Laterality of the activation of the vastus lateralis muscle in females with Parkinson's disease during the medication state compared with healthy controls

This study quantified the laterality of motor unit activation properties in females with Parkinson's disease during force production (low to high-intensity contraction) using high-density surface electromyography. Sixteen females with Parkinson's disease (age = 69.9 +/- 7.6 years, disease duration = 4.9 +/- 5.1 years) and 14 healthy female subjects (age = 68.6 +/- 3.6 years) performed submaximal ramp-up contractions during isometric knee extension. High-density surface electromyography signals were recorded from both vastus lateralis muscles. The level of heterogeneity was calculated in the spatial distribution patterns of the high-density surface electromyography signals to determine the modified entropy, coefficient of variation of the root mean square and correlation coefficient to evaluate motor unit activation properties. Pearson's correlation coefficients were calculated to examine the relationships between disease severity and the root mean square and electromyography variables. The root mean square value and heterogeneity were significantly higher and lower on the more-affected side in females with Parkinson's disease than on the contralateral side in females with Parkinson's disease or either side in control subjects (p < 0.05). Females with Parkinson's disease that exhibited temporal changes of spatial motor unit activation properties showed significant laterality when compared to healthy control subjects in both the low and high-intensity contractions. Moderate-to-strong correlations were observed between disease severity and root mean square and electromyography variables in females with Parkinson's disease (r > 0.6, p < 0.001). The laterality of motor unit activation properties was compared between the subjects with Parkinson's disease and the control subjects. The findings suggest that females with Parkinson's disease have asymmetrical motor unit activation properties, independent of the magnitude of force production.