Abstract #0867

Motor Unit Loss in Aging Skeletal Muscle Is Not Accompanied by Increased Heterogeneity of the T2 Increase After Exercise.

Theodore F. Towse¹, Jill M. Slade², Michael T. Andary³, Ronald A. Meyer¹

¹Physiology, Michigan State University, East Lansing, MI, United States; ²Radiology, Michigan State University, East Lansing, MI, United States; ³Physical Medicine And Rehabilitation, Michigan State University, East Lansing, MI, United States

Loss of motor units is often compensated for by reinnervation of fibers from nearby axons, leading to unit reorganization and fiber-type clumping. Previous studies suggest that motor unit reorganization could result in increased heterogeneity of the T2 increase observed by MRI after moderate exercise. This study shows that, despite a 50% decrease in motor unit number in anterior tibial muscles of elderly vs. younger subjects, the heterogeneity of muscle T2 after exercise is no greater in elderly than in younger subjects. The results suggest that fiber reinnervation is not a dominant mechanism compensating for motor unit loss in muscles of elderly subjects.