Ready for Return?

New device can help recovering athletes and others determine when their bodies are healed

It’s the number-one fear of most recovering athletes and weekend warriors, and the top warning issued by physical therapists and other rehab professionals—don’t overdo it too soon, or you’ll find yourself right back here.

And since every individual is different, the sometimes-vague timelines handed out for recovery can add to the frustration. No one wants to hear that their hamstring will recover in 2–6 weeks, but sometimes a range of possibilities is the best we can offer—until now.

Ongoing research at the University of Wisconsin–Madison could potentially yield a device that may someday be able to tell an injured athletes—and their trainers and therapists—when the individual is ready to return to action or activity.

The research team is led by UW–Madison mechanical engineering professor Darryl Thelen and graduate student Jack Martin. Using a noninvasive, wearable device, the team is hoping to measure tension on an injured tendon while an individual is walking or running.

The possibilities for this device are endless, but they include unprecedented insight into the mechanics of human movement and motor control. As far as practical, everyday use in practice, the device can offer previously unattainable insight into the degree of healing that has taken place since an individual’s injury—and how far they still have to go.


A recent article in the journal Nature Communications offered further insight into researchers’ approach.

“Despite many decades of work, we still cannot readily assess the forces that muscles transmit during human movement,” the article read. “Direct measurements of muscle–tendon loads are invasive and modeling approaches require many assumptions. Here, we introduce a non-invasive approach to assess tendon loads by tracking vibrational behavior.”

The article goes on to explain that the speed of axial sound (or compression) waves in tendons varies with loading during movement. This is done through elasticity, however, meaning the information is provided by a measure of tissue stiffness rather than force exerted. Current measurement systems, however, lack the ability to measure tissue wave speeds during dynamic movement.

Professor Thelen, Martin, and their colleagues are attempting to overcome this challenge by developing a simple device that can be applied to the skin directly over the affected tendon. The team can then assess tendon force by observing the changes in vibration of the tendon during movement.

Once the team determined the best way to measure vibration, they set about interpreting the measurement to determine the stress within the tendon.

Perhaps the easy portability of the device is its best characteristic. A mechanical device lightly taps the tendon at a rate of about 50 times per second, initiating waves within the tendon at each tap. The device then determines how quickly each wave travels.

Thus far, the researchers have used the device to measure forces on the Achilles, patellar, and hamstring tendons. They can also determine the effects of altering gait—in other words, what happens when the user modifies the length of their stride or their speed.

These measurement may allow clinicians and therapists to plan treatments for patients recovering from injuries and dealing with musculoskeletal conditions.

“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.”

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