Relative contribution of neuromuscular activation, muscle size, and muscle quality to maximum strength output of the thigh muscles in young individuals

• Published in: Physiological reports 2023-01, Vol.11 (1), p.e15563-n/a
• Main Authors: Yoshiko, Akito, Watanabe, Kohei, Akima, Hiroshi
• Format: Article
• Language: English
• Subjects: Electrodes; Electromyography; Female; Force; Humans; Investigations; Isometric Contraction - physiology; Knee; Knee Joint - physiology; Male; Muscle contraction; muscle size; Muscle Strength; Muscle, Skeletal - diagnostic imaging; Muscle, Skeletal - physiology; Muscles; neuromuscular function; non‐contractile tissue; Original; Physiology; Quadriceps muscle; Quadriceps Muscle - diagnostic imaging; Quadriceps Muscle - physiology; Thigh; Ultrasonic imaging
• ISSN: 2051-817X
• DOI: 10.14814/phy2.15563

This study aimed to investigate the relationship between maximal muscle strength and neuromuscular activation, muscle size, and quality of quadriceps (QF) and hamstring muscles (HM). The study included 24 young men and women. The neuromuscular activation parameter was recorded using a single‐channel surface electromyography (EMG) with the root mean square (RMS) during maximal isometric knee extension and flexion from four muscles: rectus femoris and vastus lateralis for QF; biceps femoris and semitendinosus for HM. In addition, the peak torque was measured during the same session. B‐mode ultrasonographic transverse images were obtained from the anterior, lateral, and posterior thighs. Furthermore, we calculated the muscle thickness (MT) and echo intensity (EI) of the four muscles as indicators of muscle size and quality. The averaged MT, EI, and absolute RMS of QF were calculated by averaging the values of the rectus femoris and vastus lateralis, and that of HM was calculated by averaging the values of the biceps femoris and semitendinosus. The knee extension peak torque was correlated with EI (r = −0.61, P