Objective: The chronic and acute immune responses to both heavy and moderate exercise are reviewed, with guidelines provided for the prevention and management of upper respiratory tract infection (URTI) in athletes.
Data sources: Epidemiologic and experimental exercise immunology research data were used. The MEDLINE database was searched for the years 1970 to 1997 with the terms "exercise," "immune," "infection," "lymphocyte," and "neutrophil."
Data synthesis: A descriptive review with summary figures and one table.
Conclusions/recommendations: The epidemiologic data suggest that endurance athletes are at increased risk for URTI during periods of heavy training and the 1-to 2-week period after marathon-type race events. Several researchers have reported a diminished neutrophil function in athletes during periods of intense and heavy training. Following each bout of prolonged heavy endurance exercise, several components of the immune system appear to demonstrate suppressed function for several hours. This has led to the concept of the "open window," described as the 3- to 12-hour time period after prolonged endurance exercise when host defense is decreased and the risk of URTI is elevated. There is sufficient evidence for sports medicine professionals to encourage athletes to practice various hygienic measures to lower their risk of URTI and to avoid heavy exertion during systemic illness.