抄録
The number of motor units identified from high-density surface electromyography varies depending on the target muscle and individuals. This variation could be due to differences in the anatomical characteristics of the measurement locations and inter-individual differences in those characteristics. This study aimed to examine the effect of measurement location within the vastus lateralis on the number of detected motor units in high-density surface electromyography, and to determine whether anatomical characteristics account for them. Thirteen male participants (23.2±5.5 yrs) performed isometric knee extension at 70% of their maximum voluntary contraction while high-density surface electromyography was recorded from three regions of the vastus lateralis: proximal, middle, and distal regions. Motor units were decomposed, and those with an estimated accuracy of ≥ 60% were included in the analysis. Ultrasound imaging was used to quantify subcutaneous tissue thickness, muscle thickness, pennation angle, and muscle fascicle angle relative to the skin surface at each location. The results demonstrated that the number of detected motor units was greater in the middle and distal regions compared to the proximal region (p<0.05). Additionally, at the distal region, the number of motor units was positively and negatively correlated with individual differences in muscle thickness and subcutaneous. (p<0.05). Our findings suggest that high-density surface electromyography can detect a greater number of motor units at the middle regions without the effects of inter-individual difference in anatomical characteristics in the vastus lateralis muscle.
