With the rapid increase in the use and development of wearables, heart rate variability measurement is experiencing a significant boost of late. However, it’s also becoming harder than ever to discern the actual value of HRV monitoring from marketing hype and pin down the key factors to consider to ensure that you get good, accurate, and actionable data from your HRV monitoring routine.
As a coach who has been monitoring HRV for more than a decade now, here are the top 5 misconceptions about HRV that I see circulating.
1. A High HRV Reading Is Always Good and Indicative of Readiness to Work
Many apps put high HRV readings in the “green” to indicate that athletes are ready for work. However, we should view unusually high HRV numbers with similar caution as unusually low ones, especially when they occur in concert with other key fatigue indicators.We should view unusually high HRV numbers with similar caution as unusually low ones, especially when they occur in concert with other key fatigue indicators, says @alan_couzens. Click To Tweet
A very common pattern, especially for endurance athletes under high load, is to show unusually high HRV numbers after a big training block. A very low resting heart rate and general tiredness/fatigue generally accompany this. It is worth remembering that when we measure HRV, we measure the strength of the parasympathetic nervous system—the body’s recovery system. It makes sense that this system is very activated after a big load as our body runs all of the rest and repair processes essential to recovering from that big load. This doesn’t, however, indicate that our body is ready for more load at that point.
In practice, tracking your HRV along with another metric that also indicates the strength of your “let’s do work” system—like heart rate—can add very useful additional context. Ithlete, for example, utilizes an RHR/HRV matrix that helps bring context to unusually high HRV numbers.
2. HRV Should Always Track with How I Feel
Thinking again that HRV is a marker of the strength of your recovery systems, it won’t always track with your general levels of energy. Many athletes will feel very energetic at times when HRV is low. This is due to the fact that our energy-producing system—the sympathetic nervous system—runs, to some extent, in opposition to the parasympathetic nervous system, the recovery system that our HRV tracks.
At times of high energetic output (e.g., a training camp), the athlete will often feel really good for the first few days despite low HRV and accumulating, but unrecognized, fatigue. This is due to the fatigue being masked by a very active sympathetic nervous system. HRV can be very useful during these times to give us a more honest assessment of the strength of the recovery systems to handle a given stress.
The other element of this—and one that I think confuses a lot of athletes when they first start tracking HRV—is that it won’t *always* line up perfectly with how you feel, both during the morning when you take the test and during the training session. HRV adds some, but not complete, information about the athlete’s current state: i.e., it answers a percentage of the question How tired is this athlete? For the best results, you should view it in that way and not take it as the only point to consider when determining training load.
For example, if my athlete’s HRV score is in the bottom 25%, but their wellness questionnaire scores are in the top 75%, I will view the athlete’s state differently than if both scores are in the bottom 25%. Despite not being a perfect predictor, each piece provides some valuable additional context. It is very much a situation where the whole is greater than the sum of its parts.
3. All Apps/Wearables Will Give Me the Same Measurement
It should go without saying that accurate heart rate variability calculations are, first and foremost, dependent on the accurate measurement of heartbeats!
In our desire for more and more convenience, HRV wearables are moving further and further away from the direct measurement of the electrical activity of the heart (provided by a high-quality heart rate strap) toward inferring heartbeats from measuring the way light changes as blood pulses through our blood vessels—either the blood vessels of the wrist (in the case of a watch/band wearable) or the finger (in the case of a “ring” wearable or your phone camera).I always recommend sticking with one particular app/wearable combo and strong recommend using a heart rate strap, says @alan_couzens. Click To Tweet
Because these distant cousins of the heart rate strap use light to infer heartbeats, they are subject to interference from other sources that might affect the light hitting your wearable receiver. Consequently, many of the algorithms that calculate HRV are filtered more aggressively than those that calculate HRV from a heart rate strap. This combination of added interference coupled with more aggressive filters can lead to differences in the measurement. For this reason, I always recommend sticking with one particular app/wearable combo and strongly recommend using a heart rate strap.
On a related note, many apps are now starting to move away from direct, validated measures of HRV such as RMSSD (the root-mean of successive squared differences) to their own proprietary “readiness” scores. While I have no major objection to composite metrics, I do object when the athlete is given no visibility as to what comprises these metrics, or even if/how they’re changing over time.
To compare apples to apples over the long term, I highly recommend sticking with known, validated metrics such as RMSSD or the lnRMSSD numbers provided by some of the major apps (such as ithlete or HRV4Training).
4. All Day Measurement of HRV Is More Useful Than a Single Test
On a related note, wearing something throughout the whole day/night that collects data may seem convenient and make it possible to generate a 24/7 data stream of your heart rate variability. Tempting as this may be, in my experience, you will find far better and more easily interpreted value in sticking with a single heart rate variability test: each morning, at the same time, under the same conditions.
An important thing to note about HRV is that it scales negatively and nonlinearly with heart rate. For example, if my resting heart rate is 30 bpm (i.e., an average of two seconds between beats) and yours is 60 bpm (an average of one second between beats), there is much more room for higher time variability between the beats for me than you. This is even more true for periods of increased heart rate due to exercise or stress—when heart rate variability can effectively decrease to zero due to the impact of the sympathetic nervous system.It is challenging to interpret all-day HRV meaningfully. It is far better to have a controlled, resting test where your heart rate is relatively similar to assess significant changes in HRV. Click To Tweet
With all of these influences and how heart rate changes throughout the day, it is challenging to interpret all-day HRV in any meaningful way. It is far better to have a controlled, resting test where your heart rate is relatively similar to assess significant changes in HRV.
5. HRV Measurement Is Only for Those Elite Athletes Looking to Get That Final 1%
The real strength of HRV is in its ability to quantify non-training stress. HRV may be less useful in conditions where the athlete has limited non-training stress and most of the fluctuations in adaptation reserves are related to training load—e.g., an elite living 24/7 at a National Training Center. This is because we have far better visibility into the stress that the athlete is experiencing.
In the “real world,” however, training stress typically only makes up a portion—and for amateur athletes, a tiny portion—of their total stress load. Therefore, HRV offers a way to quantify the impact of all the other stressors: the baby crying through the night, the pressure from your boss to meet a deadline, the relationship issues that you’re having with your significant other, etc.
Having a very clear window into the impact of those other stressors on the recreational athlete’s system can be a considerable advantage in balancing training with life to ensure consistent improvement and prevent injuries, illness, and general burnout. By taking an HRV-guided approach, your app will likely support that sleep-in on days you are particularly stressed out. It will similarly challenge you to get out the door on those days that all systems look good. This real-time flexibility and adaptability to the athlete’s greater life make HRV-guided training especially applicable to athletes with “real lives” to factor into the stress equation…meaning 99.99% of us!
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