I've gotten them from both boots and shoes. I just picked up a new pair of Merrell barefoot style shoes, and the back edge is very rigid which is no doubt the cause of the blistering. Just wondering if it was even possible to form a callous there, as that's really the only part of my foot that hasn't toughened up. Love the shoes, I may have to eventually cut out part of the lip on the backs, or just slap some 100 mph tape on my achilles region.
By the way, does anyone run with the barefoot style shoes made by Vibram (five finger shoes) or Merrell (trail glove)? I'm fairly new to them, but so far swear by them! I've heard of stress injuries caused by initial overtraining in them, so read up if you plan on using them. Besides the fitness perks of running in them, they are unofficially known to be a good therapeutic tool for people with bad backs, knees, and what not (IE, people who served careers in airborne units
). I highly suggest them!