Ask a weightlifter. The Valsalva maneuver “splints” your abdomen and thorax turning it into a HUGE fulcrum for leverage. Wearing a weight belt can help this effect and add maybe as much as 25% to the weight you can lift. IMHO it is mistake and poor form so I lift being careful to INHALE because a prolonged Valsalva also does a number of bad things that can be very detrimental. Watch Strong Men deadlift a thousand pounds. They can do it but “black out” for several minutes.
“Ask a weightlifter.”
No joke. I’m a dedicated powerlifter and could have told them this.
You also exhale or your BP will goes so high on the positive part of the lift, you’ll get a nose bleed (or worse).
You also don’t let all the air out, until the weight is down.