Why Does Moderate Exercise Enhance, But Intense Training Depress, Immunity ?

Irrespective of training status, exercise caused significant "priming" of neutrophils to produce H₂0₂ and HOC1 upon stimulation with OZ. The trainingtrend was confirmed by a longitudinal study conducted over a 15 month period. If prolonged by regular training, elevated cortisol may have chronically depressive effects on immunity. There had been reports in the literature suggesting that separate episodes of moderate aerobic exercise might enhance immunity whilst intensive trainingmight have chronic immunosuppressive effects. Depressed neutrophil activity is likely to be mediated through immunosuppressive glucocorticoids like cortisol which are released into the circulation to act as a counterbalancing negative signal once exercise reaches a critical intensity. A standardized exercise schedule was undertaken by each subject. Food intake before the test was restricted to a light "non-fatty" meal. All subjects exercised on a cycle ergometer for one hour at a work output equivalent to 60% of their individually-determined values.