" Lie on your back with arms straight out at your sides and very slowly, with knees straight, raise your legs high and hold them in the air. Take a deep breath and very slowly lower them again.
Then with your legs still against the floor, draw the small of your back into the floor until you can feel that your back is one straight line. Hold for a count of ten.
Then begin the leg-rising exercise again. Work up to ten times.
As your stomach muscles become firmer add this routine: Anchor your feet under the bed or a heavy armchair and raise and lower your body slowly, keeping your knees rigid and your back very straight. "

― Joan Crawford , My Way of Life