High-Intensity Interval Exercises' Acute Impact on Heart Rate Variability: Comparison Between Whole-Body and Cycle Ergometer ProtocolsSchaun, Gustavo Z.1; Del Vecchio, Fabrício B.2The Journal of Strength & Conditioning Research: January 2018 - Volume 32 - Issue 1 - p 223–229 doi: 10.1519/JSC.0000000000002180 Original Research Abstract Author Information Schaun, GZ and Del Vecchio, FB. High-intensity interval exercises' acute impact on heart rate variability: comparison between whole-body and cycle ergometer protocols. J Strength Cond Res 32(1): 223–229, 2018—Study aimed to compare the effects of 2 high-intensity interval training (HIIT) protocols on heart rate variability. 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 2 HIIT protocols, 1 on a cycle ergometer (Tabata protocol [TBT]; eight 20-second bouts at 170% P max interspersed by 10-second rest) and another with whole-body calisthenic exercises (McRae protocol; eight 20-second all-out intervals interspersed by 10-second rest). Heart rate variability outcomes in the time, frequency, and nonlinear domains were assessed on 3 moments: (a) presession; (b) immediately postsession; and (c) 24 hours postsession. Results revealed that RRmean, Ln rMSSD, Ln high frequency (HF), and Ln low frequency (LF) were significantly reduced immediately postsession (p ≤ 0.001) and returned to baseline 24 h after both protocols. In addition, LF/HF ratio was reduced 24 h postsession (p ≤ 0.01) and SD2 was significantly lower immediately postsession only in TBT. Our main finding was that responses from heart rate 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 1 day. These results suggest that subjects were already recovered the day after and can help coaches to better program training sessions with such protocols. 1Neuromuscular Assessment Laboratory, School of Physical Education, Federal University of Pelotas, Pelotas, Brazil; and 2Sport Training and Physical Performance Research Group, School of Physical Education, Federal University of Pelotas, Pelotas, Brazil Address correspondence to Gustavo Z. Schaun, firstname.lastname@example.org. Copyright © 2018 by the National Strength & Conditioning Association.