aerobic exercise provokes a systemic cytokine response, including, for example, il-6, il-1 receptor antagonist (il-1ra), and il-10 (interleukin 10). il-6 was serendipitously discovered as a myokine because of the observation that it increased in an exponential fashion proportional to the length of exercise and the amount of muscle mass engaged in the exercise. this increase is followed by the appearance of il-1ra and the anti-inflammatory cytokine il-10. in general, the cytokine response to exercise and sepsis differs with regard to tnf-α. thus, the cytokine response to exercise is not preceded by an increase in plasma-tnf-α. following exercise, the basal plasma il-6 concentration may increase up to 100-fold, but less dramatic increases are more frequent. the exercise-induced increase of plasma il-6 occurs in an exponential manner and the peak il-6 level is reached at the end of the exercise or shortly thereafter. it is the combination of mode, intensity, and duration of the exercise that determines the magnitude of the exercise-induced increase of plasma il-6.