Background : Knee pain is a common musculoskeletal concern that inconveniences daily life. A recent study revealed that knee pain occurs mainly when the knees are not aligned correctly during weight load training. Certain visual biofeedback methods enable the strengthening of the vastus medialis (VMO) muscle, whose activity keeps the lower limb in neutral alignment. However, the visual biofeedback devices in most studies are hard to use, and only a few have suggested methods for selective VMO strengthening using laser equipment during weight-bearing tasks. Objectives : The purpose of this study was to measure the electromyographic VMO and vastus lateralis (VL) activity during forward lunge with and without biofeedback. Methods : Twenty subjects with a healthy participated in this study. VMO and VL activity between forward lunges with and without visual biofeedback using a laser beam was compared. The VMO, VL, and VMO/VL muscle activity ratios with and without visual biofeedback were analyzed using paired t-tests with p < 0.05 as the significance level. Results : The VMO muscle activity was significantly higher (p = 0.020) during the forward lunge with visual biofeedback than that in the forward lunge without feedback. The VL muscle activity was decreased but not significantly (p < 0.05). The VMO/VL muscle activity ratio was significantly higher (p < 0.05) during the forward lunge with visual biofeedback than that in the forward lunge without biofeedback. Conclusions : In this study, there were significant increases in VMO muscle activity and VMO/VL muscle activity ratio with biofeedback. The results show that the use of laser equipment for visual biofeedback can affect selective muscle activation, and the visual biofeedback equipment can be useful in treatment or development of protocols for the performance of weight-bearing exercises or exercises intended to prevent knee injury.