Breathe in, breathe out for acute post-exercise stress management

Purpose: Changes in cardiac parasympathetic activity (CPA) can be evaluated by measuring heart rate variability (HRV), with the root mean square of successive differences (RMSSD) being a primary time-domain measure used to estimate vagally mediated changes in HRV. Controlled breathing (CB) during resting has a significant impact on HRV and serves as a strategy to influence CPA. However, the effects of CB on HRV and RMSSD after exercise remain poorly understood. Therefore, the objective of this study was to assess the effects of CB following a submaximal incremental treadmill exercise (SITE) on HRV and RMSSD. Methods: 9 subjects (7 men; 2 women) performed 2 SITE with a 24-h recovery between sessions. SITE protocol included 3-min warmup at a fixed slope of 1%, followed by a speed increase of 1 km/h every 2-min. The exercise ended when the participants reached 95% of their maximal heart rate. 15-min before (PRE) and 15-min after (POST) each SITE, HRV and RMSSD were measured in a quiet and distraction-free room using a heart rate monitor connected to the ‘‘Elite HRV’’ app. During PRE, subjects were instructed to maintain a calm state and breathe freely for 5-min. In POST, two breathing conditions, uncontrolled breathing (UB) and CB following the guidance provided by the ‘‘Elite HRV’’ app, were randomized and performed by each participant. The CB pattern involved 6 breaths per minute with an inhalation/exhalation ratio of 1: 1, consisting of 5 s for inhalation and 5 s for exhalation, for a total of 5-min. Repeated measures mixed models were used to examine the effects of different breathing conditions (UB vs CB) on HRV and RMSSD. Statistical significance was set at p\0.008. Results: Significant differences (p\0.0001) were observed, indicating lower HRV (49.5 ± 10.1 ms) and RMSSD values (29.8 ± 18.8 ms) in POST UB compared to all other UB (HRV PRE = 59.0 ± 8.8 ms; RMSSD PRE = 53.2 ± 27.4 ms) and CB (HRV PRE = 58.8 ± 7.3 ms; HRV POST = 57.7 ± 11.5 ms; RMSSD PRE = 50.1 ± 19.3 ms; RMSSD POST = 51.9 ± 31.4 ms) time points. On average, UB resulted in a decrease of 8.9 ms and 21.9 ms in HRV and RMSSD, respectively. Conclusions: The study findings highlight the significance of CB in modulating CPA during stress-inducing conditions, such as exercise. Post-exercise HRV and RMSSD in the UB were markedly lower compared to CB. Consequently, practitioners and athletic trainers can employ slow and CB strategies, either during recovery or as a cooldown strategy after exercise, to enhance CPA and counterbalance excessive activation of the sympathetic branch.