Lower extremity muscle power - A critical determinant of physical function in aging and multiple sclerosis

In aging, lower extremity muscle power is undoubtedly one of the most important parameters of neuromuscular function implicating lower extremity physical function (e.g. walking capacity). However, no previous studies have examined the combined effects of aging and multiple sclerosis (MS) on lower extremity muscle power concomitant with lower extremity physical function. The aim of this cross-sectional study was to examine potential decrements in pwMS vs. healthy controls (HC) across the adult lifespan in these outcomes.

In the present explorative cross-sectional study, n = 42 pwMS (females n = 29 (69%); age = 53 ± 12 years (mean ± SD), range 31-78; patient determined disease steps score = 3.7 ± 1.7, range 0-7) and n = 49 age-matched HC (females n = 34 (69%); age = 56 ± 16 years, range 24-78) were enrolled, and divided into groups of young (≤ 44 years), middle-aged (45-59 years), and old (≥ 60 years). Muscle power was obtained from bilateral leg press (Power_LegPressPeak) and maximal chair rise (Power_ChairRise) using a linear encoder. Associations were assessed between muscle power and measurements of lower extremity physical function (5 x sit-to-stand (5STS); timed 25-foot-walk-test (T25FWT)).

Muscle power was reduced in pwMS vs. HC (Power_LegPressPeak -23[-34:-12]% (mean[95%CI]); Power_ChairRise -26[-35:-17]%) and was negatively associated with advanced age in both pwMS (decline per decade -0.40 W.kg^-1 and -2.53 W.kg^-1, respectively) and HC (decline per decade -0.42 W.kg^-1 and -2.03 W.kg^-1, respectively). Muscle power was strongly associated with physical function in pwMS (r²_range = 0.45-0.61, p < 0.01) yet only moderately associated in HC (r²_range = 0.18-0.39, p < 0.01).

The combined effects of MS and aging reveal substantial decrements in lower extremity muscle power that is accompanied by (and strongly associated with) decrements in lower extremity physical function. Consequently, lower extremity muscle power should be viewed as a clinically important factor (i.e. a critical determinant of lower extremity physical function) in pwMS. We propose that lower extremity muscle power should be specifically targeted by preventive and rehabilitative exercise strategies, especially in older pwMS.