The reverse crunch works the abdominal muscles while placing less strain on the neck and lower back.
First off, lay on your back, arms down at your side.
Bend your legs so your feet are flat on the floor, shoulder width apart, raise your feet off the ground until your thighs and lower legs make a 90 degree angle.
Without moving the angle of your knees, curl them back from the hip, towards the chest by contracting the abs.
reverse the movement until you reach the same 90 degree angle.