Grant Chesbro1, David Lantis2, Brian Pribble1, Christopher Black1, Daniel Larson1 and Rebecca Larson1

1University of Oklahoma, Norman, OK

2Valparaiso University, Valparaiso, IN

Multiple Sclerosis (MS) is an autoimmune disorder that affects the central nervous system (CNS) resulting in fatigue, impaired mobility, and reduced quality of life. Bilateral differences in lower limb strength and function have been observed in patients with MS making assessment and treatment difficult. Previous research suggests that CNS disorders can reduce the complexity of a variety of physiological systems. However, it is unknown whether complexity is affected in a similar bilateral manner in MS. Purpose: The purpose of this study was to assess bilateral differences in torque variability and complexity during a fatiguing task in MS. Methods: Thirteen MS (5 Male and 8 Female, Age: 49.4±8.9yrs) performed isometric dorsiflexion contractions (30% of MVC) until task failure. Based on MVCs, limbs were classified as either the stronger or weaker leg. Five sec. of data from the start (Fresh) and the end (End-Task) of the contractions were analyzed for variability (SD: Standard Deviation, CV: Coefficient of Variation) and complexity (DFA: Detrended Fluctuation Analysis, SE: Sample Entropy). Results: Torque variability was increased from Fresh to End Task in the strong (SD: 2.67±0.78 to 5.63±1.80, p<0.001; CV: 3.10±1.10 to 7.09±2.33, p<0.001) and weak legs (SD: 4.32±0.79 to 9.36±3.24, p<0.001; CV: 4.49±1.81 to 9.49±1.92, p<0.001). There was between leg difference in torque variability at Fresh (SD: 2.67±0.78 to 4.32±0.79, p<0.001; CV: 3.10±2.33 to 4.49±1.81, p=0.26) and End Task (SD: 5.63±1.80 to 9.36±3.24, p=0.001; CV: 7.09±2.33 to 9.49±1.92, p<0.001). The complexity of the torque signals decreased from Fresh to End Task in the strong (SE: 0.47±0.08 to 0.32±0.05, p<0.001) and weak (SE: 0.35±0.03 to 0.22±0.05, p<0.001) legs. There were between leg differences in torque signal complexity at both the Fresh (SE: 0.47±0.08 to 0.35±0.03, p<0.001) and End Task (SE: 0.32±0.05 to 0.22±0.05, p<0.001) time points. There were no changes in DFA. Conclusion: Reductions in complexity are thought to reduce the adaptable states for a system to deal with stressors. Significant differences in complexity and variability were seen between limbs and between time points in MS suggesting that measures of variability and complexity could be useful for assessing the effects of bilateral asymmetry caused by MS.

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