Children as young as four are being treated in increasing numbers for injuries caused by too much physical exertion.

Contrary to a growing perception that young people are increasingly becoming sedentary couch potatoes fixated by the internet and video games, new research from Europe and the US reveals that the past 20 years have seen a rise in the number of children seeking medical help for chronic injuries caused by long-term overexercise.

"There has been an overall increase in both acute and overuse injuries in young athletes over the past 20 to 30 years. This is thought to be due to many factors including the increase in numbers of young athletes, increased intensity of training and competition, participation on multiple teams, and participation at younger ages," says a study from the University of Utah School of Medicine and Northwestern University, reported in Pediatric Emergency Medicine.

In Europe, researchers have found similar increases: "Injuries in skeletally immature individuals are continuously increasing as younger age groups are encouraged to become elite athletes," says researchers whose report appears in the European Journal of Radiology.

Cases cited include thigh muscle strain in a four-year-old boy with a history of intense running; stress fracture in a five-year-old gymnast; an eight-year-old footballer with indications of cruciate ligament damage.

In the US, there are now an estimated 2.6 million emergency department visits annually for sports-related injuries in patients aged five to 24 years.