Is a stress fracture of the calcaneus or heel bone due to the impact loads from heel striking or from the shear stress through the bone from the pull of the Achilles tendon? If I was to ask this question on a barefoot or minimalist forum, what answer do you think I would get? Of course, it will be a resounding ‘heel striking’! How do they know that? Is it because it is true or is it because they want to believe it is true? Wishful thinking does not make something true!
Calcaneal stress fractures are not very common, so no one can claim to have any great clinical experience in dealing with them (I have probably only seen a dozen or so in the last 30 or so years¹). The comments in a few of the standard textbooks that I checked is that they are due to heel striking, as it does make intuitive sense that the repeated impacts can overload the bone and cause a stress fracture if the bone is not given time to adapt to the loads. However, despite these comments, there has been a number of recent published reports of a stress fracture of the calcaneus in forefoot strikers and minimalist runners. For example, Salzer et al reported one in a minimalist runner and Reuteman et al reported another at the APTA conference. If you check around social media, blogs and forums for barefoot and minimalist runners, you do see an increasing number of reports of calcaneal stress fractures (see this for comments). Some comments I have seen are from very perplexed minimalist runners confused as to how can they get a calcaneal stress fracture if they were forefoot striking.
What now appears to be obvious is that if heel striking is “the cause“, then why are there an increasing number of these reports of calcaneal stress fractures in forefoot strikers and minimalist runners? Maybe the impact of heel striking is not the cause, but the cause is a shear stress going through the calcaneus from the pull of the achilles tendon. Maybe the foot strike pattern has nothing to do with it.
I go where the evidence takes me until convinced otherwise.
¹If my memory serves me correctly, all of those were probably in heel strikers. This was probably deceptive as most runners are heel strikers, so the assumption was that they were due to the impact loads of heel striking.