APU Health & Fitness Original Space

Exercise in Space: Physical and Economic Considerations

By Daniel G. Graetzer, Ph.D.
Faculty Member, School of Health Sciences

According to the National Aeronautics and Space Administration (NASA), the exercises that keep us healthy, happy, and strong on Earth are similar to the exercises needed to keep astronauts healthy, happy, and strong in space. While space travelers can be protected from freezing cold, blazing heat, extremely low pressure and cosmic radiation, it is very difficult to protect space travelers from the physical deconditioning that accompanies living in a weightless environment. Exercises and gyms used in space may look considerably different from ours, but the same principles apply.

What Happens to the Human Body in Space?

When humans are exposed to weightlessness, several unusual things happen. On Earth, gravity draws our body fluids into our legs when we stand or sit.  

However, in a weightless space environment, these fluids are free to move toward the head, causing necks and faces to swell. After a few days, the body’s marvelous control system causes extra urination, which eliminates the excess fluid. 

This adaptation does not make much difference in space, but when the space traveler returns to Earth’s gravity, there is trouble. The lost fluid causes the body’s blood pressure to fall, and often astronauts are unable to tolerate standing in place upon their return because blood tends to pool in their legs.

The reduced blood volume is insufficient to maintain adequate circulation to the brain, which results in fainting. When an astronaut lands back on Earth, being unable to stand could be a potentially serious problem in an emergency such as a quick evacuation.

Another change which occurs in space flight is a loss of bone mineral that could eventually lead to a type of space-induced osteoporosis. This loss is potentially more serious than fluid loss because body fluids can be quickly replaced. Bone loss, however, involves a slower replacement process and perhaps in some advanced cases, the bone may never completely recover.

Space travel also involves a loss in muscle size, strength and endurance. This loss is most severe in the legs and torso, but there is less of a problem with arm and shoulder muscles.

In a weightless environment like space, most movement involves pulling yourself around with your arms. Since you weigh nothing in space, your legs and torso do not have to support your body weight, and your legs do not have the job of carrying you from one location to another. The leg muscles become less toned and less able to prevent blood from collecting in the lower body.

Another change that occurs when humans are weightless is that the circulatory system no longer has to pump blood against the constant downward pull of gravity. In fact, “up” and “down” really have no practical meaning in space; the hundreds of small blood pressure adjustments that normally occur in healthy people as they move about on Earth are absent in space.

The circulatory system is less taxed in the space environment and readily adapts to the less stressful atmosphere. But on return to Earth’s gravity, an astronaut’s altered circulatory system might not provide the capacity needed to flee a crashed or burning spacecraft while the astronaut is wearing heavy launch and entry equipment.

Also, reduced cardiorespiratory fitness means a decreased ability to perform physical work in space. The construction of future space stations will require many hours of such work.

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Exercise Helps to Preserve Health in Space

Though there are several possible antidotes to the body’s negative adaptations to reduced- gravity environments, exercise will undoubtedly turn out to be a major health preservation tactic. For example, even a single running or cycling workout has been shown to increase the blood volume of laboratory subjects on Earth.

Astronauts lose body fluids, including blood plasma, in space. Since lowered blood volume may contribute to reduced cardiovascular fitness, a vigorous workout the day before landing may help astronauts return to Earth in better shape for an emergency.

The classic way to build muscle is pumping weights. “Weight” does not mean nearly as much in space, but the effects of resistance training on muscles, bones and blood circulation are still important for space travelers on long trips.

Aerobic and resistive exercises raise blood pressure, which may actually help space travelers maintain their heart function during long flights. As many of us have experienced, exercise may provide psychological benefits to space travelers as well as physical benefits.

Exercise of any type is certainly different in space than on Earth, but some workouts might be easier in space. For example, a rowing machine does not need to possess a seat in space and neither does an exercise cycle.

On the other hand, running on a treadmill is more difficult in space because there is nothing to hold you on the tread or apply stress to your leg muscles. Weightlifting is not simple because weights are weightless in the space environment.

Another handicap of space exercise is that there are serious limitations to the amount of space and electrical power that can be used for equipment and exercising. For instance, the U.S. space shuttle may house five to nine astronauts, who have to eat, sleep, work and exercise in an area not much bigger than a good-sized bathroom.

Noisy workout equipment is not generally welcome in the close quarters of a space shuttle. Also, storage space is limited, so bulky workout equipment simply cannot be transported to space in a shuttle. But the most distressing aspect of exercise in space for many of us would be taking a shower after exercise in an environment where water does not fall downward?

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What Type of Workout Equipment Has Been Used to Exercise in Space?

Because of all these limitations, only a few pieces of exercise equipment have been carried to space in the U.S. space program. The first products used by astronauts to exercise in space were rubber stretch cords, which allowed some resistive training. 

The cords were followed by the old Mini Gym, an early isokinetic-type resistive device. The first “space treadmill” consisted of a slippery piece of Teflon to which astronauts were tied with stretchy bungee cords.

The current treadmill used by astronauts to exercise in space is probably smaller than any treadmill you have ever seen. It is not motorized, but is pushed by the runner’s feet.

Astronauts also use a specially designed exercise cycle. The main difference is that the space cycle needs no seat, and toe clips keep an astronaut’s feet on the pedals.

Exercise in Space Is Expensive

If you think you have trouble finding time for a workout, think of those poor astronauts. Due to the expense of workout equipment, the expense of training and all the ground support people required for space flights, exercise costs close to $100,000 per man-hour in space.

As a taxpayer, how much time do you want the astronauts to spend on a stationary cycle as they exercise in space? Because of this expense, much time and effort has been devoted to develop ways for astronauts to get the most exercise accomplished in the least amount of time.

The best type and amount of exercise optimal for future space travelers is currently under investigation, but it will undoubtedly be very intense for long trips. Certainly, finding practical ways to exercise in space and stay healthy will allow us to venture to Mars and beyond.

Daniel G. Graetzer, Ph.D., received his B.S. from Colorado State University/Fort Collins, MA from the University of North Carolina/Chapel Hill, and Ph.D. from the University of Utah/Salt Lake City and has been a faculty member in the School of Health Sciences, Department of Sports and Health Sciences, since 2015. As a regular columnist in encyclopedias and popular magazines, Dr. Graetzer greatly enjoys helping bridge communication gaps between recent breakthroughs in practical application of developing scientific theories and societal well-being.

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