Latest Findings on the Role of Gut Microbiota in Effort Tolerance and Fatigue Perception During Endurance Exercise: A Narrative Review

Background: The gut microbiota has emerged as an important modulator of athletic performance in endurance sports. Through the gut–brain and gut–muscle axes, microbial metabolites influence central fatigue, perceived exertion, effort tolerance, and endurance capacity. Although the general relationship between gut microbiota and exercise has been extensively reviewed, its specific role in effort tolerance and fatigue perception during prolonged endurance exercise remains poorly synthesized. Aim: This narrative review aims to synthesize the most recent evidence (2020–2026) on the role of gut microbiota composition, stability, and the effects of probiotic and prebiotic interventions in modulating effort tolerance and fatigue perception during endurance exercise. Material and Methods: A comprehensive literature search was conducted in PubMed and Scopus in April 2026. Randomized controlled trials published between 2020 and 2026 were included. After screening, six studies were selected for the narrative synthesis. Results: The synthesis suggests that greater gut microbial stability during dietary periodization is associated with superior endurance performance. Selected probiotic and prebiotic interventions showed strain-specific potential to enhance muscular endurance and reduce fatigue. However, results were heterogeneous, with some interventions (e.g., inulin and multi-strain probiotics) producing neutral effects. Conclusion: Emerging evidence indicates that the gut microbiota may play a significant role in effort tolerance and fatigue perception during endurance exercise. Nevertheless, the current literature is limited by small sample sizes, heterogeneous populations, and a lack of studies involving elite endurance athletes. High-quality, long-term randomized controlled trials are warranted to establish clinical applicability.