Hmmm... off the top of my head, these are things that could maybe help you get the girl:
1) be her spotter
I don't think you should try hitting on her while she's working out, but helping her out will put her in a grateful mood and you've made your presence known without forcing it. This can also give you Kino opportunities.
2) get her schedule
If you can afford to bust your routine sometimes by going when she's there, then do so. Give her a chance to see you in action! No need to sacrifice your entire schedule for her though, since your body is being improved to service other women as well, hehe. Maybe you could also start an hour or two before she does so that you're actually finished with your routine and can easily approach her when she's on a break.
3) lots of small talk
Since you're both there to work out, flirting will have to play second fiddle to it. I think in this case, patience is a virtue. You don't want to hit on her too hard that she ends up avoiding you next time.
4) timing is important
You don't want to come across as someone who just goes there to Pick Up Girls. You also don't want to be approaching her when she's really into her routine, or is sweating real heavily that she's feeling ugly and dirty.