Muscle relaxation in Parkinson's disease: implications for function

Date
2018
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Older adults (OA) experience a decline in mobility due to reduced power and physical slowing. The symptom of bradykinesia in Parkinson’s disease (PD) further slows reaction time and movement with additional consequences in mobility. Mechanical power predicts function more than muscular strength. This highlights the importance of movement speed because power is the product of force and velocity. Logically, much research has focused on the rate at which the nervous system can activate muscles to develop muscular force. However, less is known about the ability to relax or ‘turn off’ muscles in OA and people with PD. Appropriately-timed muscle relaxation is likely important for direction changes, fall prevention, and rapid cyclical movements. This thesis included two projects related to the relaxation of muscle force and mobility. The first project used an isometric handgrip model to accomplish three research aims. Aim 1 was to compare peak rates of isometric muscle force development and relaxation between young adults (YA), older adults and people with PD. Aim 2 was to examine the associations between segmented motor output and force development, force relaxation and mobility in people with PD. Aim 3 was to compare mobility tests between the three groups and to relate measures of force development and force relaxation to mobility in OA and people with PD. The second project extended the scientific inquiry from isometric to dynamic conditions. Participants pedaled a stationary recumbent bicycle against low resistance in cadence conditions from 40 to 120 rpm. Surface electromyograms were obtained in six lower extremity muscles. Aim 4 was to compare muscle activity patterns during recumbent cycling between YA, OA, and people with PD at increasing pedaling cadences. Aim 5 was to examine associations between muscle activation patterns during bicycling and performance of timed tests of mobility in people with PD. The results of each project are reported in two separate chapters. The first project provided evidence that the rate of muscle force relaxation is slowed with aging and further impaired by force segmentation in PD. While correlations between muscle force relaxation and mobility were generally stronger than those involving force development, they were not particularly strong in PD. The second project revealed a prolonged duration of knee extensor muscle activity in PD at higher pedaling cadences. The duration of this EMG activity was positively and strongly correlated with timed tests of mobility, indicating that a prolonged duration of EMG bursts during cycling predicts poor performance in timed mobility tests.
Description
Keywords
Biological sciences, Health and environmental sciences, Aging, Cycling, EMG, Mobility, Parkinson's disease, Relaxation
Citation