The researchers talked about the behavior of muscles in zero gravity
Every day, a person works out unnoticed, even if they don't go to the gym or exercise. While we are standing, walking or just sitting, our muscles are constantly working, resisting the force of gravity. But once this load disappears, the body begins to rapidly lose muscle mass.
A new study has shown that cells literally "talk" to gravity, and stopping this dialogue triggers profound changes throughout the body. Why a person weakens quickly without gravity and how these discoveries will help not only astronauts, but also millions of patients on Earth - in the Izvestia article.
An invisible "conversation" that lasts a lifetime
Every time a person stands, walks, or simply maintains their posture, their muscles resist gravity. This is such a familiar process that we hardly notice it. However, for the body, it is this constant load that serves as the most important source of information. Without it, muscles don't understand how much strength they need to maintain, and cells don't understand which proteins to produce and how to expend energy.
The authors of a new study published in the journal Universe Today figuratively call this process a "quiet conversation" between muscles and gravity. While gravity affects the body on a daily basis, cells continuously receive mechanical signals and maintain the normal functioning of tissues. But if this "dialogue" suddenly stops, the body makes an unexpected conclusion: such powerful muscles are no longer needed, which means that their maintenance becomes too expensive.
At the heart of this process is a phenomenon known as mechanotransduction. This is what scientists call the ability of cells to convert mechanical effects— pressure, stretching, or gravity—into chemical signals. Due to this, the body regulates tissue growth, gene function, protein production and metabolism. In fact, each cell constantly "evaluates" the environment and rebuilds its activities depending on the load.
A study in the journal Nature has shown that gravity affects even the mitochondria, structures that are commonly referred to as the energy stations of the cell. When the mechanical load decreases, mitochondria begin to produce less energy, and muscle cells gradually lose their ability to maintain their previous strength and volume. That is why the loss of muscle mass begins much earlier than external changes can be noticed.
Interesting fact. Biologists believe that the ability of cells to feel mechanical stress arose millions of years ago, when the first vertebrates began to explore the land. It was then that for the first time living organisms had to constantly struggle with gravity.
Why does space make a person weaker
The role of gravity is best seen in space. Within a few days of entering orbit, the muscles begin to decrease in volume, and after weeks the changes become noticeable even with regular training. The muscles of the legs, back and body weaken especially quickly — they are the ones that hold a person against gravity on the Ground every day.
According to the National Aeronautics and Space Administration (NASA), without special physical exertion, astronauts can lose up to 20% of their muscle mass in just 5-11 days in the most sensitive muscle groups. That is why the crews of the International Space Station spend about two hours a day on treadmills, exercise bikes and power plants. However, it is not possible to completely stop atrophy even with this regime.
Interesting fact. In addition to muscles, bones shrink in zero gravity. If preventive measures are not taken, an astronaut can lose about 1-2% of bone mass per month — much faster than a person with osteoporosis on Earth.
The reason is not only that a person starts moving less. Even ordinary exercises in zero gravity require significantly less effort than on Earth. The body no longer feels its own weight, which means that the cells receive a completely different set of mechanical signals. The activity of genes is changing, protein synthesis is disrupted, the work of mitochondria is being rebuilt, and the rate of destruction of muscle tissue begins to exceed the rate of its recovery.
Space research has shown another curious pattern: many processes occurring in zero gravity resemble the natural aging of the body. That is why today space is called a unique laboratory of accelerated aging. Changes that take decades to develop in the elderly can manifest themselves in astronauts after just a few weeks of flight.
Do muscles have a "memory" of the Earth
Although scientists do not use the term "gravitational memory" officially, this is how one can figuratively describe the behavior of the human body. Millions of years of evolution took place under conditions of almost constant gravity. During this time, muscles, bones, joints, and even the nervous system have adapted so well to constant stress that they perceive it as the only possible norm. When this signal disappears, the body has to literally relearn how to work in new conditions.
After returning to Earth, this process starts in the opposite direction. Despite the fact that gravity begins to act on the body again, the muscles and brain do not immediately regain their former coordination. That is why many astronauts experience balance problems in the first days after landing, get tired faster, and undergo special rehabilitation programs that help their bodies adapt to Earth's gravity again.
A discovery that can help millions of people on Earth
Although the research is devoted to space biology, its significance goes far beyond the limits of orbit. Scientists emphasize that the mechanisms by which astronauts lose muscle mass largely coincide with those observed in the elderly, patients after severe surgery, strokes, fractures and prolonged bed rest. In all these cases, the muscles stop receiving the usual mechanical load and begin to gradually decrease in volume.
That is why doctors try to get patients up as early as possible after surgeries and injuries. Even a few minutes of walking or the simplest exercises can save significantly more muscle tissue than complete rest. Studies show that the first signs of atrophy appear only a few days after a sharp restriction of mobility, and the muscles of the legs and trunk are most noticeably affected.
According to the researchers, the body reacts to the absence of stress quite rationally. Maintaining muscle tissue requires constant energy expenditure, so with prolonged inactivity, the body begins to save resources. Studies show that at this moment the balance between the synthesis and breakdown of muscle proteins is disrupted: the rate of formation of new proteins decreases, and the processes of their destruction begin to prevail. It is this shift that gradually leads to a decrease in muscle mass and strength.
The new understanding of how cells respond to gravity opens up opportunities for the development of completely new therapies. If scientists can influence the molecular mechanisms of mechanotransduction, in the future there will be drugs that will mimic the effect of physical exertion and help maintain muscles even for those people who are temporarily unable to move independently.
Interesting fact. According to the World Health Organization, insufficient physical activity remains one of the leading risk factors for modern death. At the same time, loss of muscle mass is considered one of the main reasons for a decrease in the quality of life in old age.
Will Mars' gravity be sufficient
The results obtained are important not only for medicine, but also for future expeditions. If humanity really goes to Mars, astronauts will have to live in gravity, which is only about 38% of Earth's. So far, scientists do not know whether this will be enough for muscles and bones to maintain their normal condition for several years.
That is why researchers are trying to determine the minimum level of mechanical stress required by the body. The answer to this question will help design future Martian bases, training programs, and even living modules for deep space expeditions. At the same time, artificial gravity projects are being considered — rotating space stations or special centrifuges that can partially reproduce the usual terrestrial conditions.
Despite decades of research, scientists still don't know what level of gravity humans need for long-term extraterrestrial life. Various variants of artificial gravity are being actively studied, as well as the effect of the partial gravity of the Moon and Mars on muscles and bones. The authors of recent reviews note that such studies should become one of the main tasks of future space missions, since they will help determine what conditions a person needs for safe long-term expeditions.
Interesting fact. Over the course of a lifetime, a person takes about 150-200 million steps on average. Each movement of them is not just forward, it is also another "signal" to the muscles that gravity still exists, which means that the body needs to remain significant. That is why a regular walk turns out to be much more important for your health than it might seem at first glance.
Gravity, which we only notice when we lose
A new study reminds us of simple things: man has never existed apart from the Earth. People tend to think of gravity as an unchanging background, although it is gravity that shapes the work of our muscles, bones, and even individual cells on a daily basis. Every movement, from the first step in the morning to the evening walk, becomes part of the body's dialogue with the outside world.
The better scientists understand this "silent conversation," the closer technologies become that will help people maintain their strength and health for longer. Perhaps the discoveries made for the sake of flights to the Moon and Mars will one day make it possible to more effectively combat age-related muscle loss, accelerate recovery from serious illnesses and help millions of patients return to their usual lives.
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