Sit down with your legs straight and hands behind your glutes. Press down and raise your hips so your body forms a straight line. This is the reverse plank. Without lowering your hips, lift your right leg and hold for 3 seconds, then lower your leg and repeat. Do 10 with each leg.
If you're not very active, you may want to get the all-clear from a GP before starting A. Rest your hands on the back of a chair for stability. B. Raise your left leg to the side as far as is comfortable, keeping your back and hips straight. Avoid tilting to the right. C. Return to the starting position. Now raise your right leg to the side as far as possible. Raise and lower each leg five times.