Abstract: Objective To analyze electromyographic (EMG) activities of vastus medialis obliquus (VMO) and vastus lateralis (VL) in patients with patellofemoral pain syndrome (PFPS) before and after an exercise program.Methods 26 subjects with PFPS were randomly divided into the EMG biofeedback plus exercise group (group A) and exercise only group (group B) with 13 cases in each group. All patients in two groups were trained with family exercise program, but the patients of the group A used a EMG biofeedback while training. The relative activities of VMO and VL of all patients in two groups were assessed with the EMG apparatus for a continuous 6 hours period before and 8 weeks after training. At the same time the intensity of the knee pain was also assessed.Results There was no statistics difference in VMO/VL EMG ratio of the group B ( P>0.05), whereas the group A had significantly higher VMO/VL EMG ratio ( P<0.05).Conclusion The EMG biofeedback apparatus used in home exercise program of PFPS patients can improve the recruitment of VMO.

Key words: patellofemoral pain syndrome, electromyographic analysis, vastus medialis obliquus, vastus lateralis