Human Physiology

Plasma interleukin-6 (IL-6) increases during exercise and appears dependent on factors such as exercise intensity, muscle mass recruited, and mode (concentric vs. eccentric) (for review see Febbraio & Pederson, 2002). Particularly during the later stages of prolonged endurance exercise the increase in plasma IL-6 is most pronounced. Given the late appearance of IL-6 in the plasma following prolonged exercise, there is a suggestion that the plasma IL-6 response may result from damage to skeletal muscle. A single bout of eccentric exercise produces significant muscle damage. However, the same eccentric exercise bout performed some weeks afterward does not result in damage to active muscle tissue (McHugh et al. 1999). Therefore, the aim of this experiment was to investigate the plasma IL-6 response during a single damaging eccentric exercise bout, and 5 weeks later, during another ‘repeated’ bout of eccentric exercise of the same intensity and duration, to assess the contribution of skeletal muscle damage to the IL-6 response.