Abstract: Objective To explore the quadriceps muscles function in patients with unilateral knee injury.Methods 23 unilateral knee injured patients with joint dysfuntion were assessed with isometric EMG activity of vastus lateralis (VL), vastus medialis obliques (VMO) and rectus femoris(RF) of both thighs during three 5-s maximal isometric voluntary contractions at a knee joint angle of 30° (0° - full knee extension), and the torque were recorded at same time. Results The average amplitude (AEMG), mean power frequency (MPF), and median frequency (MF) of VL, VMO and RF in affected knees were significantly lower than those in unaffected knees（P＜0.01）, as well as the torque（P＜0.01）. In the unaffected side, the AEMG, MPF of VL were higher than VMO and RF（P＜0.05）, and RF than VMO（P＜0.05）. In the affected side, the AEMG, MPF of RF are higher than VMO and VL（P＜0.05）, and VL than VMO（P＜0.05）. Conclusion sEMG can provide quantitative measurements of muscle function. The isometric strength and neuromuscular activation lever are lower in affected limb, RF may be affected less than VL and VMO in knee injured patients with knee dysfunction.

Key words: knee, dysfunction, surface electromyography, Quadriceps femoris