Cardiac autonomic recovery following reduced exertion high-intensity interval training (REHIT) in physically inactive adults

Introduction Post-exercise heart rate variability (HRV) recovery is associated with cardiac parasympathetic reactivation, reflecting cardiovascular homeostasis restoration. This study aimed to compare cardiac autonomic recovery following reduced-exertion high-intensity interval training (REHIT) and moderate-intensity continuous training (MICT) in sedentary individuals. Methods Sixteen physically inactive male volunteers [aged 21 ± 0.89 years; body mass index = 20.09 ± 1.09 kg/m<sup>2</sup>; maximal oxygen consumption (VO<sub>2</sub> max) = 30.90 ± 4.76 ml/kg/min] were included in a randomised crossover study. Blood pressure, heart rate, rating of perceived exertion (RPE), and HRV were measured before, immediately after, and at 20 min, 40 min, 60 min, and 24 h after REHIT and MICT. Results Both exercise protocols resulted in a significant decrease in log-transformed (Ln) RMSSD and LnSDNN immediately post-exercise (<i>p</i> < 0.05). Following REHIT, LnSDNN and LnRMSSD returned to baseline within 24 h. low-frequency activity (LnLF) and high-frequency activity (LnHF) decreased significantly immediately, 20 min and 40 min after REHIT (<i>p</i> < 0.05). After MICT, LnSDNN and LnRMSSD returned to baseline within 20 and 40 min, respectively. Moreover, LnLF and LnHF returned to baseline within 60 and 20 min, respectively, following MICT. Conclusions These findings indicate that REHIT prolongs HRV recovery. However, HRV returned to baseline within 24 h, providing valuable insights for exercise prescription utilising the REHIT protocol.