A dramatic rise in the number of kids being injured playing organised sports has sparked warnings for parents to limit how much sport their kids participate in each week.
Experts fear kids are doing too much high-intensity sport at too young an age, causing stress and creating a spike in injuries.
Children under 10 years old suffered 63 per cent more sports-related injuries between 2008 and 2017, while those aged 10-14 were also hurt 60 per cent more.
The statistics included those playing rugby union, soccer, netball, basketball, rugby league, gymnastics and touch rugby.
ACC is trying to combat the huge spike in injuries by urging parents to restrict how much organised sport their kids play each week by following a guideline of one hour of sports for every year in age. Under this recommendation a 10-year-old would play no more than 10 hours of sport competition, training and PE a week.
ACC head of injury prevention Isaac Carlson said there was growing concern that too much sport may be as harmful for kids as not getting enough exercise.
"At least one hour a day of moderate to vigorous exercise is beneficial - either play or organised sport."
Kids were either putting themselves at risk of injury by not doing enough exercise to be properly conditioned for the activity, or were playing in higher levels of sport and training but not having enough breaks, he said.
"Too much high-intensity training reduces the energy available for growth and development. This can affect not only peak bone mass and the onset of puberty but a number of other important body systems which can have lifelong consequences for injury and physical and mental illness."
Athletics New Zealand exercise physician and medical director Dr Dan Exeter said there was no evidence to suggest that specialising in one sport early on led to a better chance of sporting success .
Instead the Australasian College of Sport and Exercise Physicians recommended kids did not specialise in a single sport until 12 years old because starting too early could lead to burnout, loss of motivation and potential mental health issues.
"Coaches and parents believe they are doing the right thing, however, there is no evidence to support this in sports where peak performance is attained in adulthood.
"On the contrary, a growing body of evidence suggests that athletes who maintain a broader sporting base before they specialise are more likely to be successful in their chosen sport, as well as maintain a lifelong love of sport," Exeter said.
Sport NZ talent consultant Alex Chiet said too much pressure was being put on young athletes instead of ensuring they enjoyed their sport, developed skills and stayed healthy.
Sharon Kearney, a physiotherapist and programme manager for Netball New Zealand NetballSmart, said many kids were involved in an extraordinary amount of sport. Some sports like gymnastics were early specialisation sports, meaning younger kids could be practising 20 hours a week.
"Some of these kids are doing an extraordinary amount of structured activity. So they might be going to swimming, then they might be going to ballet, then they might be going to football ... There are some kids on the other end of the scale who are doing an extraordinary lack of activity."
In her physiotherapist clinic, she was commonly treating kids with pain in the front of the knee or heel and sprained ankles. Also on the rise was anterior cruciate ligament ruptures in children aged 12-14.
Netball New Zealand was already working hard to minimise injuries with its NetballSmart programme aimed at children aged 10-14 because of the ACC statistics.
"We want people to stay involved in our game, but we want our injury rate to decrease."
Ross Kennedy, who is a strength and conditioning coach at Christchurch's Rangi Ruru Girls' School, said the school made sure the students played a range of different sports.
It wasn't until they reached about 15 that students started to specialise in one sport.
Kennedy believed the one hour for every year in age guideline was reasonable and would help manage burn out and fatigue.
"Having days off sport where they can just be kids and mix with families and friends - that is crucial."
While PE has been included as organised sport, he said it was often less structured and intense than a team sport.
"We just encourage a free style of play really so minimal structure."
The findings come after a group of Boston scientists warned that children should avoid contact sport before the age of 12 due to the risk of suffering degenerative brain diseases.
They found tackling or heading might be too much for the brain development of children under 12.
Number of injuries across priority sports
Age - 2008 - 2017 - % change
Under 10 - 4506 - 7353 - 63%
10-14 - 25,359 - 40,619 - 60%
15-19 - 35,375 - 45,465 - 29%
20-24 - 23,151 - 25,540 - 10%
Nine hours not enough sport for Liam
Liam Bankier loves playing sport and being in a team.
The 9-year-old spends six hours a week training and playing rugby league for his club Papakura Sea Eagles.
Then at lunchtime on a Tuesday and Thursday the sports-mad kid can be found playing rippa rugby with his school team. On top of that his class also does PE for an hour a week.
But the Year 5 Opahake School student said he loved being part of all the different sports.
"I would play more if I could ... I don't have enough time."
During summer, he also played futsal and touch rugby.
Liam, who turns 10 next week, didn't think playing more sport put him at more risk of getting hurt and said it came down to a person's fitness level and if they had the right protective gear.
The only injury he's had is a black eye.
He's been playing rugby for five years and before that also played soccer and athletics.
Liam's mum Kellie Elder-Morunga said she wasn't sure limiting how much sport a child played a week was the answer.
"He only does one or two things a season because I don't want it to be too much, but 10 hours of exercise isn't a lot to them.
"They practice safe tackling and things like that so the injury rate isn't that bad."
With his two winter sports, he was already involved in about nine hours of organised sport a week so adding one more activity would take him well over the suggested limit."