the op's question...
yes, of course.
its actually easy as hell... assuming #1 you're decent looking (face & body) #2 you're not a dick.
if you're the #1 trainer in the gym or have the best physique in the gym (or at least one of the best), it's as easy as saying "hey, you should train with me"... to which 8 times out of 10 she'll reply "i can't afford you" and smile.... to which YOU reply... "no no, you should train WITH me... here's my card, shoot me a text and we'll figure something out"
40% of the time she'll text you before she leaves the parking lot, 40% of the time she'll text you that night (and keep on texting you till midnight when she falls asleep and texts you 'good morning, i'm sorry, i fell asleep')... the other 20% probably won't text you... because she's just not interested.
pretty girls want to be seen with good looking guys... that's all you gotta do to get your foot in the door... it also helps if she's/they've seen you training with OTHER pretty girls, either AS pretty or prettier than they are (or if they know your ex gf was a fitness competitor eastern European girl with huge 500cc implants)... they'll think, "wow, he chose me over the other's" or something along those lines.
bangin pretty girls at the gym is just like high school... it's a popularity thing.