Putting aside that many women dislike like being ogled by guys in a gym, so attend a female only gym, or attend a 24 hour gym so they can go at odder hours with less people around and also that even if you're in a gym at night, it's still very much like daygame, gym daygame is easily the hardest type of daygame to do successfully and is definitely only for guys with more advanced skills.
Hence why I want to ask what guys with much more advanced daygame skills (who like staying fit and in shape), what successful, field tested techniques and openers they've used and use in a gym during the day, or even at night. In my case I've had an off peak gym membership (where it's cheaper if I go only between 11 am – 4 pm) and there's a separate room for women to train in, that you wouldn't want to enter, as it'd tick the women inside off.
Trying to open women who are on a treadmill for example, is next to impossible, not just because most are in a zone, listening to music on an iPod, but even if they aren't listening to something, the idea of being tapped or trying to talk while focusing on what they're doing, will be highly irritating to almost all females approached like that and you'd get sworn at, to leave them alone.
With regards to waiting till a lady has finished her treadmill cardio workout, the gym I'm at, doesn't really have anywhere where you can sit and watch who's on the treadmill, in the treadmill area. Also standing outside a gym waiting for women to leave, then approach, isn't wise as it'd weird most females out.