WASHINGTON — Better bones built during youth can be saved for a later day, a study says.
The finding could help today's young exercisers amass a reserve of bone mineral that may reduce their risk of developing the weak bones that plague their grandparents.
"Regular exercise can be valuable for maximizing peak bone mass and thus contributing to prevention of osteoporosis and related fractures later in life," researchers in Finland reported.
The study of elite tennis players found that, even after they cut back on competition and decreased training, the bone density they had gained earlier remained.
That's important because bones are not as enduring as people think; like other parts of the body, they change. Physical activity stimulates them to lay down more calcium and become stronger. When they are deprived of activity, bones become weaker by losing calcium.
The Finnish researchers looked at the playing arms of 13 high-level competitive tennis players who had started their careers at an average age of 11. The scientists at the UKK Institute for Health Promotion Research measured the athletes' bone density in 1992, when the players' average age was 26, and again four years later.
By the time of the last measurement, all had been out of national competition for an average of two years, four months. All had cut back their play from an average of 5.2 times a week to 2.6 times a week and their practices from 7.6 hours a week to 3.3 hours a week.
The initial measurement found the bones of the playing arms had gained from 13% to 25% more mineral content than the bones in their opposite arms. This was the result of training at an early age, the researchers decided.
The later measurement found virtually no change in the proportion of bone mineral content in the players' arms, despite the men's reduced activity.
The findings support the idea that the time to maximize bone density is in youth, when bones are most responsive, the researchers said. Bones of adults are less responsive to exercise, they said.
It might well be that, during growth, the adaptations caused by exercise change bone structure permanently in such a way that even decreased activity cannot destroy the benefit, said the study in the American College of Sports Medicine journal, Medicine and Science in Sports and Exercise.
If other studies confirm this, "regular exercise during the pubescent years should be recommended for maximizing the peak bone mass and eventually preventing osteoporosis," the report said.
"Somebody once said osteoporosis should be considered a pediatric disease," commented Dr. Brian D. Golden, director of the Osteoporosis Center at the Hospital for Joint Diseases, New York City.
Much research is done on slowing bone loss in adults, but "studies like this speak to the earlier half of the equation," Golden said. It's important to gain as much bone as possible before the age of 30, when bone strength peaks.
Bone density built in youth can be a rainy-day fund for when bones start to weaken, said research physiologist Barbara L. Drinkwater of Pacific Medical Center in Seattle. But "most schools in this country have done away with the physical activity requirement."