Abstract: Objective To investigate the activation characteristics (contraction velocity, force and anti-fatigue) of the vastus medialis (VM), rectus femoris (RF) and vastus lateralis (VL) by using surface electromyogram (sEMG) during isometric and isokinetic quadriceps femoris force tests in knee osteoarthritis. Methods The participants included an observation group (n=34) and a control group (n=34).The age, height, body weight, gender, dominant side and Q angle were matched between the two groups. The participants' quadriceps femoris force and sEMG of VM, RF and VL were tested in isometric knee extension at knee joint angles of 10°, 60°, 100° and isokinetic knee extension at velocities of 60°/s and 180°/s. Comparisons were made for recruitment rate, average amplitude, peak torque/bodyweight ratio, index of fatigue by independent-group t-test, with the alpha level set at 0.05 for significant differences between groups.Results ①Recruitment rate of VM in isometric contraction at 60° and isokinetic contraction at 60°/s and 180°/s, RF in isometric contraction at 60° and isokinetic contraction at 60°/s and VL in isometric contraction at 10°and 100° and isokinetic contraction at 60°/s were all significantly slower in the observation group than that in the control group(P<0.05). ②The average amplitudes of VM, RF in isokinetic contraction at 60°/s and 180°/s and RF, VL in isometric contraction at 10° were significantly higher in the observation group than that in the control group(P<0.05). ③Peak torque/bodyweight ratio of quadriceps was significantly lower in the observation group than that in the control group in isometric contraction at 10°, 60°, 100° and isokinetic contraction at 60°/s and 180°/s(P<0.05). ④In isokinetic contraction at 180°/s the index of fatigue was significantly higher in the observation group than that in the control group (P<0.05).Conclusion A significant decreasing contraction velocity and force, increasing anti-fatigue of the vastus medialis, rectus femoris and vastus lateralis were found in knee osteoarthritis patients when compared with healthy subjects.

Key words: knee osteoarthritis, quadriceps femoris, sEMG, isokinetic force