Temporary tattoo decals, which can be washed away or eventually wear off, have become a hot fashion accessory for people who want to experiment with looking like inked-up NBA basketball players, biker mamas or punk-rock musicians, without having to endure a tattoo needle. (There's also the advantage of not having to explain that flaming skull on your left shoulder to a nursing home attendant many years later.)
But a team of researchers at University of California-San Diego also has figured out a way to embed electrochemical sensors in temporary tattoos and use them to monitor the chemical balance and health of an athlete or exerciser. The Electrozyme temporary tattoo measures lactate, a chemical compound generated by muscles as they exert themselves, which is released in sweat. That information can be used to monitor muscular exertion, fatigue, hydration level, electrolyte balance and even the rate at which your muscles break down from exertion. The info is then relayed to a smartphone or other device to analyze your workout. It's a lot less intrusive and cumbersome than the previous method of measuring lactate, which required a person to take frequent breaks in a workout so that blood samples could be collected [sources: Kuriakose, Sacco, Jacobs School of Engineering].