Stand up straight facing away from a wall.
Position a large stability ball against the wall and rest it against your calfs just above your ankles.
Tighten your thigh and buttock muscles, pushing your knees back into the ball to lock your legs straight.
Next, bend your knees, moving your hips and body backwards.
Continue until your thighs are close to horizontal.
It should look as though you are sitting up straight in a chair.
Ensure your knees have not travelled forwards at all.
Steadily return to the upright position and repeat.
