The story of the finding, which was published online and will appear in the Nov. 6 issue of Proceedings of the National Academy of Sciences, began in 1981 when Dr. Rubin and his colleagues started asking why bone is lost in aging and inactivity.

“Bone is notorious for ‘use it or lose it,’” Dr. Rubin said. “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 Roger Federer’s arm so big?”

At first, he assumed that the exercise effect came from a forceful impact — 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 Dr. Rubin was trained as a biomechanical engineer, and that led him to consider other possibilities. Large signals can actually be counterproductive, he said, adding: “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.”

Over the years, he 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 went on, 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 said.

He discovered 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.