"Blood tests of marathon finishers and intensive care patients would be quite identical"
"The relationship between physical activity and the immune system is complex. Generally, physical activity enhances the immune system. Active people get sick less," Prof. Dan Nemet, director of the Child Health & Sports Center at Meir Medical Center, explains. "However, physical activity, like any medication, has side effects when you don't use enough of it or when it's in the wrong dosage. Physical activity is stress to the body, cortisol and cytokines [small proteins that form the basis for communication between immune system cells] are secreted, just like the effects of illness."