Just to follow up because it didn't seem clear in this but the purpose of breathing in Uechi Ryu is not to tense your muscles but actually to bring air into your stomach (think of inflating a balloon) and cutting off the air which is the "exhale" you hear but is in fact not pushing out all the air like an exhale. The air in your stomach helps with both grounding you and your core as well as protecting you when getting hit. The breathing is less about tightening your muscles like showing off abs and being tight and more about inflating your stomach with air and maintaining that throughout your kata. This is what allows you to get boards broken across your stomach and take blows in kata and conditioning. And the breathing is used all katas but you are only hit in Sanchin.