Participants will complete study assessments at the DC VAMC. Disease severity will be assessed by medical staff completing the EDSS. Peak torque assessment for the knee flexors and extensors will be performed on an isokinetic dynamometer (Biodex System 4). Muscle morphology measures of the rectus femoris will be obtained using diagnostic musculoskeletal B-mode ultrasound (Phillips EPIQ 7 180 Plus) with a 10 Mhz linear transducer. The sonographic measures will include muscle thickness and echogenicity. The mode of exercise testing and the type of muscle action will influence the assessment of fatigue. Therefore, isokinetic fatigue measures for the knee extensors will be assessed on separate visits (at least 48 hours apart). Performance-based measures of function will include an assessment of patient mobility and the 25-foot walk test. Muscle power will be estimated by the timed sit to stand test. Subjective measures of fatigue and quality of life include the MSQoL, MFIS, and Neurology Quality of Life Adult Fatigue Bank (AFB).
