Introduction: High-intensity exercise can acutely alter inflammatory responses and affect athletes’ recovery. This study investigated the temporal dynamics of pro-inflammatory and anti-inflammatory cytokines and the inflammatory marker hs-CRP following a single session of high-volume high-intensity interval training (HIIT) in endurance runners.

Methods: In this semi-experimental repeated-measures study, 10 male endurance athletes (mean age: 20.4 years) participated. All participants had at least three years of training experience, a history of league competition, and a VO₂max >50 mL/kg/min. The exercise protocol consisted of five 1000-m running repetitions at 90% of each participant’s personal best performance. Blood samples were collected at baseline, immediately post-exercise, and 120 min post-exercise. Serum IL-6, TNF-α, IL-10, and hs-CRP were measured using enzyme-linked immunosorbent assay (ELISA). Data were analyzed using repeated-measures analysis of variance and the Bonferroni test at a significance level of 0.05.

Results: The HIIT protocol significantly increased IL-6, TNF-α, IL-10, and hs-CRP (P<0.05). IL-6 showed its greatest increase immediately post-exercise, whereas IL-10 peaked at 120 min post-exercise. The increase in hs-CRP was also more pronounced at 120 min.

Conclusion: High-volume HIIT induces an acute inflammatory response accompanied by increased IL-10, indicating simultaneous activation of pro-inflammatory and anti-inflammatory responses during recovery. The different peak times of the investigated markers suggest distinct temporal patterns of post-exercise inflammatory regulation. These findings emphasize the importance of sampling time in evaluating inflammatory responses and may help optimize training and recovery management in endurance runners and in planning appropriate recovery periods after demanding training sessions.