How does breathing affect doing things like benching, curling, and sit ups? And does it affect pushups?

Anyone??

You're less likely to injure yourself by breathing with the exertion.

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Education is a progressive discovery of our own ignorance.

Speaking from the point of view of a powerlifter, breathing helps a great deal, IMO. You want the pressure of the air in your diaphragm; when you reach the "explosive" or "bottom" portion of a lift, releasing the pressure will give you moderate assistance in pushing the weight. Learning breathing techniques has really helped my bench, squat, and dead.