In August 2026, the scientific community received unexpected data regarding the impact of prolonged microgravity on heart tissue. Researchers from the University of Chicago and the University of Nebraska published the results of a study showing that nearly 40 days spent on the International Space Station (ISS) did not lead to a noticeable decrease in the ability of mouse heart cells to contract. This finding casts doubt on some previously existing hypotheses about the inevitable degradation of heart muscle in space.
Sarcomeres Under the Microscope: Strength and Sensitivity
The key object of the study was sarcomeres — the basic contractile structures of the heart cell responsible for the mechanics of muscle function. Scientists compared the indicators of five mice that spent 38.5 days in orbit with a control group that remained on Earth. The results were surprisingly stable: the maximum contraction strength of sarcomeres in the "space" animals did not differ from their earthly counterparts.
Researchers did not limit themselves to strength alone. They checked the sensitivity of sarcomeres to calcium — an ion critically important for triggering contraction — as well as the degree of their cooperative work. None of these parameters changed significantly. No differences were also found in passive force and the cross-sectional area of the cells. This indicates that the internal mechanics of the heart cell remain functional even after prolonged exposure to weightlessness.
Protein Analysis: The Hidden Immune Response
To understand the molecular processes, the team conducted a mass spectrometric analysis of heart tissue proteins. Although no significant changes were found in proteins responsible for contractile function, changes in protein composition related to immune processes were identified in the "space group." This suggests that the body reacts to flight conditions, but this reaction affects other systems rather than the heart's contractile apparatus directly.
The authors emphasize that the obtained data indicate the absence of significant changes in the internal contractile state of the cells, but do not mean a complete absence of physiological consequences of flight. The body adapts, and the immune system may play a key role in this adaptation.
Contradictory Data
Although the results look promising, there are different points of view in the scientific community regarding the interpretation of this data. On the one hand, researchers insist that sarcomeres retained their function. On the other hand, critics point out that the study is based on a small number of animals (only 5 mice). Furthermore, some scientists suggest that stress associated with returning to Earth could have influenced the results and propose conducting measurements directly in orbit. This creates room for further discussion and clarification.
Prospects: From Mice to Humans
Despite the limitations, the study is significant for future space missions. A mouse's heart beats up to 600 times a minute, whereas a human's beats about 60–100 times a minute. According to the authors' estimates, 38.5 days for a mouse are comparable to approximately 7.5–10 months of human heart function. This makes the results relevant for assessing the risks of long-duration flights, such as to Mars.
The team plans to continue research by checking longer stays in space and studying animal tissues obtained directly in orbit. This will allow them to exclude the influence of return stress and obtain a more complete picture of physiological changes. The next step will be to verify whether this result is maintained during longer flights and how the discovered changes in the immune profile relate to heart function.
