Background: The purpose of this study was to investigate the ratio of Electromyography (EMG) activities of the vastus medial is obliqus (VMO) and vastus lateralis (VL) within seven angles of knee joint range of motion using isometric contraction in open kinetic chain (OKC) and closed kinetic chain (CKC). Methods: The dominant knees of 44 healthy female subjects (mean age: 24.84 with range: 20-30 years old) were analyzed. Surface electrode pairs were attached over the VMO and VL by using Basmajian methods. The EMG biofeedback data was collected while the subject performed isometric contraction on isometric and squat exercise within 7 degrees (0° to 90°) with 15° intervals of knee flexion angle. Results: Paired T-test and ANOVA were performed between variables. Results demonstrated that in this study there are significant differences: I) between OKC and CKC exercise in 0°, 15°, and 30° of knee flex ion, II) between all angles in CKC except: 0-15°,0-30°,0-45°, 15-30°,60-75°, and 75-90°, and III) between 15-60°, 30- 60°,45-60°, and 60-90° in OKC (p<0.001). As a result in OKC and CKC respectively, 60° and 15° angles of knee flexion were most sufficient positions (i.e. increased VMONL activities ratios), -15° and 90° of knee flexion were the most insufficient positions and arc of movement between 45- 75° and 0-30° was considered as the most sufficient arc of movement.Conclusion: As the result of this research and biomechanical and neuro-physiological viewpoints, emphasized in the literature, our recommendations are: in early phase or in early sessions of treatment of patellofemoral joint dysfunction, treatment exercise done in CKC & sufficient position and after progression of the patient's condition, OKC exercises could also be considered.