Besides, the gym is a questionable place to hit on girls. You're sweaty and gross and amped up on testosterone, and likely the girls are being rather self-conscious in their routines and get-up. Often they would like nothing better than to be left alone from the creeps at the gym. I tend to enjoy the view, but never do anything to make them creeped out or discouraged from being there.
Bets are off if they come up to you, though.