Mar 24, 2026
3 min read
Researchers have discovered that gut bacteria can affect muscle strength and endurance, opening the door to probiotics that support healthy aging.
Tiny microbes live in the human gut.They help digest food, support the immune system and influence the way the body uses energy.Scientists now think that they can also affect muscle strength.
Muscles tend to weaken as we age.Exercise and diet help, but researchers believe bacteria may play a role.
Scientists noticed that a microbe appeared more often in people with strong muscles.
Researchers from the University of Almeria, the University of Granada and the Leiden University Medical Center began to investigate this connection.
The research team focused on bacteria belonging to the Roseburia genus.These microbes are already known to help the gut produce beneficial compounds during digestion.New findings suggest they may also aid muscle health.
Jonathan Ruiz, professor at the Department of Physical Education and Sport at the University of Granada and researcher at the Interuniversity Institute of Sport and Health (iMUDS), explained the broader significance of the findings.
“Taken together, our findings provide strong evidence supporting the existence of a muscle-stimulating mechanism by which a well-known bacterium modulates muscle production and strength,” Ruiz said.
To explore this link, the researchers studied stool samples from two groups of volunteers.
The first group included 90 healthy young people aged 18 to 25 years.The second group included 33 adults aged 65 and over.
Participants completed several physical fitness tests.These included hand grip strength, leg strength, and upper body strength by testing the chest muscles.
The experts also measured maximal oxygen consumption, a common way to assess cardiorespiratory fitness.
Among the many bacterial groups in the gut, Rosebury stood out.Higher levels of these microbes appeared along with greater muscle mass and strength.
One species, Roseburia inulinivorans, showed a clear correlation with fitness.Older adults who carried this bacteria showed 29% greater hand grip strength compared to those who did not.
In young adults, more of the same microbe is associated with a stronger immune system and better cardiorespiratory fitness.
Other members of the Roseburia family showed different patterns.Roseburia intestinal appears to be related to leg strength and upper body in young people, while Roseburia faecis and Roseburia hominis showed a significant link to the physical indicators measured in the study.
Human data showed a strong association, but researchers wanted to see if the bacteria could affect muscle function.To test this idea, they turned to laboratory mice.
The scientists first reduced the animals' natural gut microbes using antibiotics. Then they injected the human version of Roseburya into the mice once a week for eight weeks.
The results were astounding.Mice that received the bacteria showed a 30% increase in grip strength in their forelimbs compared to animals that did not receive the treatment.
The muscles themselves have also changed.Treated mice developed larger muscle fibers and a greater proportion of type II muscle fibers in the calf soleus muscle.
These fast-twitch fibers are closely related to strength and power.The researchers also looked at changes in proteins and enzymes involved in how muscles produce energy.
One important detail emerged when the scientists compared the younger and older participants.Roseburia bacteria appeared less frequently in older people.
This decline helps explain why muscle mass declines later in life.While these microbes play a role in muscle metabolism, the loss of their support system can weaken muscles.
Borja Martínez Téllez, a researcher at the University of Almeria, explained, "This is the possibility of using the bacteria under test as a probiotic to protect muscle strength during aging.
The concept is simple but promising.Instead of targeting muscles directly, scientists can help the body conserve energy by supporting certain gut microbes.
The research team stressed that some questions remain unansweredIn experiments with mice, the human strain of Roseburia did not persist in the intestines of the animals.
Scientists have also not directly examined biological pathways such as inflammation or neural signaling between muscles and the nervous system.
Another important question needs to be answered by future research.Do Roseburia inulinivorens help build muscle or do strong people have more of these bacteria in their guts?
Despite the uncertainty, the results suggest something interesting: the gut and muscles may be more connected than scientists ever thought.
The full study was published in the journal Gut.
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