The 8 Biggest Mistakes Made When Measuring Heart Rate Variability
As powerful and easy-to-use as Heart Rate Variability is, it is also easy to use it incorrectly or skew your measurements beyond usefulness.
After helping thousands of people from around the globe measure and analyze their HRV, here are the biggest and most frequent mistakes we’ve seen and how to avoid them. The following discussion assumes the use of short-term (under 5 minutes) rested state HRV readings.
Mistake 1 – Assuming A Low Reading Is Always Bad
Chronically low Heart Rate Variability is generally not favorable. However, a single or handful of low HRV readings is not always bad. In fact, strategic acute drops in HRV can be favorable as long as HRV recovers to normal or better levels. Here are a few situations where a low acute HRV is actually desirable.
- An acute HRV drop after a hard workout or series of workouts that returns back to normal or better within a few days or weeks’ time. To maintain fitness and health over the long run, you need to have some periods of physical stress and recovery. Failing to adequately stress the body fails to stimulate adaptation, growth, and improvement. Hormetic stressors cause positive adaptation and improvement and keep the system running optimally. Having occasional, strategic drops in HRV with returns to normal or better helps you know that you are adequately stressing your body for long-term growth and adaptation.
- A slightly lower HRV compared to a person’s baseline (associated with increased Sympathetic Nervous System activity) on a competition day can be favorable depending on the type of sport and competition style. Sympathetic (fight-or-flight) activation is necessary for performance. The length and type of the competition can play a role when deciding how you want your HRV to be when entering a competition. Short duration strength and power sports benefit the most from Sympathetic activation and are harmed the least by depressed HRV. Longer competitions where intra-competition recovery is a huge factor are sometimes more affected by a depressed HRV and may benefit more from balanced or slightly elevated HRV.
- Endurance tapering. When a high volume of low to moderate intensity training is accumulated, HRV can actually increase as training load increases. This can occur both from aerobic stimulation of the parasympathetic branch of the Autonomic Nervous System, as well as from the body trying to recover from an accumulation of low grade stress. Then when an individual begins a taper leading up to a competition, HRV declines and can sometimes dip below the starting point. The optimal drop in HRV during a taper is very individual; however, it is generally acceptable and possibly even favorable for performance for HRV to temporarily drop during a taper.
Strategic acute drops in HRV can be favorable as long as HRV recovers to normal or better levels.
Mistake 2 – Assuming A High Reading Is Always Good
Just as a low HRV reading is not always bad, a high HRV reading is not always good. If a single HRV measurement is abnormally high compared to an individual’s baseline or norm, then it can mean something is off. Here are a few examples of when a high reading does not always indicate better health and resiliency.
- For certain mild illnesses or sicknesses, an elevated immune system can increase Heart Rate Variability. This is favorable for recovery from the illness but should not be seen as an increase in health.
- If an individual is in a state of hyper recovery, their HRV can be abnormally high. When the body accumulates too much stress to the point where it can no longer effectively handle the stress and resources are depleted, the body might force itself into a hyper-recovery mode as a last resort to protect itself. This state is not ideal for long-term health or performance.
- Continuous low grade stressors can cause HRV to be higher in the short term because the body is constantly trying to recover from them. If your HRV is high but you frequently feel fatigued or drained, then you might be exposed to chronic low grade stress that is constantly stealing energy and resources from your body. This is not ideal and over the long-term, if these accumulated low grade stressors are not dealt with, they can eventually cause HRV and health to decrease.
A high reading does not always indicate better health and resiliency.
Mistake 3 – Extrapolating One HRV Reading
The body is in a constant state of flux in response to stressors and recovery processes. As such, one short Heart Rate Variability measurement might be skewed and not capture your “normal” state. One measurement could capture a really good day or a really bad day and not reflect a person’s norm needed to compare those good and bad days to. For example, your HRV the day after staying up all night drinking alcohol will be very different than your HRV on a night where you go to bed early and don’t drink any alcohol.
Even blood tests, which are touted for their accuracy, can be highly skewed by recent nutritional choices, sleep status, and a number of other factors. Similarly, Heart Rate Variability is very sensitive to acute physiological changes. Fortunately, HRV is not an invasive measurement and can be measured frequently to increase accuracy (as opposed to blood lab work).
When trying to understand your HRV and systemic condition, it is important to take several days’ worth of measurements within a week (ideally over several weeks) to ensure that the single day was not an outlier. This also increases the confidence of the baseline values that can then be used to more effectively set health and performance goals and to assess progress towards those goals.
One short Heart Rate Variability measurement might be skewed and not capture your “normal” state.
Mistake 4 – Inconsistency Between Readings
In order to minimize confounding factors or misleading results, consistency between HRV measurements is extremely important. Performing as “repeatable” and consistent measurements as possible over time allows for more accurate and relevant comparisons. When you are using HRV trends to assess and base important health and performance decisions on then you want to make sure you are comparing “apples to apples” and not “apples to oranges.” Factors that affect repeat-ability and comparability include:
- Body position – Whether you choose to sit, stand, or lay during a measurement, make sure you consistently use the measuring position every time for comparable readings. Torso angle while sitting is also very important and has been shown to affect HRV.
- Time of day (try to target the same 1 hour window each day) – Circadian rhythm has a strong effect on HRV throughout the day.
- Activity before the HRV reading – Exercising, conversing, eating, caffeine, etc. all affect HRV. For best comparability between readings try to perform the same activities between readings in which you intend to compare (for example, take baseline readings soon after waking up)
Performing as “repeatable” and consistent measurements as possible over time allows for more accurate and relevant comparisons.
