The photo below shows the instruction panel on one of the weight machines I use at the gym.
The instructions are very clear:
- As you start moving the weights breathe out as you exert force.
- As you return to the starting position gently exhale with controlled movements.
- Always warm-up and start with a light weight.
Disregarding the grammatical error in #3 (noun “warm-up” used for verb “warm up,” no doubt a product of the same writer who doesn’t know that “biceps” is singular or when to use commas), my dilemma is: When do I inhale?
WalkThoughts 
You should inhale during the warm-up. I misread the first line in the warning though, and thought you had to check for worn pants.
Loose pants would be a problem, too. And should I not use the machine if I am not in good working condition?