Universe Today
NASA and the China National Space Agency (CNSA) plan to send astronauts to Mars as early as the next decade. Naturally, this ambitious goal requires a great deal of planning, research, and the anticipation and preparation for all potential challenges in advance. Among them, astronaut health and safety are paramount. In addition to the hazards associated with the long transit times - radiation and the effects of long periods in microgravity - there's the issue of Mars itself. Aside from exposure to elevated radiation levels, Martian gravity is about 38% of Earth's.
This has the potential to lead to long-term health risks. An international team of researchers is currently studying how Martian gravity will affect a key aspect of human health: skeletal muscle. This muscle, which is the most abundant tissue in the human body (accounting for more than 40% of total body mass), is essential to movement and metabolic health. What's more, this tissue is especially sensitive, and lower gravity could potentially result in the substantial loss of muscle strength, size, and performance. It is therefore important to determine how this muscle tissue will fare in the Martian environment.
The research team was composed of scientists from the Institute of Medicine at the University of Tsukuba, Tohoku Medical Megabank Organization, the Advanced Research Center for Innovations in Next-GEneration Medicine (INGEM), the Beth Israel Deaconess Medical Center, the Brigham and Women’s Hospital, the Japan Aerospace Exploration Agency's (JAXA) Space Environment Utilization Center, and multiple universities. The results of their research appeared in the journal Science Advances
*Experiments aboard the International Space Station with mice showed that muscle atrophy can be mitigated and prevented in lower gravity. Credit: NASA/ESA–T. Pesquet*
For their experiment, the team studied how lower gravity affected skeletal muscle tissue in 24 mice sent to JAXA's Kibo experimental module. These mice were then placed in a JAXA-developed centrifuge device called the Multiple Artificial-gravity Research System (MARS), where they were subjected to four different levels of gravity - microgravity, 0.33 g, 0.67 g, and 1 g - over a 28-day period. The mice were subjected to pre-flight testing before launch at NASA's Kennedy Space Center, where they were returned for post-flight sampling.
These samples were then examined by scientists at the Metabolism and Muscle Biology Lab in the Department of Nutrition at the University of Rhode Island (URI). As Professor Marie Mortreux, who leads the MMBL, attested in a Rhoby Today news story:
While we can simulate spaceflight on Earth in humans, it’s extremely complicated and costly. We have centrifuges that can be used to temporarily expose humans to certain gravity levels, but it is not homogeneous nor constant. We used gravity levels that were equally separated, to have a better picture of the dose-response of each system to gravity. The test group that was exposed to 0.33g was extremely close to Martian gravity (0.38g). Our findings for that group can be translated into actions to enable Mars exploration.
Mortreux and her team analyzed the weight, strength, and movement of the mice once they were returned to NASA's Kennedy Space Center. Their analysis showed that 0.33 g mitigated spaceflight-induced muscle atrophy, with full prevention at 0.67 g. They also measured the mice's forelimb grip strength using Electrical impedance myography (EIM), which showed that 0.67 g was sufficient to maintain muscle performance.
*The research team at Kennedy Space Center confirming the protocol and timing prior to receiving animals for post-flight sampling. Credit: URI*
Their results collectively demonstrated that 0.67 g is a critical threshold for mitigating muscle atrophy caused by prolonged spaceflight. In addition, an analysis of the mice's blood plasma identified 11 metabolites that showed gravity-dependent changes, suggesting they could serve as potential biomarkers to monitor physiological adaptations in astronauts. This work builds on previous research she performed with Professor Mary Bouxsein (a co-author on the study) at Harvard Medical School.
Whereas Dr. Bouxsein developed the ground-based mouse model of partial gravity in the early 2010s, Montreux developed the rat model of partial gravity at Harvard. As such, the two are well-acquainted with the impact that different gravity levels have on musculoskeletal tissues.
"Since this mission aimed to assess gravity as a continuum, we were perfectly positioned to see if our ground-based results had similar outcomes when reduced mechanical loading was applied in orbit," said Montreux. "Working with an international team was challenging and exciting. I think my experience working in Italy, France, and the United States prepared me for those big-scale collaborations."
One takeaway from this study is that future missions to Mars will need to be mindful of mitigating skeletal muscle loss during the long transit between Earth and Mars. For astronauts to maintain mobility, muscle strength, and carry out regular science operations. The same holds true for their physical health upon returning to Earth.
These findings suggest that rotating toruses would be a wise addition to any future spaceflight plans, a la NASA's Non-Atmospheric Universal Transport Intended for Lengthy United States Exploration (NAUTILUS-X) and similar aspects.
Further Reading: Rhody Today, Science Advances
