How does this work ? All the scientist has to do is place the mice on a platform that vibrates at such a low frequency that some people cannot even feel it. The mice stand there for 15 minutes a day, five days a week. On being measured later on, they show 27 percent less fat than mice that did not stand on the platform — and correspondingly more bone.
Says an astounded Rubin himself: "I was the biggest skeptic in the world. And I sit here and say, 'This can't possibly be happening.' I feel like the credibility of my scientific career is sitting on a razor's edge between 'Wow, this is really cool,' and 'these people are nuts.'"
Others share his feelings. Some scientists are enthusiastic, others are skeptical.
The mice may be leaner after standing on the platform, they say, but many are not convinced of the explanation -fat precursor cells turning into bone.
Still the National Institutes of Health (NIH) is enticed enough. They plan to investigate the effect in a large clinical trial in elderly people, according to Joan A. McGowan, a division director at the National Institute of Arthritis and Musculoskeletal and Skin Diseases.
While Dr. McGowan notes that Dr. Rubin is a respected scientist and that her institute has helped pay for his research for the past 20 years, she does warn against jumping to conclusions.
"I'd call it provocative," she observes. "It says, 'Keep looking here; this is exciting.' But it is crucial that we don't oversell this." For now, "it is a fundamental scientific finding", she adds.
The study, which was published online and will appear in the Nov. 6 issue of Proceedings of the National Academy of Sciences, began in 1981. It was then that Dr. Rubin and his colleagues started investigating why bone was lost in aging and inactivity.
"Bone is notorious for 'use it or lose it,'" Dr. Rubin says. "Astronauts lose 2 percent of their bone a month. People lose 2 percent a decade after age 35. Then you look at the other side of the equation. Professional tennis players have 35 percent more bone in their playing arm. What is it about mechanical signals that makes tennis champ roger Federer's arm so big?"
At first, he presumed that the exercise effect came from a forceful impact such as the pounding on the leg bones as a runner's feet hit the ground or the blow to the bones in a tennis player's arm with every strike of the ball. But soon he considered other possibilities. Large signals can in fact be counterproductive, he thought. "If I scream at you over the phone, you don't hear me better. If I shine a bright light in your eyes, you don't see better", Rubin says.
Over the years, Rubin and his colleagues discovered that high-magnitude signals, like the ones created by the impact as foot hits pavement, were not the predominant signals affecting bone. Instead, bone responded to signals that were high in frequency but low in magnitude, more like a buzzing than a pounding.
That makes sense, he says because muscles quiver when they contract, and that quivering is the predominant signal to bones. It occurs when people stand still, for example, and their muscles contract to keep them upright. As people age, they lose many of those postural muscles, making them less able to balance, more apt to fall and, perhaps, prone to loss of bone.
"Bone is bombarded with little, teeny signals from muscle contractions," Dr. Rubin gives.
He found that in mice, sheep and turkeys, at least, standing on a flat vibrating plate led to bone growth. Small studies in humans — children with cerebral palsy who could not move much on their own and young women with low bone density — indicated that the vibrations might build bone in people, too.
Dr. Rubin and his colleagues got a patent and founded a company to make the vibrating plates. But they and others warn that it is not known if standing on them enhances bone strength in humans. Even if it does, no one knows the correct dose. It is possible that even if there is an effect, people might take more than the appropriate dose and make their bones worse instead of better.
Some answers might come from the federal clinical trial. It will include 200 elderly people in assisted living. It is being directed by Dr. Douglas P. Kiel .he is an osteoporosis researcher and director of medical research at the Institute for Aging Research at Harvard. The animal work has made him hopeful that the buzzing platforms would have an effect on human bones.