A sweat monitor can tell when you're exercising too hard

Elastic bands with built-in color-changing sensors can determine how hard muscles are working by measuring the acidity of sweat on the skin.

According to experts, the device could be used to improve worker safety in physically demanding jobs, such as in the construction industry, and to help athletes optimize their training. John Rogers at Northwestern University in Illinois.

“If you see your pH drop to a very low level, it would be a good idea to stop training,” says Rogers. “Otherwise, your muscles will be sore. But it will also tell you if you haven't been training enough.”

During high-intensity exercise, muscles produce a chemical called lactate. During prolonged exercise, levels of this substance in the blood begin to rise sharply as people approach the limits of their physical endurance. This can lead to a burning sensation in the muscles, a sudden loss of energy, and extreme fatigue. The fitter people are, the longer and more intensely they can exercise. before the blood lactate level rises to high levels.

For this reason, blood lactate levels in elite athletes are often monitored during training. This requires fingerstick sampling, so many groups are trying to develop a non-invasive alternative.

The solution Rogers and his team came up with is an elastic band with a series of tiny reservoirs that fill with sweat at different intervals. Inside each reservoir is a sensor that changes color depending on factors like lactate concentration or sweat acidity. The results are read by taking a photo with a smartphone or by attaching an electronic monitor.

When sweat sensors were tested on 12 volunteers exercise On bicycles, the team found that sweat lactate levels did not match blood lactate levels, but sweat acidity did.

“We found that sweat pH was a better indicator of blood lactate concentration than sweat lactate concentration,” Rogers says.

However, this only concerned sweat from the skin around the working muscles, which in this case was monitored using tapes placed around the ankles. Measurements using tapes on the cyclists' wrists did not reflect the level of lactate in the blood.

“It doesn't answer all the questions we want to know, but it does provide a new type of data that wasn't available before,” Rogers says.

Epicore Biosystems, the company he co-founded, already makes disposable patches that measure sweat and electrolyte levels, which it says can help prevent dehydration. Some companies are using them to monitor people doing physical work in very hot and humid conditions, as well as athletes, Rogers says.