{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,31]],"date-time":"2026-07-31T09:57:49Z","timestamp":1785491869307,"version":"3.56.0"},"reference-count":62,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2026,7,31]],"date-time":"2026-07-31T00:00:00Z","timestamp":1785456000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["J. Funct. Morphol. Kinesiol.","JFMK"],"abstract":"<jats:p>Heart rate variability (HRV) monitoring is commonly used in sport and exercise science to assess recovery, training adaptation, and performance readiness. However, the routine reporting of numerous HRV metrics with substantial conceptual and physiological overlap has created inconsistency regarding which indices should be prioritized for applied monitoring. This narrative review synthesizes the contemporary literature to provide practical recommendations regarding HRV metric selection in applied monitoring, with particular emphasis on whether the root mean square of successive differences between adjacent normal-to-normal intervals (RMSSD) may serve as the primary metric for routine HRV monitoring in many healthy sport and exercise populations. RMSSD demonstrates several characteristics favorable for applied monitoring, including strong physiological relevance, favorable reliability, compatibility with ultra-short recording durations, relative robustness during spontaneous breathing, computational simplicity, and suitability for longitudinal monitoring frameworks. Although additional HRV metrics remain valuable for addressing specific physiological, mechanistic, or research questions, the current evidence supports RMSSD as the primary metric for routine HRV monitoring in many sport and exercise settings.<\/jats:p>","DOI":"10.3390\/jfmk11030304","type":"journal-article","created":{"date-parts":[[2026,7,31]],"date-time":"2026-07-31T08:20:18Z","timestamp":1785486018000},"page":"304","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["A Narrative Review of HRV Metric Selection for Applied Monitoring: RMSSD as the Default Metric for Sport and Exercise"],"prefix":"10.3390","volume":"11","author":[{"given":"Michael R.","family":"Esco","sequence":"first","affiliation":[{"name":"Department of Kinesiology, The University of Alabama, Tuscaloosa, AL 35487, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,7,31]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"773","DOI":"10.1007\/s40279-013-0071-8","article-title":"Training adaptation and heart rate variability in elite endurance athletes: Opening the door to effective monitoring","volume":"43","author":"Plews","year":"2013","journal-title":"Sports Med."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1461","DOI":"10.1007\/s40279-016-0484-2","article-title":"Monitoring athletic training status through autonomic heart rate regulation: A systematic review and meta-analysis","volume":"46","author":"Bellenger","year":"2016","journal-title":"Sports Med."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"417","DOI":"10.1007\/s40279-019-01061-5","article-title":"The accuracy of acquiring heart rate variability from portable devices: A systematic review and meta-analysis","volume":"49","author":"Dobbs","year":"2019","journal-title":"Sports Med."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1324","DOI":"10.1123\/ijspp.2016-0668","article-title":"Comparison of heart-rate-variability recording with smartphone photoplethysmography, Polar H7 chest strap, and electrocardiography","volume":"12","author":"Plews","year":"2017","journal-title":"Int. J. Sports Physiol. Perform."},{"key":"ref_5","first-page":"535","article-title":"Ultra-short-term heart rate variability indexes at rest and post-exercise in athletes: Evaluating the agreement with accepted recommendations","volume":"13","author":"Esco","year":"2014","journal-title":"J. Sports Sci. Med."},{"key":"ref_6","unstructured":"Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology (1996). Heart rate variability: Standards of measurement, physiological interpretation and clinical use. Circulation, 93, 1043\u20131065."