There is a significant drop in children's physical activity levels by the time they finish primary school, a study has found.
Children lose on average more than an hour of exercise per week between the ages of 6 and 11, with a greater fall at the weekends, the research showed.
Researchers monitored the activity of more than 2,000 children from 57 schools across the South West of England during their primary years. They found children became 17 minutes less active per week each year.
Russ Jago, professor of paediatric physical activity at the University of Bristol, said: "Evaluating patterns of physical activity across childhood is an important way to identify key ages in which to intervene to change behaviour – and establish healthy habits for life.
"These numbers prove that more needs to be done to ensure children keep active as they approach adolescence. This isn't about getting children to exercise more, but rather maintaining their activity levels.
"Developing early intervention strategies that help children retain activity levels could include after-school physical activity programmes, focusing on participation and enjoyment in addition to popular sports – and a greater emphasis on promoting weekend activities."
In the study, children wore an accelerometer for five days, including two weekend days. This provided an assessment of how many minutes per day the children participated in moderate to vigorous physical activity – defined as making them slightly out of breath and sweaty.
The UK Chief Medical Officer recommends that children do an hour of such activity every day.
The study found that 61 per cent of children in Year 1 did at least an hour of this activity per day but by Year 6, only 41 per cent achieved the target. In girls, the figure fell from 54 per cent to 28 per cent by the time they finished primary school.
Results showed that average weekday activity decreased between ages 6 and 11 by 2.2 minutes per weekday per year, and the average weekend activity decreased by 3.1 minutes per day per year. Girls were less active than boys at all ages but the gap became wider as the children aged, with a nine-minute per day gap increasing to 15 minutes at age 11.
The research also examined how body mass index is associated with physical activity in childhood and whether associations change as children age.
Data from the 2017-18 National Child Measurement Programme shows that 10 per cent of children aged 4-5 in England were obese. This figure doubled to 20 per cent for 10- to 11-year-olds. In total, 90 per cent of children who were obese at the age of 3 remain overweight or obese in adolescence.
Professor Jeremy Pearson, associate medical director at the British Heart Foundation, said: "Almost a third of children in the UK weigh more than they should, while one in four primary school children are not meeting the recommended levels of exercise.
"We know that children living with obesity are more likely to become obese adults – putting them at increased risk of developing heart and circulatory diseases and their risk factors, such as type 2 diabetes and high blood pressure, later in life.
"Staying active must be combined with policies that help families make healthy and informed choices, such as a 9pm watershed on junk-food marketing and restricting the promotion of unhealthy foods."
The research found that at age 6, there was no difference in the activity of children who were a healthy weight compared with those classed as overweight or obese. However, a child that was obese aged 6 and remained so at age 11 engaged in 10 minutes less activity per weekday than a similar child at a healthy weight at both ages.