10^th^ grade reading level

12^th^ grade reading level

Most machines don\'t improve with use. Fords don\'t gradually become
Ferraris just by driving them fast, and a pocket calculator won\'t
change into a computer by crunching lots of numbers.\
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The human body is different. As weightlifters well know, the more that
people use their muscles, the stronger they become. The opposite is also
true: lack of use won\'t preserve muscles, it makes them waste away, or
atrophy.\
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It\'s a remarkable response, and it\'s one that scientists don\'t yet
fully understand. Somehow, muscle cells \"sense\" how they\'re being
used and then automatically remodel themselves to better fit the task.
How does this happen? And what exactly is it about exercise (or the lack
thereof) that triggers the changes?\
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Improving our understanding of these questions could lead to benefits
for athletes and for people confined to a bed or wheelchair by illness
or paralysis. NASA is interested because the answers could also benefit
astronauts, who are vulnerable to muscle atrophy while in the
weightlessness of space.\
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\"\[Normally, people\'s muscles do a lot of work that they\'re hardly
aware of just to lift their bodies and maintain posture against gravity.
In space, that constant muscular work is removed, so there\'s a danger
of atrophy,\]\" explains Kenneth Baldwin, a professor in the Department
of Physiology and Biophysics at the University of California, Irvine.

Baldwin is exploring the details of how muscles respond to various kinds
of exercise, measuring both bulk muscle growth and the changes in
cellular functioning that cause that growth. This knowledge will enable
him to reevaluate astronauts\' exercise regimen, and perhaps come up
with a better prescription. For example, might resistance training be
replaced by simpler, non-moving exercises where the astronaut merely
pushes hard against a fixed surface? Such exercise would allow for
simpler, motionless exercise equipment to be used that would be less
prone to break, thus reducing the chance for problems during a mission.
But would such exercise be effective?\
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In their experiments, Baldwin\'s group gave laboratory rats a workout by
activating the rodents\' leg muscles with painless electrical
stimulation. The scientists tested how the muscles responded to three
exercise scenarios: muscle contraction, muscle lengthening, and
\"isometric,\" where the muscle exerts a force while remaining the same
length. To imagine the difference between the three, just think of doing
push-ups: muscle contraction is equivalent to the \"up\" part of a
push-up, muscle lengthening is the \"down\" part, and isometric is
holding a push-up midway.\
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After each exercise session, the scientists performed a host of tests to
see how the rats\' muscles responded, both in terms of bulk growth as
well as on the genetic and molecular level.\
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\"What we found was that after training for 12 sessions, all of the
training modes tended to provide about the same amount of \[muscle
growth\],\" even the isometric exercises that involved no motion,
Baldwin says.\
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This counterintuitive result had been encountered by other scientists
before, but Baldwin\'s group took their analysis a step further: in
addition to measuring overall muscle mass, they performed
ground-breaking measurements of the amount of contractile proteins
within the muscle cells. These contractile proteins do the actual work
of muscle contraction, so they are what give a muscle its strength. To
their surprise, Baldwin\'s team found that while isometric exercise does
cause muscles to grow, it does not increase the amount of contractile
proteins in those muscles.\
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Why this happens remains unclear, but it does teach a valuable lesson:
bulk growth of muscles and an increase of contractile proteins don\'t
always go hand in hand, and a slight difference in exercise technique
can activate one without activating the other. Baldwin and his
colleagues plan to use their recently renewed grant from NASA\'s Office
of Biological and Physical Research to look further at how contractile
proteins respond to various exercise scenarios.

A more unconventional possibility is that astronauts could stave off
muscle atrophy by merely taking a pill. Such an anti-atrophy pill is
only speculative right now, Baldwin says, but there are reasons to
believe that it is feasible. That\'s because when atrophy sets in, the
muscle isn\'t just withering away passively \-- it\'s actively breaking
itself down!\
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\"One of the things that most people don\'t appreciate is that in order
to chop those proteins up, you use a lot of energy. It\'s a very active
process, it\'s not just something that occurs willy-nilly,\" Baldwin
says. A complex network of enzymes within the muscle\'s cells actually
disassembles muscle proteins molecule by molecule. If scientists could
pinpoint a key \"lynchpin\" enzyme in this network, they may be able to
design a drug to block the action of that enzyme, thus slowing the
breakdown of the muscle.\
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This active breakdown of muscle protein is going on all the time in
everybody\'s muscles, as is the constant assembly of new proteins.
Whether a muscle grows, shrinks, or stays the same size depends on the
*balance* between these rates of destruction and construction, a bit
like the water level in a bathtub that\'s both filling and draining at
the same time.\
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Baldwin is also taking a look at the mechanisms behind the
\"construction\" half of this balance. In particular, his group is
focusing on a hormone called Insulin-like Growth Factor 1 (IGF-1).
Muscles produce IGF-1 in response to strenuous exercise, and this
hormone in turn activates enzymes in the muscle cells that cause the
cells to grow. Indeed, Baldwin found that levels of IGF-1 in the rats\'
muscles were higher just after exercising.\
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\"Some people think that it\'s the mechanical stress that turns that
gene (for IGF-1) on, but we really don\'t understand that process yet.
What we do know is that IGF-1 \[triggers muscle growth\],\" Baldwin
explains.\
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Might supplements of IGF-1 also be used to ensure that construction of
muscle proteins keeps pace with protein destruction in astronauts?
Baldwin says they\'re entertaining the idea and are already discussing
ways in which that might be done.\
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If they\'re successful, it will be good news for more than just
astronauts. After all, we\'re all owners of that incredible,
self-adapting machine called the human body.