The crunch is more safe and effective than its antiquated cousin the sit-up.
To do the perfect crunch…
Lie on the floor with knees bent and arms crossed in front of your chest (or place your hands behind your head so that your thumbs are tucked behind your ears.)
Position your feet as wide as your hips.
Pull your belly button in towards your spine then slowly contract your abs, lifting your shoulders 1-3 inches off the floor.
Focus on shortening the distance between the bottom of your rib cage and your pelvis.
Slowly lower your shoulders back towards starting position, but don’t relax all the way. Repeat exercise.
Keep your knees bent, your feet in the same position and your back straight throughout the entire exercise.