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Billman, G.E. (2013). The LF\/HF ratio does not accurately measure cardiac sympatho-vagal balance. Front. Physiol., 4.","DOI":"10.3389\/fphys.2013.00026"},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Shaffer, F., and Ginsberg, J.P. (2017). An overview of heart rate variability metrics and norms. Front. Public Health, 5.","DOI":"10.3389\/fpubh.2017.00258"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"674","DOI":"10.1002\/mus.25573","article-title":"Reminder: RMSSD and SD1 are identical heart rate variability metrics","volume":"56","author":"Ciccone","year":"2017","journal-title":"Muscle Nerve"},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Buchheit, M. (2014). Monitoring training status with HR measures: Do all roads lead to Rome?. Front. Physiol., 5.","DOI":"10.3389\/fphys.2014.00073"},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Esco, M.R., Fields, A.D., Mohammadnabi, M.A., and Kliszczewicz, B.M. (2025). Monitoring training adaptation and recovery status in athletes using heart rate variability via mobile devices: A narrative review. Sensors, 26.","DOI":"10.3390\/s26010003"},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Laborde, S., Mosley, E., and Thayer, J.F. (2017). Heart rate variability and cardiac vagal tone in psychophysiological research\u2014Recommendations for experiment planning, data analysis, and data reporting. Front. Psychol., 8.","DOI":"10.3389\/fpsyg.2017.00213"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"e32195","DOI":"10.1016\/j.heliyon.2024.e32195","article-title":"A comprehensive evaluation of linear and non-linear HRV parameters between paced breathing and stressful mental state","volume":"10","author":"Chand","year":"2024","journal-title":"Heliyon"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"277","DOI":"10.1098\/rsta.2008.0232","article-title":"Methods derived from nonlinear dynamics for analysing heart rate variability","volume":"367","author":"Voss","year":"2009","journal-title":"Philos. Trans. R. Soc. A Math. Phys. Eng. Sci."},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Munoz, M.L., van Roon, A., Riese, H., Thio, C., Oostenbroek, E., Westrik, I., de Geus, E.J.C., Gansevoort, R.T., Lefrandt, J.D., and Nolte, I.M. (2015). Validity of (ultra-)short recordings for heart rate variability measurements. PLoS ONE, 10.","DOI":"10.1371\/journal.pone.0138921"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"117","DOI":"10.1111\/j.1542-474X.2011.00417.x","article-title":"Reliability of ultra-short ECG indices for heart rate variability","volume":"16","author":"Nussinovitch","year":"2011","journal-title":"Ann. Noninvasive Electrocardiol."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"175","DOI":"10.1007\/s00421-017-3759-x","article-title":"Ultra-shortened time-domain HRV parameters at rest and following exercise in athletes: An alternative to frequency computation of sympathovagal balance","volume":"118","author":"Esco","year":"2018","journal-title":"Eur. J. Appl. Physiol."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Fields, A.D., Mohammadnabi, M.A., Fedewa, M.V., and Esco, M.R. (2025). Modified stress score and sympathetic-parasympathetic ratio using ultra-short-term HRV in athletes: A novel approach to autonomic monitoring. J. Funct. Morphol. Kinesiol., 10.","DOI":"10.3390\/jfmk10030310"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"e19347","DOI":"10.7717\/peerj.19347","article-title":"Heart rate variability over the decades: A scoping review","volume":"13","author":"Sundas","year":"2025","journal-title":"PeerJ"},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"von Rosenberg, W., Chanwimalueang, T., Adjei, T., Jaffer, U., Goverdovsky, V., and Mandic, D.P. (2017). Resolving ambiguities in the LF\/HF ratio: LF-HF scatter plots for the categorization of mental and physical stress from HRV. Front. Physiol., 8.","DOI":"10.3389\/fphys.2017.00360"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1255","DOI":"10.1113\/expphysiol.2010.056259","article-title":"Low-frequency power of heart rate variability is not a measure of cardiac sympathetic tone but may be a measure of modulation of cardiac autonomic outflows by baroreflexes","volume":"96","author":"Goldstein","year":"2011","journal-title":"Exp. Physiol."