Exploring the Bidirectional Relationship Between Exercise and the Gut Microbiota: Impact of Training Intensity and a Supplement Intervention

Exercise and the gut microbiota interact bidirectionally, whereby exercise training influences the structure of the gut microbiota, and the gut microbiota and its metabolites may influence exercise performance. Despite growing recognition of this relationship, the influence of exercise intensity, category, and volume on the gut microbiota remains unknown, and strategies aimed at leveraging the gut microbiota to improve exercise performance are underexplored. Gut-derived metabolites such as short-chain fatty acids (SCFAs) have been proposed to influence skeletal muscle metabolism in ways that may improve performance, and synbiotics represent an exogenous strategy for increasing SCFA production. Following a 6-week, domain-based, cycling intervention in healthy adults, we demonstrated that heavy- and severe-, but not moderate-intensity exercise training increased gut microbiota alpha diversity. We also observed distinct gut microbiota profiles between exercise responders (i.e., POST intervention increase of >3.5ml·kg−1·min−1 in V̇O2max) and non-responders (increase in V̇O2max < 3.5ml·kg−1·min−1), with the bacterial genus Holdemanella consistently emerging as a feature of non-response, and markers of gut inflammation also being associated with non-responders. In a cross-sectional study of competitive athletes, we showed that exercise training category (i.e., endurance, mixed, or sprint/power) and volume (i.e., weekly training hours) together explained the greatest proportion of variation in gut microbiota profiles. Within-category analysis showed that sprint/power athletes' gut microbiota was the most sensitive to training volume, whereas endurance athletes were the least sensitive. Between-category comparisons at each training volume showed that category-specific gut microbiota profiles were most apparent at lower training volumes (≤ 15 hours a week), and became less distinct at > 15 hours. Distinct dietary patterns were also observed in endurance-categorized athletes, while sprint/power and mixed athletes exhibited more similar dietary profiles. Six weeks of supplementation with a novel synbiotic formulation did not impact endurance performance outcomes or substrate oxidation during heavy-intensity cycling, nor did it produce substantial changes in gut microbiota composition or modulate fecal SCFA concentrations in trained cyclists. Within the synbiotic group, blood lactate concentrations were numerically lower throughout the 20km time trial after the intervention compared to baseline, although this did not reach statistical significance. This thesis highlights the impact of exercise intensity, training category, and training volume on the gut microbiota. Additionally, this work increases our understanding of microbial modulating therapies on endurance performance outcomes and provides direction for future investigations exploring the bidirectional role of exercise and the gut microbiota.