Effects of different incremental treadmill exercise protocols on the autonomic nervous system in healthy college students: a comparative study based on heart rate variability analysis

(1) All three incremental treadmill protocols elicited acute HRV alterations, characterized by parasympathetic withdrawal and sympathetic activation, reflecting a transient state of autonomic imbalance; (2) HRV serves as a sensitive physiological marker for detecting exercise-induced fatigue and quantifying training load intensity. Under the Ellestad A and B protocols, heart rate variability (HRV) exhibited a sustained decline throughout the 5-min recovery period, potentially indicating that exercise-induced fatigue load may not have been fully resolved. However, this interpretation warrants further validation through additional objective physiological markers. While the rebound observed after the Bruce protocol may suggest acute autonomic recovery associated with supercompensation and adaptive responses to high-intensity exercise.