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"477","DOI":"10.1111\/psyp.12027","article-title":"The utility of low frequency heart rate variability as an index of sympathetic cardiac tone: A review with emphasis on a reanalysis of previous studies","volume":"50","author":"Langewitz","year":"2013","journal-title":"Psychophysiology"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"210","DOI":"10.1016\/j.cmpb.2013.07.024","article-title":"Kubios HRV\u2014Heart rate variability analysis software","volume":"113","author":"Tarvainen","year":"2014","journal-title":"Comput. Methods Programs Biomed."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"1359","DOI":"10.1177\/0956797611417632","article-title":"False-positive psychology: Undisclosed flexibility in data collection and analysis allows presenting anything as significant","volume":"22","author":"Simmons","year":"2011","journal-title":"Psychol. Sci."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"331","DOI":"10.1111\/cpf.12233","article-title":"Heart rate variability stabilization in athletes: Towards more convenient data acquisition","volume":"36","author":"Flatt","year":"2016","journal-title":"Clin. Physiol. Funct. Imaging"},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Shaffer, F., Meehan, Z.M., and Zerr, C.L.A. (2020). Critical Review of Ultra-Short-Term Heart Rate Variability Norms Research. Front. Neurosci., 14.","DOI":"10.3389\/fnins.2020.594880"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"131","DOI":"10.1042\/CS20070055","article-title":"Heart rate variability measures: A fresh look at reliability","volume":"113","author":"Pinna","year":"2007","journal-title":"Clin. Sci."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"5611","DOI":"10.1038\/s41598-025-89892-3","article-title":"Assessing the clinical reliability of short-term heart rate variability: Insights from controlled dual-environment and dual-position measurements","volume":"15","author":"Besson","year":"2025","journal-title":"Sci. Rep."},{"key":"ref_29","doi-asserted-by":"crossref","unstructured":"Schmitt, L., Regnard, J., and Millet, G.P. (2015). Monitoring fatigue status with HRV measures in elite athletes: An avenue beyond RMSSD?. Front. Physiol., 6.","DOI":"10.3389\/fphys.2015.00343"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"1409","DOI":"10.1007\/s00421-023-05373-3","article-title":"Inter-day reliability of heart rate complexity and variability metrics in healthy highly active younger and older adults","volume":"124","author":"Fennell","year":"2024","journal-title":"Eur. J. Appl. Physiol."},{"key":"ref_31","first-page":"602","article-title":"Ultra-short-term heart rate variability is sensitive to training effects in team sports players","volume":"14","author":"Nakamura","year":"2015","journal-title":"J. Sports Sci. Med."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"688","DOI":"10.1123\/ijspp.8.6.688","article-title":"Evaluating training adaptation with heart-rate measures: A methodological comparison","volume":"8","author":"Plews","year":"2013","journal-title":"Int. J. Sports Physiol. Perform."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"378","DOI":"10.1519\/JSC.0000000000001095","article-title":"Evaluating individual training adaptation with smartphone-derived heart rate variability in a collegiate female soccer team","volume":"30","author":"Flatt","year":"2016","journal-title":"J. Strength Cond. Res."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"994","DOI":"10.1123\/ijspp.2014-0556","article-title":"Smartphone-derived heart-rate variability and training load in a women\u2019s soccer team","volume":"10","author":"Flatt","year":"2015","journal-title":"Int. J. Sports Physiol. Perform."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"1026","DOI":"10.1123\/ijspp.2013-0497","article-title":"Heart-rate variability and training-intensity distribution in elite rowers","volume":"9","author":"Plews","year":"2014","journal-title":"Int. J. Sports Physiol. Perform."