Alternating lunges are a great exercise that not only strengthens the muscles in the lower body, but also helps to stabilize the abdominals and obliques. When the basic alternating lunge becomes too easy, try holding a set of dumbbells in order to increase the intensity.
Stand tall. Step forward with your left leg and slowly lower your body until your front knee is bent at least 90 degrees, while your rear knee is just off the floor. Keep your torso upright the entire time.
Pause, then push off your left foot off the floor and return to the starting position as quickly as you can.
On your next rep, step forward with your right leg. Continue to alternate back and forth—doing one rep with your left, then one rep with your right.