This band can collect sweat that is expelled around the wrist or ankle.
Cho Seung-won and Song Rui-hao
Elastic bands embedded with color-changing sensors can reveal how hard your muscles are working by measuring the acidity of sweat on your skin.
The device could not only improve worker safety in physically demanding jobs such as construction, but also help optimize training for athletes, the researchers say. John Rogers At Northwestern University in Illinois.
“If you see your pH dropping to a very low level, it’s best to stop exercising,” Rogers says, “otherwise you’ll end up with muscle soreness. But it will also let you know if you’re not exercising enough.”
During intense exercise, your muscles produce a chemical called lactic acid. As you continue to exercise and approach your physical limits, the concentration of lactic acid in your blood begins to spike. This can result in a burning sensation in your muscles, a sudden loss of energy, and extreme fatigue. The healthier you are, the longer and harder you can exercise before your blood lactate levels reach high levels.
For this reason, blood lactate levels in elite athletes are frequently monitored during training, and as this requires taking a finger-prick sample, many groups are working to develop non-invasive alternatives.
The solution Rogers and his team came up with is an elastic band with a series of tiny reservoirs where sweat accumulates at different intervals. Within each reservoir is a sensor that changes color depending on things like lactate concentration, or how acidic your sweat is. The results are read by taking a photo with a smartphone, or by attaching an electronic monitor.
The team tested the sweat monitor on 12 volunteers riding a stationary bike and found that while the lactate levels in sweat didn’t quite match up to blood lactate levels, the acidity of sweat did.
“We found that sweat pH is a better indicator of blood lactate concentration than sweat lactate concentration,” Rogers says.
But this only applied to sweat produced by skin close to exercising muscles, which in this case was monitored by a band worn around the ankle – measurements from bands worn on cyclists’ wrists did not reflect blood lactate levels.
“It’s not a solution to everything we want to know, but it’s providing us with a new type of data that wasn’t available before,” Rogers said.
A company he co-founded, Epicore Biosystems, already makes disposable patches that measure sweat loss and electrolyte levels to help prevent dehydration. Rogers says some companies are using the patches to monitor people who do physical labor in very hot and humid environments, as well as athletes.
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