Jun 8, 2018
Tapping Into Tendons

Thinking of a tendon like a guitar string could potentially help with gauging when it’s safe for athletes to return to activity. According to a news release from the University of Wisconsin, a group of researchers from the school are patenting a wearable device to measure tendon tension during activity.

The device measures this tension noninvasively by assessing vibrational responses when it is placed on the skin over a tendon. The tendon’s force is gauged by the vibrational characteristics during movement, similar to the way a guitar string’s tension—and resulting vibration—changes when it is plucked.

“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,” Darryl Thelen, PhD, Professor in Mechanical Engineering and Co-Director of the Neuromuscular Biomechanics Lab at Wisconsin, said.

The wearable developed by Dr. Thelen and his colleagues lightly taps the tendon 50 times per second. Two miniature accelerometers then gauge how quickly the resulting wave travels.

“The ultimate value of the shear wave tensiometers is to assess loads acting on individual muscle-tendon units during movement,” the researchers wrote in an article published by Nature Communications.

With a patent underway through the Wisconsin Alumni Research Foundation, the device would allow a relatively inexpensive and portable way of assessing tendon force. This could have a significant impact on rehabilitation by showing when people may be able to return from injury. In addition, it could be useful in orthopedics and ergonomics.

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

So far, the research team has measured forces on the patellar, hamstring, and Achilles tendons. The device has allowed changes in the tendon resulting from gait modifications to be measured. In other words, the researchers have been able to see how the tendon responds to adjustments in speed or length of stride—a big improvement for practical applications.

“Currently, wearables can measure our movement, but do not provide information on the muscle forces that generate the movement,” Dr. Thelen said.

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