Teenagers worldwide are jeopardising their health by failing to get enough exercise to reduce their risk of obesity and cardiovascular diseases.
A World Health Organisation-led study, based on data from 146 countries, found that more than 80 per cent of adolescents did not meet a WHO recommendation for at least an hour of physical activity a day.
"Four in every five adolescents do not experience the enjoyment and social, physical, and mental health benefits of regular physical activity," said Fiona Bull, a specialist in activity and health and a co-author of the work.
She urged policymakers worldwide to "act now for the health of this and future young generations".
Globally, girls are more inactive than boys, with 85 per cent of girls and 78 per cent of the boys surveyed failing to hit the daily exercise target.
The study looked at adolescents over 2001-2016 and its authors say there is nothing to suggest the pattern has improved since.
Leanne Riley, a WHO expert on non-communicable diseases and co-author, said sedentary behaviour may be due in part to a recent rapid expansion in digital technology that means young people spend more time on phones, tablets and other screens.
"We've had this electronic revolution that seems to have changed adolescents' movement patterns and encourages them to sit more, to be less active, to drive more, walk less, (and) be less active in general," she told a news briefing.
Country by country, the percentage of teenagers not meeting the goal ranged from 66 per cent in Bangladesh to 94 per cent in South Korea.
Australian Associated Press