I highly recommend this Pandagon post on exercise, muscles and women's body image. Amanda Marcotte breaks down the current rage for a super-skinny beauty ideal and the fact that diet, i.e. starving yourself, is the first choice for women over exercise. Women are given a pretty good dose of fear over becoming "bulky" or "too muscular" if they work out. The celebrity press freaks out over any famous women with a bit of muscle tone, be she actress or First Lady. This is terrible. Hitting the weights will do you far more good than stopping eating. And you'll be sexier. I've been over this before, but the fashion world is a group of people who don't find women attractive.
Not to say this is the only way to define sexy, but being attractive to members of the opposite sex is a pretty good benchmark. Look at the difference in women's bodies in magazines that sell to women and the magazines that sell to men. Cosmo and Glamor are filled with women who are Paris Hilton skinny. And guess what? Men don't buy stuff with Paris Hilton skinny. We buy stuff like American Curves, filled with women with asses you could bonce a quarter off of.
So everybody, go to the gym, you'll be healthier, live longer, and more people will want to have sex with you.