Children become less physically active as they progress through primary school, a new study has revealed.
Researchers analysed the behaviour of more than 2,000 primary school children from 57 schools across the West Country.
They found that children lost on average more than an hour of exercise per week between the ages of six and 11.
The amount of time lost was even higher at weekends.
Number of exercise minutes children lost 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."
He said the results of the research 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.
Professor Jago suggested that after-school activities, participation in popular sports and a greater emphasis on weekend activities could all help children stay active.
The children monitored during the study wore an accelerometer for five days each week, including weekends.
This assessed how many minutes per day the children were moderately or vigorously exercising.
Percentage of year 1 pupils that did at least an hour of moderate or vigorous exercise per day.
Percentage of year 6 pupils that did at least an hour of moderate or vigorous exercise per day.
In girls, the percentage fell from 54% to 28% by the time they finished primary school.
The UK Chief Medical Officers recommend that children do at least 60 minutes of moderate to vigorous exercise per day across a whole week.
What else does the report suggest?
Girls were less active than boys at all ages, but the gap became wider as the children got older.
By the age of 11, there was a 15 minute gap between daily exercise rates.
A child that was obese aged six 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.
According to figures from the National Child Measurement Programme (2017/18), 10% of children aged four to five in England are obese.
The figure is 20% for 10 to 11-year-olds.
Percentage of children who were obese at age 3 and 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."
He said that staying active must be combined with policies that help families make informed choices, like "a 9pm watershed on junk food marketing" and "restricting the promotion of unhealthy foods."