Your breath is like a fluid that moves in and out of your lungs and torso. When used right, it can help support you in your athletic movement – lifting, jumping, throwing, kicking, punching, etc.
Picture a garden hose. When water runs freely through it, the hose is soft – if you step on it, it easily compresses. If you put your thumb over the end of the hose, it becomes rigid and hard – bending or compressing it is impossible.
Now picture that hose being your torso and the water your breath. If you inhale, hold your breath, and suck your stomach in, your entire torso gets tight and tense. If you maintain this tension in a lift, jump, or punch, it will actually help you maintain structural integrity.
Try this – put an object that is heavy for you to pick up (stack of books, box, 5 gal of water, sandbag, etc.) in front of you. Before you squat down to pick it up, take a breath and hold it, drawing your stomach in. Then squat and pick up the object. Once you’ve stood up, release and re-set your breath. Do five sets of 8-10 reps.