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