Breathing is important on every exercise but critical for effectiveness on only a few. When you are crunching breathing is very important. When doing a crunch for your abs(you should be lying down on a mat with hands loose behind your ears with head starting about 3 inches off the ground. When you rise up look up towards the ceiling and hold at the highest point you can go while crunching and NOT exhaling. If you exhale a good analogy would be like blowing up a balloon and the someone comes by and puts a pin in it deflating it. Hold the top of the movement…..don’t breathe…..CRUNCH your abs and then exhale just after your crunch or on the way down and repeat. Crunches are a great finishing movement but won’t change your abs without a clean diet and cardio 4-7 days a week 45-60 minutes. In any exercise when you need to crunch or squeeze don’t breathe during that phase. Breathe out AFTER you have done the hardest part or the exertion. Trust me it works and is most effective.