What are full crunches?
To do the Full Body Crunch, lie on your back with your legs out straight. You can place your hands behind your head or across your chest. Lift your feet up off the ground and tuck your knees in toward your chest as you crunch your upper body up. ... After you kick your legs out, crunch everything back together.
How to do it: Lie flat on your back with your knees bent at a 90-degree angle. Place your hands on either side of your head. Push your lower back into the floor as you lift your shoulders a few inches off the floor – make sure your lower back stays in contact with the ground at all times. Tense your abs hard at the top point of the movement, then return under control to the start position.