When I run barefoot on pavement lately, my left foot feels less perfect than my right foot. On pavement, it seems to pick up more twisting friction at lift-off, and has a slight amount of landing friction, kinda like I am gliding forward into the landing with that foot. Before relearning to run barefoot, I had left ankle sprain issues, which was one of the factors that led me to run barefoot. Also, the extra friction thing only started this summer, around the same time I had some (now improving) Achilles tendon / PF issues. Perhaps it is a contributing factor. Also, I have been more "up on my toes" than ever before this summer - an evolution, this being my 3rd running barefoot. Last week, I noticed I do not have these twist and landing friction issues on grass. (Yeah, completely different surface features, but it is more than that. Read on...) So within the last week I have analyzed what I do different on grass as opposed to roads. I ran on that grassy strip between the road and the sidewalk, then would switch to the road or sidewalk, then back to the grassy strip. Here is what I can tell: On grass I twist my upper body slightly more when my left foot lands and lifts. That is to say, that my left shoulder travels a little more forward and back - It is a matter of about an inch difference each way. I don't know why this is. When I carry it over to the road, then I have no extra friction. But I still have to think about it. In a few weeks it will probably become autonomic. Perhaps the body twisting compensates for the foot twisting? I could not be sure of the biomechanics without complicated high speed digital imaging and computer footstrike analysis, but it feels right to me.
Vertical torso, but allow it to twist. Hips rotate with your legs, shoulders rotate with your arms."