If you were lacking a bit of motivation to go to the gym, this will help inspire you. Not only does working up a sweat eliminate toxins, but it can not generate a charge. That’s right… you can become your own battery charger.

While the technology is still in its early stages of development, it looks incredibly promising in the real of “people power.”

“Our device is the first to use sweat. It’s a proof of concept,” said Dr Wenzhao Jia of at the University of California, San Diego, who gave details of her method in the journal Angewandte Chemie.

“At the moment the power is not that high – only four microwatts. But we are working on enhancing it so it can power small electronic devices.”

Interestingly, her team did not set out to build a biobattery. Their aim was to make a wearable monitor for lactate.

Athletes in training measure their lactate levels to evaluate their work-rate and fitness.

But monitoring it can be inconvenient as it typically relies on taking blood samples.

To develop a faster, more comfortable test, Dr Jia printed a lactate sensor onto temporary tattoo paper.

“I’ve worn it myself – you don’t even feel it. It really is like a tattoo,” she told BBC News.

“It’s not just for athletes. Most people who exercise want to know how they can improve their workout.

“We can measure our heart rate – but if you combine that physical feedback with chemical data you get a much more comprehensive view of your exercise status.”

Her team then went a step further, turning the sensor into a sweat-powered biobattery.

They incorporated an enzyme that strips electrons from lactate, generating a weak electrical current.

When volunteers on an exercise bike wore the tattoo, they were able to generate up to 70 microwatts per sq cm of skin.

This is a very promising prospect for creating a phone/iPod charger that will keep your phone powered up while you gym.

Check out more details at BBC.