The increase in plasma IL-6 following sprint interval training does not depend on total sprint volume

The magnitude of the benefi cial increase in plasma interleukin-6 (IL-6) with exercise is greater with continuous exercise of higher intensity and longer duration. However, it is unknown whether a greater volume of supramaximal interval exercise also enhances the IL-6 response. Therefore, the aim of this study was to compare the eff ects of two sprint interval training (SIT) protocols involving different volumes of sprint exercise on plasma IL-6 levels. Nine healthy young men (age: 24±4 y, BMI: 23.3±3.1 kg·m-2, V̇ O2max: 42±6 mL·kg-1·min-1) completed three experimental trials in randomised order, including ‘classic’ SIT (4x30-s ‘all-out’ cycle sprints within a 22-min session), reduced-exertion high-intensity interval training (REHIT; 2x20-s ‘all-out’ cycle sprints within a 10-min session), and a control condition (seated rest). Blood samples were collected before exercise and at 0-, 30-, and 90-min post-exercise, and analyzed for lactate and IL-6. Blood lactate levels peaked directly post-SIT (1.5±0.2 mM to 11.9±2.5 mM; p<.001) and REHIT (1.7±0.4 to 9.1±3.1 mM; p<.001). Plasma IL-6 levels peaked 30-min post-exercise (0.84±0.12 to 1.31±0.17 pg·mL-1 for SIT, p=.003; 0.75±0.09 to 1.18±0.36 pg·mL-1 for REHIT, p=.028). Compared to the con-trol trial, IL-6 iAUC was signifi cantly higher for both SIT (p=.002) and REHIT (p=.013), with no signifi cant diff erence between SIT and REHIT. In conclusion, we demonstrate that the increase in plasma IL-6 levels is similar for the two SIT protocols involving a 3-fold diff erence in sprint exercise volume (120 s vs. 40 s). Our data provide support for a possible role of glycogenolysis in the IL-6 response to SIT.