Articles of Justification

Muscle Volume, MRI Relaxation Times, (T2) and Body Composition after Spaceflight 

Source:

LeBlanc, A., Lin, C., Shackelford, L., Sinitsyn, V., Evans, H., Belichenko, O., . . . Feeback, D. (2000). Muscle volume, MRI relaxation times (T2), and body composition after spaceflight. Journal of Applied Physiology, 89(6), 2158-2164.

Artifact Summary:

During the Spacelab mission – Space Shuttle Era – four male crewmembers’ muscle compositions were studied and compared before and after a seventeen-day mission. After analyzing the gastrocnemius, soleus, anterior leg, quadriceps, hamstrings, intrinsic lower back, and psoas muscles with MRI, it appeared that muscle region volume (except for those of the hamstrings) decreased from 3 to 10 percent. When evaluation periods extended to 16 to 28 weeks during the Mir Shuttle missions, muscle volume losses ranged from 5 to 17 percent (the neck region was the outlier in these secondary trials). Again, this report corroborated the soleus and calf muscles’ susceptibility to the most microgravity atrophy/deterioration. However, post-flight analysis of the calf muscle revealed swelling and elevation that persisted for weeks, which indicates a degree of muscle damage provoked by the microgravity environment. 

After normalizing and compiling the data from three separate experiments, the researchers compiled an exponential function for modeling muscle recovery. Typically, muscle volumes recovered within 30 to 60 days after missions from 16 to 28 weeks. A recovery of roughly ten days occurred for the astronauts who spent seventeen days in space. On a side note, muscle fiber diameters decreased by 8 percent on average, which stays consistent with the decrease in muscle strength. For the record, this document also analyzes bone mass loss, but such statistics do not apply to our problem after reading a NASA Johnson Space Center report that deemed the risk of microfractures highly unlikely to bar mission success. Therefore, our research and project will continue solely based on investigating muscle atrophy.  

Artifact Critique:

The prior two documents focused exclusively on the loss of muscle strength, but they did not quantify the loss of muscle volume: this article does so, establishing the degree of muscular atrophy while focusing less on the impacts of atrophy. The findings of this research corroborate the importance of my problems in two ways. First, it provides a mean magnitude of muscular deterioration in size, which further establishes the impacts of microgravity deterioration and strengthens the arguments on muscle weakening. Second, by analyzing the muscle recovery rates on Earth, one can argue that muscle weakening in space can lengthen mission times and efficacy if astronauts need to re-establish their lost muscle mass after a long time in space. Thirty to sixty days of post-flight ambulation and exercise after trips lasting less than four months? Given that a Martian mission takes roughly nine months, the time needed to re-establish muscle mass, volume, and strength will increase. Pair this conclusion with the fact that decreased volume leads to decreased strength, which also reduces further while using an EMU, and the atrophy issue rises in pertinence. 

While the aforementioned facts provided great supporting information, I must confess that the source is a bit of a research dead-end. At this point, most of my research should now focus on finding out the relationship, the equation perhaps, between muscle volume and muscle force. Doing so will allow me to contextualize the effects of muscle volume loss better, although it is quite common sense that the less muscle volume a person has, the less muscle mass they have. Therefore, the less muscle mass they have, the less force they can generate. On a side note, although the paper does provide a model for calculating muscle-recovery time, there is no way of telling how microgravity would impact the rate of recovery. Future research demands more mathematical modeling to accentuate this issue’s effects further.

Physiology of a Microgravity Environment Invited Review: Microgravity and Skeletal Muscle

Source:

Fitts, R. H., Riley, D. R., & Widrick, J. J. (2000). Physiology of a Microgravity Environment Invited Review: Microgravity and skeletal muscle. Journal of Applied Physiology, 89(2), 823-839.

