How does breathing and the diaphragm affect the pelvic floor?
Our abdominal cavity has only so much room, so as our diaphragm draws down to take in a breath, we need to learn to breathe by expanding our lower rib cage and upper chest to displace the volume that the diaphragm is taking up. If we cannot do this, then the descending diaphragm will cause an increase in abdominal pressure that will displace the pelvic floor down (although this downward displacement is natural to a certain degree). If you aren’t able to expand your lower rib cage and chest then you are a belly breather which places more downward force on your pelvic floor.
When I brace, I puff my belly out, is this wrong?
I strongly discourage you to puff your belly out. When you do that, it means you are using your rectus and your obliques to stabilize, which is the muscle recruitment pattern that is the basis for most back pain. It significantly increases intra abdominal pressure while providing minimal stability to our individual vertebrae – it is just a pressurized air pocket. Whereas drawing in your transversus abdominis (TA) is like a shrink wrap – it acts as a vacuum to pull the air pressure upwards, allowing our muscles to draw in and stabilize each individual segment of our lower spine and pelvis. This assists the work of our pelvic floor. You can feel this vacuum effect and displacement and see this effect standing or sitting in front of a mirror: as you draw in your TA, watch your ribs expand, your chest lift, you actually gain a little height as the pressure or air is displaced upward. Try it, see it, and believe it!