In front of a swing, get on your hands and knees facing away from it, then straighten into a push-up position. Step your feet up onto the swing so you are in a straight line with your feet supported and your hands on the ground. Keeping your arms still, lift your hips toward the sky and tuck your knees in toward your chest, squeezing your belly. Slowly straighten your body, returning to the starting position. Do 10-15 reps. Muscles worked: Arms, shoulders, chest, back and deep abdominal muscles.