Critical Gravity Level Identified to Prevent Muscle Atrophy in Space

An international research effort has determined a specific gravity level required to prevent muscle atrophy during long-duration space missions, particularly those to Mars. The study, conducted on the International Space Station's Kibo module, exposed mice to varying gravity levels. A minimum of 0.67 times Earth's gravity (0.67g) was found effective in maintaining muscle mass and function. This research provides crucial data for addressing in-space medical risks and informs the design of future spacecraft and astronaut health protocols.

A minimum of 0.67 times Earth's gravity (0.67g) was effective in maintaining muscle mass and function during long-duration space missions.

Research Collaboration and Objectives

Scientists from institutions including the University of Tsukuba, Tohoku Medical Megabank Organization, Beth Israel Deaconess Medical Center, Brigham and Women's Hospital, the Japan Aerospace Exploration Agency (JAXA), the University of Rhode Island (URI), and NASA collaborated on the study. A primary objective was to investigate how varying levels of gravity, specifically Mars' gravity (approximately 0.38g), affect skeletal muscle, which is highly susceptible to degradation in low-gravity environments. The research also considered implications for future missions planned by agencies such as NASA and the China National Space Agency (CNSA).

This research builds on previous work by Professor Marie Mortreux, who leads the Metabolism and Muscle Biology Lab (MMBL) at URI, and Professor Mary Bouxsein.

Experimental Design

The experiment involved 24 mice housed in JAXA's Kibo experimental module aboard the International Space Station. Using JAXA's Multiple Artificial-gravity Research System (MARS) centrifuge device, the mice were subjected to four distinct gravity levels over 28 days:

• Microgravity (zero gravity)
• 0.33g (approximating Martian gravity)
• 0.67g
• 1g (Earth-like gravity)

Pre-flight testing and post-flight sample collection occurred at NASA's Kennedy Space Center. Scientists at the MMBL at URI subsequently analyzed the collected samples.

Key Findings

Analysis of the muscle tissue revealed several key insights:

• Exposure to 0.33g partially mitigated spaceflight-induced muscle atrophy.
• Full prevention of muscle atrophy was observed at 0.67g, indicating this as a critical threshold for maintaining muscle mass.
• Forelimb grip strength measurements confirmed that 0.67g was sufficient to maintain muscle performance.
• Muscle loss in low-gravity environments was found to progress linearly.
• Below 0.67g, postural muscles exhibited weakening, compositional changes, and reduced endurance.
• Blood plasma analysis identified 11 metabolites that showed gravity-dependent changes. These metabolites could potentially serve as biomarkers for monitoring astronaut physiological adaptations in space.

The study, published in Science Advances, represents the first systematic mapping of biological responses to gravity as a quantifiable variable.

The study represents the first systematic mapping of biological responses to gravity as a quantifiable variable, addressing a prior gap in space medicine knowledge.

Implications for Future Space Missions and Beyond

The findings have significant implications for the planning and execution of future long-duration space missions, particularly those aiming for the Moon and Mars, such as the Artemis program. To maintain astronaut health, mobility, and operational capabilities, mitigating skeletal muscle loss is considered necessary.

The research suggests that incorporating artificial gravity systems, such as rotating toruses (e.g., NASA's NAUTILUS-X concept), into future spacecraft architectures could be highly beneficial. The data also provides foundational information for:

• Managing in-space medical risks.
• Informing the development of future habitats.
• Designing effective exercise protocols for astronauts.

Beyond space travel, the study's insights may have Earth-based applications, including research into age-related muscle loss and certain diseases.