T it strengthens the core muscles involved in anti-extension - that is, any movement that resists the extension of the lower back - which is 'applies to anyone working at a desk. It works all your abdominal muscles, but also works your legs, glutes (your buttocks) and shoulders. The key is to keep your hipsaligned with the rest of your body. Don't let them fall to the floor or rise up to the ceiling: easier said than done. a) Starting from a kneeling position, get into a forearm plank position; bend your elbows so they are parallel to the floor and turn your palms flat against it. b) Activate your thighs to straighten your legs. c) Push your elbows and palms into the ground, so that your shoulder blades open. d) Tuck your tailbone under, squeeze your glutes and pull your belly inward. e) Imagine pulling your feet towards your elbows and your elbows towards your feet. Hold for 30 to 60 seconds (or longer if possible). f) Repeat three times.