Lie on your back with your knees bent and your feet flat on the floor. Rest your arms on the floor, palms up, at shoulder level. Raise your hips so your body forms a straight line from your shoulders to your knees (A). Brace your abs and lift your right knee toward your chest (B). Hold for 2 counts, then lower your right foot. Repeat with the other leg. That's 1 rep. Do 2 or 3 sets of 5 to 10 reps.