This study examined the vastus medialis oblique (VMO) and the vastus lateralis (VL) onset time differences (OTD) during quadriceps contraction in different hip positions. Twelve healthy subjects were recruited (four men, eight women). Surface EMG activities of the VMO and VL were measured during a quadriceps strengthening exercise in a long sitting condition and in a sitting at a chair with feet hanging condition. For each condition, subjects were tested in two hip positions (neutral and adduction). The OTD between the two muscles was calculated for each condition, by subtracting the onset time of the VL from the VMO. Therefore, the negative value of OTD represent earlier EMG onset of the VMO compared to the VL. The OTD was not significantly different between the hip neutral and the hip adduction position in the long sitting condition (p=.064). However, the OTD was significantly different between the hip neutral position (15.83±109.51 ms) and hip adduction position (-5.58±121.08 ms) during the sitting at a chair with feet hanging condition (p=.047). The negative OTD value in the hip adduction condition during quadriceps strengthening exercises is the result of earlier onset of the VMO than VL. Therefore, quadriceps contraction in the hip adduction position can prevent the risk of patella lateral tracking. We expect that quadriceps strengthening exercise in the hip adduction position will be a safe way to prevent patellofemoral pain syndrome resulting from abnormal patella lateral tracking.