Comparison of the knee valgus angle, leg muscle activity, and vastus medialis oblique/vastus lateralis ratio during a single leg squat on flat and declined surfaces in individuals with patellofemoral pain syndrome

BACKGROUND: The knee valgus angle and knee muscles activity on a declined surface have not yet provided enough biomechanical analyses and treatment guidelines for patellofemoral pain syndrome (PFPS) patients OBJECTIVE: The purpose of this study was to investigate the knee valgus angle, leg muscle activity, and the vastus medialis oblique (VMO)/vastus lateralis (VL) muscles ratio during a single leg squat (SLS) on a declined surface in individuals with PFPS. METHODS: Fifteen young adults with PFPS (9 men, 6 women; height, 168.6 +/- 7.3 cm; weight, 62.4 +/- 17.9 kg; age, 22.7 +/- 2.8 y; body mass index, 22.7 +/- 2.8) participated in this study. Knee valgus angle and leg muscle activity and VMO/VL ratios were collected in subjects with PFPS during SLS on flat and declined surfaces. RESULTS: During the SLS, the knee valgus angle was significantly increased on the declined surface than the flat surface (p < 0.05). Also, significantly higher EMG activity in the rectus femoris (RF), VMO, and VL muscles when doing the SLSs were present during the SLSs on the declined surface (p < 0.05). CONCLUSIONS: The results of this study suggest that significantly increased knee valgus angles and muscle activity of RF, VMO, and VL during SLSs occur on a declined surface. Therefore, individuals with PFPS should be cautious when stepping down on a declined surface, such as downhill terrain on a mountain.