Reliability of heart rate measures used to assess post-exercise parasympathetic reactivation Olivier Dupuy 1,2 , Saı ¨d Mekary 1,3 , Nicolas Berryman 1,2,3 , Louis Bherer 3,4 , Michel Audiffren 2 and Laurent Bosquet 1,2,3 1 Department of Kinesiology, University of Montreal, Montreal, Qc, Canada, 2 Faculty of Sport Sciences, University of Poitiers, Poitiers, France, 3 Research Center, Montreal Institute of Geriatrics, Montreal, Qc, Canada, and 4 Department of Psychology, University of Quebec at Montreal, Montreal, Qc, Canada Summary Correspondence Laurent Bosquet, Faculty of sport sciences, 8 Jean Monnet road, 86000 Poitiers, France E-mail: laurent.bosquet@univ-poitiers.fr Accepted for publication Received 06 November 2011; accepted 25 January 2012 Key words autonomic nervous system; exercise intensity; heart rate recovery; heart rate variability Purpose: Postexercise HRR (heart rate recovery) and HRV (heart rate variability) are commonly used to asses non-invasive cardiac autonomic regulation and more par- ticularly reactivation parasympathetic function. Unfortunately, the reliability of postexercise HRR and HRV remains poorly quantified and is still lacking. The aim of this study was to examine absolute and relative reliability of HRR and HRV indices used to assess postexercise cardiac parasympathetic reactivation. Methods: We studied 30 healthy men, who underwent 10-minute heart rate recording after cessation of maximal and submaximal intensity exercises. Each condition of testing was repeated twice within 5 ± 2 days after the first one. Standard indexes of HRR and HRV were computed from heart rate and RR inter- vals. Results: We found no significant bias between repeated measures. Relative reliabil- ity was assessed with the intraclass coefficient correlation (ICC) and absolute reli- ability with the standard error measurement (SEM) and coefficient of variation (CV). A large range for ICC was observed for both indexes of HRR and HRV (0·12 < ICC < 0·87 and 0·14 < ICC < 0·97, respectively). The same heterogene- ity was observed for absolute reliability (5% < CV < 72% for HRR parameters and 24% < CV < 141% for HRV parameters). Conclusion: According to our results, Δ60 (the absolute difference between heart rate immediately at the end of exercise and after 60 s) and HFnu (High Fre- quency expressed in normalized unit; that is, in a percentage of LF+HF) represent the most reliable parameters. In conclusion, we found that the measures used to asses cardiac parasympathetic reactivation were characterized by large random variations and their reliability remains moderate. Introduction Postexercise heart rate recovery (HRR) and heart rate vari- ability (HRV) are commonly used to assess non-invasive cardiac autonomic regulation and more particularly cardiac parasympathetic reactivation. Heart rate decreases mono- exponentially towards resting values when exercise ceases (Perini et al., 1989). The exponential nature of this kinetics is an intrinsic property of the cardiovascular system and is modulated by the autonomic nervous system (ANS) (Savin et al., 1982). The rapid decrease in HR that occurs during the first 2–3 min after exercise cessation is thought to be mainly determined by the restoration of parasympathetic activity at the sinus node level (Savin et al., 1982; Kannank- eril & Goldberger, 2002). Heart rate indices calculated from this part of the signal are therefore considered as indirect measures of cardiac parasympathetic reactivation (Imai et al., 1994; Kannankeril et al., 2004; Buchheit et al., 2007b). The slow decrease in HR that takes place from the third minute after exercise cessation until the return to resting values is a complex interplay between the decrease in cardiac sympa- thetic activity and the respiratory modulation of cardiac parasympathetic activity (Perini et al., 1989; Buchheit et al., 2007b). This interaction between both branches of ANS can be assessed through the analysis of HRV, either in the time or frequency domains (Task Force, 1996). Postexercise HRR and HRV measures can therefore be considered as non-invasive measures of cardiac autonomic regulation Clin Physiol Funct Imaging (2012) doi: 10.1111/j.1475-097X.2012.01125.x 1 © 2012 The Authors Clinical Physiology and Functional Imaging © 2012 Scandinavian Society of Clinical Physiology and Nuclear Medicine