Do physical activity, cardiorespiratory fitness, and subcortical brain structures explain reduced walking performance in older adults with multiple sclerosis?

Background: As adults with multiple sclerosis (MS) age, walking speed and endurance progressively decline, yet there is limited understanding of factors that explain such age-related declines. The current study examined subcortical brain structures, cardiorespiratory fitness, and moderate-to-vigorous physical activity (MVPA) as explanations for reduced walking performance in older adults with MS.

Methods: Older adults with MS (n = 29, 62.8 ± 5.8 years) and age-and-sex matched controls (n = 28, 63.8 ± 5.5 years) completed measures of walking speed (Timed-25 ft Walk) and walking endurance (Six-minute Walk), cardiorespiratory fitness, device-measured MVPA, and underwent an MRI to provide composite volumes of the thalamus, caudate, putamen, and pallidum. We used a mediator variable framework to describe group differences, determine correlations in the overall sample, and identify variables that explain reduced walking performance.

Results: Compared to controls, older adults with MS had worse walking speed (p<0.001) and endurance (p<0.001), lower fitness (p = 0.04), lower levels of MVPA (p = 0.001), and smaller composite volumes of the thalamus (p=<0.001), putamen (p = 0.04), and pallidum (p = 0.007). In the overall sample, both measures of walking performance were significantly correlated with fitness, MVPA, and volumes of the thalamus and putamen (r range 0.34-0.65). Regression analyses indicated that MVPA (β=0.007094) partially explained the group differences in walking speed, and fitness (β=7.7640) and MVPA (β=17.5797) partially explained the group differences in walking endurance.

Conclusions: Collectively, these results suggest that cardiorespiratory fitness and MVPA, but not subcortical brain structures, may be modifiable targets of future interventions for improving walking in older adults with MS.