Scientists are discovering that the trillions of bacteria living in the human gut may influence far more than digestion.
A new study has found that a specific gut bacterium may be linked to stronger muscles and better physical performance.
The research, published online in the journal Gut, suggests that a species called Roseburia inulinivorans could play an important role in muscle health and may even help combat age-related muscle loss.
Muscle strength is essential for maintaining mobility, balance, and independence. As people age, many experience a gradual loss of muscle mass and strength, a condition known as sarcopenia.
This decline can lead to frailty, difficulty moving, a higher risk of falls, and reduced overall health. Sarcopenia is particularly common among older adults and people with chronic health conditions.
Because of these serious effects, researchers around the world are searching for ways to preserve muscle strength for longer. In recent years, scientists have begun exploring whether the gut microbiome—the community of bacteria living in the digestive system—may influence muscle function.
Gut bacteria are already known to play a role in many aspects of health. Studies have linked the microbiome to metabolic diseases, brain disorders, heart disease, and immune function. Emerging research now suggests that gut microbes may also affect how muscles grow, function, and generate energy.
To explore this idea, researchers from the Netherlands and Spain examined whether specific gut bacteria might be linked to muscle strength in humans. They also wanted to understand how these microbes might influence muscle performance.
The research team collected stool samples from two groups of participants. The first group included 90 healthy young adults between the ages of 18 and 25. The second group included 33 older adults aged 65 and above.
The scientists analyzed the stool samples to identify which bacteria were present in the participants’ gut microbiomes. They then measured several indicators of physical fitness and muscle strength.
These measurements included hand grip strength, which is a common test used to estimate overall muscle strength. Participants also performed leg press and bench press exercises to measure upper and lower body strength. In addition, researchers measured VO₂ max, which indicates how efficiently the body uses oxygen during exercise and reflects cardiovascular fitness.
After analyzing the data, the researchers found that bacteria belonging to the Roseburia group were the only microbes clearly linked to stronger muscles.
However, not all species within this group had the same effect. Two species—Roseburia faecis and Roseburia intestinalis—did not show a strong connection with grip strength or cardiovascular fitness.
One species stood out: Roseburia inulinivorans.
Among the older adults in the study, those who had detectable levels of R. inulinivorans in their stool samples showed significantly stronger hand grip strength. In fact, their grip strength was about 29 percent higher than older participants who did not have the bacterium.
Interestingly, this improvement in strength did not come with an increase in VO₂ max. This suggests that the bacterium may influence muscle strength directly rather than improving overall aerobic fitness.
Among the younger adults, higher levels of R. inulinivorans were also linked to better physical performance. Greater amounts of this bacterium were associated with stronger grip strength and higher VO₂ max values. In addition, the abundance of both R. inulinivorans and R. intestinalis was linked to stronger performance in leg press and bench press tests.
The researchers also noticed that the levels of these bacteria differed between age groups. The Roseburia bacteria were generally more abundant in younger adults.
In younger participants, R. inulinivorans made up as much as 6.6 percent of the gut microbiome in some individuals. In older adults, the highest level detected was only about 1.3 percent.
This finding may be important because the decline of this bacterium with age happens at the same time that muscle loss becomes more common.
To investigate whether Roseburia bacteria could directly influence muscle strength, the scientists carried out an additional experiment using mice.
Before the experiment began, the mice were given antibiotics for two weeks to remove most of the bacteria from their gut microbiome. The mice were then divided into four groups. Three groups received different species of Roseburia bacteria once a week for eight weeks, while the fourth group received no bacteria and served as the control group.
The researchers tested the mice’s muscle strength by measuring forelimb grip strength, which is often used as a measure of muscle function in animal studies.
The results were striking. Mice that received R. inulinivorans showed a significant improvement in grip strength. Their strength increased by about 30 percent after four, six, and eight weeks compared with the control group.
Further analysis of the mice’s muscles revealed additional changes. Mice treated with R. inulinivorans had larger muscle fibers and a greater proportion of “fast-twitch” muscle fibers.
Fast-twitch fibers, also known as type II fibers, are designed for quick, powerful movements such as sprinting, jumping, and lifting weights. These fibers produce strong bursts of force but fatigue more quickly than slow-twitch fibers.
The researchers also found changes in proteins and enzymes involved in muscle energy production. These metabolic changes suggest that the bacterium may influence how muscles produce and use energy.
Despite the promising results, the researchers caution that their findings have several limitations. In the mouse experiments, the human Roseburia bacteria did not permanently colonize the mice’s gut microbiomes. This means the results may not fully represent what happens in humans.
In addition, the study did not directly measure certain biological pathways, such as inflammation or nerve signaling between muscles and the brain. These factors could also play important roles in muscle strength.
The researchers also emphasize that it is not yet clear whether higher levels of R. inulinivorans cause stronger muscles or whether people with stronger muscles naturally have more of this bacterium.
Long-term studies will be needed to determine the exact relationship between this microbe and muscle health.
Even so, the findings support the idea of a “gut–muscle axis,” meaning that gut bacteria may influence how muscles function. If future research confirms this connection, R. inulinivorans could potentially be developed as a probiotic supplement to help maintain muscle strength, especially in older adults.
The researchers note that levels of this bacterium appear to decline with age, a period when muscle loss becomes more common. This pattern suggests that supporting the growth of beneficial gut microbes might one day help reduce age-related muscle weakness.
If confirmed in larger human studies, these discoveries could open the door to new nutritional approaches for protecting muscle health and preventing sarcopenia.
If you care about muscle, please read studies about factors that can cause muscle weakness in older people, and scientists find a way to reverse high blood sugar and muscle loss.
For more health information, please see recent studies about an easy, cheap way to maintain muscles, and results showing these vegetables essential for your muscle strength.
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