Neuromuscular rate of force development discriminates fallers in ambulatory persons with multiple sclerosis - an...

Falls as well as fall-related injuries (e.g., bone fractures) are common in persons with multiple sclerosis (pwMS). Whilst some studies have identified lower extremity maximal muscle strength (Fmax) as one among several risk factors, no previous studies have investigated the association between rate of force development (RFD; ability to generate a rapid rise in muscle force) and falls in pwMS. Not only is RFD substantially compromised (and more so than Fmax) in pwMS, studies involving other neurodegenerative populations have shown that RFD - to a greater extent than Fmax - is crucial for counteracting unexpected perturbations and avoiding falling.

To explore whether knee extensor RFD (and Fmax) can discriminate fallers from non-fallers in pwMS.

Knee extensor neuromuscular function (comprising RFD_50ms and RFD_200ms (force developed in the interval 0-50 ms and 0-200 ms, respectively) as well as Fmax) of the weaker leg was assessed by isokinetic dynamometry. Falls were determined by 1-year patient recall, with pwMS subsequently being classified as non-fallers (0 falls), fallers (1-2 falls), or recurrent fallers (≥3 falls).

A total of n=53 pwMS were enrolled in the study, with n=24 classified as non-fallers (63% females, 48 years, EDSS 2.2), n=16 as fallers (88% females, 57 years, EDSS 3.3), and n=13 as recurrent fallers (46% females, 60 years, EDSS 4.2). Compared with non-fallers, neuromuscular function was reduced in both fallers (RFD₅₀ -4.42 [-7.47;-1.37] Nm^.s^-1.kg^-1, -48%; RFD₂₀₀ -1.45 [-2.98;0.07] Nm^.s^-1.kg^-1, -24%; Fmax -0.42 [-0.81;-0.03] Nm^.kg^-1, -21%) and recurrent fallers (RFD₅₀ -5.69 [-8.94;-2.43] Nm^.s^-1.kg^-1, -62%; RFD₂₀₀ -2.26 [-3.89;-0.63] Nm^.s^-1.kg^-1, -38%; Fmax -0.38 [-0.80;0.03] Nm^.kg^-1, -19%). Across all participants, associations were observed between RFD_50ms and falls (r_s = -0.46 [-0.67;-0.24], between RFD_200ms and falls (r_s = -0.34 [-0.59;-0.09]), and between Fmax and falls (r_s = -0.24 [-0.48;0.01]).

In this exploratory study, knee extensor neuromuscular function was able to discriminate fallers from non-fallers in pwMS, with RFD being superior to Fmax. Routine assessment of lower extremity neuromuscular function (RFD_50ms in particular) may be a helpful tool in identifying pwMS at future risk of falling.