The diaphragmatic breathing is called the “valsalva maneuver” if I remember correctly. I have experimented with it but after breathing in and holding I never had the gut-out effect. I won’t attempt to explain how it works to stabilize the trunk because I’m not exactly sure how and I don;t want to make some shit up and look stupid. I found it to be most effective to use and begin breathing out forcefully at the top 1/3 of the movement. I tried holding my breath throughout (which works for some people) but I just ended up seeing stars and feeling like crap.