A specific species of gut bacteria may be linked to stronger muscles, according to new research exploring how the microbiome might influence physical performance and age-related muscle loss.
In a study published in the journal Gut, researchers found that the bacterium Roseburia inulinivorans was associated with higher muscle strength in people and improved grip strength in mice.
The findings add to a growing body of research suggesting that the trillions of microbes living in the digestive tract may influence more than digestion, potentially affecting metabolism, inflammation and physical function.
To investigate the connection, researchers analyzed stool samples from 123 adults in the Netherlands. The group included 90 younger adults between ages 18 and 25 and 33 older adults aged 65 and older.
Participants also completed several fitness assessments. Researchers measured handgrip strength, leg press and bench press performance and maximal oxygen uptake, a measure of cardiovascular fitness.
Among the various bacterial species detected in stool samples, members of the Roseburia genus showed the strongest association with muscle strength. One species in particular, Roseburia inulinivorans, stood out.
Older adults who had detectable levels of R. inulinivorans in their gut microbiome had 29% higher handgrip strength than those without it.
In younger adults, greater abundance of the bacterium was associated with stronger grip strength and higher VO₂ max, an indicator of aerobic fitness.
The researchers then conducted a second experiment in mice to explore whether the bacteria might play a direct role in muscle function.
Mice were first treated with antibiotics to reduce their existing gut bacteria. They were then given different species of Roseburia once a week for eight weeks.
Mice that received R. inulinivorans showed about a 30% increase in forelimb grip strength compared with control animals. The treated mice also developed larger muscle fibers and a greater proportion of fast-twitch muscle fibers.
Fast-twitch, or type II, muscle fibers are specialized for short bursts of power such as sprinting or lifting weights.
The researchers also observed changes in metabolic pathways involved in muscle energy production.
“Collectively, our findings provide robust evidence supporting a gut-muscle axis in which R inulinivorans positively modulates muscle metabolism and muscle strength,” the researchers wrote.
Still, the findings are early and do not show that the bacterium directly causes stronger muscles in humans.
The human portion of the study was observational, meaning it can identify associations but cannot determine cause and effect. It is also possible that people with stronger muscles or healthier lifestyles are more likely to harbor certain gut bacteria.
In addition, the bacteria given to mice did not fully colonize their digestive systems, and the researchers did not directly examine pathways related to inflammation or nerve signaling that could influence muscle performance.
The researchers note that levels of R. inulinivorans appear to decline with age, which could potentially contribute to sarcopenia, the gradual loss of muscle mass and strength that occurs with aging.
They suggest the bacterium could eventually be explored as a probiotic or nutraceutical candidate for supporting muscle health. However, much more research would be needed before such products could be developed.
For now, the findings highlight another way the gut microbiome may interact with the rest of the body, potentially linking gut bacteria to muscle metabolism and physical performance.
The study was published in the peer-reviewed journal Gut. Researchers analyzed human microbiome samples and conducted follow-up experiments in mice to explore potential mechanisms linking gut bacteria and muscle strength.