What does your clothing say about you? Perhaps we should update that age-old question to “What does your clothing say to you about you?” Your wardrobe may have a lot to say about your physical condition if you wear smart sportswear that can detect exhaustion. Researchers at the Swiss university ETH Zurich have created electronic yarn that measures how a body moves, designed to guard against fatigue-related injuries.

While one may first think of athletics when considering fatigue-related injuries, these types of injuries are more common in the workplace. The U.S. Department of Labor (DOL) says worker fatigue significantly increases the risk of illnesses and injuries. The DOL says working 12 hours a day carries a 37% increase in the risk of injury. Compared to day shifts, injury and accident rates are 18% greater during evening shifts and 30% greater during night shifts.

So how can the yarn tell when a person gets fatigued? When they tire, people move differently. For example, a runner’s strides get shorter and less regular as exhaustion sets in. The yarn senses the changes in movements. Integrated into work clothing or sportswear, the stretchable sensor generates an electrical signal when extended. The stretching creates measurable fluctuations in the yarn’s charge, reflecting changes in body movements. ETH researchers created a model that uses this data to predict exhaustion.

The researchers tested the technology with runners who wore athletic leggings with embedded sensors. The researchers recorded the changes in the electric signals as the runners got more tired. These participants could see their exhaustion levels change on their smartphones, connected wirelessly to an antenna made of conducting yarn sewn into the leggings. Researcher Valeria Galli says, “Together, the sensor and antenna form an electrical circuit that is fully integrated into the item of clothing.”

Worried all of this tech sewn into clothing could make things bulky? Nope. The fabric doesn’t use any electronic components such as chips or batteries. Expansion caused by the wearer’s movement is all the power the yarn needs to generate an electrical signal. All unbeknownst to the wearer. Researcher Carlo Menon says, “Since the sensor is located so close to the body, we can capture body movements very precisely without the wearer even noticing.” And while the smart yarn is still in the lab stage, Menon adds, “Our goal is to make the manufacture of smart clothing cost-effective and thus make it available to a broader public.”