CHICAGO (Reuters) -- Girls who do regular jumping exercises around the age of 10 may add bone mass that could delay the onset of osteoporosis in later years, researchers said on Monday.

The conclusion came from a two-year study of 34 girls given the exercise regime during regular school physical education classes who were compared to 46 comparable girls who did not do the exercise.

The girls did jumping jacks, jumped off platforms and jumped forward, and did side-to-side jumps at six stations on a track, running or skipping in between, with the height and impact of the jumps increasing over the course of the study.

Those who completed the exercise course three times a week during their school years had nearly a 5 percent better gain in bone minerals, the study found.

"We designed a safe, effective, relatively simple, and inexpensive program of diverse activities that can be implemented in elementary school physical education to enhance bone mineral accrual during childhood," the study said.

"If maintained this advantage in bone mineral accrual represents the equivalent of 3 to 5 years of post-menopausal bone loss," it added.

The study was done by researchers at British Columbia Children's Hospital and the University of British Columbia. It was published in the December issue of Pediatrics, the journal of the American Academy of Pediatrics.

Osteoporosis is a loss of bone mass that often accompanies aging. It causes bones to become brittle and more easily broken, and tends to affect women more than men because post-menopausal women have diminished estrogen production. The hormone helps maintain bone mass.

Heather McKay, one of the authors, said in an interview that exercise is recognized as the primary stimulus for skeletal development, and that even babies who kick or move about a lot in the womb appear to wind up with stronger bones.