Date of Award

Spring 1-1-2018

Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

Roger M. Enoka

Second Advisor

Alaa A. Ahmed

Third Advisor

John Harsh

Fourth Advisor

Gary D. Heise

Fifth Advisor

David E. Sherwood


This dissertation comprises five experimental studies that investigated changes in manual dexterity across the lifespan and the effects of electrical nerve stimulation on motor function and muscle activity. Three studies evaluated associations between neuromuscular characteristics and performance on the NIH Toolbox measures of manual dexterity, and two studied the effects of electrical nerve stimulation on changes in motor function and muscle activity.

The first two studies measured neuromuscular differences in middle-aged and older adults, and used performance metrics to identify age-specific associations with manual dexterity. The first study provided a tractable framework to identify latent variables underlying age-associated differences in time to complete the 9-hole and grooved pegboard tests. Mechanisms of interest included neuromuscular characteristics, cognitive function, and cutaneous sensation. The second study expanded these measures to include assessments of risk behavior and muscle activation characteristics. Significant associations were unique for each age group and pegboard test with features derived from force-matching tasks and utility of the reward providing the greatest explanatory power.

The third study assessed grooved pegboard timing and force characteristics of peg manipulation for persons with multiple sclerosis and age-and sex-matched healthy adults. Results from this study showed that grooved pegboard time for individuals with multiple sclerosis was most associated with the time to select a peg, whereas times for healthy controls were most related to peg transportation and selection.

The last two studies examined the effects of electrical nerve stimulation on force production, muscle activation characteristics, and functional outcomes. The fourth study showed that the immediate effects of electrical nerve stimulation on force and motor unit activity of the contralateral limb were present after stimulation. Lastly, an intervention of electrical nerve stimulation applied to the calf muscled improved mobility, where motor unit discharge characteristics during steady contractions partially explained differences in mobility among older adults.

This dissertation explored the changes in motor function and muscle activity with advancing age and the modulation of motor function with electrical nerve stimulation.