Date of Award

Spring 1-1-2017

Document Type


Degree Name

Doctor of Philosophy (PhD)


Integrative Physiology

First Advisor

Roger M. Enoka

Second Advisor

Alaa A. Ahmed

Third Advisor

Robert S. Mazzeo

Fourth Advisor

François G. Meyer

Fifth Advisor

David Sherwood


Motor control is the ability to produce and control movement, and is an outcome of various integrative mechanisms within the neurosensory, musculoskeletal, and neuromuscular systems. Impairment in motor function may originate from dysfunction of the central nervous system, the peripheral nervous system, or the muscular system. The NIH Toolbox for Assessment of Neurological and Behavioral Function includes tools to quantify motor function across the life span. There are four primary domains within the Toolbox: cognitive, motor, emotional, and sensory. The purposes of this dissertation were to investigate the neuromuscular and clinical determinants of manual dexterity and walking in healthy adults and individuals with multiple sclerosis; and to compare the effects of different types of electrical nerve stimulation on the walking performance of persons with multiple sclerosis.

The first study evaluated the capacity of an expanded set of force steadiness tasks to explain the variance in the time it takes young men and women to complete the grooved pegboard test. A stepwise, multiple-regression analysis indicated that much of the variance (R2 = 0.70) in pegboard times could be explained by a model that comprised two predictor variables derived from the steadiness tasks: time to match the target during a rapid force-matching task and force steadiness (coefficient of variation for force) during a single-action task. Participants with slower pegboard times placed a greater emphasis on accuracy than speed as they had longer times to match the target during the rapid force-matching task and exhibited superior force steadiness during a force-matching task.

The second study compared the times to complete the four phases of peg manipulation and the forces applied to the pegboard during peg selection and insertion in persons with multiple sclerosis (MS) and three age groups of healthy adults. Multiple-regression models that could explain the variance in pegboard times for each group of participants were compared to assess the relative significance of the peg-manipulation attributes. Pegboard times for the MS group (104.2 ± 40.3 s) were longer than those for young (55.5 ± 6.7 s), middle-aged (57.5 ± 10.9 s), and old adults (80.6 ± 17.3 s). Regression analysis indicated that the pegboard times for the MS group could be predicted by the time for the peg-selection phase (R2 = 0.78), whereas the predictors for young (R2 = 0.33) and middle-aged (R2 = 0.78) adults were the times for the peg-insertion and return phases, and the predictors for old adults (R2 = 0.49) were the times for the peg-selection and transport phases. The relative influence of peg-manipulation capabilities on a pegboard test of manual dexterity was greater for persons with MS and middle-aged adults than for young and old adults.

The third study examined the associations between neuromuscular characteristics of lower leg muscles and clinical assessments of physical function with walking performance of individuals who were moderately disabled by multiple sclerosis (MS). The regression models based on neuromuscular characteristics explained 40% of the variance in the 6-min walk distance and 47% of the variance in 25-ft walk time. The regression models that included the clinical assessments explained 63% of the variance in the 6-min walk distance and 47% of the variance in 25-ft walk time. Moderate amounts of the variance in two tests of walking performance were explained by the neuromuscular characteristics of lower leg muscles. The two walking tests were also significantly associated with a self-reported assessment of disability status and the time to complete the test of manual dexterity.

The fourth study compared the effects of a 6-wk intervention with either narrow- or wide-pulse NMES on walking performance of persons with relapsing-remitting MS. The NMES intervention was performed on the d