Fig. 2

Gastrointestinal disruption during high intensity exercise. Proper intestinal barrier function is crucial for maintaining health and immunity. During intense exercise, athletes’ body temperature increases and blood pools away from the gastrointestinal tract to periphery muscles and organs such as the heart and lungs during intense physical activity [62]. The redistribution of blood flow away from the intestines together with thermal damage to the intestinal mucosa can cause intestinal barrier disruption, followed by an inflammatory response [63]. Additionally, intense exercise over a prolonged period of time increase stress hormones and lipopolysaccharides (LPS) translocation in the gastrointestinal tract, which triggers immune responses that often results in increased pro-inflammatory cytokines and intestinal permeability. Additionally, intestinal permeability may be made worse by the increased production of reactive oxygen species (ROS) and by the alteration of gut-microbiota composition and activity (the so-called dysbiosis). Furthermore, gastrointestinal tract responds to stress by releasing hormones such as GABA, neuropeptide Y (NPY) and dopamine that have been purported to cause GI disturbances, anxiety, depression, reduced food intake and less stress coping [9]. Conversely, the microbiota’s production of butyrate and propionate can increase transepithelial resistance, which improves intestinal barrier function and decreases inflammation.