Date of Award

Spring 1-1-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Roger M. Enoka

Second Advisor

Francois Meyer

Third Advisor

Alaa Ahmed

Fourth Advisor

Rodger Kram

Fifth Advisor

Alena Grabowski

Abstract

This dissertation comprises computational and experimental studies that examined the neuromuscular factors underlying differences in manual dexterity and mobility in health and disease.

The first two studies developed models of motor unit force production. The first model used a Proportional-Integral-Derivative (PID) control algorithm to activate a pool of motor units to simulate the force trajectory during force-matching tasks. The second model comprised a probabilistic state-space model to estimate the common synaptic input to motor neurons based on the discharge times of action potentials by activated motor units. The state-space model demonstrated superior sensitivity compared with previous models.

The next three studies examined manual dexterity and begin with the use of the state-space model to quantify variability in common synaptic input for young and older adults during isometric contractions, and how this variability related to performance on a pegboard test of manual dexterity. Variability in common synaptic input was significantly associated with the coefficient of variation for force during steady contractions (force steadiness) and with pegboard times in older adults. The source of the force fluctuations was evaluated by comparing force steadiness during voluntary and electrically evoked contractions. Force steadiness was worse for old adults than young adults during voluntary contractions, but there was no difference between age groups during the electrically evoked contractions. Thus, differences in force steadiness must arise from signal transduction in the central nervous system and not the periphery. The plasticity of pegboard performance was examined by comparing peg-manipulation characteristics of persons with multiple sclerosis to healthy controls. Grooved pegboard time for individuals with MS 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 examine the influence of an orthopedic problem (sacroiliac joint dysfunction) on movement patterns. These individuals exhibited a compromised muscle synergy when walking and greater movement asymmetries during a sit-to-stand task.

This dissertation explored how common synaptic input influences force steadiness and manual dexterity, how multiple sclerosis alters manual dexterity, and how individuals with sacroiliac joint dysfunction differ from healthy controls during walking and sit-to-stand tasks.

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