Scientists from the University of Almería and the University of Granada, along with researchers from Leiden University Medical Center in the Netherlands, announced on Mar. 12 that they have identified a bacterium in the genus Roseburia that is associated with stronger muscles and better physical condition.
The findings are significant because they support the idea of an intestine-muscle axis, suggesting that certain gut bacteria may play a role in muscle metabolism and strength. "Taken together, our findings provide solid evidence confirming the existence of an gut-muscle axis in which this identified bacterium positively modulates muscle metabolism and muscle strength," said Jonatan Ruiz, professor at the Department of Physical Education and Sport at the University of Granada and researcher at the Joint University Institute for Sport and Health.
The research team studied stool samples from 90 healthy young adults aged 18 to 25 years old and 33 older adults aged 65 or above. Participants also completed several physical fitness tests measuring handgrip strength, leg strength, upper body strength, and maximum oxygen consumption as an indicator of cardiorespiratory capacity. The results showed that Roseburia was more abundant in younger adults than older ones, indicating its levels may decrease with age—a period when muscle mass typically declines.
Among various bacterial groups detected, Roseburia stood out for its association with increased muscle mass and strength. Specifically, one species—Roseburia inulinivorans—was linked to better physical fitness. Older adults who had this bacterium demonstrated 29% greater handgrip strength compared to those without it. In young adults, higher abundance correlated with both greater handgrip strength and improved cardiorespiratory capacity.
Further experiments involved mice whose gut microbiota were reduced using antibiotics before being given human strains of Roseburia weekly for eight weeks. These mice showed about a 30% increase in forelimb grip strength compared to untreated animals. They also developed larger muscle fibers and a higher proportion of fast-twitch type II fibers important for power.
However, researchers noted limitations: human strains did not permanently colonize mouse intestines, and some biological mechanisms were not directly assessed. Long-term studies will be needed to determine whether changes in R. inulinivorans levels cause improvements in muscle function or result from them.
The study was led by Borja Martínez-Téllez from the University of Almería's Department of Nursing, Physiotherapy, and Medicine; Jonatan Ruiz; Patrick CN Rensen (Leiden); as well as scientists from other Spanish institutions and Groningen University.
