This Fitness Tracking Device Could Tell Exactly How We Power Our Activities

Even the most dedicated of athletes and weekend runners can suffer from the occasional pulled muscle or tendon. Those injuries can set runners or other athletes back several weeks of training while they recover or worse, require physical therapy. New technology could help athletes in figuring out if their tendons are back in performance-ready conditions. 

Mechanical engineering researchers from University of Wisconsin-Madison developed a noninvasive way to measure tension surrounding tendons. It can even track where the body naturally places tension when someone does activities like jogging, walking and running. 

Whenever people run, their leg muscles produce the movement needed to propel their bodies forward by pulling on tendons. Those bands of tissue keep muscles attached to skeletons. They're also one of the trickiest parts of the body for athletes to keep in check. Tendon injuries often seem sudden and can be painful -- particularly a tear in the Achilles tendon. However, what seems like a giant tear is often a build up of smaller tears over time. 

By being able to monitor exactly how much tension is being put on a tendon, researchers can make sure athletes don't keep building up microtears and a path to a larger injury. 

Mechanical engineering professor Darryl Thelen and grad student Jack Martin developed the tiny device meant to go deeper than traditional fitness wearables and trackers. 

“Currently, wearables can measure our movement, but do not provide information on the muscle forces that generate the movement,” said Thelen, whose work is supported by the National Institutes of Health.

Thelen and Martin's device can be mounted on the skin over a tendon in a noninvasive manner. The device monitors tendon force by checking how much the tendon vibrates and the characteristics of those vibrations during varying degrees of stress. 

“We’ve found a way to measure the vibrational characteristics — in this case, the speed of a shear wave traveling along a tendon — and then we went further and determined how we can interpret this measurement to find the tensile stress within the tendon,” Thelen said.

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Thelen likened the movement to a guitar string. Whenever the tension on a guitar string changes, so does the vibrations on the string. This allows the team to track what happens to a particular tendon whenever a runner changes their pace or gait or stride. 

The team said this particular device could have applications beyond just those looking to advance their running careers. Overall, the engineers hope the technology could help biologists and medical practitioners better understand human motor control. It could also help out orthopedics, rehab services, office ergonomics and sports medicine. 

“We think the potential of this new technology is high, both from a basic science standpoint and for clinical applications,” Thelen says. “For example, tendon force measures could be used to guide treatments of individuals with gait disorders. It may also be useful to objectively assess when a repaired tendon is sufficiently healed to function normally and allow a person to return to activity.”

The team published their findings and more details about the device in the most recent issue of Nature Communications from April 23.