A study recently published in Multiple Sclerosis and Related Disorders showed that isometric tests could be a reliable method for assessing upper and lower extremity functions in patients with multiple sclerosis (MS).

“Isometric tests offer objective, reliable, and valid methods to evaluate upper and lower extremity motor functioning,“ the authors wrote. “The ability to relax the muscle forces quickly after quick contractions could be the principal underlying neuromuscular factor contributing to disability in [people with MS].”

The research conducted by Uygur et al included 29 patients with relapsing-remitting MS who underwent isometric and functional tests in all 4 extremities at 2 separate visits. Functional tests included the 9-hole peg test (9HPT) and finger tapping test (FTT) for the upper extremities and the 25-foot walk test (T25WT), timed up and go (TUG), 5-time sit-to-stand (5TStS), and Multiple Sclerosis Spasticity Scale (MSSS-88) for the lower extremities. 

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Overall, isometric measures showcased high reliability with intraclass correlation coefficients >0.87 and coefficients of variation <12%. Grip force tested by the rate of force development and relaxation scaling factors (RFD-SF and RFR-SF) displayed comparable results with both the 9HPT and FTT, with sample correlation coefficients (r) between 0.49 and 0.55 (P <.05). Further analysis revealed that RFD-SF might be the only indicator suitable for predicting 9HPT results. As for knee extension, RFD-SF had significant associations with the T25WT (r=0.71), TUG (r=0.60), 5StS (r=0.47), and MSSS-88 (r=0.60).

“The most important and novel finding of the current study is that the ability to relax muscle forces quickly could be the principal neuromuscular property contributing to walking speed in [people with MS],“ the authors explained. “Moreover, this variable is highly correlated with the ‘gold standard’ clinical evaluation of MS (i.e., [Expanded Disability Status Scale]) and with the patient-rated spasticity levels (MSSS-88).“

They added, “All these findings indicate RFR-SF as a key outcome measure that can quantitatively evaluate one of the major causes of disability in [people with MS]. Therefore, future studies should consider developing novel therapeutical or rehabilitative methods to improve rates of muscle force relaxation to improve both lower and upper extremity functioning.”

These findings, while yielding a novel tool to evaluate motor skills in patients with MS, also support the hypothesis that the decreased rates of muscle force relaxation could be due to either a muscular or neural etiology involving abnormal calcium kinetics or the inability of the motor unit to cease firing after a contraction, respectively.


Uygur M, Barone DA, Dankel SJ, DeStefano N. Isometric tests to evaluate upper and lower extremity functioning in people with multiple sclerosis: reliability and validity. Mult Scler Relat Disord. Published online April 25, 2022. doi:10.1016/j.msard.2022.103817