Relationship between Exercise Intensity and IL-6 Increase during an 80 km Long-Distance Running Race.

Background : IL-6 plasma concentration (IL-6PC) reflects the systemic inflammation related to exercise intensity level. This study aims to describe the IL-6PC kinetics during a long-distance running race. IL-6PC was measured in 20 male runners before (0 km), at each refreshment point (at 21 and 53 km, i.e., k 21 and k 53 , respectively) and at the end of an 80 km long-distance run (k 80 ). Methods : IL-6PC variations (absolute and relative values in each of the three sections (S)) were calculated over S1 (0_k 21 ), S2 (k 21 _k 53 ) and S3 (k 53 _k 80 ) and compared with the exercise intensity (duration*race speed) within each section. Results : The mean IL-6PC increased during the run: 2.1 ± 0.6 ng.L -1 at 0 km, 21.0 ± 11.3 ng.L -1 at k 21 , 38.9 ± 13.0 ng.L -1 at k 53 and 49.8 ± 11.9 ng.L -1 at k 80 . Exercise intensity increased between S1 (24.2 ± 0.5) and S2 (51.9 ± 3.2) ( p = 0.04) but not between S2 and S3 (67.4 ± 4.5) ( p = 0.69). IL-6PC variation was associated with exercise intensity within S1 ( p = 0.03) and S2 ( p = 2 × 10 -3 ) and showed at least a trend within S3 ( p = 0.06). Conclusions : IL-6PC increases that occur during the early stages of a long-distance run are associated with the running intensity, and then IL-6PC remain stable after the reduction in intensity related to the decrease in running speed.