A boom in the popularity of family-friendly 5km events has seen a sharp rise in the number of under-11s taking part. Is it a good thing? Peta Bee investigates

How far is safe for very young athletes to run? It is a subject that is guaranteed to divide opinion, as is evident by correspondence on the topic to AW’s Your Say pages.

With the boom in popularity of races that impose generous age restrictions, clubs report prospective junior members are turning up to join with a dozen or more 5kms under their belt before their ninth birthday. Should we applaud the enthusiasm or express concern that some under-11s are being allowed to run too far, too soon and risk damaging their bodies in the process?

Well-meaning parents keen to introduce the sport to their children certainly have no shortage of options when it comes to events that cater for those of primary school age and younger. Children as young as four can take part in 5km parkruns (provided they run with an adult) while organisers of some longer distance races set no lower age limit and are attracting hoards of medal-hungry youngsters as a result. Such thinking may be at odds with UKA rules and guidelines for junior competition, but, really, does it matter if children want to run and run?

Mark De Ste Croix, professor of paediatric sport and exercise at the University of Gloucestershire, says it can be a fine line between encouraging more activity and overdoing it.

“Most research shows that the optimal type of physical activity at primary school age is high intensity, sporadic exercise – the kind children do in the playground,” he says.

“They need to develop basic motor skills and fitness and while some running is necessary, the pay-off is that too much, too young can be detrimental.”

Very few studies have looked specifically at how harmful it is – if at all – for children to run long distances, partly because it would be unethical to subject children to the physical trauma of running lots of miles a week just to see the effect. But last year Dr William Roberts, a professor of family medicine and community health at the University of Minnesota and medical director for the annual Twin Cities Marathon where no age restriction is set, did look at the immediate effects of running a marathon on young bodies.

Analysing data for every single finisher under the age of 17 who had completed the 26.2-mile race between 1982 and 2007, Dr Roberts found that during the 25-year period, 310 youngsters – the youngest aged seven – had taken part in the event.

His findings, published in the Clinical Journal of Sports Medicine, were surprising. They revealed that only four had visited the race medical tent and even they required no treatment beyond a brief rest. In fact, the young runners had 50 per cent fewer ‘medical encounters’ than adults during the study period.

“What we found in our study,” Dr Roberts said, “is that with proper training and planning, the marathon distance can be safe for certain highly motivated children.” What wasn’t taken into account in his study was the long-term impact on developing skeletons of pounding mile after mile on pavement or trail.

Dr Roberts says that his next step is to contact the past youth marathon finishers to find out whether their knees and other joints withstood the hammering. He expects to find they have experienced no greater incidence of joint problems. Is that really likely?

Professor De Ste Croix says children are not capable of the sustained activity levels practised by adults. “We should never take an adult approach to training and apply it to a child,” he says.

“It really is not advisable to prescribe chronic, high-intensity exercise at a very young age.”

Any activity that puts excessive stress on developing joints can cause anatomical imbalance, a mismatch of growth rates and so-called “growth diseases” that often force youngsters to be sidelined from any form of activity for months on end.

Trevor Painter, the Wigan-based coach of Jenny Meadows and a clutch of young middle-distance runners warns: “Children naturally have huge levels of endurance, partly because their bodies are so light. But the big problem is that their aerobic capacity is limited by poor running technique and lack of strength. They need to have reached their peak velocity height – or stopped growing – before they do any hard, long running sessions otherwise you could be asking for trouble.”

What’s more, just because a child can run 5km or further before they know their times tables doesn’t mean they gain a competitive advantage by their late teens.

“Becoming a good athlete is about progression over many years,” says Painter. “It doesn’t happen overnight and elite distance runners peak in their late twenties with their minds and bodies strong from years of training. There is no advantage from starting too young.”

POSSIBLE RISKS OF TOO MANY MILES

Chrondomalacia patellae

Caused by an imbalance in muscle strength on either side of the knee cap. Girls are more likely to suffer because of their wider pelvis which pull the knee cap over to one side causing a searing pain around the edges of the patella at the front of the knee. It requires children to wear heavy strapping until muscles are re-educated when gentle activity is resumed.

Osgood-Schlatter disease

A condition in which the growth plates at the top of the shinbone (or tibia) become inflamed when tendons attached pull hard on it during high-impact exercise. It can affect any child, but is more common among boys and usually strikes between the ages of 8 and 16, when growth spurts reach a peak. Symptoms include a tender swelling on the knee and pain during activity and treatment can involve setting the knees in plaster for up to six weeks. Often the medical advice is to do no sport for up to a year in order to allow growth plates to recover and muscles and tendons the chance to develop fully.