = 31) group received only non-perturbed walking trials (ClinicalTrials.gov NCT03199729; https://clinicaltrials.gov/ct2/show/NCT03199729). After training, all groups had 30 min of rest and three post-training non-perturbed walking trials, followed by a reslip and a novel trip trial for St, a retrip and a novel slip trial for Tt, and randomized novel slip and trip trials for Ctrl. The margin of stability (MOS), step length, and toe clearance of post-training walking trials were compared among three groups to examine interferences in proactive adjustment. Falls, MOS at the instant of recovery foot touchdown, and hip height of post-training perturbation trials were investigated to detect interferences and generalization in reactive responses. Results indicated that prior adaptation to slip perturbation training, resulting in walking with a greater MOS (more anterior) and a shorter step length (p < 0.01) than that of the Ctrl group, would be associated with a greater likelihood to forward balance loss if encountered with a trip. The trip adaptation training mainly induced a higher toe clearance during walking (p < 0.01) than the Ctrl group, which could lead to reduced effectiveness of the reactive response when encountered with a novel slip. However, there was no difference in the reactive MOS, limb support, and falls between the control group and the slip and trip training groups on their respective opposing novel perturbation post-training (MOS, limb support, and falls for novel slip: Tt = Ctrl; for the novel trip: St = Ctrl, both p > 0.05). Current findings suggested that, although perturbation training results in proactive adjustments that could worsen the reactive response (interference) when exposed to an unexpected opposing perturbation, older adults demonstrated the ability to immediately generalize the training-induced adaptive reactive control to maintain MOS, to preserve limb support control, and to reduce fall risk.

Keywords: SLIP; TRIP; contextual interference; fall; perturbation.

Figure 1

The research design for the hypothesis and the planned comparisons were performed. Post-training walking trials (PW) were compared to examine interferences of training adaptations on the responses to opposing perturbations in the proactive control. Post-training perturbation trials were studied to investigate interferences of training adaptations on the responses to opposing perturbations in the reactive control. R = randomized assignment of subjects among groups.

Figure 2

(A). The experimental setup of the over-ground walkway, the overhead harness, and the motion system. (B-1) to (B-5) Still images indicate the instance of right foot touchdown (RTD) before the slip onset to recovery left foot touchdown (LTD). (C-1) to (C-5). Still images indicate the instance of RTD before left foot hitting the obstacle to recovery foot touchdown.

Figure 3

The training protocol used for the study. The slip-training (St) group received 24 repetitive slip perturbations, the trip-training (Tt) group received 24 repetitive trip perturbations, and the control (Ctrl) group received no training but only walking trials (W). Specifically, after 25–35 unperturbed normal walking trials (W) received by all groups, Group St received a block of eight repeated slip trials (S1–S8), followed by three unperturbed trials, another block of eight slip trials (S9–S16), an additional three unperturbed trials, and a final block of 15 mixed trials (including eight slip and seven unperturbed trials) (S17–S24). Group Tt experienced trials in the same design as Group St but trips as perturbation (T). Group Ctrl experienced an additional 37 unperturbed walking trials. After a 30-min break, all groups received three unperturbed post-perturbation walking trials (PW). Then, Group St received a reslip followed by a novel trip, Group Tt received a retrip followed by a novel slip, and Group Ctrl experienced these two perturbations in random order.

Figure 4

(A,B) The proactive adaptation and the short-term (30-min) retention in the margin of stability (MOS) during slip perturbation (indicated by filled circles) and trip perturbation (indicated by filled triangle) trainings. (C,D) The reactive adaptation and the short-term (30-min) retention in MOS during slip perturbation (indicated by filled circles) and trip perturbation (indicated by filled triangle) trainings. S1, S8, and S24 indicated the 1st, 8th, and the 24th slips, respectively, during the slip-training session. Reslip indicated the retest slip after a 30-min break. T1, T8, and T24 indicated the 1st, 8th, and 24th trips, respectively, during the trip-training session. Retrip indicated the retest trip after a 30min break. The mean value of MOS and the positive value of standard deviation for each trial are displayed. **p < 0.01; ***p < 0.001.

Figure 5

Fall outcomes among the reslip trial in the St group, the novel slip trial in the Tt group, and the novel slip trial in the Ctrl group. Significant differences were shown as the top two lines. Fall outcomes among the retrip trial inTt and the novel trip trial in St and in Ctrl. Significant differences were shown in the middle two lines. ^***p < 0.001.

Figure 6

(A) Proactive adjustments among PW in the St group, the Tt group, and the Ctrl group in a) the MOS at the RTD, (B) the step length normalized by body height (BH), and (C) the toe clearance normalized by BH. The mean value of MOS, step length, and toe clearance and the positive value of SD for each variable in each trial are displayed. ^**p < 0.01; ^***p < 0.001.

Figure 7

(A) Reactive MOS at the recovery LTD among the reslip trial in the St group and the novel slip trials in the Tt group and in the Ctrl group (indicated by filled circles). Significant differences are shown as the bottom two lines. The reactive MOS at the recovery LTD among the retrip trial in the Tt group and the novel trip trials in St and in Ctrl groups (indicated by triangles). Significant differences are shown in the top two lines. (B) Limb support (represented by the minimum hip height normalized by BH) among the reslip trial in the St group () and novel slip trials in the Tt group and in the Ctrl group (indicated by filled circles). Significant differences are shown in the top two lines. Limb support among the retrip trial in the Tt group and the novel trip trial in St and in Ctrl groups (indicated by triangles). The vertical line indicates the significant differences between the novel slip and the novel trip of the Ctrl group. The oblique line indicates the significant differences between the novel trip in the St group and the novel slip in the Tt group. The mean value of MOS and limb support and the positive value of the SD for each variable in each trial are displayed. ^*p < 0.05; ^**p < 0.01; ^***p < 0.001.