Variation Characteristics Of Quadriceps Femoris Fatigue On Its Reaction Time And SEMG

Objective: Quadriceps femoris are the main knee extensors. Muscle balance of them has a great impact on the contact stress and the distribution state of the patellofemoral joint, and on patella trajectory as well. In this study, effects of different fatigue modes on reaction time and sEMG, are investigated, In order to provide a theoretical basis for further revealing the quadriceps activity patterns of the knee joint.Methods: The knees of 12 male subjects were tested in this study. The CON-TREX isokinetic dynamometer and the biovision system were synchronously used to collect peak torque, the angle of the joint and sEMG of rectus femoris(RF), vastus medialis (VM) and vastus lateralis (VL) during the different fatigue modes. The action time, iEMG and median frequency(MF) of sEMG were the dependent variables before and after the exercise .Results: (1) During exercise, iEMG and MF of the quadriceps decreased significantly(P <0.05orP <0.01).(2) The RT of quadriceps femoris are higher significantly after than before exercise, 81.08ms higher immediately after than before concentric exercise (p < 0.01), 81.71ms higher immediately after than before eccentric exercise, 67.82ms higher immediately after than before isometric exercise. (3) The PMT of quadriceps muscle increases significantly after exercise (p < 0.01) . The Vastus medialis'is 110.03ms more higher after than before eccentric exercise, The Rectus femoris'is 79.91ms higher after than before isometric exercise, but the growth is the smallest(.4) The EMD of the quadriceps decreased after exercise (p < 0.01). The Vastus medialis'is 39.54ms lower within 3min after than before isometric exercise, and the decline is the highest. The Rectus femoris'is 13.81ms lower within 10min after than before isometric exercise, and the decline is the lowest.Conclusion:(1) iEMG and MF of Vastus medialis muscle of sEMG change most obviously among the quadriceps after than before exercise(.2) During the extension of the knee joint, the generation of action potential in Vastus medialis muscle is earliest among the quadriceps.(3) The RT of the quadriceps is mainly dependent on PMT.