When I began experimenting with weight lifting in my mid teens the last thing I thought about was breathing.
How many pounds I could lift and how much sinewy muscle I could pack on were my only concerns.
Valsalva maneuvers (when you perform a strenuous lift you hold your breath too long and may faint or become dizzy and disoriented from lack of oxygen) were never mentioned by my older mentors.
I learned the hard way by passing out while doing military presses a year later and ended up with a bump on my head while sprawled out on the rubberized floor.
It didn't take rocket science to figure out what had happened and I make certain to guard against holding my breath too long.
During my career as a New york City Fireman the breathing phenomenon was reinforced as lack of oxygen from fire and smoke can bring the most powerful to their knees During resistive exercise you use the ATP-CP energy system which is contained in the cells and can normally last for the ten seconds it requires to perform a set (10-12 repetitions with the weights).
Just as you would do in a one hundred yard dash you could probably hold your breath for the entire ten to twelve seconds to achieve maximum performance.
However, you require oxygen to prevent a valsalva maneuver so I recommend strong intermittent breathes when performing strenuous exercise.
It is impossible to perform tremendous lifts when breathing freely as if you're running on a treadmill because your spine would collapse.
Short breathes are necessary to achieve intrathoracic pressure to enable spine stabilization and complete a maximum effort.
If you are only performing lifts at fifty percent of your maximum capacity breathing aerobically is adequate but your respiratory system will let you know when maximum exertion is necessary for the last difficult repetitions.
Any time you are performing sets of lifting weights to failure your pulmonary function will become labored as you near completion.
Common sense and experience will dictate how you breathe.
The easier the work load the more aerobically your breathing and vice-versa.
What I teach my clients is to push themselves as hard as they can at least once a week during their routines.
With experience they will find a breathing technique that works for them.
In reality there is no set rule for any individual who takes up weight lifting.
I've observed individuals breathe abnormally fast and loud while others breathe slowly with no effort.
The only constant is to keep breathing or you'll end up on the floor.