Stress fracture? Your foot hitting pavement may not be the main problem

It starts as a persistent and irritating pain in the foot or lower leg, then it gets more intense, maybe with swelling, and soon a runner knows she’s being sidelined by one of the most common running injuries: a stress fracture.

These tiny cracks in the bone can halt training for months or even end a sports season.

A segment of the multibillion-dollar wearables industry aims to save potential victims from this fate, but a Vanderbilt University engineering professor found a major problem: the devices are measuring the wrong thing.

Working with a local running club, an orthopedic specialist who advises the NFL Players Association and a team of Vanderbilt engineers, the team discovered that sensors only measuring the impact of the foot hitting pavement—which is what virtually all of them do—tell users little about the forces on bones that lead to stress fractures.

The research confirmed that the vast majority of force on the bone is actually from muscles contracting, not from the foot’s impact on the ground, a finding widely overlooked by both the wearables industry and many scientific studies.

The research offers the most clear and simple demonstration of the problems underlying the existing tools and prevailing methods for assessing bone stress and injury risk.

Wearable accelerometer and pressure sensors already on the market may help monitor bone stress injury risks, but only if they combine information about the ground reaction force and the force from muscles pulling against the bone.

The team performed the lab work that the study outlines, testing 10 runners over a range of speeds and slopes.

In several cases, lower ground reaction forces actually meant more stress on the tibia, a finding opposite of what most athletes believe and counter to how most existing wearables work.

The team said the combination of wearable sensors and new algorithms the team is developing gives a far better picture of bone stress, with the potential to help runners lower their chance of injuries.

The study is published in the peer-reviewed journal PLOS One.

Source: Vanderbilt University