By Jason Hildalgo
Gannett News Service

Kids love to hop and jump outdoors, indoors, off the swing, on top of the bed - just about any surface that offers the slightest bit of altitude.

But as crazy as it makes parents, you might want to channel that bouncing in a positive direction. That's because hopping and jumping happen to be two of the best ways to help kids stave off osteoporosis, said Mary Sanders, adjunct professor at the University of Nevada Reno.

BONE-BUILDING

Want strong bones? Here are some bone-building guidelines from Mary Sanders, of the University of Nevada Reno. Dynamically load the body using forceful and fast exercises that impact the bone from variable directions (ski jumps, bounding on diagonals). The number of exercises does not need to be great. Short duration work (a few loading repetitions at each site) is enough. Loading has to occur frequently (several times per week) and continue over a lifetime in order to maintain bone mineral density. Bone adapts to loads, making it less responsive. Loading intensity must increase periodically to increase stimulation.

ON THE WEB

- Information from the National Osteoporosis Foundation's campaign for optimal bone health for children ages 9-12. - Physical activity guidelines for infants and toddlers from the National Association for Sport & Physical Education. Click on the NASPE tab, then type "toddlers" in the "Enter Query" box at the bottom right of the NASPE page.

Kids and osteoporosis? Isn't that worrying about things a little too early?

"What researchers have found is that the ages between 9 and 12 are just critical (when it comes to building bone)," Sanders says.

"Kids need to build their bone bank now. As they age later in life, lower activity levels, changes in hormones - all those things create changes in the bone and they will be withdrawing from their bone bank. This is a big investment ... for them."

Fortunately, that big investment doesn't take a lot. Just 10 minutes of exercise a day, three times a week is enough to build a bone bank with a high enough return for the future. And if you think it requires a variation of complicated exercises, think again. For kids, bone health may be just a skip and a hop away.

The amount of bone that a person has later in life depends on how much bone that person accumulates during youth and how well that bone is maintained, Sanders says.

Experts estimate 90 percent of bone growth occurs between the ages of 10 and 20, which makes it easy to see why focusing on kids now rather than later is essential in preventing osteoporosis.

For exercise to be effective in building strong bones, the activity has to "load" the bones enough to stimulate bone growth. Walking, for example, results in ground reaction forces that are about equal to a person's body weight - not quite sufficient enough to stimulate growth. Simple hops and side-to-side jumps, on the other hand, result in impact that's 3.8 times a person's body weight, which can stimulate growth.

Coming up with an exercise program can be as easy as going to a playground or even your back yard. Last year, Sanders had an article published in the American College of Sports Medicine's Health & Fitness Journal. It included a section on the "Bones of Steel Circuit," which featured five "stations" or exercises: jumping jacks, lunge jumps, hopping, jumping over obstacles and drop jumps from a platform. A second variation is: jumping rope, tuck jumps, drop jumps, hopping on one leg and alternating, and side-to-side jumps.

Ideally, you would like to spend 11/2 to two minutes doing each exercise before progressing to the next one. Beginners should start with 10 jumps per station, slowly progressing to a maximum of 20 per station once they get used to the exercises, Sanders says.

"Start gradually," Sanders said. "Just do enough where it feels comfortable and safe."

Once a child gets used to the exercises, you can have them switch from basic two-footed jumps to tuck jumps and more advanced movements. You can also increase the height of platform-based jumps; the maximum suggested height is between 20 and 24 inches.

Although you want to make sure your kids are getting enough exercise, you also want to make sure that they don't get too much. It's easy for kids to overdo physical activity, especially within a competitive environment, Sanders says. Signs to look out for include injury, loss of appetite, mood changes, fatigue, constipation and diarrhea.

How much of a difference will these exercises make? Sanders cites the original study she based her "Bones of Steel Circuit" on, which appeared in the Journal of Pediatrics. The study showed that girls ages 9-12 who did the exercises three times a week for seven months had an increase between 1.5 and 3.1 percent in bone mass in the hip and spine. Their nonexercising counterparts, on the other hand, showed no changes.