Muscle Activities of the Quadriceps during Knee Extension Isometric Contraction at Different Angles of Knee Joint Flexion

[Purpose] The changes in muscle activities of the quadriceps during knee extension isometric contraction associated with changes in knee joint flexion angle were investigated. [Subjects] The subjects were 10 healthy individuals who provided their informed consent. [Methods] The subjects performed isometric contraction of 40% maximum voluntary contraction at four different angles of knee flexion. The EMGs of the vastus medialis obliquus, vastus medialis longus, rectus femoris, and vastus lateralis were measured. [Results] The relative integrated EMG values of the vastus medialis obliquus and vastus lateralis at 90° knee flexion were significantly greater than their respective values at 20° knee flexion. [Conclusion] To train the vastus medialis obliquus, knee extension with the knee joint at 90° flexion is appropriate.