High physical fitness is associated with reduction in basal- and exercise-induced inflammation.

C-reactive protein (CRP) increases after strenuous exercise. It has been a concern that prolonged strenuous exercise may be harmful and induce a deleterious inflammatory response. The purpose of this study was to (a) assess and quantify the magnitude of CRP response following an endurance cycling competition in healthy middle-aged recreational cyclists. (b) Identify important determinants of this response. (c) Identify the relationship between CRP, myocardial damage (cardiac Troponin I (cTnI)), and myocardial strain (B-type natriuretic peptide [BNP]). (d) Identify the relationship between CRP and clinical events, defined as utilization of healthcare services or self-reported unusual discomfort. Race time was used as a measure of physical fitness. A total of 97 individuals (43±10 years of age, 74 [76%] males) were assessed prior to and 0, 3, and 24 hours following the 91-km mountain bike race "Nordsjørittet" (Sandnes, Norway, June 2013). There was a highly significant increase in CRP from baseline to 24 hours (0.9 (0.5-1.8) mg/L vs. 11.6 (6.0-17.5) mg/L (median[IQR]), P<.001), with no correlation of CRP to cTnI and BNP at any time-point. CRP was strongly correlated to race time at baseline (r=.38, P<.001) and at 24 hours following the race (r=.43, P<.001), In multivariate models, race time was an independent predictor of CRP both at baseline and at 24 hours (P<.01). There was no relationship between CRP levels and clinical events. In conclusion, high physical fitness was associated with reduction in both basal- and exercise-induced CRP. No adverse relationship was found between high intensity physical exercise, CRP levels, and outcomes.