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"783","DOI":"10.1123\/ijspp.2013-0455","article-title":"Monitoring training with heart-rate-variability: How much compliance is needed for valid assessment?","volume":"9","author":"Plews","year":"2014","journal-title":"Int. J. Sports Physiol. Perform."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"1","DOI":"10.2165\/00007256-200030010-00001","article-title":"Measures of reliability in sports medicine and science","volume":"30","author":"Hopkins","year":"2000","journal-title":"Sports Med."},{"key":"ref_38","doi-asserted-by":"crossref","unstructured":"Laborde, S., Mosley, E., and Mertgen, A. (2018). Vagal Tank Theory: The Three Rs of Cardiac Vagal Control Functioning\u2014Resting, Reactivity, and Recovery. Front. Neurosci., 12.","DOI":"10.3389\/fnins.2018.00458"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"2310","DOI":"10.1152\/jappl.1993.75.5.2310","article-title":"Important influence of respiration on human R-R interval power spectra is largely ignored","volume":"75","author":"Brown","year":"1993","journal-title":"J. Appl. Physiol."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"365","DOI":"10.1046\/j.1365-2281.2001.00337.x","article-title":"Time domain, geometrical and frequency domain analysis of cardiac vagal outflow: Effects of various respiratory patterns","volume":"21","author":"Helminen","year":"2001","journal-title":"Clin. Physiol."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"263","DOI":"10.1016\/j.biopsycho.2005.11.014","article-title":"Toward understanding respiratory sinus arrhythmia: Relations to cardiac vagal tone, evolution and biobehavioral functions","volume":"74","author":"Grossman","year":"2007","journal-title":"Biol. Psychol."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"534","DOI":"10.1080\/17461391.2013.767947","article-title":"The impact of breathing on HRV measurements: Implications for the longitudinal follow-up of athletes","volume":"13","author":"Saboul","year":"2013","journal-title":"Eur. J. Sport Sci."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"14","DOI":"10.1159\/000495519","article-title":"Validity of commonly used heart rate variability markers of autonomic nervous system function","volume":"78","author":"Thomas","year":"2019","journal-title":"Neuropsychobiology"},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"e650","DOI":"10.1016\/S2589-7500(20)30246-6","article-title":"Heart rate variability with photoplethysmography in 8 million individuals: A cross-sectional study","volume":"2","author":"Natarajan","year":"2020","journal-title":"Lancet Digit. Health"},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"1259","DOI":"10.1007\/s40279-013-0083-4","article-title":"Cardiac parasympathetic reactivation following exercise: Implications for training prescription","volume":"43","author":"Stanley","year":"2013","journal-title":"Sports Med."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"34023","DOI":"10.1038\/s41598-025-13540-z","article-title":"Individual training prescribed by heart rate variability, heart rate and well-being scores in experienced cyclists","volume":"15","author":"Alfonso","year":"2025","journal-title":"Sci. Rep."},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"113537","DOI":"10.1016\/j.physbeh.2021.113537","article-title":"Monitoring training in women\u2019s volleyball: Supine or seated heart rate variability?","volume":"240","author":"Rabbani","year":"2021","journal-title":"Physiol. Behav."},{"key":"ref_48","doi-asserted-by":"crossref","unstructured":"Holmes, C.J., Wind, S.A., and Esco, M.R. (2018). Heart rate variability responses to an undulating resistance training program in free-living conditions: A case study in a collegiate athlete. Sports, 6.","DOI":"10.3390\/sports6040121"},{"key":"ref_49","doi-asserted-by":"crossref","unstructured":"Ernst, G. (2017). Heart-rate variability\u2014More than heart beats?. Front. Public Health, 5.","DOI":"10.3389\/fpubh.2017.00240"},{"key":"ref_50","doi-asserted-by":"crossref","unstructured":"Michael, S., Graham, K.S., and Davis, G.M. (2017). Cardiac autonomic responses during exercise and post-exercise recovery using heart rate variability and systolic time intervals\u2014A review. Front. Physiol., 8.","DOI":"10.3389\/fphys.2017.00301"},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"46","DOI":"10.7453\/gahmj.2014.073","article-title":"Heart rate variability: New perspectives on physiological mechanisms, assessment of self-regulatory capacity, and health risk","volume":"4","author":"McCraty","year":"2015","journal-title":"Glob. Adv. Health Med."