Scientists have identified a specific type of gut bacteria that may be linked to greater muscle strength, according to a new study published in the journal Gut. The research adds to a growing understanding of a connection between the digestive system and physical performance.
Researchers analyzed stool samples from two groups: 90 healthy young adults between the ages of 18 and 25, and 33 older adults aged 65 and up. The team then measured physical fitness in the participants through handgrip strength tests, leg press and bench press assessments, and VO2 max testing, which measures how efficiently the body uses oxygen during exercise.
The goal was to find if any specific bacteria in the gut microbiome were consistently linked to stronger muscles or better performance. Out of all the microbes detected, one group stood out: Roseburia, a genus of bacteria already known for producing beneficial short-chain fatty acids in the gut. Within that group, one species in particular drew the researchers’ attention: Roseburia inulinivorans.
Older adults who had detectable levels of this bacterium showed 29% higher handgrip strength compared with those who did not. In younger adults, higher levels of the same microbe were linked to both stronger grip strength and higher VO2 max. Other Roseburia species did not show the same pattern, suggesting that different bacteria within the same family may influence muscle health in different ways.
To explore whether the bacteria might actually cause changes in muscle performance, the researchers ran a follow-up experiment in mice. After temporarily reducing the animals’ gut microbes with antibiotics, the scientists introduced different Roseburia species into the mice’s microbiomes once per week for eight weeks.
Mice given R. inulinivorans developed about 30% greater grip strength compared with the control group. Their muscles also showed structural changes. Specifically, the mice developed a greater proportion of type II (fast-twitch) muscle fibers, the kind responsible for explosive movements like sprinting, jumping, and lifting heavy weights. Their muscle fibers were also larger overall. Researchers also observed shifts in metabolic pathways involved in muscle energy production, suggesting the bacteria may influence how muscle tissue processes fuel.
The findings support the idea of a “gut–muscle axis,” where microbes in the digestive tract help regulate muscle metabolism and strength. However, the research is still early. The study shows strong associations, but it does not prove that increasing this bacteria directly boosts strength in humans. Long-term studies are still needed to determine whether higher levels of R. inulinivorans actively improve muscle function or simply reflect other healthy behaviors that support strength.
There are already several evidence-backed ways to support beneficial gut bacteria that may indirectly benefit muscle health. Roseburia species thrive on fermentable fibers found in foods like oats, beans, lentils, onions, garlic, and asparagus. Resistance training remains the most reliable way to maintain muscle mass and power, especially with age. A varied diet rich in plants, fermented foods, and whole ingredients helps cultivate a more diverse gut microbiome, something strongly associated with better health outcomes.
Muscle strength has traditionally been viewed through the lens of workouts and nutrition. This new research suggests another key player may be involved: the microbes living in the gut. The research does not replace the fundamentals like lifting, eating protein, and getting adequate recovery, but adds a layer to the conversation. What is fed to the gut may be shaping muscle health in ways that show up at the cellular level long before they are noticed in the weight room.
