Predictive and Reactive Locomotor Adaptability in Healthy Elderly: A Systematic Review and Meta-Analysis

Abstract

Background: Locomotor adaptability is based on the implementation of error-feedback information from previous perturbations to predictively adapt to expected perturbations (feedforward) and to facilitate reactive responses in recurring unexpected perturbations ('savings'). The effect of aging on predictive and reactive adaptability is yet unclear. However, such understanding is fundamental for the design and application of effective interventions targeting fall prevention.

Methods: We systematically searched the Web of Science, MEDLINE, Embase and Science Direct databases as well as the reference lists of the eligible articles. A study was included if it addressed an investigation of the locomotor adaptability in response to repeated mechanical movement perturbations of healthy older adults (≥60 years). The weighted average effect size (WAES) of the general adaptability (adaptive motor responses to repeated perturbations) as well as predictive (after-effects) and reactive adaptation (feedback responses to a recurring unexpected perturbation) was calculated and tested for an overall effect. A subgroup analysis was performed regarding the factor age group [i.e., young (≤35 years) vs. older adults]. Furthermore, the methodological study quality was assessed.

Results: The review process yielded 18 studies [1009 participants, 613 older adults (70 ± 4 years)], which used various kinds of locomotor tasks and perturbations. The WAES for the general locomotor adaptability was 1.21 [95% confidence interval (CI) 0.68-1.74, n = 11] for the older and 1.39 (95% CI 0.90-1.89, n = 10) for the young adults with a significant (p < 0.05) overall effect for both age groups and no significant subgroup differences. Similar results were found for the predictive (older: WAES 1.10, 95% CI 0.37-1.83, n = 8; young: WAES 1.54, 95% CI 0.11-2.97, n = 7) and reactive (older: WAES 1.09, 95% CI 0.22-1.96, n = 5; young: WAES 1.35, 95% CI 0.60-2.09, n = 5) adaptation featuring significant (p < 0.05) overall effects without subgroup differences. The average score of the methodological quality was 67 ± 8 %.

Conclusions: The present meta-analysis provides elaborate statistical evidence that locomotor adaptability in general and predictive and reactive adaptation in particular remain highly effective in the elderly, showing only minor, not statistically significant age-related deficits. Consequently, interventions which use adaptation and learning paradigms including the application of the mechanisms responsible for an effective predictive and reactive dynamic stability control may progressively improve older adults' recovery performance and, thus, reduce their risk of falling.

Fig. 1

Flowchart of the systematic review process

Fig. 2

Forest plots for the meta-analysis of human locomotor adaptability in response to repeated perturbations. The general adaptive potential displayed here includes the predictive and reactive components. The footnotes explain the data from the original study used for the present analysis. CI confidence interval, IV inverse variance, SMD standardized mean difference, TD touchdown

Fig. 3

Forest plot of the effect of predictive adaptation on locomotion. The footnotes explain the data from the original study used for the present analysis. CI confidence interval, H hard surface (unperturbed), IV inverse variance, NS-1 non-slip trial (unperturbed), SD standard deviation, SMD standardized mean difference, TD touchdown

Fig. 4

Forest plot of the effect of reactive adaptation on the response to repeated unexpected locomotor perturbations. The footnotes explain the data from the original study used for the present analysis. CI confidence interval, IV inverse variance, SMD standardized mean difference, TD touchdown