Tendon-tapping wearable could help doctors understand human movement

Engineers have developed a wearable device to help measure when people are ready to return to physical activity after tendon injuries.

A team of researchers at the University of Wisconsin-Madison created the non-invasive device, which lightly taps the tendon 50 times per second, and then uses two miniature accelerometers to measure how quickly it moves.

Using this information, researchers are able to determine how the vibrational characteristics of the tendon change during movement. It is similar to a guitar string, where the vibrational response changes depending on the amount of force applied when the string is plucked.

"We've found a way to measure the vibrational characteristics – in this case, the speed of a shear wave travelling along a tendon – and then we went further and determined how we can interpret this measurement to find the tensile stress within the tendon," explained Darryl Thelen, a mechanical engineering professor at the university.

With graduate student Jack Martin, Thelen has used the device to measure forces on the Achilles tendon, as well as the patellar and hamstring tendons, looking at how they behave differently when users modify their gait by changing step length or speed.

By measuring how muscles and tendons move within the body, the researchers hope the device will enable doctors to plan more effective treatments for patients with musculoskeletal diseases and injuries.

“We think the potential of this new technology is high, both from a basic science standpoint and for clinical applications,” said Thelen. “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.”