High-Intensity Interval Exercises' Acute Impact on Heart Rate Variability: Comparison Between Whole-Body and Cycle Ergometer Protocols.Schaun, Gustavo Z.; Del Vecchio, Fabrício B.Journal of Strength & Conditioning Research: Post Acceptance: August 04, 2017 doi: 10.1519/JSC.0000000000002180 Original Research: PDF Only Abstract Study aimed to compare the effects of two high-intensity interval exercises (HIIT) protocols on heart rate variability (HRV). Twelve young adult males (23.3 +/- 3.9 years, 177.8 +/- 7.4 cm, 76.9 +/- 12.9 kg) volunteered to participate. In a randomized cross-over design, subjects performed two HIIT protocols, one on a cycle ergometer (TBT; eight 20 s bouts at 170% Pmax interspersed by 10 s rest) and another with whole-body calisthenic exercises (MCR; eight 20 s all-out intervals interspersed by 10 s rest). HRV outcomes in the time, frequency and non-linear domains were assessed on three moments: (a) pre-session; (b) immediately post-session; and (c) 24h post-session. Results revealed that RRmean, Ln rMSSD, Ln HF, Ln LF were significantly reduced immediately post-session (p < 0.001) and returned to baseline 24h after both protocols. Additionally, LF/HF ratio was reduced 24h post-session (p < 0.01) and SD2 was significantly lower immediately post-session only in TBT. Our main finding was that responses from HR autonomic control were similar in both protocols, despite different modes of exercise performed. Specifically, exercises resulted in a high parasympathetic inhibition immediately after session with subsequent recovery within one day. These results suggest that subjects were already recovered the day after and can help coaches to better program training sessions with such protocols. Copyright (C) 2017 by the National Strength & Conditioning Association.