Researchers have supplied a great excuse to keep using the couch as a launch pad. It’s good for your health. Jumping exercises performed during childhood may provide long-lasting protection from bone-depleting osteoporosis, researchers at Oregon State University report.

Hundreds of Corvallis grade-school students repeatedly jumped from a 2-foot-high box for about 15 minutes, three times a week during one school year. After seven months, the jumping routine triggered sharp increases in hip-bone density, 4 percent to 8 percent greater on average than children who didn’t do the exercises.

Eight years after the study ended, jumpers still maintained higher bone mass than non-jumpers, averaging about 1.4 percent greater, researchers report in a forthcoming study in the Journal of Bone and Mineral Research. In a second study with four years of follow-up, hip-bone density was 3.2 percent greater in kids who jumped. Whether that much extra bone growth in childhood can protect women and men from osteoporosis and broken bones later remains unknown. “That’s what we’re hoping,” said Kathy Gunter, an assistant professor at Oregon State and lead author of the study.

Heather McKay, a professor at the University of British Columbia, called the study “remarkable” for being the first to track the bone-firming effects of exercise in children over many years. The results bolster the case that load-bearing exercise during childhood can lower the risks of broken bones from osteoporosis in old age, McKay said.

“There are key time points during young age when we need to encourage children to exercise,” she said. “Get them away from the TV.”

Why jumping?

Studies of gymnasts’ and other athletes’ bones led the Oregon State team to focus on jumping exercises.

In one study of young gymnasts before puberty, Australian researchers found that the bone density increase in one year for the gymnasts was as much as 85 percent greater than in non-gymnasts. They also found that greater bone density seemed to persist among retired gymnasts in their 20s. Oregon State studies found that gymnasts have denser bones than most other athletes.

What sets gymnasts apart, Gunter said, is repeatedly enduring landing forces 10 to 14 times their body weight. Animal studies, she said, have shown that high forces delivered rapidly stimulate bone growth and structural changes that resist breakage.

Jumping from a 2-foot box delivers a force about eight times the jumper’s body weight – not as powerful as landings in gymnastics but safer and about four times greater than the forces from running, Gunter said. The children in the Oregon State study started with 40 or 50 jumps per session and easily worked up to 100.

“We’ve done numerous studies,” she said. “Not once was there any injury related to the jumping activity.”

Sports that involve jumping and falling impacts, such as volleyball, basketball and wrestling, are probably beneficial for bones, too, Gunter said.

“Figure out a way you enjoy doing the exercise,” she said. “That’s what’s important.”

Targeting grade-schoolers makes sense, Gunter said, because that’s when children’s bones grow the fastest. Bone mass reaches its highest point early in life – about the time teenagers emerge from puberty.

The higher the peak bone mass, the lower the risk later for fragile bones and fractures, research has shown. During older adulthood, a loss of 10 percent to 15 percent of skeletal mass doubles the risk of hip or spine fractures.

Adults, too, can benefit from jumping, Gunter said, but not in the same way as children. She cites a 1998 study at Oregon State in which post-menopausal women incorporated jumping in place into a strength-training routine. Non-exercisers in the five-year study lost 4.5 percent of bone mass. The jumpers maintained but didn’t gain bone mass.

More important, Gunter said, the jumpers made great strides in strength, balance and mobility to help them avoid falls and fractures.

RB END ROJAS-BURKE

(Joe Rojas-Burke is a staff writer for The Oregonian of Portland, Ore. He can be contacted at joerojas(at)news.oregonian.com.)

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