Rodger Federer has big arms???

http://www.nytimes.com/2007/10/30/health/research/30bone.html?em&ex=1193889600&e
n=f8072daca1d3f9a8&ei=5087%0A

EXCERPTS

All he does is put mice on a platform that buzzes 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. Afterward, they have 27
percent less fat than mice that did not stand on the platform - and
correspondingly more bone.

...

"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.

...

Dr. Rubin and his colleagues got a patent and formed a company to make
the vibrating plates. But they and others caution that it is not known
if standing on them strengthens bones in humans. Even if it does, no
one knows the right dose. It is possible that even if there is an
effect, people might overdose and make their bones worse instead of
better.

Some answers may come from the federal clinical trial, which will
include 200 elderly people in assisted living. It is being directed by
Dr. Douglas P. Kiel, an osteoporosis researcher and director of
medical research at the Institute for Aging Research at Harvard. The
animal work made him hopeful that the buzzing platforms would have an
effect on human bones.

"This work is fascinating and very legitimate," Dr. Kiel said.

But then Dr. Rubin reported that the mice were also less fat, which
led to the revised plans to look for changes in body fat as well.

...

Dr. Rubin says he decided to look at whether vibrations affect fat
because he knows what happens with age: bone marrow fills with fat. In
osteoporosis, the bones do not merely thin; their texture becomes
lacy, and inside the holes is fat. And a few years ago, scientists
discovered a stem cell in bone marrow that can turn into either fat or
bone, depending on what signal it receives.

No one knows why the fat is in bone marrow - maybe it provides energy
for failing bone cells, suggests Dr. Clifford J. Rosen, director of
the Maine Center for Osteoporosis Research and Education. And no one
knows whether human fat cells ever leave the bone marrow and take up
residence elsewhere.

But Dr. Rubin had an idea. "We thought, Wait a second," he said. "If
we are mechanically stimulating cells to form bone, what isn't
happening? We thought maybe these bone progenitor cells are driving
down a decision path. Maybe they are not becoming fat cells."