Background Gut bacteria have been implicated in a wide range of health conditions, yet their potential role in preventing and treating muscle-wasting disorders remains largely unexplored. Objective We aimed to investigate whether specific gut microbial species are associated with muscle strength and to explore underlying mechanisms linking the gut microbiota to muscle health. Design We conducted metagenomic analyses in cohorts of younger and older adults extensively phenotyped for muscle strength. Associations were tested between bacterial taxa and performance measures. Causality was assessed by oral supplementation of candidate species in antibiotic-treated mice. Metabolomic profiling and muscle phenotyping were performed to elucidate mechanisms. Results The relative abundance of Roseburia inulinivorans , but not other Roseburia species, was positively associated with multiple strength measures including handgrip, leg press and bench press in humans. Supplementation of R. inulinivorans in mice significantly enhanced forelimb grip strength, whereas other Roseburia species had no effect. Metabolomic analyses revealed that R. inulinivorans reduced amino acid concentrations in the caecum and plasma, while activating the purine and pentose phosphate pathway in muscle. These changes coincided with increased muscle fibre size and a shift from type I to type II fibres. Accordingly, we observed that the relative abundance of R. inulinivorans is lower in older adults compared with young adults. Conclusion R. inulinivorans emerges as a species-specific modulator of muscle strength, linking gut microbiota to muscle metabolism and function. These findings support its potential as a probiotic candidate for nutraceutical interventions targeting age-related muscle-wasting diseases. Trial registration number NCT02365129 .
Martinez-Tellez et al. (Tue,) studied this question.