You’ve likely heard about Heart Rate Variability (HRV) but thought it’s just an exclusive training tool for Olympians and endurance athletes. Sure, they use it to maintain a competitive edge on their opposition, but did you know just about anyone can harness the benefits behind HRV to lead an optimal life and get more out of their daily routines? Loops was designed to help the “everyday person” unlock their full potential using our HRV-guided platform. H-R-V can sound like a complex acronym but fear not, our Guide to HRV will show you the ins and outs of this life-altering health metric.
WHAT IS HEART RATE VARIABILITY?
Heart Rate Variability (HRV) is a measure of the variation in time between the beats of your heart. We define your Heart Rate as a number of beats per minute, although those beats don’t occur at the same interval each time, the variability in time between these beats is what we refer to as HRV1.
The periods of time between successive heart beats are known as RR intervals (named for the heartbeat’s R-phase, the spikes you see on an ECG), measured in milliseconds. Your Apple Watch samples your HRV in milliseconds by using the standard deviation of beat-to-beat measurements (SDNN) which are captured through the heart rate sensor. This sampling is done by your watch passively throughout each day but can also be manually triggered by completing a Breathe Session via the Mindfulness app on your Apple Watch.
HRV AND THE AUTONOMIC NERVOUS SYSTEM
HRV is a measure of the variation in time between each heartbeat. This variation is controlled by a part of the nervous system called the autonomic nervous system (ANS). Our ANS controls our involuntary bodily functions like our heart rate, blood pressure, breathing, digestion, etc.
I’m going to get scientific for second but stay with me…
The ANS is subdivided into two large components, the sympathetic and the parasympathetic nervous system, also known as the fight-or-flight mechanism and the relaxation response. These two systems simultaneously send signals to your heart to keep your nervous system balanced.
The parasympathetic nervous system (PNS), often referred to as the “rest-and-digest” network, kicks in during calmer moments to cause a decrease in your heart rate. Examples of parasympathetic activation include deep breathing techniques as well as mediation and yoga.
The sympathetic nervous system (SNS), often referred to as the “fight-or-flight” network, kicks in to respond to stressors by increasing your heart rate. Just about any activity that requires you to be sharp and ready for action can be example of sympathetic activation. However, it is important to remember too much sympathetic activation can be a sign of prolonged stress, overtraining, and/or poor sleep2.
In short, HRV is a non-invasive way to identify these internal imbalances that we’ve simplified on the Loops app with the Daily Outlook feature.
WHY IS HRV IMPORTANT?
In a healthy individual, HRV changes naturally from minute-to-minute and day-to-day, based on activity levels, life stressors and overall wellbeing. If a person is chronically stressed or overloaded – physically or mentally – the natural balance between the sympathetic and parasympathetic systems can be disrupted. When this happens, the body can experience a sympathetically dominant state with low HRV and high stress hormone levels, even when the person is resting. This is extremely taxing on the body and can result in various mental and physical health problems.
A higher HRV is generally considered an indicator of a healthy heart and has been found in many studies to be associated with reduced morbidity and mortality, improved psychological well-being and quality of life3.
WHY IS HRV A SIGN OF FITNESS?
When you have high HRV, it means that your body is responsive to the different types of stressors you put it through, both good and bad. This means that your nervous system is balanced (that’s a good thing!). So, why is a balanced nervous system good? Well, that means your body is able to adapt to its environment.
On the other hand, if you have low HRV, one branch of your nervous system is dominating and sending stronger signals to your heart than the other. Sometimes this is a good thing – like when you’re running a race and you want your body to send energy to your legs (sympathetic activity) rather than digesting food (parasympathetic activity).
If you’re not working out, a low HRV reading indicates your body is working hard for another other reason (maybe you’re tired, dehydrated, stressed, or sick and need to recover), which leaves fewer resources available to dedicate towards exercising, giving a presentation at work, etc4.