},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"108728","DOI":"10.1016\/j.biopsycho.2023.108728","article-title":"Putting back respiration into respiratory sinus arrhythmia or high-frequency heart rate variability: Implications for interpretation, respiratory rhythmicity, and health","volume":"185","author":"Ritz","year":"2024","journal-title":"Biol. Psychol."},{"key":"ref_53","doi-asserted-by":"crossref","unstructured":"Garabedian, C., Champion, C., Servan-Schreiber, E., Butruille, L., Aubry, E., Sharma, D., Logier, R., Deruelle, P., Storme, L., and Houfflin-Debarge, V. (2017). A new analysis of heart rate variability in the assessment of fetal parasympathetic activity: An experimental study in a fetal sheep model. PLoS ONE, 12.","DOI":"10.1371\/journal.pone.0180653"},{"key":"ref_54","doi-asserted-by":"crossref","unstructured":"Billman, G.E. (2013). The effect of heart rate on the heart rate variability response to autonomic interventions. Front. Physiol., 4.","DOI":"10.3389\/fphys.2013.00222"},{"key":"ref_55","doi-asserted-by":"crossref","first-page":"1210","DOI":"10.1038\/s41598-020-79808-8","article-title":"Direct measurement of vagal tone in rats does not show correlation to HRV","volume":"11","author":"Marmerstein","year":"2021","journal-title":"Sci. Rep."},{"key":"ref_56","doi-asserted-by":"crossref","unstructured":"Billman, G.E. (2011). Heart rate variability\u2014A historical perspective. Front. Physiol., 2.","DOI":"10.3389\/fphys.2011.00086"},{"key":"ref_57","doi-asserted-by":"crossref","first-page":"676","DOI":"10.1016\/j.clinph.2019.11.013","article-title":"Heart rate variability (HRV): From brain death to resonance breathing at 6 breaths per minute","volume":"131","author":"Schwerdtfeger","year":"2020","journal-title":"Clin. Neurophysiol."},{"key":"ref_58","doi-asserted-by":"crossref","first-page":"452","DOI":"10.1123\/ijspp.2014-0235","article-title":"Two new indexes for the assessment of autonomic balance in elite soccer players","volume":"10","year":"2015","journal-title":"Int. J. Sports Physiol. Perform."},{"key":"ref_59","doi-asserted-by":"crossref","first-page":"301","DOI":"10.3233\/IES-230088","article-title":"Heart rate variability: Obtaining the stress score from SDNN values","volume":"32","year":"2024","journal-title":"Isokinet. Exerc. Sci."},{"key":"ref_60","doi-asserted-by":"crossref","first-page":"e70357","DOI":"10.14814\/phy2.70357","article-title":"Heart rate variability and overtraining in soccer players: A systematic review","volume":"13","author":"Lipka","year":"2025","journal-title":"Physiol. Rep."},{"key":"ref_61","doi-asserted-by":"crossref","unstructured":"Addleman, J.S., Lackey, N.S., DeBlauw, J.A., and Hajduczok, A.G. (2024). Heart rate variability applications in strength and conditioning: A narrative review. J. Funct. Morphol. Kinesiol., 9.","DOI":"10.3390\/jfmk9020093"},{"key":"ref_62","doi-asserted-by":"crossref","unstructured":"Hannon, J., O\u2019Hagan, A., Lambe, R., O\u2019Grady, B., and Doherty, C. (2025). Associations between daily heart rate variability and self-reported wellness: A 14-day observational study in healthy adults. Sensors, 25.","DOI":"10.3390\/s25144415"}],"container-title":["Journal of Functional Morphology and Kinesiology"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2411-5142\/11\/3\/304\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,7,31]],"date-time":"2026-07-31T09:01:59Z","timestamp":1785488519000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2411-5142\/11\/3\/304"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,7,31]]},"references-count":62,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2026,9]]}},"alternative-id":["jfmk11030304"],"URL":"https:\/\/doi.org\/10.3390\/jfmk11030304","relation":{},"ISSN":["2411-5142"],"issn-type":[{"value":"2411-5142","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,7,31]]}}}