Fair enough the women on this site are less than 1% of the female population. Should I not be with my girl if I constantly fantasize about these women? I'm attracted to my girl's face, but man would it be nice if she had a good set of legs. She doesn't work out sadly.
You stand a chance of getting her into working out, but only if you do so intensively yourself. And that will definitely happen very gradually, if it does. Convincing her will take lots of charm, subtlety and suitable examples.
I managed to convince my wife to start working out after she got to know I like muscular women. She was always rather thin. She started to do some yoga first and then resistance training with focus on her glutes. It was quite a long process for her to actually notice the first results but when she finally saw her ass get rounder and firmer she got hooked. She's now in her mid thirties (two kids) and she looks better now than ever before (and she knows it). Basically she gradually got addicted and now I can see heavier and heavier dumbbells in her training room. For example - she now does her bicep curls with 10kg dumbbels and after the workout she looks sooo sexy and pumped we almost always end up in the bed.
The funny thing is - since she started the weight based training 5 years ago she didn't change her own weight too much (+/- 4kg) but her body changed from soft and rounded to quite hard and toned overall.
She's not into gym/supplements/juice and does the training at home but her workouts are really visible in her figure. Basically - you'd probably assume her as novice fitness model in the standards of this site - but hey, she's real, she's my wife and she still makes progress.
As @Chatzki said, I try to subtly encourage her to put higher weights on the rack. It requires lots of patience since you'll probably hear the stereotypical "I don't want to look manly/bulky, etc" at the beginning but if you genuinely show her you're sexually attracted to her ever-more-muscular body and she discovers how hard it is to actually build that muscle - you'll be the winner.
I think the biggest challenge is to reveal your muscular women preferences to her. Most women still suffer from stereotypes. However some of her female friends have already complimented her that she starts to look like a fitnes model!
I can assure you, if that's the girl you want to be with, try to make her your muscle-girl. It's heaven on earth experience.
My girlfriend is the opposite of the girls on here!
I like both. My skinny girlfriend is great. But the girls here are absolutely awesome