Spatial electromyography distribution pattern of the vastus lateralis muscle during ramp up contractions in Parkinson’s disease patients

Parkinson's disease (PD) related decreases in muscle strength may result from both central and peripheral factors. However, the effect of PD on the neuromuscular system, such as motor unit activation properties, remains unclear. The purpose of the present study was to compare the spatial distribution pattern of electromyographic activity during sustained contractions in healthy subjects and PD patients. Twenty-five female PD patients and 25 healthy age-matched female control subjects performed ramp submaximal contractions during an isometric knee extension from 20% to 80% of the maximal voluntary contraction (MVC). To evaluate alterations in the spatial electromyography (EMG) potential distribution, normalized root mean square (RMS), modified entropy, coefficient of variation, and correlation coefficients were calculated from multi-channel surface electromyography at 10% force increments. The comparison between PD and healthy subjects revealed that, during increased force exertions, PD patients exhibited less change in normalized RMS, modified entropy, coefficient of variation, and pattern of spatial EMG distribution. These data showed that the heterogeneity and the changes in the activation pattern are smaller in the PD patients than in healthy subjects. This finding may be associated with central adaptation and/or peripheral changes in PD patients.