Artifact Summary:

The research presented stems from STS-78 (Columbia space shuttle expedition 78), which documented muscle atrophy in both rats and humans during a 17-day long mission. Unlike previous documents, however, this journal article delves deep into the cellular causes of atrophy in space – please bear with the jargon. Type II quick-twitch fibers disproportionally lost more mass than type one fibers. Moreover, according to rat trials, muscular damage occurred after atrophy when reintroduced to Earth’s gravity. Therefore, this journal suggests against in-flight muscular damage due to atrophy, but rather establishes that most damage will occur once an astronaut reloads or ambulates normally. Again, this may pose a risk for low-gravity environments, but the exact relationship is unknown. 

Microgravity exposure results in an unequal loss of contractile proteins in muscles instead of other cellular proteins. Moreover, the actin thin filament of muscles decays much faster than myosin thick filaments. These trends result in a decrease in generable force per cross-sectional area (in a fiber) and increased type 1 muscle fibers in space travel. Furthermore, it is worth noting that both the rats and humans experienced increased susceptibility to fatigue during the experiment, but the exact causes are unknown (all one can speculate is that the fatigue has something to do with the atrophy of muscles). For the sake of brevity, I will also simplify the genetic reason for muscular atrophy. It appears that unloading – reducing gravity – reduces protein synthesis and alters gene expression in cells, resulting in reduced rates of polypeptide chain translation. This fact explains why muscle proteins decreased, although I must confess that it is difficult for me to explain the specific chain of events that result in the altered gene expression due to microgravity – this issue stems more into the fields of scientific research than engineering design and development, at the moment. Moreover, mitochondria in muscle fibers decreased in concentration, which correlates to a sapped ability to generate cellular energy. At any rate, the document also cites other research that recorded a 54 percent reduction in astronaut leg peak power, although power is mathematically different from force – all this statistic does is further quantify the loss of efficacy in space due to muscular decay.

Artifact Critique:

Once again, this document proves my assertion, but I consider it vital to my research due to its provision of different arguments supporting my problem statement. Unlike previous documents, the document establishes that in-flight muscular damage due to microgravity alone is unlikely and unfounded. While this may lessen the concerns raised by a previous source, the statement that followed in the discussion suggested that microgravity muscle damage may be significant in another space flight phase: reloading. Reintroducing rats to the Earth’s gravity caused muscular damage and tearing (refer to the first document for specific examples), implying that microgravity increases muscle damage risk. Therefore, if astronauts reload in an environment with a weakened gravity, is it not possible to see some of these risks, albeit to a lesser extent?

Even if the moon’s gravity is roughly a sixth of the Earth’s, and Mars’ gravity is approximately a third of the Earth’s, this potential for reloading damage still exists and poses potential problems for surface excursions. At this point, I believe each source has given me a distinct argument in support of the mitigation of muscular loss. However, this article is even more critical in that it helped me establish a more intimate understanding of how muscles lose their strength in space. Microgravity alters gene expression, resulting in a lower concentration of muscular fiber mitochondria and proteins that promote usage. I cannot mitigate cellular damage, but I can perhaps find a way of increasing the use of the muscles most affected by microgravity, namely the soleus of the calf.  

Muscle Volume, Strength, Endurance, and Exercise Loads During 6-Month Missions in Space

Source:

Gopalakrishnan, R., Genc, K. O., Rice, A. J., Lee, S. M., Evans, H. J., Maender, C. C., . . . Cavanagh, P. R. (2010). Muscle Volume, Strength, Endurance, and Exercise Loads During 6-Month Missions in Space. Aviation, Space, and Environmental Medicine, 81(2), 91-104.

 Artifact Summary:

I believe that this research article was one of the numerous sources cited in the first report on risks of muscle decay in space, and with good reason. The following data come from a six-month study aimed at quantifying changes in muscle volume, strength, and endurance (a super-study, if you will) of astronauts during a six-month stay on the International Space station. The study builds upon several of the experiments detailed in previous sources, including the STS-78 expedition. Although the duration lasted as long as the 23-week MIR study, the ISS study resulted in a 0.23 percent decrease in quadriceps muscles, 0.28 percent decrease in hamstring muscles, 0.72 percent decrease in soleus muscles, 0.40 percent decrease in gastrocnemius muscles, and 0.41 percent decrease in the anterior calf per week. In fine, these data points corroborate an 18.6 percent decrease in soleus muscle volume over the course of six months, even with improved exercised regimens derived from the findings of previous studies. Granted, specific muscles have shown a significant reduction in atrophy rate over the years of the space program. The hamstrings, for example, show a lower percentage of decay when compared to the MIR results. 

