It's common for people have a lack of strength in their abdominal muscles. When this is the case, your body will lose core integrity while attempting ab exercises and create tension in your neck or jaw. This is not what we want.
We'll do this exercise three times, but you should do it three to five times, two to three times a day. This drill will help you feel precise small movements happening in your belly, and it will alleviate stress around your back.
Work your way up slowly to elbow-to-knee and other crunches.