A pair of smart sports leggings can tell when you've had too much exercise.

Researchers at ETH Zurich have developed an electronic yarn capable of precisely measuring how a person’s body moves.

Integrated directly into sportswear or work clothing, the textile sensor predicts the wearer’s exhaustion level during physical exertion and can alert a special phone app.

The innovation addresses the issue of exhaustion making people more prone to injury when exercising or performing physical tasks.

The ETH Zurich researchers, led by Professor Carlo Menon, Head of the Biomedical and Mobile Health Technology Lab, have tested their sensor by integrating it into a pair of athletic leggings.

Simply by glancing at their smartphone, testers were able to see when they were reaching their limit and if they ought to take a break.

This invention, for which ETH Zurich has filed a patent, could pave the way for a new generation of smart clothing. They point out many of the products currently on the market have electronic components such as sensors, batteries or chips retrofitted to them. In addition to pushing up prices, this makes these articles difficult to manufacture and maintain.

The researchers are working on turning their prototype into a market-​ready product.

Valeria Galli, a doctoral student in Menon’s group, explains: "We believe this is the future of wearables. You will wear your smart clothes very day without even noticing."

Professor Menon sees the potential applications stretching beyond sport to the workplace – to prevent exhaustion-​related injuries – as well as to rehabilitation medicine.

"Our goal is to make the manufacture of smart clothing cost-​effective and thus make it available to a broader public," Menon says."

HOW IT WORKS:

The team have studied how when people get tired, they move differently – and running is no exception: strides shorten and become less regular. Using their new sensor, which is made of a special type of yarn, the ETH researchers can measure this effect.

The innovation works thanks to the yarn’s structure: the inner fibre is made of a conductive, elastic rubber. The researchers wrapped a rigid wire, which is clad in a thin layer of plastic, into a spiral around this inner fibre.

"These two fibres act as electrodes and create an electric field. Together, they form a capacitor that can hold an electric charge," says Tyler Cuthbert, a postdoc in Menon’s group, who was instrumental in the research and development that led to the invention."

Stitching this yarn into the thigh section of a pair of stretchy running leggings means that it will stretch and slacken at a certain rhythm as the wearer runs.

Each movement alters the gap between the two fibres, and thus also the electric field and the capacitor’s charge.

Under normal circumstances, these charge fluctuations would be much too small to help measure the body’s movements. However, the properties of this yarn aid analysis.

"Unlike most other materials, ours actually becomes thicker when stretched," Cuthbert says."

As a result, the yarn is considerably more sensitive to minimal movements. Stretching it even a little produces distinctly measurable fluctuations in the sensor’s charge. This makes it possible to measure and analyse even subtle changes in running form.

Professor Menon highlights another benefit: "Since the sensor is located so close to the body, we can capture body movements very precisely without the wearer even noticing."

In previous research, Cuthbert and Menon observed a series of testers, who ran while wearing athletic leggings equipped with a similar sensor. They recorded how the electric signals changed as the runners got more and more tired.

Their next step was to turn this pattern into a model capable of predicting runners’ exhaustion which can now be used for their novel textile sensor.  But they add that ensuring that the model can make accurate predictions outside the lab will require "a lot of additional tests and masses of gait pattern data"."

To enable the textile sensor to send electrical signals wirelessly to a smartphone, the researchers equipped it with a loop antenna made of conducting yarn, which was also sewn directly onto the leggings.

"Together, the sensor and antenna form an electrical circuit that is fully integrated into the item of clothing," says Valeria Galli."

The electrical signal travels from the stretchable sensor to the antenna, which transmits it at a certain frequency capable of being read by a smartphone.

The wearer runs and the sensor moves, creating a signal pattern with a continuously fluctuating frequency, which a smartphone app then records and evaluates in real time. But the researchers say they "still have quite a bit of development work to do to make this happen"."