Unfortunately (for me, really), there appears to be no directly proportional relationship between muscle volume and muscle strength. One astronaut reported a 17.6 percent loss in muscle volume after the mission, which corresponded to a 19.5 percent loss in isokinetic strength and 31.5 percent loss in isometric strength. While these numbers aren’t exactly new, their derivation from the same experiment shows that one cannot merely calculate muscle strength loss from volume loss without a mathematical equation with some sort of constant. Fortunately, the data to prove, once again, the direct relationship between muscle volume and strength.

Artifact Critique:

After a profuse degree of research concerning muscular atrophy in space, it becomes increasingly evident that many studies will cross-reference. Understandably, this is since only a few agencies across the world have sent individuals to space. However, this source dramatically contributes to my stance by updating and corroborating most of the data accumulated across the years of space flight. This document’s data tables provide a nail in the proverbial coffin that establishes this issue’s importance and future baselines for developing a potential solution. At this point, all future research should be, with instructor permission, aimed at learning how to develop a solution, not if I should develop a solution.

The research provided also introduces an exciting prospect that can ultimately assist in the development of a solution. Although the following note is somewhat tangential to the contribution of the source to defending a solution – because, in all honesty, this source strengthens all of the research previously found – I can run a couple of calculations to create a model on my own. By averaging the results found in the astronaut muscle volume changes, I believe I can use a linear regression model to determine if there is an applicable equation that sets muscle strength as a function of volume. Doing so would remove the need for additional research, moving me straight into the situation simulation phase of this project! Furthermore, on a side note, the data provided does offer an in-depth analysis of the kinds of motion depreciation recorded by astronauts in the study. If I can find research on what movements are most repeated in an EVA, these statistics will further solidify my claims while also giving my product development direction.

An Overview of Sarcopenia: Facts and Numbers on Prevalence and Clinical Impact

Source:

Haehling, S., Morley, J. E., & Anker, S. D. (2010). An overview of Sarcopenia: facts and numbers on prevalence and clinical impact. Journal of Cachexia, Sarcopenia and Muscle, 1(2), 129-133.

Artifact Summary: 

This report concerns the prevalence of human muscle decay in elderly individuals (here on Earth). After the age of fifty, muscle mass declines at a rate of one to two percent per year. On average, muscular strength declines by 1.5 percent per year between 60 and 70, and by three percent per year afterward. Up to 13 percent of older adults aged 60-70 suffer from Sarcopenia, while up to 50 percent may suffer from Sarcopenia after 80 years. However, neither of these statistics is as important as the fact that Sarcopenia may lead to frailty later in life. 

Artifact Critique:

This article cursorily does not correlate to microgravity-related muscular decay. However, its real importance lies in the clinical data provided. Astronauts can lose up to 23 percent of muscle strength in six months – at least five percent of total strength throughout the body, given the aggregation of individual muscle strength losses, by my speculation – it is clear that the muscular atrophy is exacerbated in space. Beforehand, the statistics referenced in previous documents had magnitude but no frame of reference with which to compare the loss of muscular strength. On average, it will take an active human on the Earth five to twenty years (extrapolated values) to lose the strength an astronaut loses in six months in space. 

Yes, this source does not corroborate any pre-existing data on the decay of muscles in space. But by analyzing the decay of muscles here on the Earth, it becomes increasingly clear that space-related muscular atrophy is inherently a genuine and potentially dangerous problem. If the elderly fall prey to fall-sustained damage and frailty in later life due to Sarcopenia, it is easier to imagine the potential decay of muscles in space over prolonged periods without any physical training.