Multiple Sclerosis is a chronic neurological disease whose prevalence within the world's population is increasing. Symptoms of this disease are fatigue, loss of coordination, numbness and tingling, paralysis, and blindness. Currently there is no cure for the disease and, with its disabling variety and severity of symptoms, it is important to look for possibilities that could help slow its progression. Physical activity is one health behavior that promises to slow the progression of the MS among persons afflicted with this disease. Research has revealed that an exercise program improves several measures of well-being, reduces fatigue, and improves strength. While physical activity has been suggested as a management tool, those with MS demonstrate lower levels of physical activity compared to those without MS in the U.S. population. This thesis investigates what influences individuals with MS to participate in physical activity. Its purpose is to look into the possibility that demographic, social hierarchy, social support, and psycho-social/personality characteristics may help predict physical activity regimens among persons with MS. Isolating the determinants of voluntary exercise in the MS subpopulation would enable clinicians and the public health community to develop effective policies and interventions that promote physical activity.

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Several recent studies have suggested that persons with multiple sclerosis (MS) have diminished syntactic complexity. A greater variability in responses to a variety of tasks has also been noted for persons with MS. However, naturalistic data on syntactic complexity and the complexity's variability in persons with MS have not been examined. In the present study, 8 volunteers with MS (age 18-70 years) and 10 adults without MS participated in both a 15-minute conversational language sample and a sentence completion task in two different sessions. No significant differences were found between groups on any measure, and variability within the groups was similar. This may have been because volunteers were people with mild cases of MS or those in a state of remission and may not be representative of persons who were at a more advanced stage of the disease or in a state of exacerbation.

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Physical activity is one approach that may help manage the symptoms experienced by personswith MS and the burden faced by their care-partners. This thesis examined: i) the efficacy of aphysical activity intervention for increasing physical activity in dyads affected by moderate-to-severe MS; and (ii) the interdependence in physical activity in MS-care-partner dyads. A 12-week, randomized pilot feasibility trial was conducted in five (two intervention; three control)MS-care-partner dyads. Participants self-reported physical activity and wore an accelerometerfor 7-days at baseline and 12-weeks (i.e., follow-up). A large effect of the intervention wasobserved on self-reported physical activity (d= 0.98) and time spent sedentary (d= -1.26). Mostcorrelations in physical activity within dyads were moderate-to-strong at baseline (rs range=0.33-0.72) and over time (rs range= 0.40-0.80). The results from this pilot case study lay thefoundation for larger physical activity interventions in dyads affected by MS

Skeletal muscle weakness is a problem for people living with Multiple Sclerosis (MS). Alterations in the central nervous system may be the primary source of muscle weakness because of the pathophysiology of MS. However, changes in peripheral mediators of force production may also contribute to muscle weakness in persons with MS. The main objective of the dissertation was to systematically identify key neural (motor unit discharge rates, spasticity) and muscular (muscle size, contractile function) mechanisms of force production that may explain lower isometric strength and dynamic power in persons with MS compared with age-matched controls. The knee extensor muscles of the weaker leg were studied, because this muscle group is commonly affected by MS. We showed that persons with MS had lower peak isometric torque and dynamic power compared with controls. Persons with MS had lower motor unit discharge rates, smaller muscle size, and lower specific power compared with controls. There was no difference in passive torque (spasticity), specific strength, or maximal rate of force development between groups. Because differences in isometric strength between persons with MS and controls were abolished when torque was normalized to muscle size, smaller muscle size may explain a large portion of lower isometric strength in persons with MS. Differences in dynamic power were reduced when peak power was normalized to muscle size, but remained lower in persons with MS compared with controls, suggesting that changes in neural factors (e.g., lower motor unit discharge rates) may explain lower dynamic power in persons with MS. These results suggest that different mechanisms may contribute to muscle weakness in MS, depending on the mode of contraction. Lower motor unit discharge rates and smaller muscle size were identified as key mechanisms of muscle weakness in persons with MS. Each of these mechanisms has been shown to improve with resistance training in controls. Thus, this dissertation provides an evidence-based rationale for resistance training interventions in persons with MS, to improve isometric strength and power production by increasing motor unit discharge rates and muscle size.

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