Wearable devices are being touted as a way to help runners avoid those painful stress fractures but a new study says they may not be doing the job.
Stress fractures in the foot, those tiny cracks in the bone, can sideline runners for months and even end a sports season. The symptoms start slowly, with persistent pain. The pain intensifies and sometimes there is some swelling.
You haven’t fallen, or tripped, so what’s causing it? Conventional wisdom holds that it’s all that foot-pounding on hard pavement. A segment of the emerging 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.
Karl Zelik, an assistant professor of mechanical engineering at Vanderbilt University, says wearables that only measure 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.
Zelik says most of the 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.
“We looked through the recent scientific literature, and we found that more than 50 scientific publications each year report or interpret their results based on this incorrect assumption that ground reaction force is representative of internal structure loading — the stress on bones and muscles inside the body,” said Zelik, a former college track and field standout. “Measuring ground reaction force may be convenient, but it’s the wrong signal.”
Zelik says 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.
Research compiled by Zelik and his team appears in the peer-reviewed journal PLOS One.