ELECTROMYOGRAPHIC RESPONSES OF THE SUPERFICIAL MUSCLES OF THE QUADRICEPS FEMORIS DURING ISOKINETIC MUSCLE ACTIONS

PURPOSE The purpose of the present investigation was to examine electromyographic (EMG) responses of the superficial muscles of the quadriceps femoris during isokinetic muscle actions in young untrained females. METHODS Ten untrained female subjects (M±SD age=19.2±1.5 yrs; mass=67.8±10.7 kg; height=169.0±7.9 cm) performed maximal isokinetic muscle actions of the leg extensors at randomly assigned velocities of 30, 150, and 270°s−1 on a Cybex II isokinetic dynamometer while EMG was recorded over the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM). RESULTS The results of the EMG analyses indicated a significant (p < 0.05) velocity by muscle interaction. Subsequent analyses revealed a significant change in EMG amplitude across velocity for RF (M±SD 30°s−1=636.7±153.0 μ V; 150·s−1=763.3±151.4 μV; 270·s−1=657.5±126.8 μV) and VM (30·s−1=252.1±126. μV; 150·s−1=354.0±162.5 μV; 270·s−1=370.0±177.8 μV), but not for VL (30·s−1=129.3±97.8 μV; 150·s−1=124.7±32.8 μV; 270·s−1=131.5±40.2 μV). In addition, the peak torque data indicated a significant decrease in the mean values as muscle velocity increased (M±SD 30·s−1=135.1±13.7 Nm; 150·s−1=87.1±19.0 Nm; 270·s−1=48.6±4.8 Nm). CONCLUSION These data indicate that electromyographic responses of the superficial muscles of the quadriceps femoris differ across velocity in young untrained females.