Relationship between rectus femoris stiffness, muscle activity, and force production during graded isometric contractions measured by handheld myotonometry

= 0.561). Although the EMG amplitude increased with contraction intensity, no significant difference was observed between 70% and 100% MVC, whereas stiffness continued to differentiate between these higher contraction levels. RF muscle stiffness was strongly associated with sEMG amplitude and knee extension force during graded-isometric contractions. These findings suggest that handheld myotonometry may provide a practical complementary measure of the muscle mechanical response associated with the activation level under standardized conditions.