I know that some people wear undies beneath their spandex (don't they know better??? ), but undies on top of the spandex is just plain silly.
Just an odd observation....as if anything doesn't fit in with this thread, lol.
I think it all started with woman wearing leotards, but like the one-piece bathing suit the backside continues to creep upward and inward. It's so funny now that you think about it...woman will just reach around, put their fingers under the fabric and just reset the position, right there in public, call it a casualty of attire. It's usually done discretely and quickly, but still....."ass creep" or whatever you call it prevails, I think it even happens with dancers & tights.
Somewhere around the late 70's or early 80's unitards make the scene and the one-piece comes into fashion, but then you have visable panty lines or a lack of liner to hide certain 'parts'....then gals still take it to a new level by wearing thongs or briefs over the unitard, just like the underwear of the super-heros. Tagged with a matching cropped-top, suddenly the Olivia Newton-John look is born and a spandex explosion runs the gyms.
That all abruptly ends somewhere around '95 and today we have sweats with words like Juicy or Pink tagged right on the ass, and the sports-bra comes along or various renditions of it. In my gym you'll see no leotards, unitards or anything of the like. I can't even get the gals in my spin class to join me in the pool....seems none of them can even fathom the notion of wearing a bathing suit. I think it's quite simple...these gals workout and strive for good bodies, but they just can't quite get back to their 18-27 year-old bodies, so seeing the flaws they figure "until they get there" they won't define things by going skin-tight. Jokes on them; there's nothing but a bunch of senior citizens doing the aqua-motion class in the pool anyways.
But on the whole, it all comes down to how confident you are and how you feel others will perceive your body when you offer it up in the confines of a skin-tight material. As the saying goes, 'wearing spandex is a privelege' and 'lycra is unforgiving'. To which I say, let that be a challenge, let it inspire you, let it drive you to want that better body. Because, much as you might look at someone elses sexy body and like what you see...so too should you have such a body that others might enjoy as well. Or some philosophical crap like that.