The least fit British children 20 years ago would be considered among the fittest children today, according to research.
The report, which features on a BBC television programme about childhood fitness initiative Super Movers, said that the least fit child in a class of 30 in 1998 would be among the five fittest in 2018.
Although childhood obesity has been falling for 10 years, the study found that childhood fitness has continued to fall.
The shift from active play outdoors to indoor screen-based activities has meant that today’s children are the first generation since the Second World War to be less fit than their parents.
“If we could time travel to hold a one-mile race so today’s parents and their children were both 10 years old, mums and dads would win it by about 90 seconds,” said Dr Gavin Sandercock, a sports scientist at the University of Essex.
“About a third of children have clinically low aerobic fitness,” said Dr Sandercock.
The Super Movers programme is a joint venture between the BBC and the Premier League to encourage children to get more active.
“This is an issue families increasingly worry about. By highlighting it, we’re hoping we can help people make a difference in their lives,” said Sinead Rocks, the BBC’s director of education.
“Just a little exercise can have huge benefits,” said Dr Sandercock.
Super Movers is featured on Inside Out, shown on BBC One at 7.30pm on January 22.