b'INTENSIFIED TRAINING AND COMPETITIVE EVENTSWe all know that regular exercise provides a multitude of health benefits, including reduced risk of acute illness and infection, chronic disease and stress, and improved mental health. Regular physical activity also appears to beneficially modulate the GI microbe population. However, intense training can transiently depress the athletes innate and acquired immune function, possibly increasing the risk of pathogens overriding the bodys immune defences, leading to infection, most commonly upper respiratory tract infections (URTIs). infection associated with immunosuppression in response to heavy training remains contentious. It appears that overall, Following a bout of heavy exercise, innate immune functionathletes experience similar rates of infection compared to is transiently depressed 12 . Lymphocytosis and neutrophiliathe general population, however, some athletes appear to occur following a bout of prolonged, strenuous exercise,have greater susceptibility to recurrent infection impeding on proportional to the duration and intensity of exercise.training and competition. Moreover, it should be noted that Functional responses, including neutrophil degranulation,training outdoors and inhaling cold, dry air can cause non-phagocytosis, and oxidative burst activity, and monocyte TLRinfectious inflammation of the upper airways, with symptoms expression, are diminished after 90 minutes of moderatemimicking that of an URTI 15 . to intense exercise. Innate mucosal immunity is also alteredThe athletes energy, macro- and micronutrient status are by very prolonged exercise (e.g., post-marathon). Secretoryknown to modulate immunoregulatory processes 16 . Adequate immunoglobulin A (SIgA) concentration decreases in salivaenergy, specifically carbohydrate, is an essential fuel for and tears, while secretion of saliva antimicrobial proteinsimmune cell activity, while amino acids (AAs) are required for including lysozyme, lactoferrin and -defensin increases.synthesis of proteins such as immunoglobulins. Additionally, Acquired immune functions, such as antigen presentationseveral micronutrient deficiencies, such as iron, vitamin D by monocytes or macrophages, immunoglobulin productionand zinc, have been linked with increased risk of illness and by B lymphocytes, T lymphocyte cytokine productioninfection. Tolerogenic nutrients, such as anti-inflammatory- and proliferation are also reduced. This acute, exercise- (i.e., vitamin D) or antioxidative- (i.e., vitamin C and E) induced immunodepression is likely mediated via increasednutrients, and nutrients targeting the microbiota (i.e., pre- circulating stress hormones (e.g., catecholamines andand probiotics), may reduce the infection burden in athletes cortisol) and disruptions to the pro/anti-inflammatory cytokineby improving immune tolerance and the ability to endure profile. Periods of heavy training, or overreaching, havemicrobes 17 .also been shown to depress cellular immune function and surveillance. This includes impaired redeployment of cytotoxic lymphocytes, reduced natural killer cell cytotoxic (NKCC) activity, and reduced T cell migration and proliferation. It is important to note, however, that a causitive link between these acute alterations to immune function (independent of other factors such as perceived psychological stress and under-nutrition) and increased risk of infection has not yet been established 12,13 . There is evidence to suggest that successive bouts of exercise, repeated on the same or consecutive days, prohibits restoration of innate and acquired immune indices 12 . Heavy training, or overreaching, may depress cellular immune function and surveillance. This includes impaired redeployment of cytotoxic lymphocytes, reduced NKCC, and reduced T cell migration and proliferation 14 . Again, the increased risk of 4'