Muscles and Microgravity: Lessons from Space to Combat Aging on Earth

Introduction

Microgravity research has far-reaching implications for human health. By studying the effects of long-term weightlessness, scientists are gaining vital knowledge that benefits astronauts on extended missions and those facing muscle and bone degeneration on earth. 

Thanks to Organ-on-a-Chip devices, and to microgravity simulation hardware by companies like Litegrav, progress in this area is rapidly accelerating. 

Many scientists view interplanetary travel as a necessary next-step for civilization. However, the path forward is not without obstacles. Prolonged exposure to microgravity has detrimental effects on human health, particularly on muscles and bones. Understanding and countering challenges of muscle atrophy (sarcopenia) and bone density loss (osteopenia) is paramount. 

Muscle mass decreases approximately 3–8% per decade after age 30. This not only predisposes us to frailty and falls, but has consequences for metabolic health. From diabetes and heart disease to, more recently, Alzheimer’s and other forms of dementia, muscle mass is consistently linked with many areas of well-being (Kim, 2020; Boyle, 2022; Tessier, 2022). 

Microgravity and Muscles

In both real and simulated microgravity, muscle mass and strength decline. This is largely due to reduced use and protein production. Muscles lose their “anti-gravity load,” which causes a rapid loss of contractile proteins responsible for strength and movement. 

Actin proteins degrade even faster than myosin, leading to weakened but more rapidly moving muscles upon return from orbit (Fitts, 2000).

In an experiment with NASA’s rotating cell culture system, scientists observed that while weightlessness stimulates cellular growth, it also reduces muscle proteins and interferes with muscle cells’ ability to fully mature (Slentz, 2001). 

Moreover, muscles become more susceptible to damage, especially when readjusting to gravity. Microgravity conditions also lead to increased production of free radicals, which can worsen muscle degradation, although antioxidants could counteract these effects (Powers, 2014).

Another factor is mitochondrial dysfunction. Microgravity disrupts cellular respiration and energy production, leading to muscle fatigue. PGC-1α, which is essential for mitochondrial health and muscle preservation, plays a critical role in this process (Bonanni, 2023).

Bones in Microgravity

Bone density loss is a major concern for long-duration space missions. As early as December 1989, U.S. and Russian researchers observed drastic bone loss in cosmonauts aboard the Mir space station, noting reductions in spine and hip density within four months. Exercise alone was insufficient to counteract bone deterioration (LeBlanc, 2000).

In microgravity, astronauts experience a 1–2% monthly drop in bone density. This loss occurs as bone breakdown accelerates while formation either stalls or decreases (Man, 2022). Within the first two weeks in space, bone resorption spikes, releasing calcium from bones and disrupting the hormone PTH, which, in turn, affects vitamin D activation. 

Though overall vitamin D levels remain sufficient, lower calcium absorption impedes new bone formation. Additionally, microgravity impairs bone-forming cells and accelerates bone cell death (Caillot-Augusseau, 2000).

Current Solutions and Future Directions

Researchers are actively investigating strategies to counteract muscle and bone atrophy in microgravity. 

Astronauts aboard the International Space Station (ISS) engage in intensive, two-hour daily exercise regimens using specialized equipment that mimics Earth-based weightlifting and aerobic exercises to preserve muscle and bone mass (NASA, n.d.).

In addition, researchers at the University of Florida have developed a tissue chip model for age-related muscle loss, using the ISS’s microgravity environment to study muscle wasting and aging on a cellular level. 

These tissue chips, derived from human skeletal muscle cells, reveal how microgravity triggers muscle-aging genes, providing insight into sarcopenia, a condition which, in its more severe forms, affects up to 13% of the elderly population (von Haehling, 2010; Parafati, 2023).

Implications for Muscles and Bones in Deep Space

While exercise alone may not fully prevent bone and muscle loss, advancements in exercise technology, diet, and medicine are promising. NASA’s Vegetable Production System (and other advances in space agriculture) are allowing astronauts to grow fresh produce, ensuring essential nutrients for maintaining health (NASA, 2019). 

Ongoing research into space-specific medications by institutions like the Baylor College of Medicine’s Center for Space Medicine may also lead to medical solutions for mitigating microgravity’s effects, benefiting astronauts and helping to combat muscle and bone deterioration in the elderly (Baylor College of Medicine, n.d.).

Conclusion

Microgravity is a new window on biology. Although space-related muscle and bone loss remains a challenge, these findings open doors to optimized treatments and preventative measures for sarcopenia, osteopenia, and a growing list of other health conditions.  

We move closer to a future where the physiological challenges of space are mitigated—both for those exploring the cosmos and for individuals on earth.

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References and Suggested Reading

Baylor College of Medicine. (n.d.). Center for space medicine. https://www.bcm.edu/academic-centers/space-medicine

Bonanni R, Cariati I, Marini M, Tarantino U, Tancredi V. Microgravity and Musculoskeletal Health: What Strategies Should Be Used for a Great Challenge? Life (Basel). 2023 Jun 21;13(7):1423. doi: 10.3390/life13071423. PMID: 37511798; PMCID: PMC10381503.

