Fig. 1.

Summary of the proposed microbially mediated mechanisms contributing to improvements in endurance exercise performance. Non-digestible carbohydrates are fermented by the commensal gut microbiota (including probiotic microorganisms) to produce SCFA. SCFA influence skeletal muscle substrate metabolism and promote glycogen sparing effects, leading to enhanced energy utilization. Probiotic microorganisms produce lactate as a by-product of fermentation. Microbially produced lactate can be transported into systemic circulation to become available to oxidizing skeletal muscle fibers, or it can be consumed by lactate-utilizing bacteria that concomitantly produce butyrate and ATP. Butyrate fuels colonocytes, which enhances the intestinal barrier. Lactate produced by muscle fibers during exercise enters the gut (an additional removal site for lactate) and is metabolically converted by Veillonella atypica into propionate, which enters systemic circulation and is available to SCFA receptor expressing tissues, including skeletal muscle. (Created with BioRender.com). ATP = adenosine triphosphate; SCFA = short-chain fatty acid.