books.google.com - How could something we have for free—our bare feet—be better for running than $150 shoes? The truth is that running in shoes is high-impact, unstable, and inflexible. Shoes promote a heel-centric ground strike, which weakens your feet, knees, and hips, and leads to common running injuries....http://books.google.com/books/about/Barefoot_Running.html?id=upV6L09gn7wC&q=muscles&utm_source=gb-gplus-shareBarefoot Running
