Teenagers in South Korea are the laziest in the world, according to a global study.
A country-by-country breakdown of physical activity levels has revealed just one in five 11 to 17-year-olds get as much exercise as they need to stay healthy.
In some countries, led by South Korea and including the Philippines, Cambodia and Sudan, more than 90 percent of teenagers are inactive.
Meanwhile the US outperformed almost every country on Earth with just 72 percent of children inactive – higher only than Bangladesh, Slovakia and Ireland.
Experts said the statistics were 'concerning' and that encouraging exercise is vital for tackling the most dangerous child health concern – obesity.
'Children who are more active have better health and wellbeing and generally do better in school,' said Professor Russell Viner, president of the Royal College of Paediatrics and Child Health.
Researchers from the World Health Organization have produced the report which outlines worrying levels of adolescent laziness all over the world.
It said all children between the ages of 11 and 17 should do at least an hour of exercise every day, but the in reality only around 19 percent manage it.
In the country with the most active children – Bangladesh – still only a third of children (33.9 percent) hit that target, according to the study of 1.6 million youths.
Girls were less active than boys in all but four out of 146 countries, the WHO revealed, with only Tonga, Samoa, Afghanistan and Zambia bucking the trend.
buck the trend: 反潮流，扭转潮流
Study author Dr Regina Guthold said: 'Urgent policy action to increase physical activity is needed now, particularly to promote and retain girls’ participation in physical activity.'
Dr Guthold and her team said physical activity was important for developing young people's hearts, lungs, bones and muscles and keeping them a healthy weight.
In the UK one in three children are overweight before they finish primary school and even fewer (18 percent) eat five or more portions of fruit and vegetables each day.
NHS figures last month showed 24.6 percent of 10 and 11-year-olds are obese in England, while 34.3 percent are overweight to some degree.
According to its Centers for Disease Control and Prevention, the US's childhood obesity rate is 18.5 percent and affects some 13.7 million young people.
In a comment published alongside the study, in the journal The Lancet Child & Adolescent Health, a Canadian researcher said modern society is to blame for inactivity.
Dr Mark Tremblay, from the Children's Hospital of Eastern Ontario Research Institute, wrote: 'The changing world is changing people, with movement being one of the clearest indicators of this change.
'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 (e.g., houses, schools, workplaces, and vehicles), most often in chairs.
'People sleep less, sit more, walk less frequently, drive more regularly, and do less physical activity than they used to.
'They are increasingly moving from one country to another, from rural to urban areas, from outdoors to indoors, from standing to sitting, from walking to driving, and from active play to digital play.
WHERE DO CHILDREN DO THE LEAST EXERCISE?
South Korea (94.2% of children are active for less than one hour a day)
New Zealand (88.7%)
WHERE DO CHILDREN DO THE MOST EXERCISE?
Bangladesh (66.1% of children are active for less than one hour a day)
United States of America (72%)
Republic of Moldova (75.7%)