Long-Term High-Level Exercise Promotes Muscle Reinnervation With Age

Abstract

The histologic features of aging muscle suggest that denervation contributes to atrophy, that immobility accelerates the process, and that routine exercise may protect against loss of motor units and muscle tissue. Here, we compared muscle biopsies from sedentary and physically active seniors and found that seniors with a long history of high-level recreational activity up to the time of muscle biopsy had 1) lower loss of muscle strength versus young men (32% loss in physically active vs 51% loss in sedentary seniors); 2) fewer small angulated (denervated) myofibers; 3) a higher percentage of fiber-type groups (reinnervated muscle fibers) that were almost exclusive of the slow type; and 4) sparse normal-size muscle fibers coexpressing fast and slow myosin heavy chains, which is not compatible with exercise-driven muscle-type transformation. The biopsies from the old physically active seniors varied from sparse fiber-type groupings to almost fully transformed muscle, suggesting that coexpressing fibers appear to fill gaps. Altogether, the data show that long-term physical activity promotes reinnervation of muscle fibers and suggest that decades of high-level exercise allow the body to adapt to age-related denervation by saving otherwise lost muscle fibers through selective recruitment to slow motor units. These effects on size and structure of myofibers may delay functional decline in late aging.

Muscle Quality in Aging: a Multi-Dimensional Approach to Muscle Functioning with Applications for Treatment

“…As a result, the size of each motor unit increases with age [68]. As neural innervation changes with aging, muscle fiber types that are generally dispersed in the muscle in younger adults tend to group together in older inactive adults [57,69], reflecting reduced reinnervation. Also, older muscle fibers tend to be angulated in shape, reflecting denervation of muscle fibers [69].…”

Functional electrical stimulation as a safe and effective treatment for equine epaxial muscle spasms: Clinical evaluations and histochemical morphometry of mitochondria in muscle biopsies

“…28 An expanding list of studies are indicating that the application of FES on healthy muscle can elicit some of the same metabolic benefits as voluntary muscle active exercise. [29][30][31] The purpose of this study was to confirm that FES is an effective and safe means to reduce chronic muscle spasms in the top line of horses. The present study will add objective histological evidence to previous clinical findings, 27 through the evaluation of equine epaxial muscle biopsies harvested before and after 8 weeks of FES treatments.…”

Interventions for Human Frailty: Physical Activity as a Model

“…For example, the frequency of mitochondria is higher in athletic than sedentary seniors, with mitochondria being even more positively affected than the excitation -contraction coupling apparatus. Zampieri et al (2015) have shown that the frequency of calcium release unit (CRU)-mitochondrial pairs is threefold higher in senior sportsmen; this functional coupling up-regulates ATP production when muscle is active (Brookes et al 2004;Shkryl and Shirokova 2006;Mosole et al 2014). Notably, there is also significant up-regulation of miR-206 expression in senior sportsmen, compared with young adults and healthy sedentary seniors; this microRNA has been shown to play a specific role in the early events of regeneration (Cacchiarelli et al 2010).…”