The focus of this exercise will be on the quadriceps, but it also builds the glutes, hamstrings, and calves. This exercise can also help to build balance and stability.
Begin with your feet together, your torso upright, and holding a dumbbell in each hand. Next, take one pretty big step (about 2 feet) forward with your right foot. You want this step to be far enough so you can squat down, but not too far to throw your balance off. With your right foot forward, you want squat down with that leg, making sure that your knee does not go in front of your toes. You should lower your body down until your left knee nearly touches the ground. Then, push through your heel up and back to the starting position. Once you return to the starting position you can either repeat again with the right leg for a set number of repetitions, or you can switch legs after each rep.
There are a few variations of lunges that can be done with dumbbells or with a barbell across your back. One variation is to keep your right foot out in front and instead of returning to the starting position, just squat up and down for a number of reps. Another variation would be walking lunges, rather than bringing your foot back to the starting position, bring your back foot to the front foot. Then continue this for a certain distance. This should not be used until you have mastered the lunge.
Make sure to keep your knee behind your toes of the leg that is forward, this will keep stress off the knee joint and prevent injury. Also, balance can be an issue with this exercise, make sure you can do lunges with your bodyweight before using added weight.