Is maximal muscle strength and fatigability of three lower limb muscle groups associated with walking capacity and fatigability in multiple sclerosis? An exploratory study

Background: Both muscle fatigability and walking fatigability are prevalent in persons with MS (pwMS), but their associations remains unclear. The aim of this study was to examine the association of muscle strength and fatigability from both isometric and concentric protocols of three different muscle groups, and their association to walking capacity and walking fatigability. Methods: Twenty-seven pwMS and 13 Healthy Controls (HC) were included in this exploratory study. All participants performed a six-minute walking test (6MWT), where the distance walked index (DWI) was calculated to measure walking fatigability with a cut-off score of -10%. In three different muscle groups (knee extensors (KE), knee flexors (KF), ankle dorsiflexors (DF)), isometric and concentric muscle fatigability protocols (FIisometric or FIconcentric) were used to quantify maximal voluntary contraction (MVC) and muscle fatigability. Pearson or Spearman correlation coefficients and linear regression models were calculated to establish the association between muscle strength/fatigability and walking capacity/fatigability. Results: Higher MVCs values for all muscle groups were found in HC compared to pwMS (mainly those having walking fatigability) (p < 0.05). FIisometric of DF was lower in pwMS having walking fatigability compared to no walking fatigability. MVC of KE, KF and DF had a low to moderate association with walking capacity (range r = 0.52-0.56; p < 0.05) and walking fatigability in pwMS (range r-rs: 0.39-0.50; pconcentric of KF and DF, but not of KE, were associated with walking fatigability (r = 0.39 and rs = 0.47, respectively; p < 0.05). In contrast, FIisometric for all muscle groups were not related to walking capacity or walking fatigability. Conclusion: MVC of KE, KF and DF are associated with walking capacity and walking fatigability, while concentric (but not isometric) muscle fatigability of KF and DF are associated with walking fatigability.