The Astronaut Dilemma

By: Jonna Ocampo, Expert Contributor, TMF

Edited by: Jack Grierson, Expert Contributor, TMF

From the first space mission to Scott Kelly’s spending a year in space, there are major changes impacting the human body. Comparatively, gravity on Earth has an impact on the body and microgravity does too. Microgravity is a term used to describe when people or objects experience weightlessness, also known as zero g or the experience of zero gravity. This can be done on Earth during a parabolic flight or in space, which occurs to astronauts when they are floating around on the International Space Station.

When spending an extended period of time in zero gravity, there are notable effects for astronauts that scientists are trying to solve.

On Earth, gravity allows us to stand up and walk around. It makes it possible to develop strength, stability, and agility, but as you age, you may begin to feel the effects of gravity more, for instance when you experience an injury. Every injured step makes gravity seems so much greater. You may feel the weight of gravity more when you become more sedentary or workout less because of a detraining effect. A detraining effect can be described as the loss of strength due to a decrease in bone density and an increase in muscle atrophy, often attributed to a sudden break in fitness training. The body’s ability to adapt to a force will also decrease. As a result, the human body experiences a decrease in bone mass and muscle atrophy. Hence, you may start to feel aches and pains. In space, there is less physical activity due to microgravity; therefore, a decrease in both nitrogen (required for muscle growth) and muscle functions. This is therefore a problem that can potentially affect an astronaut’s performance in terms of their activities and health. Spaceflight changes protein metabolism and prevents the body from keeping its resting respiration rate, affecting the astronaut’s mobility.

Research shows that the body’s hormone levels being in an anabolic (processes making molecules for metabolism) or catabolic (processes that break down molecules in metabolism to release energy) state can add to these issues. When studying these dilemmas, the current methods used to tackle the problem of extended microgravity on the body are through analogs resembling spaceflight. One of these analogs is throuigh the use of bed rest studies. This model simulates a microgravity environment to duplicate the problems experienced by astronauts due to their time spent on the International Space Station and their body’s physiological changes. As a result, bed rest studies have shown in adding a small amount of resistance exercise keeps muscle protein synthesis. Upon conducting these studies, analysis of bone loss, muscle atrophy, fluid shifts and hormonal changes of those in space becomes apparent. These studies can also potentially benefit those on earth who are aging, recovering from trauma, injury, or orthopedic surgery.

Spaceflight leads to a loss of lean body mass, protein, and nitrogen, which can affect the health, and daily activity levels of the crew. The loss happens quickly, which affects muscle function and strength. A prime example is the common occurrence of MRI images showing a loss in muscle of volume of the back and legs by 6–10% after eight days aboard the Space Shuttle. As mission length increases so does its effects on the body. In a 28-day Skylab mission, besides the loss of muscle in the back and the legs, it also included a loss of arm strength. With even longer missions and exposure to microgravity, performance is compromised, creating a potential for injury and trauma to the body. Data has shown that when there is an excess of 10% of a loss of lean body mass, impaired immune function occurs and can slow down the ability for wounds to heal, thus prolonging rehabilitation after a long-term spaceflight.

For skeletal muscle, protein turnover enables the human body to utilize the limited amount of available amino acids . The cycle of protein utilization and breakdown allows the body to regulate enzymatic systems, get rid of defective proteins, and regulate metabolic processes. During spaceflight, this synthesis and loss create a negative net balance resulting in loss of muscle nitrogen. Scientists’ are using a combination of factors try to tackle these issues, and ongoing studies show promise that with adding essential amino acids and carbohydrate supplementation may slow down the loss of lean body mass and muscle strength. In space, there is a reduced dietary intake, due to a lower energy needs with an apparent reduction of consuming 30% fewer calories and a change in the body’s hormonal levels. For example, when a crewmember was given 20% more calories in space than they had in preflight, their body’s protein synthesis was still 30% below their preflight levels.

The body’s hormonal response in microgravity increases cortisol excretion (a hormone affiliated with stress) and therefore the concentration of cortisol in the blood elevates. Unfortunately, it remains in a range of an upper normal to above-normal level throughout the microgravity experience. Even urinary cortisol excretion appears to stay high during both short-term and long-term spaceflights. Other hormonal changes occur such as a decrease in testosterone, which decreases by 50% after only five-day in space.

Presently, nothing is perfect, and there are still many problems that need solutions concerning spaceflight. Research studies do their best to duplicate spaceflight weightless on the human body, but it is not yet fully replicated in nature. Over the years, spaceflight is trying to resolve the issue of bone loss and muscle atrophy with an increase in relevant atrophy preventing technology. The addition of both aerobic and anaerobic exercise opportunities for astronauts in space and the development of programs by Astronaut Strength and Conditioning Specialists on the ground at Johnson Space Center plays a large role in this. Food scientists are continuously working on perfecting the nutritional needs of astronauts whilst providing an increase in the ration’s quality, taste, aesthetics of color and texture. The use of analogs, such as bed rest studies at NASA JSC and a current one in Cologne, Germany with the German Space Agency, are simulating low-gravity environments, conducting research on individuals, and developing countermeasures to combat the effects of microgravity to the human body.

Works Cited:

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LeBlanc A, Rowe R, Schneider V, Evans H, Hedrick T. Regional muscle loss after short duration spaceflight. Aviat Space Environ Med 1995;66:1151

Stein TP, Leskiw MJ, Schluter MD. Diet and nitrogen metabolism during spaceflight on the shuttle. J Appl Physiol 1996;81:82

Stein TP, Leskiw MJ, Schluter MD, Donaldson MR, Larina I. Protein kinetics during and after long-duration spaceflight on Mir. Am J Physiol (Endocrinol Metab) 1999;276:E1014

Tipton KD, Ferrando AA, Phillips SM, Doyle D, Wolfe RR. Post-exercise net protein synthesis in human muscle from orally administered amino acids. Am J Physiol (Endocrinol Metab) 1999;276:E628

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