For athletes suffering from serious tendon injuries, the rehabilitation process is painfully slow and far from risk free. One slip could undermine months of physiotherapy and put the process back to square one.
In part, this is because physiotherapy is based on prescriptive timelines rather than real-time monitoring of muscles and tendons. Researchers at the University of Wisconsin–Madison are developing a wearable to address that problem. Their new approach was set out in a paper published on April 23rd in the journal Nature Communications.
Measuring muscle force
Muscles enable us to move by exerting force upon our tendons. These bands of tissue connect muscles to the skeleton. “Currently, wearables can measure our movement, but do not provide information on the muscle forces that generate the movement,” says UW–Madison mechanical engineering professor, Darryl Thelen, lead researcher on the project.
Alongside graduate student Jack Martin, Thelen has devised a wearable that’s able to non-invasively measure tendon tension while an athlete is walking, running, or performing specialised physio exercises.
The device is mounted on the skin above the tendon. It measures the force exerted by the muscles by tracking the vibrational characteristics of the tendon as it takes on a load.
This phenomenon, the researchers say, is comparable to what happens when you pluck a guitar string: “The speed of the wave traveling along the string, and thus the vibration frequency, is related to the tension, or force, applied to the string,” they said.
“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,” added Thelen.
Clinical applications
The technology has the potential for a far-reaching impact. Measuring tendon activity in real time could give physiotherapists insight into motor control and the mechanics of human movement, with applications ranging from orthopaedics to rehab and ergonomics.
“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.”
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Yet more evidence that 2018 is shaping up to be the year of the personal health sensor, with new specialist devices, e-skin developments, and low-cost wearables, and the discovery that some consumer devices, such as the Fitbit and Apple Watch, can run specialist applications that can help diagnose heart complaints, diabetes, and more, by monitoring electrical and chemical activity.
Low-cost, non-invasive wearable sensors have even been developed for the teeth, to help monitor diet.
Behind many of these research programmes are big data analytics and AI, using the technologies’ ability to detect and analyse underlying patterns in data, behaviour, or signals from the body, and link these – via clinical trials and anonymised health records – with medical conditions.