Muscle Weakness in Persons with Multiple Sclerosis

MUSCLE WEAKNESS IN PERSONS WITH MULTIPLE SCLEROSIS SEPTEMBER 2010 LINDA H. CHUNG, B.S., UNIVERSITY OF OREGON M.S., UNIVERSITY OF MASSACHUSETTS AMHERST Ph.D. Candidate, UNIVERSITY OF MASSACHUSETTS AMHERST Directed by: Professor Jane A. Kent-Braun Skeletal muscle weakness is a problem for people living with Multiple Sclerosis (MS). Alterations in the central nervous system may be the primary source of muscle weakness because of the pathophysiology of MS. However, changes in peripheral mediators of force production may also contribute to muscle weakness in persons with MS. The main objective of the dissertation was to systematically identify key neural (motor unit discharge rates, spasticity) and muscular (muscle size, contractile function) mechanisms of force production that may explain lower isometric strength and dynamic power in persons with MS compared with age-matched controls. The knee extensor muscles of the weaker leg were studied, because this muscle group is commonly affected by MS. We showed that persons with MS had lower peak isometric torque and dynamic power compared with controls. Persons with MS had lower motor unit discharge rates, smaller muscle size, and lower specific power compared with controls. There was no difference in passive torque (spasticity), specific strength, or maximal rate of force development between groups. Because differences in isometric strength between persons with MS and controls were abolished when torque was normalized to muscle