While jumping lunges are an excellent way to shape the legs and backside, they can be a bit hard on the knees — especially if you have bad knees to begin with, or you're on the mend from an injury. Decrease the knee impact by hopping your feet together before you switch sides in this modification of a tried-and-true move. It'll get your heart rate up while toning and strengthening your booty and legs.

• Stand with your feet together and your knees soft.
• Jump and come into a lunge with your left leg forward.
• Push off with both feet, jumping them together, then hopping into a lunge with your right leg in front.
• Jump your feet back together to complete one rep.