The purpose of the study was to evaluate the effect of different relative loading levels on the EMG activity of Vastus Medialis (VM) and Vastus Laterialis (VL) during knee open kinetic chain exercises. Eleven anterior cruciated ligament surgery participants were recruited (four men and six women). EMG activity of VM and VL was measured at three load levels: 75%, 50%, and 25% of MIVC in ten symptomatic subjects. No difference in muscle activity was found according to VM (p>0.05) and a significant difference in muscle activity was found according to VL (p<0.05). No difference in onset of activity was found between VM and VL for the 25% load (p>0.05). A significant difference in onset of activity was found between VM and VL for the 50% and 75% loads (p<0.05). The findings indicate that relative load levels can have significant affects on the anterior cruciated ligament surgery participants. Further studies are required to generalize the results of this study.