Wearable fitness technology has become mainstream in our society. With consumers’ desire to monitor health by tracking personal data at their fingertips, technology companies continue to expand the metrics provided on these apps. In addition to tracking movement (e.g., step counts, standing hours) and measuring heart rate levels, fitness apps now measure and report several other data. Heart Rate Variability (HRV), in particular, has emerged as a new and popular cardiovascular metric on fitness apps. Understanding fitness app data and applying it to daily fitness routines can be a helpful motivational and accountability tool. In this month’s Wellness Read, our fitness coaches define HRV, discuss its utility, and clarify which metrics you should pay attention to when it comes to cardiac health.
What is Heart Rate Variability?
HRV, in the broadest sense, is a cardiac health measure of the deviation in time between consecutive heart beats. As described in apps and trackers, HRV is an indicator of the body’s readiness to handle a workload, providing elite athletes and routine exercisers insight into their recovery.1 It is important to note that HRV is not synonymous with heart rate, which is typically categorized as the number of heart beats per minute.2
The Autonomic Nervous System (ANS) regulates essential processes that we do not consciously control. The ANS is made up of two branches that allow our bodies to react and adapt – the parasympathetic (rest-and-digest) and sympathetic (fight-or-flight) branches. In addition to HRV, the ANS regulates multiple processes including digestion, blood pressure, breathing, and heart rate. This system plays a vital role in controlling our physiology in normal and pathological circumstances.3,6
HRV and Exercise
When we exercise, we put stress our bodies, challenging homeostasis. The amount of stress we put on our bodies’ systems varies based on type of workout, intensity, and duration. Following exercise, it is important to give ourselves adequate time before the next workout because the recovery period, or the time in between stressors, is when we see cardiovascular and muscular adaptations. However, when our bodies do not have adequate rest and recovery, both physically and psychologically, it can negatively affect adaptation and even the return to normal homeostasis. Factors like poor sleep, stress, an unhealthy diet, and disease can heavily influence how our body and the ANS respond.3,4,5Since HRV is deemed a reflection of the ANS, it can be used to analyze how our unconscious physiological response is working.
In general, current research around HRV claims:
- High HRV indicates good recovery (i.e., you are ready to handle a workload or stress)
- Low HRV indicates stress, illness, or overtraining (i.e., your body is unable to respond well to a workload or stress)
Cardiologists have summarized HRV scores on a 0 to 100 scale, with lower scores indicative of poor or decreased adaptability. Since HRV is predicted to peak between 20 and 30 years of age before declining, targets are specific to age.1The chart below characterizes target HRV scores with respect to gender and age.3
Unfortunately, there are limitations in measuring HRV. Calculating this score is not simple, and the gold standard requires 24 hours in a clinical setting, typically using an ECG and other clinical applications. This calculation includes analysis of core body temperatures, metabolism, sleep cycles, circadian rhythms, and many other factors.4 This method of testing does not translate to apps, which are not able to measure some of these factors. Moreover, research has been conducted predominately on small sample sizes of athletic or clinical cohorts, which does not easily lend itself to generalizability.2,8 Lastly, devices that use apps referencing HRV do not have regulating agencies, which casts further doubt on the accuracy and reliability of such information.
So, how do I best measure my cardiac health?
Studies have been conducted to analyze correlation between VO2 Max (tested at SHIFT), a well-researched indicator of cardiac health, heart rate and HRV. Findings indicate HRV may not add significant value in predicting cardiovascular fitness.9 Moreover, heart rate stood out as the most important predictor of changes in VO2 Max. 9
Ultimately, we suggest that you do not get too caught up in trendy apps and what they report. Paying attention to your energy, sleep, stress levels, physical activity, and fatigue more often provides you with the information you need about readiness to exercise (also something that HRV apps claim to provide). Apps can be a great tool to analyze habits and some health markers, but when it comes to measuring HRV, metrics provided should be taken with a grain of salt.
For more questions about improving your cardiovascular health, please reach out to your SHIFT team.
In Real Health,
Scott Schafer and the SHIFT Fitness Team
- Benson R, Connolly D. Heart Rate Training. Champaign, IL: Human Kinetics; 2020.
- Tegegne BS, Man T, van Roon AM, Riese H, Snieder H. Determinants of heart rate variability in the general population: The Lifelines Cohort Study. Heart Rhythm. 2018;15(10):1552-1558. doi:10.1016/j.hrthm.2018.05.006
- Marcelo Campos MD. Heart rate variability: A new way to track well-being. Harvard Health. https://www.health.harvard.edu/blog/heart-rate-variability-new-way-track-well-2017112212789. Published November 22, 2017.
- Tobaldini E, Nobili L, Strada S, Casali KR, Braghiroli A, Montano N. Heart rate variability in normal and pathological sleep. Frontiers in Physiology. 2013;4. doi:10.3389/fphys.2013.00294
- Abdelnabi MH. Cardiovascular clinical implications of heart rate variability. International Journal of the Cardiovascular Academy. 2019;5(2):37. doi:10.4103/ijca.ijca_36_18
- Vanderlei LC;Pastre CM;Hoshi RA;Carvalho TD;Godoy MF; Basic notions of heart rate variability and its clinical applicability. Revista brasileira de cirurgia cardiovascular : orgao oficial da Sociedade Brasileira de Cirurgia Cardiovascular. https://pubmed.ncbi.nlm.nih.gov/19768301/.
- Perrotta AS;Jeklin AT;Hives BA;Meanwell LE;Warburton DER; Validity of the Elite HRV Smartphone Application for Examining Heart Rate Variability in a Field-Based Setting. Journal of strength and conditioning research. https://pubmed.ncbi.nlm.nih.gov/28195974/.
- Shaffer F, Ginsberg JP. An Overview of Heart Rate Variability Metrics and Norms. Frontiers in public health. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5624990/. Published September 28, 2017.
- Grant CC;Murray C;Janse van Rensburg DC;Fletcher L; A comparison between heart rate and heart rate variability as indicators of cardiac health and fitness. Frontiers in physiology. https://pubmed.ncbi.nlm.nih.gov/24312058/.