Heart rate variability (HRV) provides us a rough snapshot of the current relationship between our sympathetic (sNS) and parasympathetic (pNS) nervous systems. As such, it will change throughout the day, so getting a good reading is important if you want to make a decision regarding training. The best time to take the HRV measurement is first thing in the morning, right when you wake up. This is the closest you will be able to get to a true baseline level of your pNS and sNS for the day, giving you the cleanest view of your HRV. Some wearable devices, such as WHOOP, measures your HRV during deep sleep, a valid way to measure but it’s hard to compare HRV derived from deep sleep to HRV obtained in the early morning when you wake up. So if you are using both methods to track, choose one when comparing across days, don’t mix-and-match.

 

How should I read my HRV?

So once you have established a consistent time when you measure your HRV, now to understand what it is telling you. Just like how checking your weight daily when on a diet doesn’t tell you much and just causes anxiety, HRV readings are the same. A single measurement is no help if you do not have an established baseline, or base range to compare it to. This base range you want to compare your measurement to comes from two or three weeks of consistent data. 

 

Having this initial range when you first start out is just so you have a point of reference, do not worry too much about if it’s high or low, we just need a starting point. Based off your baseline, what you can now do is assess how your new daily measurements compare. There are four different things your can see when you do this comparison:

 

  1. Your daily measurement is on the high side or slightly higher than your normal range. This is an indicator of improved recovery and your body is ready for a high workload. If this trend continues over the course of several days or weeks, this leads to an increased baseline and indicates that you are adapting optimally to your training regime and approaching a level for peak performance. This is a positive sign.
  2. Your daily measurement is within your normal range, close to the middle. This is an indicator of sufficient recovery and your body is ready to take on the day. This is where most of us live as we go through our normal training regimens. We are not becoming better rested and our current training is not putting us in a hole, but maintaining and managing the workload effectively. This is a positive sign.
  3. Your daily measurement is on the low side or slightly lower than your normal range. This is an indicator that you may not have recovered sufficiently from your workload the day before, whether due to a lack of sleep, alcohol the night before, or nutrition that might have been off point. A single day of this is not a reason to change your plan for the day but a focus on recovery the next night should be prioritized. Multiple days of this type of measurement though will lead to a decreasing baseline and leaving your body more susceptible to illness or injury in training. This is a negative sign.
  4. Your daily measurement is widely different from your baseline in either the positive or negative range. This is a less common occurrence and is almost always a sign of excessive stress to the body. The large deviation is a sign that your body is having either a tough time regulating your heart rate (a very HIGH HRV reading), a sign of high stress, or you’re body is not able to slow your heart rate down sufficiently due to an overactive sNS and is usually accompanied by an increased resting heart rate (a very LOW HRV reading). In either instance, this is a negative sign and training should be altered for the day or a rest day should be taken. 

 

It is always important to keep in mind that everyone’s HRV is unique to them, and there are times where you might feel great waking up with a really low HRV and you proceed to crush the day, there are other times when you wake up with HRV levels that suggest peak performance but you feel like crap. HRV is one tool to help measure and predict performance, it is not the end-all-be-all, we just don’t understand it well enough yet. Listen to your body and if you see a dropping HRV consider a little more rest, and if you see a rising HRV consider a little more go.

 

Part 3 (and maybe part 4???)  will include questions I’ve received from my athletes around the country regarding specific things they have noticed with their HRV, so definitely check it out. If you have any friends or teammates who have been struggling to understand HRV, please share this post and Part 1 with them. And as always, shoot me an email with any questions or comments that I haven’t answered or that you would like to see me write about.