We forgot to mention this article by Davis and Yavuz on plantar shear forces: Plantar shear stress distribution in athletic individuals with frictional foot blisters. The article concludes that “biomechanical interaction on the plantar surface of a blister-prone person is different from that of individuals who are less prone to the problem.” The biomechanics of athletes prone to friction blisters may induce greater shear forces on the plantar surface.
The full article is $12 from the Journal of the American Podiatric Medical Association. (Follow the link above.) Not a bad deal in this day of $35 to $40 journal articles.