Teenagers are at an increased risk of fracturing their arms, researchers have found.
Sports such as skateboarding have been linked to fractures
A study published in the Journal of the American Medical Association found forearm fractures have increased by 42% compared to 30 years ago.
Researchers from the Mayo Clinic in Minnesota say growth spurts do increase the risk of fractures.
But they add the rise may also be linked to too little calcium in diets and injuries sustained in sports.
A particular type of fracture of the distal forearm (near the wrist) typically peaks at around age 12 in girls and 14 in boys.
Most of these fractures occur around the time of the growth spurt during puberty.
Boys at most risk
Researchers looked at the number of forearm fractures that occurred in people under 35 who lived in Rochester, Minnesota in 1969 to 1971, 1979 to 1981, 1989 to 1991 and 1999 to 2001.
It was found the forearm fracture rate among young people increased from 265 per 100,000 people per year in 1969 to 1971 to 469 per 100,000 in 1999 to 2001, mostly because of an increased number of fractures in people aged under 20.
In the 1999 to 2001, girls between eight and 11 and boys between 11 and 14 had higher fracture rates than all other age groups studied.
Twelve-year-old boys had the highest fracture rate of all, with 1,536 per 100,000 people, or 1.5% per year.
The researchers also looked at the causes of fractures.
They found the incidence of fractures linked to recreational activities, such as baseball, football, skating and rollerblading, had almost doubled.
Dr Sundeep Khosla said: "Our study does not explain why these fracture rates increased, but the data raise concerns about whether bone-mass development in today's children may be impaired by other lifestyle and dietary factors such as increased soft drink consumption, decreased milk consumption or changing patterns of physical activity."
Bone health expert Joseph Melton, who also worked on the study, said developing adequate bone-mass during childhood was critical to preventing osteoporosis and the related bone fractures in adult life.
"Increasing rates for forearm fractures in children could mean we will see a dramatic increase in the risk for hip fractures and other more serious fractures when these children become older adults."
Trevor Reid, a spokesman for the National Osteoporosis Society. told BBC News Online: "We welcome these observations, but at the same time they point to a worrying trend.
"We have already seen studies showing that there are more hip fractures and vertebral fractures now than several decades ago, but this is the first time that we have seen this trend of broken bones in such a young age group.
"This new report is speculating that some of the problems which are associated with osteoporosis are laid down very early in life."
He added: "Children and teenagers need to ensure they put 'bone in the bank' for their later years, and healthy eating and weight bearing exercise all play their part."