High-impact exercises help young people build strong bones, according to a new study.

For the research, about 100 young teenagers were given jumping, skipping and lunging exercises to do for about 10 minutes, twice a week as part of a physical education class.

After eight months, 14-year-olds who did the work -- up to 300 jumps per session -- had stronger bones and muscles than those who didn't, said author Ben Weeks of Australia's Griffith Institute of Health and Medical Research.

"Eighty percent of bone mass is accrued in the first 20 years and especially around puberty due to the circulating hormones. This study targets a window of opportunity in adolescence to maximize peak bone mass with high-intensity, weight-bearing activity," he said.

He also found that girls gained bone particularly in the hip and spine. That could be significant, since those are typical fracture sites in the elderly.

Weeks said much longer studies would be needed, however, to discover if the benefit lasts into adulthood.