Neutrophil but not lymphocyte response to matched interval and continuous running differs between protocols and sex.

When considering the acute effects of different modalities of endurance training on cellular immune components, the matching of duration and mean intensity and the consideration of sex-dependent differences have received less attention so far. The aim of the study was to compare the effects of interval running (IR) vs. continuous running (CR) on circulating immune cells and cellular immune inflammation markers. Additionally, we analyze sex-dependent differences in these effects. In a cross-over study design, 24 recreational runners completed a mean intensity and duration-matched session of IR and CR. Blood samples were taken immediately before, after, and 1 h after exercise cessation for cell counts and cortisol level quantification. Neutrophil counts showed a sustained increase after both exercise modalities with significantly greater values after IR compared to CR at 1 h after exercise and greater increases in females. Neutrophil-to-lymphocyte ratio and systemic immune-inflammation index increased 1 h after exercise with significantly higher values after IR compared to CR with greater values in females. Platelet-to-lymphocyte ratio decreased in both immediately after IR and 1 h after exercise in both sexes and modalities. The cortisol level shows a lower value immediately after CR compared to IR with no sex-dependent differences. The IR protocol induces greater immune cell mobilizations in comparison to CR, which is primarily based on a systemic increase in neutrophil counts. Neutrophil-to-lymphocyte ratio and systemic immune-inflammation index are suitable to distinguish this effect between training modalities. Sex-dependent differences confirm that biological sex influences the immune cells response to acute exercise. Protocol registration: German Clinical Trials Register, DRKS00017686, Date of registration: 11.02.2020.