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Mary Stenson


During exercise sympathetic nervous activity increases and parasympathetic nervous activity decreases to fuel energy demands. Heart rate variability (HRV) indicates activity of the autonomic nervous system and the balance of its two branches. Slow breathing (SB) (6 breaths/minute) increases parasympathetic activity both spontaneously during practice and at rest after long-term practice. Thus, SB may increase parasympathetic activity after exercise. PURPOSE: This study aimed to determine whether post-exercise SB increases parasympathetic activity as measured by HRV. METHODS: Ten recreationally active college aged males (21 +/- 1 years old) completed the study. A VO2 max test was used to determine 70% of VO2 max for subsequent testing sessions. Each individual completed a control trial consisting of a 5-minute ECG (from V5) recording to measure baseline HRV, a 30-minute treadmill run at 70% VO2 max, and a seated 30-minute recovery during which ECG was recorded. The experimental trial was completed after at least 48 hours and was identical to the control trial except for a SB intervention of 6 breaths/minute conducted during the first 10-minutes of recovery. HRV data were analyzed using frequency and time-domain analyses as well as non-linear analysis. 2x7 repeated measures ANOVAs and simple effects tests were conducted to determine differences between control and experimental trials in high frequency (HF) activity, low frequency (LF) activity, LF/HF ratio, standard deviation between consecutive R waves (SDRR), root mean square of standard deviation (RMSSD), and percent of consecutive R wave intervals greater than 50 milliseconds (PRR50) HRV variables. RESULTS: HF activity and LF/HF ratio did not significantly differ between control and experimental trials over time (F(1.039, 9.35) = 2.178; p = 0.267 and F(1, 9) = 0.074; p = 0.792). SDRR (F(2.150, 19.351) = 17.359; p = <0.001), RMSSD (F(1.869, 16.819) = 7.464; p = 0.005), PRR50 (F(2.303, 20.727) = 7.186; p = 0.003), and LF (F(1.737, 15.629) = 9.107; p = 0.003) activity were all greater in the experimental trial than the control trial during the slow breathing intervention intervals of 0-5 minutes (SDRR p = 0.002; RMSSD p = 0.013; PRR50 p = 0.007; LF p = 0.01) and 5-10 minutes (SDRR p = 0.001; RMSSD p = 0.005; PRR50 p = 0.001; LF p = 0.004) . SDRR was also greater in the experimental trial than the control trial during the interval of 10-15 minutes (p = 0.049). CONCLUSION: SB post-exercise increased parasympathetic activity during the SB intervention as indicated by higher SDRR, RMSSD, and PRR50; but not after cessation of the SB intervention in SB naive participants. Elevated LF activity as well as nonsignificant HF and LF/HF ratio values indicate traditional frequency-domain HRV analysis was not effective in analyzing HRV during SB of 6 breaths/minute. SB may benefit athletes by increasing parasympathetic activity after exercise, but immediate post-exercise .appears to only have a reflexive effect.