The missing links in exercise effects on mucosal immunity.

This review highlights research limitations within the existing exercise immunology literature and summarises unanswered questions to assist researchers and clinicians interested in exploring relationships between exercise, training and mucosal immunity. The primary limitations of the existing literature include: inadequate descriptions of training stimuli, age, gender and physical activity of subjects; failing to account for the influence of these factors and the underlying fitness and health status of subjects; methodological differences in assessments of mucosal immunity; limited understanding of the sources of biological variability in mucosal immunity; limited clinical and laboratory diagnosis of respiratory illness; and neglect of psychological, environmental, nutritional and pharmacological influences. Despite a considerable volume of research on mucosal immunity the unanswered research questions include: whether athletes are really more prone to illness; whether illness impacts on athletic performance; identifying subject or training characteristics that influence the mucosal immune responses to exercise; defining how exercise influences the acute mucosal immune response; assessing whether moderate exercise can enhance mucosal immune status; defining more clearly the treatment and management strategies for the athlete suffering recurrent illness, overtraining or long-term fatigue; and the effectiveness of dietary and therapeutic interventions. Answers to these questions should define future research strategies and assist clinicians seeking guidance on the assessment, treatment and management of athletes suffering from respiratory illness, particularly those with recurrent illness, long-term post-viral fatigue or suspected of being overtrained.