Playboy.com says it was inspired to compile the list after recent reports showed that the Fortune 500 now includes more women CEOs than ever before.
Knee runs the West Loop fitness facility that offers a women's only experience that can feel as much like hanging out at a nightclub than at a gym.
She wasn't even aware the list had been public when contacted by NBCChicago.com Tuesday morning. She has been approached by the magazine before asking if she'd pose, but this was the only way she was having it.
"It's very business-like. I'm wearing a suit -- not your typical type of Playboy, but it's fun to be included," Knee said.
"I think confidence is one of the sexiest things a woman can have, and women gain an enormous amount of self-confidence when they come to Flirty Girl, because nobody ever teaches you how to be sexy. Everybody always expects you to already know these things," Knee said.