And ALWAYS ALWAYS use the following statement or a modified version of it with the same message:
"If there is anyone here today with any kind of medical condition, for example but not limiting to, knee, ankle and lower back injuries, or if you are pregnant, you should have clearance from your doctor before you start the class today."
This will clear you for anyone accidentally injuring themselves and then trying to go for legal action against you. It's also an OH & S policy at most clubs. And if it isn't, it should be!!!
I do it before I start any class, not just pump.