Take a DEEEEEEEEP breath (through your nose- we are not mouth breathers.)
Now hold that breath.
Hopefully, as you're reading this, your tummy is expanded to make room for those powerful lungs of yours. I'd like you to now attempt exhaling WHILE not actually releasing any air from your body.
For comparison sake, think about when you're sitting on the toilet (hopefully you're actually squatting but whatever) and you have to push out this turd so you can get back to dominating your day. What you do to make that happen is basically what I'm asking you to try doing now, holding your breath while trying to push it out, flexing your midsection increasing the pressure in your chest.
You feel that?
Okay exhale that carbon out and get yourself some fresh oxygen, fam.
So if you did this correctly, you're basically trying to push air out while holding it in, which creates pockets of pressure in your abdominal and thoracic cavities. They therefore reduces the load on, the lumbar (lower) and thoracic (middle) spine, keeping it straight and safe. This gives your body the stability to increase your power output/strength during movements that require strong core support (Deadlifts, Squats, Bench Press) to protect your lower back from injury.
Check it out. It's called the Valsalva Maneuver, named after the seventeenth century ear-specialist physician Antonio Maria Valsalva.
Now, I'm not saying yo hold your breath for the entire concentric part of the movement, only up to the sticking point, during the harder portion of the movement. After that, do whats comfortable, as long as your core stays tight and you finish the rep properly of course.
And please do more research on the Valsalva Maneuver, because learning is pretty rad.
See you later