The anterior lunge exercise is a closed chain kinetic exercise that has been developed to improve the function of the lower limb and to strengthen the hamstrings and quadriceps, simultaneously. In this study, a three-dimensional biomechanical analysis of this exercise was conducted in order to understand the mechanics of this rehabilitation activity. Experimental conditions were recorded using an active optoelectronic kinematic data capture system (OPTOTRAK), two force plates (AMTI) and electromyography (EMG). Data were collected from healthy male subjects while performing several lunges. When the distance between the toe of the rear leg and the heel of the front leg (lunging distance) was maximum, a large net flexion moment was predicted in the front leg in the extented position. This moment was reversed to a large net extension moment in the flexed position. A large increase in the net extension moment in the rear leg was also predicted as the front knee was bent from 5 degrees to 90 degrees of flexion. These data suggest that quadriceps and hamstring muscles co-contraction occur during a maximum lunge in the front leg when it is in the flexed position.