Scientists from the University of Almería and the University of Granada, in collaboration with researchers from the Leiden University Medical Center (LUMC, the Netherlands), have identified gut bacteria of the genus Roseburia that are associated with stronger muscles and improved physical condition.
This result supports the concept of a gut-muscle axis. “Taken together, our findings provide solid evidence supporting the existence of a gut-muscle axis in which this identified bacterium actively regulates muscle metabolism and muscle strength,” says Jonathan Lewis, professor in the UGR Faculty of Physical Education and Sport and researcher at the Interuniversity Research Institute for Sport and Health (iMUDS).
Additionally, scientists have observed that the amount of this bacteria is lower in older adults than in younger adults, suggesting that its levels may decrease with age when muscle mass is lost.
This opens up the possibility that the bacteria under study could be used as a probiotic to help maintain muscle strength during aging. ”
Borja Martínez Telles, Researcher, University of Almería
Relationship between intestinal bacteria and muscle performance
The research team analyzed whether specific gut microbes were associated with muscle strength and physical condition. To do this, they studied stool samples from 90 healthy young people (18 to 25 years old) and 33 older adults (65 years and older).
The participants also underwent physical fitness tests, including grip strength, leg strength, and upper body muscle strength (chest muscles), as well as measuring their maximum oxygen consumption, an indicator of cardiopulmonary capacity.
Among the numerous bacterial groups detected, the genus Roseburia stands out because its abundance is associated with increased muscle mass and strength. In particular, certain species of Roseburia inulinivorans show a relationship with physical fitness.
Experiments demonstrated that older adults with this bacteria had 29% higher grip strength than those without the bacteria. In young adults, higher abundance of this bacterium is associated with better grip strength and cardiorespiratory fitness.
Other species of the genus Roseburia show different patterns. Roseburia intestinalis is associated with leg and upper body strength in young adults, whereas Roseburia fesis and Roseburia hominis do not show significant associations with the studied indicators.
Evaluate the connection between the intestines and muscles
To find out whether roseburia directly affects muscle function, researchers conducted experiments on mice. After temporarily reducing the gut flora with antibiotics, the animals were fed the human strain of bacteria once a week for eight weeks.
Mice that received the bacteria had about 30% more forelimb grip strength compared to mice that did not receive the bacteria.
Additionally, the mice had larger muscle fibers and a higher proportion of fast-twitch type II muscle fibers in the soleus muscle of the calf, which is important for strength and power. These changes were also accompanied by metabolic changes in proteins and enzymes that are key to muscle energy production.
Restrictions
The researchers point out several limitations. In experiments with mice, human Roseburia strains did not permanently colonize the intestine, and the study did not directly assess specific biological mechanisms such as inflammatory pathways or neuromuscular signaling. Therefore, long-term studies will be required to determine whether changes in R. canis riborans levels cause or are a consequence of improved muscle function.
The study was led by Ramón y Cajal researcher Borja Martínez Telles from the Department of Nursing, Physiotherapy and Medicine at the University of Almería, in collaboration with UGR professor Jonathan Ruiz and researcher Patrick CN Rensen (LUMC). Scientists from the University of Groningen (Netherlands) and other Spanish institutions in Valencia and Cadiz also participated in the study. This project was funded by the Martín Escudero Foundation, the Health Research Fund of the Carlos III Health Institute, and the Leiden University Fund.
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Reference magazines:
Martinez Telles, B. others. (2026). Roseburia inulinivorans increases muscle strength. intestine. DOI: 10.1136/gutjnl-2025-336980. https://gut.bmj.com/content/early/2026/03/03/gutjnl-2025-336980
