From my experience as an active fitness enthusiast for an extended period of time, it is quite hard for someone that is actually in the gym to do some serious workout, because if you follow a program you really have not so much time to do some chit chat with anyone. The same goes for girls.
The only chances are if you are doing an aerobic exercise and than just start a casual conv.with the chick next to you, or try to jump her as she is leaving.
On the other hand, if you are a pro trainer, than you will have A LOT of opportunities to game the chicks in the gym, while showing them the workouts and similar. I found that this is one of the best calls a wannabe PUA can have if he has his game right, as he really meets tons and tons of new HB˙s weekly. Just imagine all the kino escalation possibilities while showing some exercises...
I am witnessing the trainers in my gym trying to game almost EVERY new HB that enters the door of the gym. Just incredible...