Technology gets the blame for a lot of health problems: cars make you lazy, video games make you violent and MP3 players make you deaf. Now researchers at the University of Southern California are hoping to prove that mobile phones, at least, can have a positive effect. They plan to connect 50 obese teenagers to a battery of sensors and use mobiles to text the kids thin.

Each child will be hooked up to a “mobile body area network” that includes a heart-rate monitor, accelerometer, GPS satellite navigation unit, blood glucose meter and a device to measure the electrical conductivity of their skin.

Each sensor is linked to a smartphone that sends the data to the university’s computers. Here, software decides what all the data means. If the heart-rate monitor and accelerometer show motion but the GPS is stationary, the system might decide that the teenager is dancing, whereas low physical readings combined with a high skin conductivity could mean a stressful homework test — or just an exciting TV show.

The important bit is that the system can detect lethargy — and correct it.

Too much sitting around will trigger a stream of text messages either nagging the teenager to take some exercise or putting them in touch with other participants for group activities.

This, say university researchers, could provide a new incentive to getting fit, if and when it is rolled out commercially: a sort of electronic conscience that sends out nice reminders when you’re not fulfilling your new year resolution to eat less and exercise more. With one in six American teenagers classed as overweight or obese, the virtual personal trainer will have no problem finding a market.

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