All living things on Earth are accustomed to gravity. We don't often think about how gravity keeps us from floating away or how it keeps us strong. The pull of gravity on our bodies gives us a bit of a workout -- strengthening our muscles, bones and cardiovascular system. Gravity places a load on our muscles and bones. Every time we stand, walk or pick up something, our muscles work against gravity. 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?
In space, astronauts experience "microgravity." This means the pull of gravity that they feel is only about one-millionth of the gravity we feel on Earth. The prefix "micro" means small or one-millionth. Without regular use and exercise, our muscles weaken and deteriorate. It's a process called atrophy. Studies have shown that astronauts experience up to a 20 percent loss of muscle mass on spaceflights lasting five to 11 days. When bones do not get exercise, they lose minerals. This loss is called disuse osteoporosis.
NASA uses countermeasures to prevent some of the damage that occurs to the bones and muscles of space explorers. A countermeasure is an action to counteract, or change the effects of, another action. NASA uses the term "countermeasures" to describe procedures, strategies, medications and exercises that help keep astronauts healthy and productive while they are traveling in space and after they return to Earth. Exercise countermeasures prevent or counteract some of the bone and muscle loss in an astronaut's body.
Resistive Exercise Resistive exercise, or strength training, is like lifting weights. Remember that weight depends on the force of gravity. In microgravity, it is useless to lift weights because everything is practically weightless. Instead of lifting weights, astronauts do exercises that offer resistance. The Interim Resistance Exercise Device, or IRED, has two cylinders. Inside each cylinder are 13 disks that are joined together by a series of rubber connections. Astronauts can change the setting for the number of disks to use. When an astronaut pulls on a cord connected to the machine, the disks create resistance.
The newest resistive exercise device is the Advanced Resistive Exercise Device, or ARED. It was taken to the International Space Station on space shuttle mission STS-126 in November 2008. The ARED provides a load of up to 600 pounds and has a touchscreen that makes it easier for crew members to follow a personalized exercise plan. Resistive exercise is a countermeasure. This kind of exercise prevents the major muscle groups from weakening and lessens bone loss. Resistive exercise helps astronauts maintain strength and endurance.
Exercise Bike Floating around in space doesn't require much legwork. But astronauts' leg muscles still need a workout, so they use an exercise bike in space. The cycle ergometer exercise consists of pedaling an exercise cycle. The cycle ergometer provides strength exercise for the upper legs. It also provides a workout for the heart and lungs just as other aerobic exercises do. Cycle ergometry can be performed in either a manual mode, where the astronaut controls cycling workload, or an electronic mode. The exercise bike on the space station is called the Cycle Ergometer with Vibration Isolation and Stabilization, or CEVIS.
Treadmill Exercise Treadmill exercises include walking, running, deep knee bends and some resistive exercises. The treadmill is used to maintain bone mass, cardiovascular fitness and muscle endurance. The treadmill also helps to maintain reflexes needed for walking on Earth or other planetary surfaces. Crew members can run the treadmill in active or passive modes. Active is with the motor running. Passive is without the motor. With the motor, astronauts can adjust the speed to 10 mph in increments of 0.1 mph. Astronauts must wear a harness to use the treadmill in microgravity. The treadmill on the space station is called the Treadmill Vibration Isolation System, or TVIS.
During her stay on the space station, astronaut Sunita Williams participated in the annual Boston Marathon by running on the treadmill. She ran up to eight mph and her official completion time was 4:23:10.
Astronauts living on the space station are required to work out for as much as two hours a day. This amount will probably increase as NASA prepares to send explorers to live on outposts on the moon and travel to Mars.
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