There is concern that young athletes are dropping out of sport because of avoidable injuries related to overtraining.
Sports coaches should avoid pushing young athletes too hard, says a doctor concerned about injury risk around the age of puberty.
Too much fitness training can lead to overuse injuries to the knees and other vulnerable body parts, says Dr Carolyn Broderick, medical director of the Australian team for the 2014 Youth Olympic Games.
Her main concern is that many teenagers, particularly girls, drop out of sport after an injury.
This means they miss out on the health benefits of exercise.
Many young people are naturally fit and coaches should focus on skills training until they reach skeletal maturity, says Dr Broderick.
She is lead author of a study that shows Australian children and adolescents make around 900,000 GP visits a year for muscle and bone pain.
Sport injuries tend to be a small proportion until puberty.
For boys there is an increase from the age of 10 to 17.
That corresponds to their growth spurt, which is a vulnerable time for the skeleton.
Girls have increased sport injuries in the 10 to 14 age group.
Around eight per cent of teenagers drop out of sport a year because of injury, says Dr Broderick of The George Institute for Global Health and The Children's Hospital at Westmead.
"If we are going to encourage sport and physical activity, we need to make it as safe as it can be.
"One idea is to look at modified rules. The use of protective equipment is also important."
For children in the upper levels of sport, it is essential to monitor training loads, says Dr Broderick, whose study is published in the journal BioMed Central.
"There are lots of kids who do school sport and club sport as well as sport at a higher representative level. No one is keeping an eye on the overall loading. The coaches need to start liaising with each other.
"Data from the US shows that some of the most promising young baseball pitchers never make it to the adult league because of overloading," she says.
Now they have set age-based guidelines for the number of balls that can be pitched as well as the number of rest days the children must take.
Sport helps build long-term self-esteem as well as physical endurance, bone mass and motor skills, says co-author Dr Damien McKay, a Westmead children's hospital paediatrician.
However, it is important for sporting organisations, coaches, trainers and parents to be aware of the potential risk.