A new study published in the Journal of Foot and Ankle Research found that arch height decreased in runners after running a half marathon. The study measured the navicular height of runners before and after a half marathon race. After the race, runners’ arches were 5 mm lower than they were at the start.
The authors of the study were not exactly sure what caused the change in arch height. They speculated that it may be a combination of muscle fatigue and repeated stretching of the ligaments that support the arch. The study did not measure how long it took after running for the runners’ arches to return to their pre-race height.
Navicular height is a common way to measure the size of the arch. The navicular bone helps form the arch on the inside of the foot.
So basically this study showed that after running a long distance the arches in our feet tend to flatten out. There a couple of things I find interesting about this study.
First, this study illustrates the potential of the arch to change shape. Now, the flattening may have been from stretching of the connective tissue holding the bones of the foot together, fatigue in the muscles that support the arch, or some combination of both factors.
If it is indeed muscular fatigue causing these changes, then it makes sense that strengthening the muscles that control pronation could produce positive changes in the height of the arch.
These findings may also shed light on the mechanism of some running injuries. The amount a runner pronates may increase during a long run which would then likely result in a change in their running form. These changes could subject the runner’s body to different stresses and increase their injury risk. Assessing a runner’s form in a non-fatigued state may not be a good indicator of what happens over the course of a run.
This is one of the difficulties in predicting a runner’s risk of injury. Most injury risk studies don’t evaluate a runner’s mechanics after a run. This study shows that we can’t assume a runner will be running with the same form throughout the duration of a long run.
For runners, I think the important message here is to be careful training past the point of fatigue. For people with flat feet and pronation problems, this study is another reason to start strengthening those arch supporting muscles.