You might consider changing your walking style. Children most often walk middle-footed or even forefooted when barefoot, and this is considered the most natural way of moving. Setting down the rear end of the foot before lowering it completely is a necessity when wearing normal shoes, but it's not natural. Before I adapted fully to the Vibrams my soles even started burning on the heels when I ran longer distances. I read that it's best to just set down the whole foot plainly (or forefoot first) when walking/running with Vs.