This study aimed to investigate the electromyographic activities and balance of Vastus Medialis Obliquus (VMO) and Vastus Lateralis (VL) muscles during Straight Leg Raise (SLR) in individuals with and without Patellofemoral Pain Syndrome (PFPS). Methods: Through an analytical case-control study, 26 persons with PFPS and 26 healthy subjects were recruited by non-random and convenience sampling method. All subjects performed SLR movement. The EMG activity of VMO, VL and VMO/VL ratio were recorded and measured. The muscles activation level were compared between the 2 groups using the Independent t test. The obtained data were analyzed using SPSS. Results: The mean and maximum EMG activity of VMO, VL and VMO/VL ratio did not have any significant differences between the PFPS and healthy groups (P>0.05). In other words, during SLR, the VMO and VL muscles activation in the PFPS group were approximately the same as the healthy group. Conclusion: These data suggest that not all individuals with PFPS had weak quadriceps muscles. Many factors may contribute to PFPS that should be considered in the assessment and rehabilitation of individuals with PFPS.

Exercise therapy to strengthen quadriceps muscle is recommended in rehabilitation program for people with patellofemoral pain syndrome (PFPS). This study aimed to investigate the electromyography (EMG) activity of vastus medialis obliquus (VMO), vastus lateralis (VL) and VMO/VL ratio during PNF in individuals with and without PFPS. Methods: 26 persons with PFPS and 26 healthy subjects participated to study. All subjects performed PNF patterns (Flexion-Adduction-External Rotation (D1FL), Extension-Adduction-External Rotation (D2EX), D1FL+ load, D2EX+ load) and straight leg raise (SLR). The normalized EMG activity of VMO, VL and VMO/VL ratio were measured and analyzed using repeated measure ANOVA. Results: There were significant main effects of group and exercises for the both VMO and VL (p<0.05). It was found that except SLR and D2EX, in the other motions PFPS group had lower VMO activity compared to healthy group (p<0.05). For VL except SLR, in the other motions PFPS group had lower VL activity too (p<0.05). The PNF patterns activated VMO more than SLR, however it was not significant (p >0.05). Also; there weren't any significant difference between the two groups in VMO/VL activation ratios. Also, performing the PNF patterns with load increased VMO and VL muscles activity significantly (p<0.05). It also found that in PFPS group the VMO/VL ratio values in PNF patterns were significantly more than SLR and the highest VMO/VL ratio value (0.96) was found during D2EX. Conclusion: The PNF patterns due to provide optimal VMO/VL ratio value than SLR and proper balance between these two muscles can be recommended in rehabilitation of individuals with PFPS.