Effect of tasks on intramuscular regional differences in rectus femoris elasticity during isometric contraction: An...

This study aimed to investigate intramuscular regional differences and task specificity of rectus femoris (RF) elasticity during isometric contraction.

Sixteen healthy males (aged 24.3 ± 4.1 years) participated in this study. The tasks included isometric hip flexion (HF) and knee extension (KE). The contractions were maintained at 0%, 30%, and 60% of their respective maximum voluntary isometric contraction (MVC) forces for 5 s each at 50˚ hip flexion and 90˚ knee flexion. RF elasticity was measured in two regions, proximal (33%) and distal (67%). The shear modulus (kPa), measured by shear wave elastography, was used to determine RF elasticity.

A significant interaction effect was observed (intensity × region × task) (P = 0.01). Regarding regional differences during contraction, the proximal region exhibited a greater shear modulus than the distal region at 60% MVC in the hip flexion task (P = 0.001). Conversely, no regional differences were observed at either 30% MVC (P = 0.625) or 60% MVC (P = 0.568) in the knee extension task.

Muscle shear modulus during contraction reflects active force, suggesting that mechanical stress can be applied primarily to the proximal region of the RF during the HF task.