As in there is no difference in height from the heel to toe when we're talking running shoes. It seems the buzz around the running world now is the minimal / barefoot running experience and it seems like all the major shoe companies have started producing a shoe just for that type of running. I'm not sure that I'll ever get on board with the barefoot trend but I did just recently purchace a pair of Altra Zero Drop trail shoes called the Altra Lone Peak. They are strictly a trail shoe with sticky lugs and a rock guard that protects your feet from protruding roots and rocks and anything else that you might be running over on the trails. The zero drop promotes a more natural running gait, better running posture and form and forces a forefoot strike, (which I conciously try to do all the time) and when on trails you want to be running on your forefoot opposed to your heels and this is just what this shoe does. It's going to take a few weeks to get used to running in them since I have been running in traditional 6-11 mm drop shoes since the 80's, so I expect to have some sore calf muscles and tendons for a bit. I did run on them for a short distance last night and I must say on the grass and sides of the road they feel pretty neat, but on the road it was a much different feeling, much like running in slippers but with stability and cushion. I will rotate them in for a few miles each time I run on the trails taking my other shoes with me so I can run back to the car and change until I can soley run in the Altras. I'm looking forward to being able to race in them on the 14th in Brecksville so I'll give a recap afterward.