How our space mission is studying muscle loss

INDIA rejoiced when astronaut Shubhanshu Shukla returned to Earth after the Axiom-4 mission to the International Space Station. But as he was helped into a wheelchair, we were reminded of the harsh toll space travel takes on the human body. Microgravity turns muscles to jelly in weeks. Just like prolonged bed rest weakens patients, space makes even strong astronauts stumble like toddlers.

Unlike skin cells, muscle cells are not replaced; instead, they repair themselves using special satellite cells that patch up tiny tears caused by movement, keeping muscles strong.

When we do not move much for a long time, such as during bed rest, the body’s signals to repair muscles become weakened. Then, muscles start breaking down faster, lose their strength and get tired easily. It is similar to how a rubber band becomes weak if not used for an extended period of time. This slow weakening is identical to what occurs in diseases like muscular dystrophy or in old age, when muscles become weaker. While muscular dystrophy is genetic and more severe, prolonged bed rest or ageing causes muscle loss through inactivity, poor energy production and inflammation.

While astronauts float through their spacecraft and conduct daring spacewalks, their antigravity muscles, the very muscles that usually fight Earth’s gravity daily, go unused. These postural muscles, including calves, thighs, back and core, work constantly to maintain your posture, whether you are standing, sitting or walking. They are your built-in support system, with endurance-focussed muscle fibres designed for sustained activity against gravity’s pull.

Microgravity mimics that brief, weightless sensation in your stomach when an elevator begins descending, your body and the elevator drop together for a split second before the descent smoothens out. In space, astronauts experience this feeling continuously. Gravity has not disappeared (Earth’s pull is still at work), but their spacecraft is in a perpetual, controlled free-fall around the planet. Like an elevator that never stops dropping, this endless fall creates the illusion of weightlessness, known as microgravity. In space, the antigravity muscles do not have to work much and they become lazy and weak, just like during bed rest. That is why astronauts find it challenging to walk when they return home.

From astronauts to bedridden patients to the elderly and those with muscular dystrophy, maintaining muscle strength is a constant challenge. While exercise remains the gold standard, researchers are now asking: Could flavonoid-rich foods do more than just slow muscle wasting, might they actually help rebuild and strengthen muscles? Early studies hint at this possibility, but the evidence is far from conclusive.

Flavonoids are natural compounds — found in foods such as berries, apples, onions, green tea and dark chocolate — known for their health benefits. They might help keep skeletal muscles healthy by acting like tiny helpers inside your muscle cells. Flavonoids can boost mitochondrial biogenesis, assisting cells to create more mitochondria, the “powerhouses" that produce ATP, the energy muscles need to work. More mitochondria mean stronger, more energetic muscles. Plus, flavonoids act as antioxidants, combating harmful molecules called reactive oxygen species (ROS) that damage muscle cells during stress, exercise or ageing. By neutralising ROS, flavonoids protect muscle cells, potentially keeping them stronger.

The Axiom-4 Myogenesis-ISRO experiment, led by Arvind Ramanathan’s group in Bangalore, studied how weightlessness in space affects muscle growth and tested whether plant-based flavonoid nutrients could help prevent muscle wasting. They used special lab containers called BioCells, like tiny high-tech “cell homes", to grow human muscle stem cells. These containers function like mini-labs in space, allowing researchers to feed the cells, alter their liquid environment and preserve samples for study. Unlike regular lab dishes, BioCells can mimic how cells naturally attach or float, making them ideal for space experiments.

During the Axiom-4 mission, a set of BioCells containing human muscle stem cells was placed under Shukla’s care. Over eight days in microgravity, he administered differentiation media every 48 hours to stimulate the stem cells’ development into muscle fibres. Think of these muscle precursor cells as raw clay, the differentiation media acts like a potter’s skilled hands, using precise biochemical signals such as growth factors to shape them into functional muscle fibres. The experiment tested multiple flavonoid combinations, different BioCell wells received distinct cocktail formulations, while control groups received no flavonoids.

For ground-based comparison, Ramanathan’s team maintained an identical set of BioCells in their inStem lab. They repeated the experiment by giving the same mix of nutrients and flavonoids at the same time as was done in space. They watched how the muscle cells grew both in the lab and on International Space Station.

Shukla has safely returned to Earth with the space-exposed samples, which will be shipped to inStem. The scientists will compare them with the ones grown on Earth. They will use special methods to study them. RNA sequencing will reveal how microgravity impacts genes that facilitate muscle repair and support energy production in cells. Proteomic profiling will help track changes in proteins that maintain muscle strength and stimulate energy production. High-resolution microscopy and functional assays will be be used to study differences in cell structure, proliferation and differentiation capabilities. The Earth-based cultures, grown identically but under normal gravity, serve as the baseline to isolate microgravity-specific effects.

This study aims to advance our understanding of muscle degradation by revealing key molecular mechanisms and evaluating how metabolic supplements affect mitochondrial function and muscle regeneration through comparative analysis of treated and untreated cells. The findings may lead to new therapeutic approaches for sarcopenia, muscular dystrophy and disuse atrophy.

Space gives a unique chance to study muscles. In microgravity, astronauts lose muscle quickly — what takes years on Earth can occur in a few weeks in space. This enables one to observe how muscle cells cease to repair and become weak.

Earth-based simulations, such as bed rest or laboratory models, cannot fully replicate space conditions, as they fail to reproduce the unique disruption of cellular energy production (mitochondrial function) and repair signalling pathways that occurs in microgravity. By studying these processes in actual microgravity, researchers gain clearer, more reliable insights into muscle deterioration and recovery mechanisms, benefiting both space medicine and terrestrial healthcare applications.

The blind receive sight, the lame walk — not by miracles, but through meticulous science.

TV Venkateswaran is Visiting Professor, IISER Mohali.

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