Remember that whenever you feel any unusual pain while working out, stop exercising immediately and consult a physician. No Gain can be a fallacy. So whenever you feel pain during an exercise, don't try to work through the pain. The crunch is the most fundamental exercise for the abs. Crunches should be done on a flat surface to protect your lower back from potential strain or injury.
Many people use a mat or pad for additional comfort.
To perform a proper crunch, lie flat on your back with a slight bend in your knees and your feet flat on the floor about two feet apart. Tilt your pelvis and be sure your start the exercise with your back and butt on the floor. Exhale as your curl your torso up and inhale as you lower your torso back down. Concentrate on isolating your abs during this movement. All of the effort required to curl your torso up should come exclusively from your abs, so don't pull yourself up with your arms behind your neck and don't use your momentum to swing yourself up.