It feels silly saying this, but I’m not doing a great job breathing while I brace during the Big3 or carry exercises. I’ll also feel some minor pain in my lower lumbar during an exhale at times when I’m really squeezing (fist, lats, core, pecks, neck). I’m pretty sure this means I’m not using my thoracic diaphragm correctly. Any tips are much appreciated.
When I breathe during the bracing exercises, I use really shallow “sipping” type of breaths that allow me to stay super tight during the exercise. I agree with Mike, maybe try to lower your duration times until you find a way that works and you can build up a little more endurance for longer. It took me a while to find an effective way to incorporate breathing while trying to stay tight.
Hope this helps