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.

In order to give more effective instruction for running in sports medicine, the mechanical stresses in the knee joint during running at various speeds and step lengths were investigated.
The subjects were five male sprinters. Running conditions were as follows : 1) running at four speeds (2.5 m/s, 4.5 m/s, 6.5 m/s and maximum running speed) with natural step lengths, 2) run-ning with three different step lengths (1.0 m, 1.5m and preferred step length) at 4.5 m/s running speed, and 3) running at maximum speed using four different step lengths (1.0 m, 1.5m 2.5m and preferred step length) . Running movements were recorded using a high speed video camera. And ground reaction forces were also measured by a force platform. The compressive force and shear force in the tibiofemoral joint were computed from the results of two dimensional motion analysis. That is, the external force caused by ground reaction forces, the internal force produced by the mus-cle to develop joint torque and total force (external+internal force) were computed for both com-pressive and shear forces.
The total compressive force that affects the meniscus and articular cartilage in the tibiofemoral joint depended on the magnitude of internal force. The total compressive force increased with running speed and step length. Therefore, caution should be employed in changing running speed and step length for regulating the magnitude of total compressive force on the tibiofemoral joint. On the other hand, the total shear force that caused traction stress in the posterior cruciate ligament depended on the magnitude of external force. The posterior shear force was generated during the foot contact period, and increased with step length. As for total shear force in the tibiofemoral joint, care must be taken to regulate step length.