Lie on a flat bench with your hands under your hips supporting your back. Your legs should be unsupported by the bench from below your knees. With your feet together and your toes flexed upwards, raise your straight legs up a few cm off the bench; both of your legs should have no contact with the bench. This is your starting position. Keep your legs straight with a slight bend in the knees and raise your legs to just before 90 degrees with your hips. Pause at the top and lower your legs in slow controlled manner back to the starting position.