School children should have their fitness tested in the same way as subjects like maths and English to get them more physically active, a report has suggested.
Not-for-profit health body ukactive said the recording of children's fitness in primary schools is "rare and at best sporadic", with fewer than half of the schools surveyed (43%) tracking the amount of time children spend actually being active in PE lessons, excluding time spent changing into kit or carrying out other tasks.
It warned the nation is facing a "ticking time bomb" of a physical inactivity pandemic, with only half of seven-year-olds meeting the guidelines of carrying out 60 minutes a day.
Its Generation Inactive report said that while it would be considered unacceptable for pupils to leave primary school without their parents and teachers having a basic understanding of their ability in maths and English, it is normal for them to not have a formal understanding of their fitness levels and the impact this could have in their later life.
Currently, schools in England aim to provide two hours of PE or sport a week for pupils aged five to 16, but the report said that many still fail to achieve even that.
It has set out a series of recommendations including that headteachers adopt a "whole day" approach to physical activity by ingraining it into the entire school day, incorporating a variety of lessons and subjects within the curriculum as well as unstructured and structured activity.
It points out that a slim child does not automatically mean a healthy child, and calls for the Government to extend the National Child measurement programme to measure fitness in addition to the current measurement of body mass index (BMI).
And no child should be left "lagging behind", it said, in the same way that a teacher would not leave a child struggling to read in a class full of children that could do it well.
The report stresses that better measurement of physical fitness and health needs to be done in a fun, inclusive and age-appropriate way, citing the example of Montpelier Primary School in Ealing, west London, which already sees physical activity carried out throughout the entire school day.
Examples of how they do this include "Kung Fu punctuation" in English lessons, where children make Kung Fu style hand movements to signify where an exclamation mark or full stop should go rather than simply raising their hands or shouting out. Head teacher Am Rai said the measures have also led to improvements in pupils' behaviour.
Chair of ukactive and champion Paralympian Baroness Tanni Grey-Thompson, said changes as simple as children standing in lessons and developing more structured use of play time could be implemented.
"The current national ambition focused solely around PE lessons is simply not bold enough," she said. "We should aim higher and demand more.
"The focus should be on ensuring that children are given all the necessary support possible in order to achieve the 60 minutes of daily activity recommended in the Chief Medical Officer's guidelines.
"This does not mean we wish to see 60 minutes of timetabled PE per day. Instead, we are calling for a focus on a 'whole school approach'.
"Schools which have adopted such an approach have had outstanding success in enhancing the health and wellbeing of their students as well as their educational attainment."
Professor Russell Viner, officer for health promotion for the Royal College of Paediatrics and Child Health, which is backing the report, said: "A sedentary lifestyle doesn't just mean a child could be overweight, it is an issue that can affect a child's entire life, from poor concentration levels impacting on life chances post school, and increased risk of emotional and well-being issues like depression, right through to developing life-long medical conditions like type two diabetes - all of which can have dire consequences if not managed properly.
"We already know that a healthy child is much more likely to go on to be a healthy adult, so it is important that we set children on the right trajectory from an early age and continue to encourage healthy lifestyles as they move through life.
"That means instilling positive behaviour early such as ensuring parents are supported to be healthy before and during pregnancy, teaching children about healthy eating in school and working with local authorities to ensure roads are safe for children to cycle, scoot or walk to school by implementing 20mph speed limits in built up areas."
A Government spokeswoman said: "Tackling obesity is a major priority for this Government, which is why as part of our plan for education, we want to continue to encourage children to enjoy sports - both in lessons and after school.
"We have already given primary school headteachers over £300 million of additional funding to spend on improving PE and we know they are using it to deliver more and better sport.
"Research shows that primary schools are delivering more than two hours of PE each week, and 83% of schools have reported an increase in participation in after school sports since the introduction of the funding."