Four in five 11- to 17-year-olds around the world are not taking enough physical exercise, according to the first such analysis. The World Health Organization says children's health is being damaged as well as their brain development and social skills. It says failing to take the recommended hour a day of exercise is a universal problem in rich and poor countries. Boys were more active than girls in all but four of the 146 countries studied.
What exercise counts?
Pretty much anything that makes the heart beat more quickly and the lungs breathe harder.
It could include:
The target is 60 minutes of moderate-to-vigorous exercise a day.
"I don't regard it as a ridiculous target," the WHO's Dr Fiona Bull says.
"It is evidence-based to establish good health and development."
The difference between moderate and vigorous is you can still have a natter while doing moderate exercise but vigorous exercise would leave you too breathless to chat.
The main reason is health, both now and in the future.
In the short term, being active means:
fitter heart and lungs
stronger bones and muscles
better mental health and wellbeing
"Active adolescents are likely to be active adults," the WHO's Dr Regina Guthold says.
And over a lifetime being active can decrease the risk of many diseases, from heart attacks and stroke to type-2 diabetes.
In that time, inactivity in boys fell from 80% to 78%, while in girls it stayed at 85%, according to the study.
What do experts think?
Dr Mark Tremblay, from the Children's Hospital of Eastern Ontario Research Institute, in Canada, says: "The electronic revolution has fundamentally transformed people's movement patterns by changing where and how they live, learn, work, play, and travel, progressively isolating them indoors, most often in chairs.
"People sleep less, sit more, walk less frequently, drive more regularly, and do less physical activity than they used to."
Prof Russell Viner, the President of the Royal College of Paediatrics and Child Health, says the findings are "concerning".
"Children who are more active have better health and wellbeing and generally do better in school," he says.
"We should be making it easier for children and young people to have active and healthy lives - this is easier said than done."
To offer you a better browsing experience we are using cookies.
Leaving the site will be interpreted as not accepting the policy.
You can always revoke this authorization by changing setting in your browser and deleting the cookies.