Exercise and immunity

An important question is to what degree exercise-associated changes in immune function are of clinical significance, e.g. whether exercise influences the resistance to acute or chronic diseases that have an immunological component either in etiology or pathogenesis. Clinical relevance of exercise-mediated immunomodulation has been harder to demonstrate than the phenomenological aspects.

It has been known for about 100 years that exercise or training before exposure to infection decreases morbidity or mortality, whereas exercise during the infection has the opposite effect. Thus, acute exercise to exhaustion after infecting laboratory animals with anthrax bacilli or Streptococcus pyogenes resulted in increased mortality compared to sedentary controls. In contrast, repeated exposures to exercise prior to exposure with type 1 Pneumococcus was associated with reduced mortality in experimental animals relative to sedentary-controls. Epidemiological studies suggest that the relative risk for upper respiratory tract infections (URTI) is increased during and for 1-2 weeks following overtraining or marathon-type exercise in endurance athletes. Since prolonged, intense exercise is also associated with some immune suppression, this has led to the 'open window' hypothesis (Figure 1). This hypothesis suggests that during the period immediately following heavy and prolonged training, host immunity is suppressed and risk of URTI is elevated. Testing of this hypothesis will require investigations with necessary methodological rigour (e.g. in selection of appropriate control groups) including adjustment for confounders (such as season and air temperature) and potential bias (such as selection and recall bias) which have limited the conclusions of existing studies in this area.

Moderate exercise

Moderate exercise

Risk of Upper Respiratory Infections

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