Sex differences in heart rate recovery and cardiac vagal reactivation following high-intensity functional training

Abstract

Background: Heart rate recovery is key indicator of cardiovascular health, influenced by vagal reactivation and sympathetic withdrawal. However, research on sex differences in cardiac vagal reactivation following highintensity functional training (HIFT) is limited. Aim: This study aimed to test the hypothesis that women exhibit slower heart rate recovery compared to men after HIFT workout, attributed to reduced cardiac vagal reactivation. Material and Methods: Young recreational HIFT practitioners, all apparently healthy individuals, voluntarily participated in this study. All subjects performed a HIFT session, the “workout of the day” (WOD), based on the structure of the training session: “as many repetitions as possible” (AMRAP) “Cindy”, which consisted of as many rounds possible of five pull-ups, 10 push-ups, and 15 air squats in a 20-minute period. Anthropometric measurements, body composition, hemodynamic parameters, and heart rate variability (HRV) were analyzed at rest and during HIFT. Following this, cardiac vagal reactivation was indexed by the fall in heart rate and the HRV metric over the 5-minute period in 30-second intervals after the end of the HIFT workout. Results: The men showed lower values of the resting heart rate compared to women (p = 0.023). Nonlinear time series analysis of baseline HRV evidenced that men had higher resting short-term variability (p < 0.001, 2p: 0.771) and 2V (p = 0.013, 2p: 0.105) indices in comparison to women, as well as lower 0V variation indices (p = 0.048, 2p: 0.250). In addition, the male group showed lower vagal withdrawal (short-term variability [p = 0.012, 2p: 0.375 and 2V [p < 0.001, 2p: 0.885 indices), sympathetic outflow (0V variation [p < 0.001, 2p: 0.773) and sympathovagal balance (short- and long-term variability ratio [p < 0.001, 2p: 0.748) to the heart than women during HIFT performance. Women presented a slower recovery in heart rate than men regardless of the time point (p < 0.001, 2p: 0.724). Post-HIFT vagal tone metrics (pNN50 and RMSSD) were faster and increased by a greater magnitude in men compared to women (p = 0.004, 2p: 0.460 and p = 0.005, 2p: 0.437; respectively). Conclusion: Our findings suggest that women had a slower heart rate recovery compared to men after recreational HIFT training session, suggesting a sex-related difference in cardiac vagal reactivation.