Acute Effects of High-Intensity Interval Training (HIIT) on Heart Rate Variability and Psychoaffective Responses Among Bipolar Patients andtheir Control Peers: A Randomized Crossover Trial

INTRODUCTION: to evaluate the acute effects of continuous moderate-intensity aerobic exercise and high-intensity interval training (HIIT) on heart rate variability (HRV) and psychoaffective responses in patients with bipolar disorder (BD) and healthy controls. METHODS: Eight BD patients and eight controls underwent baseline assessments, including anthropometric measurements and a submaximal exercise test to determine VO2Max, followed by two randomized exercise sessions. In one session, participants performed 12 min of continuous exercise at 65%VO2Max, and in the other, during the HIIT protocol, participants engaged in six 45-s bouts at 100%VO2Max, each followed by a 1-min and 15-s recovery period at 40%VO2Max. Pre- and postexercise measurements included psychoaffective scales (feeling scale - FS, felt arousal scale - FAS, and SUDs anxiety scale) and HRV assessments recorded during a 10-minute rest period under controlled conditions. RESULTS: Regarding RMSSD, both participants and sessions demonstrated a significant increase in this indicator (p=0.012). The BD significantly increased VLF and LF values and reduced HF values for both exercise sessions. Meanwhile, the LF/HF ratio showed a significant increase only in the HIIT session. For the control group, only a significant reduction in the HF index in both sessions and an increase in the LF/HF ratio only in the HIIT session. The FAS showed significant increases in bodily activation post-exercise across groups and modalities, while the FS demonstrated significant positive shifts in affective valence, with larger improvements following HIIT. Both exercise protocols produced significant reductions in anxiety levels (p=0.001), with HIIT showing a trend toward superior anxiolytic effects in BD patients. DISCUSSION: The improvement in vagal tone and HRV modulates the function of critical brain regions involved in emotional regulation, such as the prefrontal cortex, amygdala, and anterior cingulate cortex. This modulation reduces limbic hyperactivity and impulsivity while influencing monoaminergic pathways, attenuating excessive dopaminergic signaling, thereby contributing to enhanced mood stability and the reduction of affective disturbances in individuals with BD. CONCLUSION: Both continuous moderate-intensity exercise and HIIT elicited favorable acute autonomic and psychoaffective responses in BD patients and healthy controls. Notably, HIIT tended to produce greater affective and anxiolytic benefits in individuals with BD.