Purpose: We compared the effects of exercise intensity (EI) on the cytokine response to an acute bout of running. Methods: Ten males (mean ± SD VO2max = 56.2 ± 8.1 mL/min·kg) completed three, counterbalanced, 8-d trials. After three control days, on day 4, participants completed 60 min of running at 55%, 65%, and 75% VO2max. The cytokines tumor necrosis factor (TNF)-a, interleukin-1ß (IL-1ß), IL-6, and IL-1 receptor antagonist (ra), and creatine kinase were measured during and for 3 h after exercise and on four follow-up days (FU1-FU4). Results: RER was higher at 75% VO2max compared with both 55% (P < 0.001) and 65% (P < 0.01) VO2max. IL-1ß was undetectable in six participants. There was a small (18%-27%) increase in TNF-a during exercise but no effect of EI. IL-6 concentrations peaked at the end of exercise, with a greater increase at 75% VO2max, resulting in higher concentrations at the end of exercise and at 30 min after exercise compared with 55% (P < 0.001) and 65% VO2max (P < 0.01). IL-1ra concentrations peaked at the end of exercise at 75% VO2max, resulting in higher (P < 0.05) concentrations at 1-2 h after exercise compared with 55% and 65% VO2max. Creatine kinase was increased at FU1 and FU2, but there was no effect of EI. Conclusions: Sixty minutes of treadmill running at 75% VO2max results in a greater increase in IL-6 but not TNF-a compared with 55% and 65% VO2max. The higher IL-1ra concentrations at 75% VO2max might be related to the higher IL-6 concentrations that precede them.
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