Fitness & Exercise

Build a Stronger Skeleton

Train Smart continued...

Women who overdo it may develop a condition called amenorrhea, which is triggered when overall body fat drops below 15%-17%. This is basically exercise-induced menopause. An amenorrheic woman stops menstruating and her estrogen levels take a dive. With low estrogen levels, bone loss speeds up, just like it does in post-menopausal women. Many female athletes, DiNubile says, are pleased with their lean, cover-girl bodies, "Yet they're not healthy. They've got disease.

"You need to train smart," he says. You should maintain a healthy weight -- not too plump, but not too hard -- and allow your bone enough time between workouts to heal and grow.

Good Vibrations

Clinton Rubin, PhD, a scientist at the State University of New York in Stony Brook, thinks he may have found another way to build bone: vibration. His experiments have shown that gentle, high-frequency vibrations greatly increase bone growth. In a recent study, he had sheep stand on a vibrating platform for 20 minutes, five days a week, over the course of one year. The density and volume of their leg bones increased by more than 30%.

Rubin's research is funded by NASA's National Space Biomedical Research Institute. NASA is interested because bone loss is a bane to astronauts. According to Rubin, we lose about 2% of our bone per decade here on Earth. Astronauts lose about 2% of their bone per month in space. Under no stress from gravity, bone dissolves. "It's doing exactly what it thinks it should do," Rubin says. That is, a weightless body doesn't really need bones. It's responding to the environment.

At present, both American astronauts and Russian cosmonauts try to fight bone loss with intense exercise programs. They spend four hours a day doing high-impact, bone-building workouts, Rubin says. Still, the bone loss doesn't stop.

Rubin thinks a healthy skeleton depends on the body's natural vibrations, in addition to the strain placed on bone by exercise. Even when sitting upright or standing still, your muscles are working to maintain your posture. The muscles vibrate at 10-50 hertz, and Rubin thinks these subtle vibrations stimulate bone growth. In space, a human body doesn't strain against gravity to hold its posture. The muscles are relaxed, and bone is not constantly subjected to muscular vibrations.

If Rubin is right, a vibrating platform could remove one more obstacle to sending astronauts on a mission to Mars. What's more, vibration might become a first-line treatment for osteoporosis, as well as a way to prevent it. Better treatments for osteoporosis are sorely needed. DiNubile says he worries about what will happen when today's young women go through "the change" some 40 years from now. "They're not even close on calcium intake," he says. What's more, teens tend be sedentary and guzzle massive quantities of soft drinks. All things considered, it looks like an epidemic of shattered hips may plague us mid-century.