Hip muscle strengthening and knee extensor strengthening are common training exercises for patellofemoral pain syndrome (PFPS). PFPS engendered by insufficient hip abductor and external rotator muscle strength has been of interest, but these exercise movements may increase the lateral vector force of the patella warrants clarification. So, the purpose of this study was to assess muscular activations of vastus lateralis (VL), vastus medialis oblique (VMO), and gluteus medius muscles in electromyographic analysis during hip abduction and external rotator movements and open and closed kinetic chain knee extension movements.The gluteus medius, VMO, and VL muscles, in addition to the ratio of the VL and VMO muscles, were assessed through surface electromyography in 4 movements. Each muscle's amplitude expressed as a percent of maximum voluntary contraction (MVC). The differences on MVC at the terminal joint angle and during the movements were compared.Thirty female patients with PFPS were recruited. During hip abduction and external rotation movements, the MVC of the gluteus medius muscle increased, and those of the VMO and VL muscles increased in the open and closed kinetic chain knee extension movements. The MVCs of VL in the hip abduction and external rotation movements were significantly higher than those of the VMO muscle (P < .05). The ratios of the VL and VMO muscles in the open and closed kinetic chain knee extension movements approached 1, and they were significantly higher than those in the hip abduction and external rotation movements (P < .05). The highest MVC of the VMO muscle was observed at the terminal joint angle in the closed kinetic chain knee extension movement.Selective gluteus medius muscle activation was induced during the hip abduction and external rotation movements, accompanied by an increase in VL muscle activation. In open and closed kinetic chain knee movements, the ratios of the VL and VMO muscles approached 1. More selective VMO muscle activation was induced during the closed kinetic chain knee movements.