TIP 8: STRETCH THE ABDOMINALS BETWEEN SETS 

Did you ever have to stop performing an ab exercise because of cramping? If so, then you probably don’t need to train harder but smarter, by stretching the abdominals between sets. A simple stretch for the abdominals is to lie face down and prop yourself up on your hands, keeping your hips in full contact with the floor. This exercise will stretch the rectus abdominis. To stretch the obliques in this position take a deep breath... hold it... and twist your torso slightly to the right. trying to look back over your shoulder as you do so. Hold this stretch for about 20 seconds... exhale... and repeat on the other side. 

TIP 9: DON’T PLACE YOUR HANDS BEHIND YOUR HEAD

It doesn’t matter how careful you are, never hold your hands behind your head during abdominal exercises in which you pull your head toward your knees. If you do. it’s a virtual guarantee that as soon as you start fatiguing. you’ll pull on your head. Pulling on the head will stretch the neck muscles and connective tissues. 

Begin curl-up and sit-up exercises by retracting your chin, so your head stays in alignment with your back, and keep your fingers on the side of your head just behind your ears. Paul Chek says it’s also effective to cup your hands on your jaw during these exercises so you look like the kid in the shaving scene in Home Alone. To give adequate support  to the neck and to keep the head aligned with the spine.