Yesterday I went for my first run in my new Vibram FiveFingers. It's crazy how different my stride was. It took me a little while to get the hang of it - being so used to running in sneakers. I used completely different muscles and felt my form changing as I got used to them.
They recommend slowly transitioning from sneakers to FiveFingers so I only ran a mile and half. A VERY short distance for me, but I figured better safe than sorry.
Well, I am GLAD I didn't run any farther. Today my muscles are BEAT. Now, I used to be a dancer so there is a good chance I used these other muscles at some point, but not for years.
I can't wait to get back out there in them tho. :)