Stress fractures are, unfortunately, a relatively common running injury. These injuries are the result of an unbalanced scale of activity at your bone; essentially stress (training) is occurring too fast for the body to rebuild the bone at an adequate rate.
There are a number of factors that can contribute to a stress fracture: anatomy, training error, recovery errors, running mechanics, poor nutrition... the list goes on. Here I’ll talk about a particular aspect of running mechanics that can affect your metatarsals (the toe bones that are in your foot and connect to your actual toes). The metatarsals are a common site for stress fractures in runners.
Researchers recruited 200 marathoners - all running the same race - to assess how pressure from running loaded onto their feet before and after the marathon. The runners were assessed barefoot and walking. While a running assessment would have been more accurate, the general effects of muscular fatigue can be derived from the walking assessment.
Results showed that the contact times (amount of time on the ground- so the higher contact time, the less efficient running and more force on the body) of the heel, mid-foot, and metatarsals all increased after the marathon, and that there was an increase in pressure specifically under metatarsal heads. Increased time on the ground and increased pressure both can contribute to stress fractures.
As expected at the end of the marathon, the leg muscles are extremely fatigued, and in this case researchers looked specifically at how that fatigue affects the foot. Unsurprisingly, the contact time increased due to fatigue and the amount of pressure under the metatarsal heads increased, because of poor pushing off the ground and poor landing (most likely due to muscle fatigue). Keep in mind that these results were found in uninjured marathoners, meaning it is probably a direct result of the grueling task of the marathon. It emphasizes the need for proper training; just imagine what the pressures and contact times would look like in a poorly trained marathoner!
Cat Fitzgerald, PT, DPT, CSCS
Nagel A Fernholz F Kibele C Rosenbaum D. “Long distance running increased plantar pressures beneath the metatarsal heads: a barefoot walking investigation of 200 marathon runners”. Gait & Posture. 2008; 27: 152-155