Researchers in the University of Southern California are ready to use text messaging as a way to promote physical activity.

The research team plan tohook up 50 obese children to a "mobile body area network" that includes a heart rate monitor, GPS satellite navigation unit, a blood glucose meter, an accelerometer and a deviceto measure the electrical conductivity of their skin.

Each sensor is linked to a smart phone that sends the data to the University of Southern California team for them to interpret. For example if the heart rate is increased but the GPS system suggests the location hasn't change, it could be suggested that the children are dancing, amongst other things.

Importantly, the system will also detect the children performing sedentary activities which will trigger a series of text messages nagging the teenagers to get up and perform someexercise. Crucially, it will put teenagers in touch with other teenagers in the same position.

The researchers suggest this inventive way to tackle child and teenage obesity will promote activity in a way that this age group understand. With over 15% of all American teenagers classed as obese, the smart phone personal trainer will be not short of a market if the research works and a public device goes live.