Electronic Thesis and Dissertation Repository


Master of Science




Timothy John Doherty


Aging of the human neuromuscular system is associated with gradual decline in motor unit (MU) number leading to denervation of muscle fibers and subsequent compensatory reinnervation from surviving MUs. Lower limb muscles exhibit age-related increased MU instability (measured electrophysiologically), however not much is known regarding MU stability of aging upper limb muscles. The purpose of this study was to examine agerelated MU loss in upper limb muscles (first dorsal interosseous [FDI] and biceps brachii [BB]) and the impact on MU stability in younger and older healthy subjects using electrophysiological near fiber analysis from decomposition-based quantitative electromyography (DQEMG). FDI and BB muscles from older (74 ± 5 years) and younger (31 ± 13 years) healthy subjects were examined through surface and intramuscular collection of EMG signals during volitional contractions, which were analyzed with DQEMG. Older subjects showed significantly larger MUs associated with greater instability in the form of near fiber (NF) jiggle and NF jitter in the FDI and BB muscles when compared to younger controls. These results suggest that age-dependent MU remodeling and progressive reduction in FDI and BB MU pools are associated with greater transmission instability at the neuromuscular junction.