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Microgravity

Author(s): Joanne R. Lupton, PhD
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Strategies to Conserve Muscle Mass

This schematic depicts some of the current activities proposed to maintain the homeostasis of the musculoskeletal system. In an ideal world, one could create a gravitational field on the International Space Station (ISS) or in the spacecraft used for long-term transportation. This strategy would go a long way toward maintaining the physiological status and health of humans while in space. However, for now, this strategy appears too costly. Nevertheless, artificial gravity, especially when generated by the astronaut, is a definite possibility that has been proposed by many individuals for a long time. The current NSBRI muscle team contingent has made this approach a high priority, in fact, it is the epicenter of the strategies to conserve muscle mass and enhance human performance. There also is strong advocacy for including two types of exercise regimens. The first pertains to resistance exercise, in which the astronaut would use sophisticated machines that do not require free weights for loading the muscles (use of free weights are currently considered the “gold standard” for resistance exercise on Earth). The second regimen involves some form of aerobic exercise, designed to challenge both the cardiovascular and skeletal muscle systems and enhance endurance properties in the muscle. This could involve running on treadmills or cycling bicycle-type ergometers. In addition to physical exercise strategies, many scientists believe that the homeostasis of various organ systems, including skeletal muscle and bone, can be attained through some form of nutritional supplements and/or specific pharmacological agents that can enhance (or interfere with) biological processes involved in building up (or breaking down) muscle protein content. Many individuals, in essence are looking for a “magic pill,” which may include known growth factors, to solve the problems of body wasting in space.

Whether such a pill can be designed remains a big question. What do you think of efforts by scientists to design a “magic pill” to prevent muscle wasting?

Suggested Reading:
Shackelford, L. C., LeBlanc, A. D., Driscoll, T. B., et al. (2004). Resistance exercise as a countermeasure to disuse-induced bone loss. J. Appl. Physiol. 97: 119-129.
Caiozzo V. J., Rose-Gottron, C., Baldwin, K. M., Cooper, D., Adams, G., Hicks, J., & Kreitenberg, A. (2004). Hemodynamic and metabolic responses to hypergravity on a human-powered centrifuge. Aviat Space Environ. Med. 75: 101-108.

ADDITIONAL NOTES FROM SPEAKER’S TRANSCRIPT (http://www.bioedonline.org/presentations/)
So what are we going to do about this problem (of maintaining muscle mass and strength) among astronauts in prolonged space travel? Within the National Space Biomedical Research Institute, we have developed a strategy with several components. One component is the idea that if we could reconfigure or capture gravity, or develop a gravity stimulus while individuals are in space, we probably could solve a lot of our problems, because this is really a gravity problem. If we could recapitulate gravity, we might be able to maintain normal muscle health, normal bone health, etc. Another component is weight lifting, shown in the upper left corner, of the slide. We call this resistance exercise. The big challenge for space travelers is to find a device that can load the muscles and subject them to an exercise routine, just like many of you are probably doing when you go to the gym. Obviously, we need to enable individuals to have muscle endurance, which is primarily a factor of having the individual contract the muscles at a very high frequency. This is usually done by having individuals cycle. The challenge is: can we design a cycle or a treadmill for use in space? We know that astronauts really enjoy having some form of physical activity. The treadmill or cycle might be their primary choice, but there are other strategies that people are trying to develop, including some involving growth factors. Can we give individuals a hormone, referred to as an insulin-like growth factor, that inherently induces a growth related process in the muscle? Other strategies involve better nutrition, pharmacological strategies to try to block the degradation process, and phytochemicals (referred to an anti-oxidants) in the normal diet, to decrease oxidative stress on the muscle. Some people think what is really needed is a “magic pill.” But the question is, could we design a pill that could take the place of gravity? That is a big item of debate. I think it is better to have individuals exercise.