All ETDs from UAB

Advisory Committee Chair

Marcas M Bamman

Advisory Committee Members

C Scott Bickel

Glenn Rowe

Leland Dibble

Document Type

Dissertation

Date of Award

2017

Degree Name by School

Doctor of Philosophy (PhD) School of Health Professions

Abstract

Neuromuscular morphology and function undergo changes with increasing age and Parkinson disease (PD) pathology. Motor unit reorganization occurs by denervation-reinnervation events which lead to diminishing random distribution of myofibers and type I myofiber grouping. Grouped type I myofibers maintain type II features such as hypertrophic capacity and myonuclear addition, sarco(endo)plasmic reticulum Ca2+ ATPase 1 expression, and lower capillarization. Though age-related type I myofiber grouping has been qualitatively described in the literature, this was the first study to characterize the phenotype of grouped type I myofibers in older adults. Furthermore, we identified a magnified degree of type I myofiber grouping in PD beyond normal aging. This led to an investigation of the relationship between type I myofiber grouping and neuromuscular performance. Though neuromuscular performance deficits are present in PD compared to age- and sex-matched older adults (CON), myofiber grouping does not appear to be the mechanism. Rather, a divergent effect of increased type I myofiber grouping is present in PD vs. CON. High levels of grouping in PD are associated with superior strength, rate of torque development, submaximal torque steadiness, and less fatigue. Conversely, CON with high levels of grouping demonstrated worse neuromuscular performance than CON with low/mod levels of grouping. Though much remains to be understood, the effects of type I myofiber grouping on neuromuscular performance are different in older adults and PD.

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