Development of a Non-Invasive Method for Evaluating Motoneuron Activity During Explosive Knee Extensor Contractions
【Supercategory：7. DESCENTE SPORTS SCIENCE Subcategory：7.47 Vol.47】
ABSTRACT
The rate of force development observed during explosive knee extensor contractions is a physiologically meaningful index closely associated with motor performance and physical function, particularly in athletic and aging populations. This rapid force generation is underpinned by distinct motor unit behavior, including highfrequency discharges not typically observed during sustained contractions. This study aimed to determine how anatomical characteristics under the electrode?specifically subcutaneous tissue thickness and fascicle orientation?influence the number of motor units identified from high-density surface electromyography （HD-sEMG） during explosive contractions of the vastus lateralis. Twelve healthy young adults performed explosive isometric knee extensions while HD-sEMG signals were recorded from the proximal, middle, and distal regions of the vastus lateralis. At each site, subcutaneous tissue thickness and the angle between the skin surface and muscle fascicles were assessed via ultrasonography. Motor unit discharge patterns were extracted using the convolution kernel compensation algorithm. The number of motor units detected during explosive contractions was significantly greater at the proximal and distal regions than at the middle region （p<0.001） . The proximal and distal sites yielded more motor units on average compared to the middle site. Significant negative correlations were observed between motor unit count and both subcutaneous tissue thickness （p=0.003, r=-0.475） and fascicle angle （p=0.002, r=-0.506） across all regions. In conclusion, the proximal and distal regions of the vastus lateralis provide more favorable recording conditions for HD-sEMG-based motor unit decomposition during explosive contractions. These findings suggest the importance of accounting for local anatomical characteristics in electrode placement when assessing motor unit behavior in explosive contractions tasks.
DECENTE SPORTS SCIENCE Vol.47/The DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE
The rate of force development observed during explosive knee extensor contractions is a physiologically meaningful index closely associated with motor performance and physical function, particularly in athletic and aging populations. This rapid force generation is underpinned by distinct motor unit behavior, including highfrequency discharges not typically observed during sustained contractions. This study aimed to determine how anatomical characteristics under the electrode?specifically subcutaneous tissue thickness and fascicle orientation?influence the number of motor units identified from high-density surface electromyography （HD-sEMG） during explosive contractions of the vastus lateralis. Twelve healthy young adults performed explosive isometric knee extensions while HD-sEMG signals were recorded from the proximal, middle, and distal regions of the vastus lateralis. At each site, subcutaneous tissue thickness and the angle between the skin surface and muscle fascicles were assessed via ultrasonography. Motor unit discharge patterns were extracted using the convolution kernel compensation algorithm. The number of motor units detected during explosive contractions was significantly greater at the proximal and distal regions than at the middle region （p<0.001） . The proximal and distal sites yielded more motor units on average compared to the middle site. Significant negative correlations were observed between motor unit count and both subcutaneous tissue thickness （p=0.003, r=-0.475） and fascicle angle （p=0.002, r=-0.506） across all regions. In conclusion, the proximal and distal regions of the vastus lateralis provide more favorable recording conditions for HD-sEMG-based motor unit decomposition during explosive contractions. These findings suggest the importance of accounting for local anatomical characteristics in electrode placement when assessing motor unit behavior in explosive contractions tasks.
DECENTE SPORTS SCIENCE Vol.47/The DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE
| Researcher | Taichi Nishikawa, Ryosuke Takeda, Marino Karaki, Kohei Watanabe |
|---|---|
| University or institution | Chukyo University |
Keywords
high-density surface electromyography, vastus lateralis, motor unit, rate of force development, muscle strength