The effect of fitness level on cardiac autonomic regulation, IL-6, total antioxidant capacity, and muscle damage responses to a single bout of high-intensity interval training

The higher fitness level was associated with the less pronounced postexercise cardiac autonomic changes and their faster restoration, even when there were similar acute cardiorespiratory responses. These findings were simultaneously accompanied by the higher postexercise IL-6 and TAC concentrations and less significant changes in muscle damage biochemical markers in well-trained individuals.