Mistake 5 – Only Measuring on “Important” Days
It is tempting to only measure HRV on “important” days such as workout days or days that you know you will have stress. Only measuring on important days means you are likely missing the bigger picture and could even be missing unexpected, but important changes that happen on non-important days.
Since stress and recovery parameters are cumulative, non-important days can still heavily influence your systemic condition as measured by HRV. The introduction of unplanned for stressors through diet, the environment, social/emotional situations, or poor quality sleep can all impact your HRV and your systemic condition.
Measuring HRV infrequently also decrease the accuracy of and confidence in your HRV values. This can lead to poor decision making and a false sense of “readiness” or a false understanding of the state of your Autonomic Nervous System (ANS). Elite athletes with consistent high-volume training need to measure at least three days per week as determined by Dr. Plews et al. The New Zealand High Performance sports research team also found that people with less structured training should measure HRV at least five times per week which also corroborates my personal experience working with thousands of individuals directly over recent years.
Since stress and recovery parameters are cumulative, non-important days can still heavily influence your systemic condition as measured by HRV.
Mistake 6 – Not Contextualizing the HRV Readings
I like to call Heart Rate Variability “the glue marker”. It is a powerful biomarker that binds together other subjective and objective data for more effective decision making. When measured alone, without any other context, HRV tells you the general state of your nervous system and health but cannot tell you what is causing or affecting your condition.
Tracking HRV in conjunction with additional context such as energy levels, fitness tests, sleep quality, a food log, etc. can help you identify what specific lifestyle factors are most affecting your systemic health and progress.
What you track alongside HRV depends very much on your goals, and working with a coach or health practitioner is hands down the best way to determine what additional metrics to pay attention to.
Some common examples include:
- Perceived energy levels or fatigue
- Muscle soreness
- Body weight
- Blood pressure / glucose
- Drop jump force output testing
When measured alone, without any other context, HRV tells you the general state of your nervous system and health but cannot tell you what is causing or affecting your condition.
Mistake 7 – Paced Breathing During “Readiness” Readings
Using paced or guided breathing during an HRV measurement is not necessarily a mistake in itself. Paced breathing becomes a “mistake” when unnatural breathing patterns are used during a readiness or daily baseline HRV measurement.
It is well established that certain breathing patterns, especially slow, deep breathing, influences Vagus Nerve and Parasympathetic Nervous System activation and increases Heart Rate Variability. If you breathe at artificially slow breathing rates during a readiness or daily HRV reading, it can artificially skew the reading results to show your HRV to be higher than it actually would be in your natural state.
Because of this, paced breathing during a readiness or daily measurement is not recommended unless done at an individual’s normal breathing pace. An average adult’s natural breathing rate usually falls within 12-18 breaths per minute, however more aerobically fit individuals may have slower natural breathing rates. The best case for following a breathing pacer during a morning or daily readiness measurement is to help avoid fidgeting, distracting thoughts, or to help stay relaxed.
Note: Paced or guided breathing is perfectly acceptable and even encouraged when used for live HRV biofeedback training or other HRV testing.
If you breathe at artificially slow breathing rates during a readiness or daily HRV reading, it can artificially skew the reading results to show your HRV to be higher than it actually would be in your natural state.
Mistake 8 – Not Using An Accurate Heart Rate Monitor
An inaccurate measurement means an inaccurate (and invalid) HRV value. The most important thing when using HRV as a tool for training or health is to get an accurate measurement. We regularly get the question of why heart rate monitors like the Fitbit Charge or other wrist-based PPG or pulse-oximetry monitors are not compatible for measuring HRV.
The simple answer is that many of these devices are not intended for measuring the more detailed heart rate fluctuations needed to calculate true HRV. They either do not record the RR intervals (times between each heartbeat) needed to calculate HRV or they provide smoothed, averaged, or altered RR intervals that remove the variability that makes up Heart Rate Variability.
These devices can be perfectly fine for measuring basic heart rate, but there is no such thing as a “quick and dirty” or “good enough” or “almost accurate” HRV measurement.
Heart Rate Variability values are a measure of normally imperceptible changes in heart beat activity that often correlate with activity of the Autonomic Nervous System. A “quick and dirty” measurement using an inaccurate device yields a completely useless HRV value that should not be used for decision making.
An important thing to note is that just because a HR monitor captures and transmits RR intervals does not necessarily mean it is accurate. Several popular wrist-based monitors on the market provide RR intervals, but they are smoothed, averaged, or altered and therefore cannot be used to calculate Heart Rate Variability.
There are many new HR devices with bold promises and the lure of being convenient and sexy. While wearable technology is progressing very quickly, you should still be weary of these devices and do your due diligence in understanding if the device is compatible for HRV calculations. If you are unsure if your HR monitor is accurate enough to measure HRV, then check with the device manufacturer or your HRV application.
An inaccurate measurement means an inaccurate (and invalid) HRV value.
These 8 common mistakes can be boiled down to 2 basic concepts: Accuracy and Context. In reverse order, here are one line summaries of what to do to avoid making these mistakes.
- Use accurate hardware.
- Determine if paced breathing is right for your situation.
- Track a few other subjective and/or objective metrics alongside HRV dependent on your goals.
- Measure 5+ days per week.
- Measure in the same position at the same time of day (or understand the effects of these differences).
- Measure more than once before making any conclusions (5+ is best).
- High HRV can be good or bad – context helps.
- Low HRV can be good or bad – context helps.
If you stick to these basic rules you will likely have very useful, reliable, and actionable Heart Rate Variability data for decision making.