Begin the forward lunge in a standing position with your feet shoulder width apart. Take a big step forward with the right leg and plant your foot out front, keeping your body relatively straight.
Your knee should stay over your ankle and not extend out over your toes to minimize stress on the knee joint. Keeping your weight balanced on your right heel and left toes, lower your hips toward the floor. Your back leg should bend at the knee during a forward lunge.
The knee of the lead leg should remain over your ankle (bottom image)and should not be less than 90 degrees. Raise your hips back up, and pushing off with the front foot, bring your right leg back to the starting position. Repeat with the left leg. Continue until you have completed the desired number of lunges on each leg.
You can modify this exercise in two ways: