How intense is high-intensity interval training? Biomarker responses and associations with training load and fitness
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High-intensity interval training (HIIT) enhances physical performance but requires close monitoring to avoid illnesses/injuries. We monitored physiological responses at rest during and up to 14 days following a 7-day HIIT intervention to identify chronic physiological changes and to explore correlations between blood biomarkers (blood count, cytokines, creatine kinase [CK], urea, ferritin, and transferrin), training load, cardiorespiratory fitness (VO2max), and muscle soreness. Thirty participants were randomly allocated to either HIIT shock cycle (10× HIIT in 7 days) (1) with or (2) without additional low-intensity training after each HIIT session or (3) control group. Repeated HIIT resulted in a chronic decrease of hemoglobin, hematocrit, red blood cells, CK, interleukin [IL]-2, -4, -9, -17A, -17F, tumor necrosis factor alpha (TNF-α), and ferritin. CK showed highest positive correlation with training load and muscle soreness, while VO2max correlated with cytokines IL-5, -6, -10, -17F, -22. The present study revealed reliable biomarkers reflecting training load and VO2max, suitable for personalized monitoring of health and recovery and performance optimization.
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iScience, 28, 11, Elsevier, Amsterdam ; Boston ; London ; New York ; Oxford ; Paris ; Philadelphia ; San Diego ; St. Louis, 2025, https://doi.org/10.1016/j.isci.2025.113738