She gives you the courage to finally try that crazy new fitness class you've always been too intimidated to try -- and the two of you end up totally owning the class from the front row.
Your stretching routine starts to resemble something out of the "Kama Sutra" or you regularly show off with acrobat-like moves when prepping for your workout together.
You don't feel well, you have a big deadline coming up, you're allergic to running, blah, blah, blah -- your feeble excuses may work with anyone else, but your fitness buddy has almost witchlike abilities to prevent you from quitting.
