Reactive oxygen species and IL-6 responses to resistance-based HIIT: A time-dependent analysis

Acute exercise is known to increase reactive oxygen species (ROS), contributing to oxidative stress. Although this relationship has been widely studied, most investigations rely on indirect biomarkers and endurance-based exercise models. Resistance-circuit training, however, remains underexplored in this context. This study aimed to evaluate the time-dependent effects of rest and a novel resistance-based high-intensity interval training (HIIT) protocol on ROS and Interleukin-6 (IL-6) levels in sedentary, healthy young women. Thirty participants completed a resistance-circuit HIIT protocol. Capillary blood samples were collected at four time points: Baseline (after overnight fasting), after a two-hour seated rest, immediately post-HIIT and 15-min post-HIIT. ROS levels were measured using electron paramagnetic resonance (EPR) spectroscopy, and IL-6 via high-sensitivity ELISA. A significant decline in ROS (-8.5 %, p < 0.001) and IL-6 (-12.3 %, p < 0.05) occurred during rest. Throughout HIIT, both markers increased significantly (ROS +12.3 %, p < 0.001; IL-6: +48.1 % p < 0.01), with partial reductions observed after 15 min (ROS: -6.9 %, p < 0.01; IL-6: -20.4 %, p < 0.01). These findings suggest that resistance-based HIIT can serve as a valid model for studying acute oxidative and inflammatory responses in exercise science, offering a complementary approach to traditional endurance-focused protocols.