Today's youngsters are not as fit as those from a decade ago as their lifestyles are more sedentary, research shows.

Children's fitness in the UK has declined by eight per cent, while the worldwide average is four per cent, the study published in the Archives of Disease in Childhood reveals.

The researchers warn that falling activity levels may be worse for kids' health than being overweight and call on schools to do more.

"Children are not doing as much physical activity as before," said Dr Gavin Sandercock from the Centre for Sports and Exercise Science at the University of Essex, who carried out the study.

"They don't climb trees any more, they don't use their bikes any more," he added.

Children are using most of their spare time to play computer games or watch TV, Dr Sandercock continued, pointing out that Britain has more computers per household than anywhere else in Europe and that youngsters could be spending a quarter of their waking lives in front of screens.

"The drop in fitness is very, very large."

The Department of Health says that in order to turn the tide on obesity for good, children need to be active for 60 minutes a day.

Concept2 is working with schools around the country to promote indoor rowing as an accessible sport for all youngsters to get involved in.

Its Where To Start guide highlights the fact that indoor rowing can be used to teach about and encourage kids to take part in a healthy lifestyle and benefit their all-round wellbeing.