At the WMAC 2026 in Daegu last month, a 106-year-old athlete threw the discus and javelin, and athletes in their 80s cleared hurdles. The athletes were elderly, but their bodies and minds were young. Exercise not only builds muscle strength but also boosts immunity and keeps the brain young.
Even if illness or age makes it hard to move, a path has opened to enjoy the benefits of exercise. Transplanting muscle cells made from stem cells appears to deliver the health effects seen during exercise, even at rest.
A team led by Professor Shyh-Chang Ng at the Institute of Zoology, Chinese Academy of Sciences, said it developed a contractile muscle graft (myograft) that can mimic the benefits of exercise, including increased muscle strength and bone density, reduced body fat, and improved cognitive function, according to a paper published Aug. 26 in the journal Nature Aging.
◇ Rejuvenating muscle with thigh muscle stem cells
The team first collected stem cells from the thigh muscles of mice. In the lab, they cultured the stem cells and made a thin graft composed of muscle cells—essentially a transplantable muscle. They implanted this muscle graft under the skin on the backs of mice. To prevent immune rejection, each graft was made from the recipient mouse's own cells.
They first tested the effect of muscle transplantation in mice 8 to 10 weeks old, roughly equivalent to humans in their early 20s. Mice that received the graft developed thicker muscle fibers than other mice. Muscle inflammation and fat decreased.
Next, they tested old mice 18 months of age, equivalent to humans in their early 60s. Eight weeks after transplantation, the ratio of muscle to bone was higher than in other mice. After 15 weeks, grafted mice had higher bone density than others. They ran farther and had stronger grip strength than age-matched mice. As the muscles rejuvenated, physical performance improved.
The graft's effects did not stop at physical performance. The researchers induced obesity by feeding a high-fat diet. Mice that received the muscle graft had a lower fat ratio than other mice. Blood sugar and cholesterol levels were likewise lower. Even with plenty of food, the grafted muscle prevented obesity.
◇ Preventing obesity and enhancing cognitive function
Changes also appeared in metabolism and cognition. Grafted mice showed lower triglyceride levels and reduced liver damage and inflammation. In particular, mice with grafts spent more time exploring unfamiliar areas in maze escape tests than other mice. That is evidence of superior brain function.
The team said the graft's benefits appear to stem from myokine proteins released when muscle contracts. Myokines are linked to exercise effects such as reduced inflammation and improved brain health. Ng explained that the muscle graft continuously secretes myokines that would otherwise be obtained only after hours of exercise.
The researchers noted that although the work is still at the mouse experiment stage, if applicable to humans it could help prevent muscle loss and bodily changes caused by aging or chronic disease. Ng said the team is discussing clinical trials with physicians to assess the graft's effects in actual patients.
Other researchers, however, say it is still a long way from applying these results to humans. They said the therapeutic mechanism must be clearly defined before moving to clinical trials. Gordon Lynch at the University of Melbourne suggested that testing the graft's effects in mice with muscle diseases such as Duchenne muscular dystrophy could be informative.
◇ Rejuvenating the brain by contracting neural cells instead of exercising
Even if the mechanism is clarified, implanting muscle just to gain exercise benefits is not an easy decision, even for people confined to bed. U.S. scientists have proposed a way to capture at least the brain-rejuvenating effects of exercise without muscle transplantation.
A team led by Justin Rhodes at the University of Illinois at Urbana-Champaign found that exercise contracts brain cells and regenerates nerves. They also identified substances secreted by neural cells in the process. Administering only these substances, instead of exercise, also produced nerve-regenerating effects. The work points toward a potential exercise pill.
Scientists have found in animals that physical activity promotes the growth of neurons in the hippocampus, the brain region for learning and memory. Rhodes found that astrocytes play a key role in this process. True to their name, these star-shaped cells do not transmit nerve signals themselves but supply substances that help neurons grow and recover—a kind of neural support corps.
The team confirmed that mice running on a wheel showed biomarkers associated with astrocyte contraction. That means exercise induced astrocyte contraction. To test this, they collected substances secreted when mouse muscle cells contract. Applying these to astrocytes also caused contraction. The finding shows that when exercising, muscle cells and brain astrocytes contract together.
Finally, the team administered substances released by astrocyte contraction to neurons in the mouse hippocampus. Immature neurons then appeared. Nerves had regenerated. Substances from astrocytes with stronger contraction produced greater nerve-regenerating effects. The scientists said that identifying the components in astrocyte secretions that promote nerve regeneration could lead to treatments that maintain brain function in patients who find it hard to exercise.
References
Nature Aging (2026), DOI: https://doi.org/10.1038/s43587-026-01190-3
bioRxiv (2026), DOI: https://doi.org/10.1101/2026.08.06.742872