The sweat monitor could reveal when you’re working out too hard

Bands equipped with color-changing sensors can reveal the intensity of muscle work by measuring the acidity of sweat on the skin.

The device could be used to improve the safety of workers in physically demanding jobs, such as construction, and to help athletes optimize their training, he says. John Rogers at Northwestern University in Illinois.

“If you see your pH drop to very low levels, it would be a good idea to stop working out,” Rogers says. “Otherwise you end up with sore muscles. But it will also tell you if you haven’t been working out enough.”

During high-intensity exercise, muscles produce a chemical called lactate. With continued exercise, blood levels of this chemical begin to rise as people approach their physical endurance limits. 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 harder they can exercise. before blood lactate reaches high levels.

For this reason, blood lactate levels of elite athletes are often monitored during training. This requires obtaining samples from a finger prick, so many groups are trying to develop a non-invasive alternative.

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

When sweat monitors were tested on 12 volunteers on exercise bicycles, the team found that sweat lactate levels did not correspond well to blood lactate levels, but that sweat acidity did.

“What we found is that sweat pH is a better indicator of blood lactate concentration than sweat lactate concentration,” Rogers says.

However, this was only the case for sweat from the skin near the working muscles, which in this case was monitored by bands around the ankles. Measurements from bands on the cyclists’ wrists did not reflect blood lactate levels.

“It’s not a solution to everything you want to know, but it provides a new type of data that wasn’t available before,” Rogers says.

A company he cofounded called Epicore Biosystems is already making disposable patches that measure sweat loss and electrolyte levels, which the company says can help prevent dehydration. These are used by some companies to monitor people exercising in very hot and humid conditions, as well as by athletes, Rogers says.