After an exercise session, our bodies release hormones known as endorphins. They bring on a sense of euphoria and a general wave of happiness. Maybe this is a good time to let her go? Wrong. If your girl just left a weight training session or kick boxing class, save the "we're done" conversation until after she's done feeling like Lara Croft. Throw up two fingers for the deuces and she may respond with two letters: K.O.