Surface EMG characteristics of people with multiple sclerosis during static contractions of the knee extensors

Objectives: This study was designed to determine whether any alterations existed in surface electromyography (sEMG) in people with multiple sclerosis (MS) during isometric contractions of the knee extensors. Methods: Fifteen people with MS and 14 matched controls (mean ± SD age and body mass index 53·7 ± 10·5 versus 54·6 ± 9·6 years and 27·7 ± 6·1 versus 26·5 ± 4, respectively) completed 20%, 40%, 60% and 80% of their maximal voluntary contraction (MVC) of the knee extensors. sEMG was recorded from the vastus lateralis where muscle fibre conduction velocity (MFCV) and sEMG amplitude (RMS) were assessed. Body composition was determined using dual‐energy X‐ray absorptiometry and physical activity with the use of accelerometry. Results: People with MS showed significantly (P<0·05) faster MFCV during MVC (6·6 ± 2·7 versus 4·7 ± 1·4 m s^?1) and all submaximal contractions, while RMS was significantly (P<0·05) less (0·11 ± 0·03 versus 0·24 ± 0·06 mV) in comparison with the controls. MVC along with specific thigh lean mass to torque, rate of force development and mean physical activity were significantly (P<0·01) less in PwMS. Conclusion: People with MS have elevated MFCV alongside reduced RMS during isometric contraction. This elevation in MFCV should be accounted for when interpreting sEMG from people with MS.