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Above: On the Mir space station, a U.S. astronaut works up a sweat
during his daily treadmill exercise.
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Above: Despite the physical and psychological benefits, exercise is
an all too rare activity for many of us.
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Above: A bicycle ergometer will be part of the Space Station exercise
program to maintain bone, muscle, and cardiovascular strength.
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Out of This World Workout - The Role of Exercise in Space
The news isn’t good. Nearly half of adolescents and young adults get
no vigorous exercise on a regular basis. Only 40 percent of adults exercise regularly,
while 25 percent never do. For people ages 75 and over, the numbers are even worse.
It’s clear that, on Earth, exercise is an all too rare activity for many
of us. We may have good intentions, but never quite make it off the couch or out
the door. On long duration space flights, where physical fitness can impact crew
safety and the success of a mission, good intentions aren’t good enough.
Exercise is a necessity.
Gravity Makes the Workout Work
Gravity is good for us, though it may not seem that way after puffing up a
few flights of stairs or lugging a 40-pound bag of top soil. The pull of gravity
on our bodies helps to keep our muscles, bones, and cardiovascular system strong
and healthy. Every time we stand, walk, or pick something up, our muscles work
against gravity. With each gravity-defying activity, our bones react by triggering
the formation of additional bone mass. 
The more we lift and the faster we move, and the more often we do both, the
stronger our bones and muscles become. If we are active enough for long enough,
our cardiovascular system gets a workout as well. But what would happen if we
no longer had gravity to work against?
During space flight, astronauts experience microgravity, a force one millionth
as strong as the gravitational force we feel on Earth. The human body, which evolved
to thrive in Earth’s gravity, adapts to this new environment. Bones that
supported body weight on the ground no longer have that load to bear. They begin
to lose mass and strength, as do weight-bearing muscles in the lower body. Reduced
physical activity and a shift of fluids into the upper body combine to reduce
cardiovascular capacity. This process is known as deconditioning.
While in space, these changes don’t present a problem, but gravity can
be hard on a body no longer used to it. Whether returning to Earth or landing
on some other planet, the body’s adaptation to microgravity increases the
risk of broken bones, reduces work capacity, and can result in balance disorders
and even blackouts when standing.
A Highly Exclusive Health Club
To minimize microgravity’s impact, NASA employs inflight exercise as a
countermeasure. Exercise maintains bone mass, muscle strength, and cardiovascular
capacity, but microgravity makes it tricky. You can’t just pump some iron
or go for a run. Special equipment is required in this health club.
Three types of exercise are planned for the International Space Station. Together,
they help counteract the effects of microgravity. Cycling using a bicycle ergometer,
or exercise bike, offers a good cardiovascular and leg-muscle workout. With a
shoulder brace to keep the astronauts from floating away, the ergometer is relatively
easy to use in a weightless environment. What it doesn’t do so well is provide
adequate loading forces to keep bones strong.
Treadmill running offers a superior workout for maintaining bone strength.
The downside is that an elasticized harness must be used to simulate gravity by
pulling the user against the running surface. This makes the process so uncomfortable
that astronauts are forced to take breaks every five or ten minutes.
While treadmills and ergometers have been used in space since Skylab in the
1970s, they tend to cause a good deal of vibration. This can disrupt sensitive
experiments elsewhere in the spacecraft, making sophisticated shock absorption
systems necessary. Resistive exercise, a relative newcomer to the inflight workout,
sidesteps the vibration issue. Astronauts load their bones and muscles by working
against a resistive force, usually by pulling against strong bungee cords. Less
motion is involved and so there is very little vibration.
On the Space Shuttle, where flights usually last less than two weeks, half
an hour of daily exercise is recommended, but not mandatory, for crew members.
In the Space Station era, astronauts will be living in microgravity for months
at a time. To counteract greater, and potentially dangerous, levels of deconditioning,
NASA will require one to two hours of exercise each day. Other countermeasures,
such as drug therapy, will also be used.
In the future, NASA hopes to develop ways to make exercise in space more effective,
more efficient, and more pleasant. Research in this area has already resulted
in technologies that benefit the disabled and those needing rehabilitation. Eventually,
it could offer all active people technologies or fitness programs that generate
maximum health impact in minimum time.
Regular exercise reduces the risk of everything from heart disease to diabetes
to colon cancer. It can also reduce depression and anxiety. But even these benefits
haven’t convinced millions of Americans to lace up their running shoes. If
NASA could just find a way to get all those people up and moving, it would really
have something there.
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