The gut microbiota as a driver of increased muscle strength. A recent Chinese study published in Scientific Reports suggests a potential link between sport, physical activity in general, and improvements in the composition, in terms of diversity, of intestinal bacterial microbiota.
If this finding were confirmed by further studies, it could open new approaches to promoting healthy longevity, for example by counteracting sarcopenia, a recurring and impactful factor in the rapid physical decline seen in older adults and/or in contexts of organ impairment.
The Data
They are preliminary, experimental results, but promising and worthy of further investigation. Some laboratory studies, i.e., on animal models, would demonstrate the potential of certain gut bacteria to improve muscle strength and motor performance.
A potential demonstration, even in humans, could pave the way for new, innovative approaches in prevention and treatment of sarcopenia, the loss of muscle mass and strength that accompanies aging, promoting a faster functional decline. Muscle capacity is critical in the context of healthy, active aging: it preserves independence, reduces fall risk, supports metabolic activity, and slows the onset of age-related chronic diseases.
Addressing sarcopenia today relies mainly on lifestyle factors: regular physical activity and a balanced diet, for a synergistic effect. Recent research highlights the participation of the gut microbiota as a mediator, where the intestine would act as a transmitter of signals to the muscles, thereby influencing metabolism, inflammation, and growth. This is what emerges from experiments conducted on nine-month-old mice, an age and response range comparable to a late-adult life, in which muscle strength tends to decline.
The mice were pretreated with antibiotics and antifungals to foster a uniform “reset” of the microbiota, thereby reducing intestinal variability, and were subsequently subjected to a fecal microbiota transplant (FMT) from healthy human donors. The effects of the transplant were then assessed using two specific tests: the Rotarod test, where balance, coordination, and endurance were measured as the animals ran on a rotating rod, and the Wire Suspension Test, in which forelimb strength was evaluated by letting the mice grip a metal wire. The tests were conducted before and three months after the transplant, with parallel collection of blood, intestinal contents, and feces. This biological material was used to analyze metabolic parameters and microbial composition.
The Results
The researchers observed a significant increase in the diversity of bacterial species present in the gut after FMT, with this effect being more pronounced in the intestinal contents than in the fecal samples, which are less representative of the true internal state.
However, the impact on muscle strength was not uniform, with clear improvements in endurance and coordination in some rodents, intermediate changes in others, and in some cases even worsened performance.
In the mice with the greatest benefits, there were also improvements in HDL cholesterol, the “good” cholesterol, and most notably a substantial increase in muscle mass, up to 157% more than controls, while overall body weight fell. This suggests a favorable transformation of fat mass into more efficient muscle tissue.
The Bacterial Populations
Lactobacillus johnsonii, Limosilactobacillus reuteri, and Turicibacter sanguinis are the three bacterial strains that showed the greatest incremental growth. The first two species, common in probiotics and highly prevalent, were further tested by administering them to 12-month-old mice, considered an optimal aging model for humans. It was observed that the combination of L. johnsonii and L. reuteri produced the greatest benefits, with a significant increase in strength in the tests and a rise in muscle mass.
The phenomenon, according to the researchers, is linked to certain molecular markers in muscle tissue, specifically Follistatin (FST), a protein that inhibits myostatin, known to block muscle growth, with higher levels in mice treated with L. johnsonii, IGF-1 (Insulin-like Growth Factor 1), an anabolic factor that stimulates the proliferation of muscle cells, with levels highest in mice given both L. johnsonii and L. reuteri.
Moreover, the muscle fibers were broader and better developed, with markedly reduced levels of triglycerides and LDL cholesterol, as well as inflammatory markers. For instance, interleukin-6, elevated in chronic inflammatory processes, showed a drastic drop after the combined administration of the two bacteria.
Future Applications
If further research confirms these findings, with demonstrated efficacy in humans, there could be opportunities for treatment with new probiotic therapies to combat sarcopenia using specific probiotic strains, offering a noninvasive, natural supplement alongside exercise and a protein-rich diet that remain the gold standard.
The identification of bacteria capable of influencing muscular aging could lead to the development of preventive strategies starting in adulthood to extend physical performance as long as possible, while bearing in mind the variability in response to therapy observed in mice that could also occur in humans, where a probiotic’s effectiveness may be influenced by the starting microbiota, necessitating personalized interventions. In light of these considerations, further studies will be needed to investigate the molecular mechanisms involved, including metabolites produced by the bacteria and how they directly affect muscle cells.
Sources
Ahn JS, Kin HM, Han EJ et al. Discovery of intestinal microorganisms that affect the improvement of muscle strength. Scientific Reports, 2025, Article number: 30179. Link: https://www.nature.com/articles/s41598-025-15222-2
Abbonati a Karla Miller
