Exercise of mechanisms of dynamic stability improves the stability state after an unexpected gait perturbation in elderly

Abstract

Unexpected changes during gait challenge elderly individuals to a greater degree than young adults. However, the adaptive potential of elderly seems to be retained, and therefore, the training of the mechanisms of dynamic stability as well as muscle strength training may improve the dynamic stability after unexpected perturbations. Thirty-eight subjects (65-75 years) participated in the study, divided into two experimental groups (stability training group, ST, n = 14 and mixed training group, MT, n = 14) and a control group (CG, n = 10). Both experimental groups performed exercises which focused on the mechanisms of dynamic stability. Additionally, the MT group executed a training to improve muscle strength. Session volume and duration were equal for both groups (14 weeks, twice a week, ~1.5 h per session). Pre- and post-intervention, subjects performed a gait protocol with an induced unexpected perturbation. Post-intervention, the margin of stability was significantly increased after the unexpected perturbation in the ST group, indicating an improvement in stability state (pre, -30.3 ± 5.9 cm; post, -24.1 ± 5.2 cm). Further, both intervention groups increased their base of support after the intervention to regain balance after gait perturbation, whereas only the ST group showed a statistically significant improvement (STpre, 90.9 ± 6.6 cm, STpost, 98.2 ± 8.5 cm; MTpre, 91.4 ± 6.2 cm; MTpost, 97.9 ± 12.7 cm). The CG showed no differences between pre- and post-measurements. The exercise of the mechanisms of dynamic stability led to a better application of these mechanisms after an unexpected perturbation during gait. We suggest that the repeated exercise of the mechanisms of dynamic stability contributes to significant improvements in postural stability. Additional strength training for healthy elderly individuals, however, shows no further effect on the ability to recover balance after unexpected perturbations during gait.

Fig. 1

Flow chart of recruitment and participation in the study. The performed gait measurement is named as “GAIT.” MTU refers to the strength measurements of the muscle tendon unit (knee extensors and ankle plantar flexors)

Fig. 2

Walkway (a) and gait protocol (b) for the test of the dynamic stability. The walkway (a) included one covered, exchangeable element, which allowed changing the surface condition from hard to soft without the knowledge of the participants. Three valid gait trials on the hard surface formed the baseline and were followed by one unexpected soft surface trial (b). This soft trial was performed to induce reactive behavior. Analysis was made for the step prior to the perturbation and the step after the perturbation (c)

Fig. 3

Individual and mean values of margin of stability before and after the intervention at the step after the unexpected perturbation for the stability training group (ST), mixed training group (MT), and control group (CG). Asterisk, statistically significant time effect, F(1, 35) = 8.046, p = 0.008, part.η² = 0.187); Numbersign, statistically significant differences between pre- and post-measurement [follow up; F(1, 13) = 12.125, p = 0.004, part.η² = 0.483]