Joe Maller.com

Barefoot running stress fractures: A theory

Stress fractures are ridiculously common among runners, but this post will specifically address the apparent rash of metatarsal stress fractures afflicting minimalist and VFF runners, including myself.

First off, the term “barefoot” needs to be clarified. In every case I’ve found the runner wasn’t actually barefoot. We were all running in minimal shoes: Vibram FiveFingers, Nike Frees or something similar.

I noticed several consistencies among runners’ accounts of their injuries:

  1. Running in Vibram FiveFingers or other minimalist shoes, not barefoot.
  2. Running faster than normal (races, speed work, or just having too much fun)
  3. Mostly older than 35 years old (past the age of peak bone mass)
  4. Injury occurs months after transitioning to minimalist or barefoot running

So here’s my theory:

The majority of stress fractures affecting minimalist runners are not impact-related, but rather result from overloading weak metatarsals with increased toe push-off. These injuries arise several weeks or months after switching to natural running because the runner’s muscles strengthened faster than their bones.

Metatarsals are most susceptible to injury because they’ve been immobilized and weakened by conventional shoes. The second metatarsal, being the longest, endures the most stress.

Skin protection offered by VFFs and minimal shoes likely increases the risk of injury, friction on bare toes would have limited activity before the bones could have been hurt.

Barefoot & Minimalist stress fractures: A theory Pushing off with the toes places an enormous amount of stress across the midfoot. With the metarsals acting as a lever, the forefoot is pulled down and back against the ground with enough force to throw our full body weight forward. This motion also creates substantial sliding friction under the toes. Bare toes, no matter how calloused, would not be able to withstand this friction and would limit activity before bones could be overstressed.

Anecdotal evidence

As I’ve been researching this, I’ve found a lot of stories similar to my own:

If you’re a near-barefoot, minimalist or VFF runner and have suffered a stress fracture, please email me or leave a note in the comments.