Objective: Patellofemoral pain syndrome (PFPS) is one of the most common knee chronic disorders especially among females that is closely related to forces imbalance of vastus medial is oblique (VMO) and vastus lateral is (VL) muscles. The purpose of study was to examine the effect of knee isokinetic extension in maximum lateral tibia rotation on VMO and VL amplitudes in PFPS patients.

Materials & Methods:  Thirty-six women with PFPS participated voluntarily in this study and were randomly placed in one of three groups included the VMO selective isokinetic strengthening exercise, quadriceps general strengthening and control groups. Each exercise was performed for 8 weeks. Muscle RMS of VMO and VL and VMO/VL RMS ratio were recorded and calculated before and after training using of an 8-channels electromyography system. Data analysis was made by analyses of variance with repeated measures.

Results: In baseline, VMO amplitude was less than VL in all groups (P≤0.05), but after interventions, it was more than VL in selective group (P=0.01) and less than VL in general (P=0.001) and control (P=0.036) groups. Before interventions, there was no difference between groups in muscles amplitude (P>0.05). Yet, after interventions, VMO amplitude and VMO/VL amplitude ratio were more in selective group than in general and control groups (P≤0.001), and VL amplitude was more in general group than in selective and control groups (P≤0.01).

Conclusion: According to the study results, isokinetic extension training with maximum lateral tibia rotation and in close to knee full extension can be recommended as an appropriate training for improving VMO/VL electrical activity ratio and decreasing imbalance between lateral and medial vastus muscles amplitudes in patients with PFPS.