Only one in 30 children does the recommended amount of daily physical activity, new research suggests.
Guidelines from the Chief Medical Officer say people aged five to 18 should do at least 60 minutes of "moderate-to-vigorous intensity physical activity" every day.
Previous research has often used less than seven days of data on children's activity and created an average based on that.
But a study by the universities of Exeter and Plymouth of Year Five children (aged nine or ten) found that although almost a third (30.6%) achieved an average of 60 minutes per day, just 3.2% did so every day.
Activity levels among girls were even lower, with just 1.2% hitting the 60-minute daily target - compared to 5.5% of boys.
"Previous studies based on average activity are likely to have overestimated the percentage of children meeting the recommendations," said Dr Lisa Price, of the University of Exeter.
"Our findings suggest that just under a third of children are achieving an average of 60 minutes per day, but only 3.2% meet the 60-minute target every day.
"We were surprised to find such a big difference.
"We don't know whether averaging 60 minutes a day will be different in terms of health outcomes compared to 60 minutes daily - more research is needed to look into this.
"We do know that most children aren't doing enough physical activity, and that this has consequences not just in childhood but in adulthood too."
The data was gathered from 807 Year Five children from 32 schools in Devon, with a full seven days of data gathered on each child using an activity tracker watch.
Previous studies collecting activity data have been limited by the ability to obtain a full seven days of data, so this study has some of the most robust data on nine and ten year olds' activity.
The research was carried out as part of the Healthy Lifestyles Programme, an innovative school-based obesity prevention trial that encouraged children and their families to live healthier lives.
The programme is funded by the National Institute for Health Research (NIHR).
The paper, published in the Journal of Physical Activity and Health, is entitled: "Are we overestimating physical activity prevalence in children?"
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