Retention of gait stability improvements over 1.5 years in older adults: effects of perturbation exposure and triceps surae neuromuscular exercise.

The plantar flexors play a crucial role in recovery from sudden disturbances to gait. The objective of this study was to investigate whether medium (months) or long-term (years) 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 female adults (65{plus minus}7y) were recruited to a perturbation training group (n=13) or a group which additionally completed 14 weeks of TS neuromuscular exercise (n=21), 12 of whom continued with the exercise for 1.5 years. The margin of stability (MoS) was analyzed at touchdown of the perturbed step and first recovery step following eight separate unexpected trip perturbations during treadmill walking. TS muscle-tendon unit mechanical properties and motor skill performance were assessed using ultrasonography and dynamometry. Two perturbation training sessions (baseline and after 14w) 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 weeks and over 1.5 years, 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.