Boyle PA, Buchman AS, Wilson RS, Leurgans SE, Bennett DA. Association of muscle strength with the risk of Alzheimer disease and the rate of cognitive decline in community-dwelling older persons. Arch Neurol. 2009 Nov;66(11):1339-44. doi: 10.1001/archneurol.2009.240. PMID: 19901164; PMCID: PMC2838435.

Caillot-Augusseau A., Vico L., Heer M., Voroviev D., Souberbielle J.C., Zitterman A., Alexandre C., Lafage-Proust M.H. Space flight is associated with rapid decreases of undercarboxylated osteocalcin and increases of markers of bone resorption without changes in their circadian variation: Observations in two cosmonauts. Clin. Chem. 2000;46:1136–1143. doi: 10.1093/clinchem/46.8.1136.

Fitts RH, Riley DR, Widrick JJ. Physiology of a microgravity environment invited review: microgravity and skeletal muscle. J Appl Physiol (1985). 2000 Aug;89(2):823-39. doi: 10.1152/jappl.2000.89.2.823. PMID: 10926670.

International Space Station National Laboratory. (2024, October 24). A unique opportunity to study sarcopenia in microgravity. ISS National Laboratory. https://issnationallab.org/press-releases/release-upward72-malany-sarcopenia/

LeBlanc A, Schneider V, Shackelford L, West S, Oganov V, Bakulin A, Voronin L. Bone mineral and lean tissue loss after long duration space flight. J Musculoskelet Neuronal Interact. 2000 Dec;1(2):157-60. PMID: 15758512.

Malany, S. (2024, October 24). A unique opportunity to study sarcopenia in microgravity. ISS National Laboratory.https://issnationallab.org/press-releases/release-upward72-malany-sarcopenia/

Man J, Graham T, Squires-Donelly G, Laslett AL. The effects of microgravity on bone structure and function. NPJ Microgravity. 2022 Apr 5;8(1):9. doi: 10.1038/s41526-022-00194-8. PMID: 35383182; PMCID: PMC8983659.

Narici MV, de Boer MD. Disuse of the musculo-skeletal system in space and on earth. Eur J Appl Physiol. 2011 Mar;111(3):403-20. doi: 10.1007/s00421-010-1556-x. Epub 2010 Jul 9. PMID: 20617334.

NASA. (n.d.). Counteracting bone and muscle loss in microgravity. NASA. https://www.nasa.gov/missions/station/iss-research/counteracting-bone-and-muscle-loss-in-microgravity/#:~:text=In%20microgravity%2C%20without%20the%20continuous,induced%20muscle%20and%20bone%20atrophy.

NASA. (2019, April). Veggie: Veg-01 plant growth system onboard the International Space Station. https://www.nasa.gov/wp-content/uploads/2019/04/veggie_fact_sheet_508.pdf

Parafati M, Giza S, Shenoy TS, Mojica-Santiago JA, Hopf M, Malany LK, Platt D, Moore I, Jacobs ZA, Kuehl P, Rexroat J, Barnett G, Schmidt CE, McLamb WT, Clements T, Coen PM, Malany S. Human skeletal muscle tissue chip autonomous payload reveals changes in fiber type and metabolic gene expression due to spaceflight. NPJ Microgravity.2023 Sep 15;9(1):77. doi: 10.1038/s41526-023-00322-y. PMID: 37714852; PMCID: PMC10504373.

Powers SK. Can antioxidants protect against disuse muscle atrophy? Sports Med. 2014 Nov;44 Suppl 2(Suppl 2)

. doi: 10.1007/s40279-014-0255-x. PMID: 25355189; PMCID: PMC4213375.

Slentz DH, Truskey GA, Kraus WE. Effects of chronic exposure to simulated microgravity on skeletal muscle cell proliferation and differentiation. In Vitro Cell Dev Biol Anim. 2001 Mar;37(3):148-56. doi: 10.1290/1071-2690(2001)037<0148

>2.0.CO;2. PMID: 11370805.

Statista. (2023). Projected global median age 2022-2100. Statista. https://www.statista.com/statistics/672669/projected-global-median-age/

Tessier, Anne-Julie, et al. "Association of low muscle mass with cognitive function during a 3-year follow-up among adults aged 65 to 86 years in the Canadian longitudinal study on aging." JAMA Network Open 5.7 (2022): e2219926-e2219926.

University of Oxford. (n.d.). Materials science. https://www.ox.ac.uk/admissions/undergraduate/courses/course-listing/materials-science

von Haehling S, Morley JE, Anker SD. An overview of sarcopenia: facts and numbers on prevalence and clinical impact. J Cachexia Sarcopenia Muscle. 2010 Dec;1(2):129-133. doi: 10.1007/s13539-010-0014-2. Epub 2010 Dec 17. PMID: 21475695; PMCID: PMC3060646.

https://pmc.ncbi.nlm.nih.gov/articles/PMC2804956/#:~:text=Muscle%20mass%20decreases%20approximately%203,to%20disability%20in%20older%20people.

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