THE OPEN WINDOW OF SUSCEPTIBILITY TO INFECTION AFTER ACUTE EXERCISE IN HEALTHY YOUNG MALE ELITE ATHLETES Acute immune system response in elite cyclists

The ‘open window ’ theory is characterised by short term suppression of the immune system following an acute bout of endurance exercise. This window of opportunity may allow for an increase in susceptibility to upper respiratory illness (URI). Many studies have indicated a decrease in immune function in response to exercise. However, many studies do not indicate changes in immune function past 2 hours after the completion of exercise, consequently failing to determine whether these immune cells numbers, or importantly their function, return to resting levels before the start of another bout of exercise. 2 Ten male ‘A ’ grade cyclists (age 24.2 ± 5.3 years; body mass 73.8 ± 6.5 kg; VO2max 65.9 ± 7.1 mL.kg-1.min-1) exercised for two hours at 90 % of their second ventilatory threshold. Blood samples were collected pre-, immediately post-, 2 hours, 4 hours, 6 hours, 8 hours, and 24 hours post-exercise. Immune variables examined included total leukocyte counts, neutrophil function (oxidative burst and phagocytic function), lymphocyte subset counts (CD4+, CD8+, and CD16+/56+), natural killer cell activity (NKCA), and NK phenotypes (CD56dimCD16+, an