This article has provided evidence to support the hypothesis that moderate intensity exercise reduces inflammation and improves the immune response to respiratory viral infections. We hypothesize that acute and chronic moderate exercise induces a level of stress hormones that down-regulates excessive inflammation within the respiratory tract and aids in activating innate anti-viral immunity shifting the immune response towards a Th2 profile (Fig. 4), thereby balancing the Th1/Th2 responses to prevent an excessive Th1 immune reaction to these pathogens. Prolonged, intense exercise may do this as well but may shift the balance too much towards Th2 and away from Th1 actually allowing the virus to gain a better foothold and cause greater pathology. Further research is necessary to examine cellular and molecular mechanisms through which exercise modulates immune function. Additionally, human studies should attempt to elucidate the most common respiratory pathogens responsible for infections associated with high intensity exercise training and athletic competitions, and the methods they employ to evade immune response, as well as attempt to translate mechanistic studies to a human experimental model. Based upon the available evidence, moderate intensity exercise training should be used as an adjunct to other preventative measures against respiratory tract viral infection