The study, led by researchers from the University of Tsukuba and international partners, used a world-first system aboard the International Space Station to raise mice under controlled gravity conditions ranging from microgravity to Earth-like levels.
Conducted inside Japan’s Kibo laboratory module, the experiment exposed mice to four environments – zero gravity, Mars-like gravity (0.33G), an intermediate level (0.67G), and full Earth gravity – over a month-long period using JAXA’s unique variable gravity system.
The results were striking. Researchers found muscle loss in low-gravity environments occurs in a near-linear fashion, with at least 0.67G required to maintain muscle mass and function. Below that threshold, key postural muscles began to weaken and shift in composition, reducing endurance and performance.
The study also identified 11 potential blood biomarkers that reflect how the body responds to different gravity levels, opening the door to simple blood tests to monitor astronaut health during missions.
Published in the journal Science Advances, the findings mark the first time scientists have been able to systematically map how biology responds to gravity as a measurable variable, a longstanding gap in space medicine.
The implications are significant. As the US-led Artemis program ramps up plans to return humans to the moon and eventually push on to Mars, understanding how reduced gravity impacts the body is a major challenge.
Scientists said the research provides a foundational dataset for managing medical risks in space, including muscle degradation, and could inform the design of habitats, exercise regimes and even artificial gravity systems for future missions.
Beyond spaceflight, the findings could also have applications on Earth, particularly in treating age-related muscle loss and disease, offering a rare example of space research delivering direct benefits back home.