RESUMEN
To clarify the function of the vastus medialis obliquus (VMO) and longus (VML), we investigated the electromyographic properties of superficial quadriceps femoris during fatiguing knee extension task.Ten healthy male and 10 female volunteers participated in this study. The subjects performed fatiguing knee extension task at maximal effort (10 times×10 set at 60 deg/sec). Surface electromyography (EMG) was recorded from the VMO, VML, vastus lateralis(VL) and rectus femoris(RF) during isometric knee extension (knee bent at 60 deg and 30% of the maximal voluntary contraction level) with a 90-sec interval between each set. Knee extension peak torque, integrated EMG (IEMG) and median power frequency (MDF) of four muscles during each set were compared using Dunnett's test.Knee extension peak torque decreased gradually and peak torque decreased significantly starting from set 9 in male subjects, while there was no significant decrease in female subjects. IEMG from VMO and VL increased linearly. IEMG increased significantly from set 7 in VMO and set 6 in VL for both male and female subjects. Then, IEMG from both VML and RF increased significantly starting from set 9 in VML and set 8 in RF in male subjects, while there was no significant change in female subjects.MDF of VMO, VL and RF also increased significantly at timepoints similar to those showing increases in IEMG in male subjects. However, MDF of VML increased significantly from set 4 in male subjects. On the other hand, MDF did not change significantly in female subjects.As a result of this study, it was suggested that VMO and VL were facilitated to maintain target knee extension torque during fatigue. Therefore, it was considered that VML and RF facilitated the maintenance of target torque under fatiguing conditions.