Abstract
The plantarflexors play a crucial role in recovery from sudden disturbances to gait. The objective of this study was to investigate whether medium (months)- or long(years)-term exercise-induced enhancement of triceps surae (TS) neuromuscular capacities affects older adults' ability to retain improvements in reactive gait stability during perturbed walking acquired from perturbation training sessions. Thirty-four adult women (65 ± 7 yr) were recruited to a perturbation training group ( n = 13) or a group that additionally completed 14 wk of TS neuromuscular exercise ( n = 21), 12 of whom continued with the exercise for 1.5 yr. The margin of stability (MoS) was analyzed at touchdown of the perturbed step and the first recovery step following eight separate unexpected trip perturbations during treadmill walking. TS muscle-tendon unit mechanical properties and motor skill performance were assessed with ultrasonography and dynamometry. Two perturbation training sessions (baseline and after 14 wk) caused an improvement in the reactive gait stability to the perturbations (increased MoS) in both groups. The perturbation training group retained the reactive gait stability improvements acquired over 14 wk and over 1.5 yr, with a minor decay over time. Despite the improvements in TS capacities in the additional exercise group, no benefits for the reactive gait stability following perturbations were identified. Therefore, older adults' neuromotor system shows rapid plasticity to repeated unexpected perturbations and an ability to retain these adaptations in reactive gait stability over a long time period, but an additional exercise-related enhancement of TS capacities seems not to further improve these effects. NEW & NOTEWORTHY Older adults' neuromotor system shows rapid plasticity to repeated exposure to unexpected perturbations to gait and an ability to retain the majority of these adaptations in reactive recovery responses over a prolonged time period of 1.5 yr. However, an additional exercise-related enhancement of TS neuromuscular capacities is not necessarily transferred to the recovery behavior during unexpected perturbations to gait in older adults.
Highlights
Falls are a leading cause of injuries among elderly populations (MacAulay et al 2015; Terroso et al 2014)
We suggest that to improve the ability to cope with disturbances to gait older adults may benefit more from exposure to unexpected gait perturbations than from interventions targeting the leg extensor neuromuscular capacities
The present findings provide evidence that older adults are able to partly retain the reactive response improvements in fall-resisting skills acquired during perturbation training sessions over a prolonged period of 1.5 yr
Summary
Falls are a leading cause of injuries among elderly populations (MacAulay et al 2015; Terroso et al 2014). To prevent a fall in such an unstable position, the neuromuscular system must execute postural adjustments to control the velocity and position of the center of mass in relation to the base of support and thereby maintain dynamic stability. During gait, such adjustments can be reactive (feedback driven) or predictive (feedforward driven) in nature (for example, see Arampatzis et al 2011; Bhatt et al 2006b; Bierbaum et al 2011; Bohm et al 2015; MacLellan and Patla 2006). As falls often occur in the anterior direction during walking, it is not surprising that effectively increasing the base of support in response to a sudden external perturbation is vital for regaining dynamic stability (Hof 2007; Maki and McIlroy 2006)
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