Dr. Sara Campbell returns to discuss her lab's cutting-edge research on the bidirectional relationship between exercise and the gut microbiome — including why consumer gut tests oversimplify a complex ecosystem, how antibiotics devastate exercise capacity in animal models, and why single-microbe probiotics miss the bigger picture of functional guilds. She also shares new findings on short-chain fatty acids, amino acid metabolomics after antibiotic treatment, and the emerging neuromuscular junction hypothesis.