This exercise from Jen Widerstrom, a trainer on The Biggest Loser, is great for shaping your thighs and butt. Remember to put equal weight on both legs so you move straight up and down, not forward.

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Here's how to do it: Start with your feet hip-width apart and hands on your hips. Step your right foot forward, coming into a wide stance with both feet pointing forward and your left heel lifted off the ground. Bend your knees, lowering until both legs form a 90-degree angle. Do 10 reps. On the last rep, remain in bottom of lunge and pulse 10 times. Repeat sequence on opposite side.

Try this move: Stationary Lunge with Pulse