Playing "active" computer games on consoles such as the Nintendo Wii is no substitute for playing real sports, warn UK experts.
Nintendo Wii is topping Christmas' "must have" list
Young people are advised to take an hour of moderate to vigorous exercise each day, such as playing football.
The energy used when playing active Wii Sports games is not of high enough intensity to contribute towards this, a British Medical Journal study found.
Wii players used only 2% more energy than players of regular computer games.
This year, the Nintendo Wii is topping Christmas' "must have" list. Even at the height of summer, almost 90,000 Wiis a week were being sold across Europe.
Time spent in front of television and computer screens has been linked to physical inactivity and obesity.
Beating the bulge
However, the new generation of wireless-based computer games is meant to stimulate greater interaction and movement during play.
They require the player to move their whole body rather than simply press buttons or move a joystick.
Professor Gareth Stratton and colleagues at Liverpool John Moore's University decided to measure whether this extra activity would be enough to count as exercise.
They asked six boys and five girls aged 13-15 to play Nintendo Wii (active) and Microsoft XBOX 360 (inactive) computer games for an hour.
Playing Wii Sports games increased energy expenditure by 60kcal (250 kJ) per hour compared with playing the other console.
But in real life terms, this would in no way be enough to suggest active computer game playing could be a substitute for doing real sport, say the authors.
"These increases were of insufficient intensity to contribute towards recommendations for children's daily exercise."
But they added: "Although this figure is trivial it might contribute to weight management.
"New generation computer games stimulated positive activity behaviours - the children were on their feet and they moved in all directions.
"Given the current prevalence of childhood overweight and obesity, such positive behaviours should be encouraged."