[The immune system and physical training].

The effects on the immune system of sudden physical exercise and degree of training are reviewed. During moderate as well as strenuous physical exercise natural killer (NK) cells especially, but also T and B cells are released into the blood. A few hours after moderate physical exercise the immune system is back to the pre-exercise state, but following strenuous exercise the lymphocyte concentration and the NK and B cell functions are suppressed. The immune suppression following strenuous exercise is at least partly due to release of prostaglandins from an elevated number of monocytes in the circulation. The importance of stress hormones for mediating the immune modulation is discussed. Examination of trained persons at rest show that these have elevated NK cell activity when compared to matched controls. There are sporadic reports in the literature, showing that persons who train moderately have fewer infections, while persons who train very hard have increased risk of upper respiratory diseases. These findings are in accordance with the observed immune modulation on moderate versus strenuous exercise. The effects of physical training in relation to acute and chronic diseases are evaluated.