WHAT IS A NORMAL HEART RATE VARIABILITY?
Unfortunately, there is no ‘correct’ answer to this question. Since HRV is an extremely individualized measure, values will vary greatly from person to person. Don’t compare your HRV values to others – it doesn’t mean anything! Rather, a more practical way to track your HRV is to monitor your own HRV trends.
In general, a higher HRV value is a sign of better health. A number of factors play a role in determining what your individual HRV values mean, but here’s our general rules.
The younger the person, the higher the HRV, with males having a slightly higher value than females. In terms of athletes, strength-based athletes usually have lower HRV values than endurance athletes5.
HEART RATE VARIABILITY TRENDS ARE WHAT MATTERS
Since HRV is a very sensitive measure, day-to-day fluctuations do not always indicate changes in your overall health. When you begin to monitor your HRV, you may notice that your HRV varies greatly each day. This can be attributed to the many factors that affect HRV such as a morning workout, a cup of coffee, a stressful day, your diet, or just about anything, really.
Rather than analyzing your HRV on an hourly and day to day basis, a more sensible use of HRV is to follow your own trends. Loops monitors your HRV trends for you, and informs you of your optimal workout schedule based on your current trend.
WHAT IS YOUR HRV BASELINE RANGE?
Since your HRV is constantly changing throughout a 24-hour period, we need to first establish your “normal” range of HRV values – consider this your baseline level. We do this by measuring your HRV at the same time each morning for the first 5 days6. Your HRV Baseline Range is used as a reference point to evaluate your progress against and identify unique trends that exist within your personal range.
As you continue to use Loops, we’ll make your Baseline Range increasingly personalized by using 14-days of HRV readings and aggregating them into a simple moving average that constantly updates itself each day as new measurements are taken. This average is presented as a range of values and is referred to as your HRV Baseline Range.
WHAT DO YOUR HRV TRENDS MEAN?
Positive Change in HRV Baseline Trends
If you are taking steps to improve your overall health and fitness level, you should see your HRV Baseline Range increase, both in range and value. An increase in your HRV Baseline Range can be a sign that you are becoming more resilient to different forms of life stressors and exercise.
Negative Change in HRV Baseline Trends
A consistent trend below your HRV Baseline Range is something to watch closely. It can mean many things and is likely a combination of a few of the following: lack of sleep, overtraining, possible illness, poor diet, prolonged stress, or dehydration. However, a drop in HRV below your Baseline Range for one or two days at a time is nothing to worry about!
- Akselrod S, Gordon D, Ubel FA, Shannon DC, Barger AC, Cohen RJ. Power spectrum analysis of heart rate fluctuation: a quantitative probe of beat-to-beat cardiovascular control. Science.1981; 213:220-222.
- Cygankiewicz I, Zareba W. Heart rate variability. Handb Clin Neurol. 2013;117:379-93. doi: 10.1016/B978-0-444-53491-0.00031-6. PMID: 24095141.
- Thayer JF, Yamamoto SS, Brosschot JF. The relationship of autonomic imbalance, heart rate variability and cardiovascular disease risk factors. Int J Cardiol. 2010 May 28;141(2):122-31.
- Pomeranz B, Macaulay RJB, Caudill MA, Kutz I, Adam D, Gordon D, Kilborn KM, Barger AC, Shannon DC, Cohen RJ, Benson H. Assessment of autonomic function in humans by heart rate spectral analysis. Am J Physiol.1985; 248:H151-H153.
- Golosheykin S, Grant JD, Novak OV, Heath AC, Anokhin AP. Genetic influences on heart rate variability. Int J Psychophysiol. 2017 May;115:65-73. doi: 10.1016/j.ijpsycho.2016.04.008. Epub 2016 Apr 22.
- Shaffer, F., & Ginsberg, J. P. (2017). An Overview of Heart Rate Variability Metrics and Norms. Frontiers in public health, 5, 258.