Rates of neuromuscular excitation during cycling in Parkinson's disease compared to healthy young and older adults

Background: Bradykinesia affects mobility in some people with Parkinson's. Fall risk makes the neural control of maximal speed ambulatory movements difficult to study in Parkinson's. Stationary recumbent bicycling favors the use of electromyography at high movement speeds, and may better reveal neuromuscular rate limiters. Methods: Subjects were 18 adults with Parkinson's, 14 older adults and 14 young adults. Electromyograms were recorded from two muscles during stationary recumbent bicycling at 60, 80, 100, 120 RPM and peak voluntary cadence. Rate of electromyogram rise was calculated. Subjects performed the timed up and go and four square step test. Parkinson's sub-groups were formed based on whether they could pedal >= 120 RPM. Mixed models were used to compare groups and spearman's correlations quantified relationships. Findings: Eight people with Parkinson's and four older adults could not complete the 120 RPM condition. Faster people with Parkinson's (n = 10) had greater maximum cadence (F = 42.85, P < 0.05), higher rates of electromyogram rise in both muscles (F > 16.9, P < 0.05), and faster mobility test times (F > 6.5, P < 0.05) than slower people with Parkinson's (n = 8). In Parkinson's, correlations between vastus lateralis rate of electromyogram rise and four square step test (rho =-0.62), timed up and go (rho =-0.53), and peak cadence (rho = 0.76) were significant (all P < 0.05). Interpretation: People with Parkinson's with slower peak pedaling cadence had slower mobility performance and lower vastus lateralis excitation rates at higher cadences. Vastus lateralis excitation rates had moderate to strong relationships with peak cadence and mobility. Exercise interventions may seek to improve peak cadence or excitation rates in people with Parkinson's.