The effects of high-speed, low-force recumbent cycling: an intervention in older a dults [sic] and Parkinson's disease
University of Delaware
Decreased mobility substantially reduces independence and quality of life while contributing to increased rates of disability and health care costs. Exercise is a proven strategy to improve these qualities. Exercise is known to benefit every physiological system with the strongest literature support for cardiovascular health and strength gains. However, less is known about the potential to enhance mobility with exercises that target rapidly adapting central nervous system (CNS) factors. While the current exercise recommendations from federal agencies (CDC, NIH, and DHHS) are prudent, they neglect the potential benefits of high speed exercises that target the CNS correlates of muscular quickness. Results of this research are expected to inform improvements in exercise recommendations for older adults and people with movement disorders. Additionally, results are expected to fill a gap in the literature related to neural adaptations to high speed training in older adults and people with Parkinson's disease (PD). The purpose of Aim 1 was to determine whether there exist age-related differences in the speed and control of rapid isometric force pulses in different muscles in young and older adults. It was hypothesized that older adults would have lesser rate of force development-scaling factors (RFD-SF) and more variability in the performance of rapid force production. The purpose of Aim 2 was to determine the effects of a six week exercise intervention that uses high-speed, low-resistance stationary recumbent cycling in older adults. Participants completed pre- and post-exercise tests as well as 4 week follow-up to determine retention of changes. It was hypothesized that there would be improvements in the following measures: 1) Time to peak force and the RFD-SF during isometric knee extension; 2) Standardized measures of walking function; 3) Perceived function and quality of life. It was also hypothesized that improvements in the previous measures would be retained four weeks after training. To elucidate the neuromuscular mechanisms that occur with improved speed in older adults, it was hypothesized that this would be most strongly related to the rate of rise in the surface electromyogram (RER). We also aimed to determine if training the legs affects CNS mechanisms that transfer to the following in older adults: 1) Increased time to peak force and RFD-SF during isometric elbow extension; 2) Improved RER in elbow extensors; 3) Improved hand dexterity. It was also hypothesized that improvements in the previous measures would be retained four weeks after training. The purpose of Aim 3 was to develop an improved method to selectively quantify paired motor unit discharge behavior underlying tremor. The method was then tested before and after three different treatments. It was hypothesized that interspike interval serial correlation with cluster analysis would allow us to quantify paired motor unit discharge behavior from isometric contractions in which motor unit discharge behavior is not solely bimodal.