Relationship between cytokines and running economy in marathon runners

Background: Running economy (RE), expresses the relationship between the energy cost of running (Cr) and the work performed by a runner and is an predictor of performance. Given the intense effort of marathon runners during training and competition and the dearth of studies that address performance and cytokines in this population, the objective of the current study was to investigate the relationship between RE and cytokines in marathon runners. Methods: A total of 22 recreational marathon runners were examined. Using data obtained from VO2max assessments and sub-maximal tests, the following formula was applied to determine RE: Cr (mLO(2).kg(-1) . km(-1)) = VO2 (mL . kg(-1) . h(-1)) x 60 divided by speed (km . h(-1)). Results: Cr values shows no correlation with levels of the serum IL-1 beta, IL-4, IL-8, IL-10 and TNF-alpha 24h before, immediately after or 72h after the completion of an official marathon. However, the IL-6 level shows a significant correlation with Cr. Discussion and conclusion: The relationship between higher values of IL-6 and lower RE leads to the hypothesis of a physical under-recovery state by some athletes. Considering the stress caused by training, associated with the higher energetic cost in less economic athletes, it's possible that the period of resting may not totally compensate for the inflammatory state.