Smart Yarn That Tracks Muscle Activity In Body

Sunghoon Lee's job as a materials engineer at RIKEN allows him to combine his love of sports with his passion to pursue research. "Personally, I'm interested in baseball," says Lee, whose research team previously developed a fingertip sensor to monitor the pitching motion of baseball players.

Now the team has developed a thin, comfortable textile that is intended to help monitor health, analyze sports performance and inform rehabilitation¹.

Lee, who is based at the RIKEN Center for Emergent Matter Science, says the technology can monitor muscle activity across the body with high precision during dynamic movement. It has the potential for clinicians to better track recovery, athletes to optimize their movement and researchers to improve understanding of biomechanics.

The textile uses electromyography (EMG), which measures tiny electrical signals generated when muscles contract, revealing how they activate during movement.

However, since the signals from muscles are very weak-just a few millivolts-they are easily swamped by electrical noise. This problem has hindered EMG from being widely adopted.

Noiseless measurements

Conventional EMG systems employ relatively bulky amplifiers or wireless modules placed close to muscles, which add weight and restrict movement. But the new flexible EMG textiles should make it much easier to acquire signals over the whole body, says Lee.

A critical component of flexible EMG textiles is an intrinsically stretchable electromagnetic conductor that senses the muscle signals, Lee explains. For the study, Lee's team used commercially available silver-plated nylon wrapped around a polyurethane core, but they are now developing their own stretchable wiring.

However, larger stretchable systems using these types of conductors suffer from electrical noise arising from physical contact, motion or electromagnetic fields from nearby electronics.

These factors can generate a surprising amount of noise, says Lee, "so we needed a good wiring shield system to suppress the noise."

To insulate the technology from outside interference, Lee's team fabricated a yarn with a triple-layered structure. A conductive fiber at the core carries the signal and is surrounded by a layer of polyurethane insulation.

The outer shielding layer is made by embedding silver flakes-tiny, highly conductive particles-inside a fluoroelastomer matrix, which is a rubber-like polymer. The elastomer provides flexibility, while the silver flakes maintain conductivity by forming an overlapping network that stays connected even when stretched. High conductivity allows the shield to absorb and redirect electromagnetic noise away from the signal wire.

This combination results in a continuous, protective layer that stretches without breaking, preserving electromagnetic shielding even when stretched to 120% of its original length.

Knitted devices

The researchers then integrated the yarn into a knitted textile that included electrodes and wireless EMG modules to interpret and relay the wearer's muscle signals. The modules are worn on the waist to avoid hindering limb movement.

In testing, the yarn stretched enough for most joint movements, while maintaining shielding integrity. It also exhibited good suppression of noise. "Even when someone pressed on the wiring, the signal stayed clean," Lee says.

In shoulder range-of-motion tests, the shielding was particularly critical to signal acquisition during passive movements assisted by another person, such as one might see in a rehabilitation facility. This was because without the shielding, electrical noise from the touch of the other person obscured the EMG signal.

Subsequent testing of muscles in the lower body demonstrated the system's capability during dynamic activities. Eight electrodes were used to effectively monitor four lower-body muscle groups during jumping, cycling and running.

The garment itself resembles thin sportswear. "It's a bit like a thin inner layer," Lee says. "So you actually feel quite comfortable."

Repeated wear tests showed no significant signal degradation, although washability remains a challenge.

"The textile's ability does not change after a few wears," Lee says. "However, if washed, this version could be easily damaged. So we need to find a way to further protect the shielding layer."

Tailoring the garment

Next steps for the researchers include personalizing the garment. A one-size-fits-all garment is not ideal for accurate EMG monitoring because muscle positions vary between individuals. Current prototypes work for average body shapes, but precision measurements for all body types will require tailoring.

"We're now interested in how to 100% personalize the textile for a specific person," Lee says.

He envisages 3D scanning each wearer's body and then digitally designing and printing electrode placement and wiring paths to match their anatomy. This would ensure electrodes align perfectly with target muscles, improving signal quality and comfort.

It's a step toward custom-fit smart garments, similar to bespoke athletic gear, but with embedded electronics.

The team also plans to improve sweat management and explore biodegradable elastomers and carbon-based conductors for sustainability, says Lee.

He believes that textiles are the ultimate platform for wearable electronics. Clothing naturally covers large areas, enabling full-body monitoring, he explains. Textiles also offer comfort, stretchability and seamless integration into everyday life.

"We believe textiles are a great platform and now we have tackled the noise issue, which was a key problem," Lee says. "This is a highly useful system that can be used to measure multiple activities."

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Reference

• 1. Lee, S., Takano, K., Yukita, W., Tagawa, Y., Sun, L. et al. A body-scale textile-based electromyogram monitoring system with coaxially shielded conductive yarns. Smoking affects gut immune system of patients with inflammatory bowel diseases by modulating metabolomic profiles and mucosal microbiota. Science Advances 11 eadx4518 (2025). doi: 10.1126/sciadv.adx4518

About the researcher

Sunghoon Lee