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.

Perturbation-based balance training: Principles, mechanisms and implementation in clinical practice

“…Early research demonstrated that a single session of repeated-perturbations (such as slip- or trip-like perturbations) results in acquisition of fall-resisting skills through implicit learning (without instruction) ( 78 – 81 ) across age-groups (young and old) ( 78 ) and tasks (standing, sit-to-stand transitions and walking) ( 82 ). In such single training sessions, the reduction of “in-task” falls can occur rapidly, i.e., in three–five trials ( 83 ).…”

“…A vital function of the central nervous system is its ability to apply motor adaptations obtained in one situation to a different situation. The central nervous system can generalize response adaptations to similar perturbations to an untrained limb ( 56 , 129 – 131 ); untrained tasks [e.g., gait-slip to sit-to-stand slip ( 82 )]; untrained contexts [e.g., moveable platform to vinyl floor ( 132 – 135 )]; and to different perturbation types [slips to trips ( 136 ) and waist pull perturbations to treadmill slips ( 137 ), though minor interference has also been reported ( 81 , 136 )]. Generalization between contexts (treadmill to overground slips) may also be retained over longer periods ( 138 ).…”

Mechanisms that stabilize human walking

“…Repeated exposure to slip-and trip-like perturbations has been shown to cause improved recovery responses in which the state of the center of mass relative to the base of support is better controlled [82][83][84][85][86][87][88][89] . This is in part accounted for by improved foot placement, as reflected in larger margins of stability at recovery step foot placement after training 86,88,89,90,91,92 . However, improved recovery responses were also associated with lesser deviations in trunk movement after the perturbation 86,[92][93][94] , which are most likely accounted for by improved stance leg control 87,95 .…”

Measures of falls efficacy, balance confidence, or balance recovery confidence for perturbation-based balance training

“…Studies have often posited that the training mechanisms of PBT improve physical abilities, such as generating more effective recovery step response and trunk movement to arrest falls in the face of a slip, trip or a loss of balance caused by volitional movement (3). This explanation has also been offered for studies employing a single PBT session (4,5). PBT is likely to influence psychological factors.…”