Serious injuries such as torn knee ligaments have soared among older children playing popular sports in the last decade, new figures from ACC show.
Last year the Accident Compensation Corporation received 69 claims for anterior cruciate ligament (ACL) injuries from 10 to 14-year-olds in what it calls the seven key sports - basketball, football, gymnastics, netball, rugby league, rugby union and touch.
In 2008 there were less than five ACL claims from this age group.
ACL injuries, which often involve an extremely painful tearing of ligaments in the knee, are usually associated with top-level sports players. For instance, a ruptured ACL has forced All Black utility back Damian McKenzie out of this year's Rugby World Cup in Japan.
ACC said the figures reinforced its claim last week that a big increase in sporting injuries among young people could be explained by over-specialisation in major sports at too young an age, rather than any other factor such as larger playing numbers.
"It is highly unlikely that an increase of this magnitude – for an injury so debilitating – can be explained by increased participation in these sports," said senior media adviser Lisa Rautenbach.
"We are in the process of doing additional analysis on the severity of injuries that we are seeing in this age group. We will be publishing this in due course."
ACC provided the new data to the Herald in response to questions about its media release a week ago, which showed a 60 per cent increase in claims for accidents in the seven major sports from 2008 to 2017.
Further research by the Herald found the overall growth in claims among this age group was much lower. As the graph below shows, claims in other sports rose by a similar amount and there has been a large decrease in the "Other claims" category, making the overall rise a more modest 16 per cent.
Auckland University statistician Professor Thomas Lumley said he did not think ACC's theory about the increase in "Key sports" injuries could explain the simultaneous increase in "Other sports and recreation" and the compensating decrease in "Other claims".
If the massive surge in "key sport" claims was due to early specialisation or too much organised sport, the other sports and recreation category - consisting of over 100 different activities - would not be expected to look so similar.
The variations between the different sports also made it difficult to see any single factor driving the change - such as children playing too much sport.
The chart above shows rugby union injury claims peaking in 2014 and then starting to fall for an overall change of only 19 per cent. The only sport with consistently increasing claims is New Zealand schools' fasted growing sport - basketball.
There is no directly comparable data for sports participation but the Secondary Schools Sport Census (below) shows an increase of about 8000 - mainly driven by basketball - in 13 to 17-year-olds playing the four highest-injury sports in the same time period.
Rautenbach replied that ACC fully stood by its data and pointed to the growing number of ACL injuries in this age group as further evidence.
"When we published these figures, we were very clear that there are likely to be several reasons for this increase. One of those reasons is likely to relate to a trend in overtraining underdeveloped bodies with too much structured sport.
"There is growing concern among academics, sports administration bodies and health professionals that too much structured sport can be just as harmful for kids as not getting enough exercise. This is backed up both by international research and by a wide range of physiotherapists, sports psychologists and sports physicians that are working in the field.
"We are actively working with our sporting partners to address both the volume and severity of sporting injuries in this crucial developmental stage."
Sports medicine specialist Dr Mark Fulcher told Radio Sport last week that children were playing more structured sport which could lead to more injuries but added that greater intervention also played a part.
"I think you are more likely to take your kids to physio than you once were.
"Physiotherapists are often working in a school environment so the access is better too. If you look at some of the more measurable significant injuries like ACL injuries they are definitely on the rise, but I think there is also better access and people are more likely to seek care."
ACC told the Herald it did not test to see whether the increase in sports and recreation claims and the corresponding drop in "other" claims was due to a change in reporting practises such as the introduction of online claim filing.