Ok, First of all I want to say I have been sold on the Vibram Revolution thing. That normal running shoes have made average persons feet weak. Humans back in the stone age didn't have shoes and they did full on sprints to kill their prey and feast, Humans didn't jog back then they either walk to new habitual areas, or sprint from predators sprint towards prey. sprint to chase prey.. When a person sprints, they are pushing of their top middle part of their foot, mostly the ball of their foot, Humans were meant to run hard on their ball of their foot. Most of the best athletes in the world are at least flat or mid striker runners, even for marathons, theirs discomfort and wasted energy when you land your heel to roll it to ball of your foot to push off. you should just be running on the ball of your feet eliminate extra partial second and discomfort of landing on your heel!. I encourage all those who haven't tried mid strike running give it a try. The whole thing about Vibram material shoes, it is a minimalist type of running style. And what do I mean by Minimalist you may ask.. Minimalist will have the minimal essentials to survive. So minimalist type shoe, wont have any cushion barley any rubber and it will be as light as possible, to help simulate running in bare feet. Vibram shoes will help the feet build stronger muscles, imagine your self running miles you are doing now but only on the balls of your feet as if you were sprinting. If you can run on the balls of your feet 2 miles straight you basically ready and able to sprint 1 mile at anytime. and your feet will be defines and so are those sexy calves.