Firm your abs and back with these moves from Mark Fenton, author of The Complete Guide to Walking.
Isometric side support: Lie on your right side with your body straight and your left shoulder directly above your right, left hip above the right. Lift your body, supporting yourself only on your right elbow, forearm and foot. Keep your left arm lying on your straight body. Hold for 5 to 10 seconds, breathing slowly or deeply, then rest and switch sides. Work up to three reps on each side.
Alternate extensions: Start on your hands and knees, and lift your left leg straight out behind you. Hold for five seconds, relax and switch legs. After three lifts on each side, lift your left leg and straighten your right arm in front of you. Relax and switch sides, doing three lifts on each side. Build up to 10 lifts on each side.
Curl-ups: Lie on your back with one knee bent, the other straight (both feet on the floor), and your hands flat below the small of your back. Tighten your stomach so you curl up, lifting your head, shoulders, and upper torso off the floor. Keep your gaze on a point above you on the ceiling so your neck stays relaxed. Hold the up position for a moment, then relax. After 5 repetitions, switch the straight and bent legs. Start with as few as 10 curl-ups at a time, but work up to 20 or 30 in a row, with all your movements slow and controlled.