Changes in serum cytokines after repeated bouts of downhill running.

The purpose of this study was to examine changes in serum cytokines after repeated bouts of aerobically biased eccentric exercise. Six untrained males ran down a -13.5% treadmill grade for 60 min on two occasions (RUN1 and RUN2) at a speed equal to 75% of their VO2 peak on a level grade; runs were spaced 14 d apart. Serum was collected before, after, and every hour for 12 h, and every 24 h for 6 d. Cytokines were assessed using 17 multiplex bead technology (Bio-Rad). Creatine kinase (CK) and delayed-onset muscle soreness (DOMS) were assessed before and 24-120 h after. Results were analyzed using a repeated measures analysis of variance (p <or= 0.05). All comparisons were between RUN1 and RUN2. CK and DOMS were significantly elevated after RUN1 compared with RUN2, indicative of a repeated bout effect. Regarding cytokines, during the initial 12 h period after RUN2, there was a 50% decrease in pro-inflammatory interleukin-6 (IL-6), a 10% decrease in pro-inflammatory macrophage chemotactic protein-1, and a 95% elevation in anti-inflammatory interleukin-10 (IL-10). Regarding 24 h periods, after RUN2 there was an 8% reduction in pro-inflammatory interleukin-8 (IL-8). However, pro-inflammatory macrophage inflammatory factor-1beta (MIF-1beta) was 18% higher during the 12 h after RUN2. The overall cytokine profile suggests a slight reduction in systemic inflammation after RUN2.