... unless you're under water!!!
I haven't posted in a while, but I wanted to take a brief moment to give you this tip...
If I got paid every time I tell my clients to not hold their breath while exercising i'd be a millionaire!
Unfortunately, most folks, at least that I've witnessed, will hold their breath while straining to lift weight. It's called the Valsalva Maneuver... you may have heard of it.
Folks do this for a variety of reasons, including as a way to keep their abs engaged, but it's much safer to engage your abs during the lift while still breathing in and out. i.e... Exhale as you exert energy lifting the weight, and Inhale as you lower the weight or finish the movement. Counting your reps out loud is a nice little trick to use... as long as you're not waking the "neighbors"! :-)
The risk... potentially increasing your blood pressure which can cause dizziness, fainting, decreased blood flow to the heart, and even stroke.
Bottom line... just keep breathing!!!