Non-uniform surface electromyographic responses to change in joint angle within rectus femoris muscle

Introduction: Our recent studies have demonstrated region-specific neural activation within the rectus femoris (RF) muscle. However, these studies involved a fixed joint angle or posture. In this study we investigated the effect of hip and knee joint angles on neural activation within RF using multichannel surface electromyography (SEMG).

Methods: Eleven healthy men performed isometric maximal voluntary contraction (MVC) during knee extension and hip flexion at different hip or joint angles. During the contractions, SEMG of the RF was recorded using 46 electrode pairs covering most of the superficial area of the muscle.

Results: During knee extension MVC, an increase in the hip joint angle was associated with a significant increase in SEMG amplitude in the proximal region and a decrease in the distal region (P < 0.05). Higher SEMG amplitude during hip flexion MVC compared with knee extension MVC was observed in proximal regions with the flexed knee and hip joint angles. This task-dependent spatial distribution of SEMG amplitude was seen at the extended hip, but not at the extended knee.

Conclusions: SEMG amplitudes within the RF muscle are not modified uniformly with changes in joint position.