Scientists in the United States have developed a flexible microfluidic device that easily sticks to the skin and measures sweat levels to show how the wearer's body is responding to exercise.

The low-cost device, which can quickly analyze key elements such as lactate, pH or glucose levels and let the user know if they should stop or change their activity, could also in future help diagnose and monitor disease, the researchers said.

"Sweat is a rich chemical broth containing a number of important chemical compounds with physiological health information," said John Rogers, a professor at Northwestern University in the United States who led the development of what he called a "lab on the skin."