As part of the Programa of Parceria of Plataforma Aberta Japão-USA (JP-US OP3), the Agência of Exploração Aeroespacial of the Módulo Experimental Japonês “Kibo” at Estação Espacial Internacional (ISS). Utilizando JAXA’s exclusive Sistema of Pesquisa of The results of this pioneering study, published on March 14, 2026, in the prestigious journal *Science Advances*, reveal a remarkable linear dependence on gravity in biological responses, with crucial implications for the health of astronauts.
The investigation specifically focused on the soleus muscle, an antigravity muscle vital for maintaining posture. Comprehensive analyzes were not limited to molecular changes such as gene expression, but also included functional assessments such as muscle strength and electromyography. The findings indicate that muscle atrophy in microgravity varies almost linearly with severity levels, suggesting that a minimum of 0.67G is essential to preserve muscle mass and function.
In parallel with muscle analysis, a detailed investigation of blood components identified severity-dependent changes in hematic indicators. Foram identified 11 candidate biomarkers that reflect differences in gravitational environments, opening new doors for assessing the impact of gravity on living organisms through minimally invasive methods such as blood tests. Simulated gravity environments included:
– Microgravidade: absence of gravity.
– 0.33G: equivalent to Martian gravity.
– 0.67G: intermediate severity between Marte and Terra.
– 1G: equivalent to Earth’s gravity.
Advances in understanding muscular responses to gravity
The research delved deeper into the analysis of the soleus muscle, crucial for posture, subjecting the mice to a battery of tests that ranged from the molecular to the functional level. The international team of scientists from JAXA, Universidade of Tsukuba, Universidade of Tohoku, Universidade of
The results provided unprecedented clarity about the linearity of muscle wasting, or atrophy, under microgravity conditions, and its relationship to different gravitational levels. The discovery that at least 0.67G is necessary to maintain muscle mass and function offers fundamental data for defining strategies to protect the health of astronauts.
Innovative blood biomarkers for spatial assessment
In addition to the muscle study, the team carried out a detailed analysis of the blood components of mice exposed to different gravity environments. Esta complementary approach aimed to identify systemic indicators that could reflect adaptations or stresses caused by gravity.
The identification of 11 promising blood biomarkers represents a significant advance. Estes markers not only corroborate biological changes observed in environments of varying gravity, but also offer a potentially revolutionary tool for monitoring the health of astronauts in a less invasive way, allowing for regular, real-time assessments of the effects of gravity during long missions. The possibility of estimating the degree of impact of gravity on a living organism through a simple blood test could optimize health protocols in future explorations.
Challenges of human space exploration and partial gravity
With the Artemis program, led by the Estados Unidos, driving manned lunar exploration and the vision of missions to Marte, humanity is preparing for a new era of deep space presence. One of the biggest obstacles to be overcome is the deleterious impact of reduced gravity on living organisms, both in deep space and on the lunar and Martian surface.
Although knowledge about skeletal muscle has advanced considerably in recent decades, there remains a gap in understanding how biological responses behave in partial gravity environments, which lie between total microgravity and terrestrial gravity (1G). Especificamente, the existence of a linear relationship in responses to gravity and how this connects with easily assessable indicators, such as blood, was not fully understood.
This JAXA-NASA study offers the first global systematic understanding of biological responses using gravity as a quantitative parameter. Essa scientific basis is crucial for assessing medical risks and developing effective countermeasures for future long-duration manned missions, including those targeting Lua and Marte, where exposure to partial gravity will be a constant.
The crucial role of the MARS system in module Kibo
The ability to carry out this innovative research is largely due to the Sistema of Pesquisa of Gravidade Variável (MARS), a unique device developed by JAXA and installed on the ISS’s Módulo Experimental Japonês “Kibo”. MARS is the only equipment in the world that can grow mice in artificial gravity environments that range continuously from microgravity to 1G.
Before MARS, terrestrial simulations and short-term space experiments already indicated that microgravity affected the quantity and quality of muscles. However, the severity “threshold” needed to prevent atrophy and changes in muscle fiber type remained a mystery. MARS overcame this limitation, allowing researchers to accurately reproduce and compare different gravity levels in the microgravity environment of space, providing invaluable data.
Skeletal muscles: sensitivity and adaptation in space
Gravity is one of the most fundamental and important environmental factors for maintaining the bodily functions of living organisms in Terra. Diversas Biological functions, including the cardiovascular, immune, and balance systems, are profoundly influenced by gravity. Skeletal muscle, in particular, demonstrates a marked sensitivity to any variations in this factor.
It is a known fact that astronauts experience a significant decrease in muscle mass, known as muscle atrophy, and a corresponding reduction in strength during prolonged stays in space. Este phenomenon represents one of the greatest medical challenges for long-duration space missions. Muscles are made up of different types of muscle fibers, such as slow-twitch and fast-twitch, each with different speeds and energy use patterns. Na Terra, slow-twitch fibers continually work against gravity to maintain posture. Contudo, in a microgravity environment, their activity decreases drastically, leading to a reduction in these fibers and a “muscle fiber type conversion”, which transforms them into fibers with fast twitch characteristics. Essa change not only decreases muscle mass, but also compromises endurance and overall muscle function, impacting the physical capacity of astronauts.
Impact for future missions and astronaut safety
This research from JAXA and NASA establishes a fundamental scientific framework for evaluating and mitigating medical risks associated with future long-duration manned missions. By quantifying the dependence of biological responses on gravity and identifying a critical threshold for muscle maintenance, the study provides essential data. The findings will directly assist in developing more effective countermeasures and formulating guidelines to protect the health and performance of astronauts on their journeys to Lua and Marte, ensuring the sustainability of human space exploration.
