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Does prolonged cycling of moderate intensity affect immune cell function?
  1. J Scharhag1,
  2. T Meyer1,
  3. H H W Gabriel2,
  4. B Schlick1,
  5. O Faude1,
  6. W Kindermann1
  1. 1Institute of Sports and Preventive Medicine, University of Saarland, Saarbrücken, Germany
  2. 2Department of Sports Medicine, Friedrich-Schiller-University, Jena, Germany
  1. Correspondence to:
 Dr Jürgen Scharhag
 Institute of Sports and Preventive Medicine, University of Saarland, Campus, Building 39.1, 66123 Saarbrücken, Germany;


Background: Prolonged exercise may induce temporary immunosuppression with a presumed increased susceptibility for infection. However, there are only few data on immune cell function after prolonged cycling at moderate intensities typical for road cycling training sessions.

Methods: The present study examined the influence on immune cell function of 4 h of cycling at a constant intensity of 70% of the individual anaerobic threshold. Interleukin-6 (IL-6) and C-reactive protein (CRP), leukocyte and lymphocyte populations, activities of natural killer (NK), neutrophils, and monocytes were examined before and after exercise, and also on a control day without exercise.

Results: Cycling for 4 h induced a moderate acute phase response with increases in IL-6 from 1.0 (SD 0.5) before to 9.6 (5.6) pg/ml 1 h after exercise and CRP from 0.5 (SD 0.4) before to 1.8 (1.3) mg/l 1 day after exercise. Although absolute numbers of circulating NK cells, monocytes, and neutrophils increased during exercise, on a per cell basis NK cell activity, neutrophil and monocyte phagocytosis, and monocyte oxidative burst did not significantly change after exercise. However, a minor effect over time for neutrophil oxidative burst was noted, tending to decrease after exercise.

Conclusions: Prolonged cycling at moderate intensities does not seem to seriously alter the function of cells of the first line of defence. Therefore, the influence of a single typical road cycling training session on the immune system is only moderate and appears to be safe from an immunological point of view.

  • AU, arbitrary unit
  • CRP, C-reactive protein
  • fMLP, formylised-1-methionyl-1-leucyl-1-phenylalanin
  • IAT, individual anaerobic threshold
  • IL-2, interleukin-2
  • IL-6, interleukin-6
  • NK cells, natural killer cells
  • NKCA, NK cell cytotoxic activity
  • acute phase response
  • monocytes
  • neutrophils
  • NK cells
  • phagocytosis

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  • This study was supported by a grant from the National Institute for Sports Sciences (Bundesinstitut für Sportwissenschaft, VF 0407/01/11/99-2000), Bonn, Germany

  • Competing interests: none declared