Research

I have read multiple places that using a heart rate monitor can help people with ME/CFS, which is an illness with post-exertional malaise (PEM) like long COVID.

I summarized what I found from hopefully reputable sources, but remember I’m just a guy on the internet with no medical training.

In the next section I describe my experience following these findings.

Limiting Heart Rate

This talk by Todd Davenport explains how people with post-exertional malaise (PEM) reach their anaerobic threshold at a much lower heart rate than other people. The video explains in more detail than I possibly can, but your body uses oxygen during aerobic exercise. Once that is exceeded, there is a high intensity, anaerobic, energy system which provides the energy in a last-ditch effort to get away from the tiger. The high intensity system does not use oxygen, can only be used for a couple of minutes, and has physiological consequences. People with post-exertional malaise have been shown to have a lower anaerobic threshold, so their body gets into that high intensity system easily, which can cause all kinds of bad symptoms.

The idea is that PEM patients keep their heart rate below their anaerobic threshold to help avoid crashes. There are two formulas that Davenport uses to estimate that threshold:

resting heart rate + 15
60% of max heart rate

Max heart rate can be estimated using the classic formula of 220 - age, or the updated Tanaka formula of 208 - 0.7 * age.

Unfortunately, research has shown the formulas to estimate the anaerobic threshold for patients with PEM are not very accurate, but they are a place to start.

Resting Heart Rate

The Workwell Foundation produced a fact sheet that says if resting heart rate is 10 bpm above or below normal first thing in the morning, then the patient should rest that day.

Heart Rate Variability

Heart rate variability (HRV) measures small variations in the time between heart beats as your heart responds to your body. The general wisdom is that higher variation (to a point) is good.

In one very small study HRV was lower in people with long COVID, but that study only had 21 long COVID patients and 20 controls.

HRV has also been used to measure the recovery time of athletes. One meta-analysis said, “if HRV-guided training is superior to predefined training for producing group-level improvements in fitness and performance, current data suggest it is only by a small margin.”

Davenport talks about HRV more in this interview.

My Experience

My experience is that monitoring heart rate, resting heart rate (RHR), and heart rate variability (HRV) is not a magic bullet.

Visible Round 1

When I first realized that I wasn’t recovering from COVID, I tried using the Visible app.

Visible encouraged me to keep my heart rate below 60% of max heart rate. In fact, it counted everything above RHR + 5% to be “exertion.” Read more.

Perhaps this is not shocking, but I rested a lot because the app encouraged me to keep my heart rate down. When I was crashing, it helped me stop crashing and get to a baseline.

Once I was at baseline, I found it encouraged me to rest too much. I was trying to make the app too happy and as a result, I felt absolutely terrible. Fortunately a doctor suggested I stop using the app and arm band and as soon as I stopped doing that, I started moving more and feeling better.

I did not find the HRV or RHR measures in Visible to be useful or to correlate to how I felt.

Visible Round 2

A couple of months later I kept crashing and I couldn’t figure out how to get out of it, so I started using Visible with the arm band again. Once again it helped me get out of the crash. Also once again I started feeling terrible after a couple of weeks and stopped using the app.

I attributed the bad feeling I had to the morning routine that Visible enforced. Read more

Garmin Smartwatch

After Visible I tried using a Garmin vivoactive 5 smartwatch.

I found very low heart rate zones configured on the watch. They probably came from the LongCOVID Pacing App for Garmin watches, which I installed, but did not use. Here are the zones I started with:

Zone 5 - 65-100%
Zone 4 - 51-65%
Zone 3 - 48-51%
Zone 2 - 44-48%
Zone 1 - 40-44%

The zones seem to match the research.

Using these zones and setting the “Moderate Intensity” to Zone 3 and the “Vigorous Intensity” to Zone 4, I was able to use Garmin’s “Intensity Minutes” very much like the “Pace Points” in the Visible app to measure my daily physical activity. Just like Visible, this helped me rest.

I started going on short walks, keeping my heart rate around 100, which is a little bit below my estimated anaerobic threshold. I generally wasn’t feeling great, but I was tolerating longer and longer walks.

One morning I woke up and my watch told me that my overnight HRV had fallen 4 days in a row and that my RHR had risen three days in a row. From the research I had done (above), that was not good. I also wasn’t feeling great overall and that made me even more worried that I wasn’t pacing properly. I had been very, very slowly working back to my normal morning walks. That morning I walked a mile, keeping my heart rate around 100 (58% of my estimated max heart rate). When I got home I felt terrible. I tried eating breakfast and drinking electrolytes. Still felt terrible.

Then I remembered that when I was using the Visible app and keeping my heart rate down I felt bad. I decided to just ignore the watch and do the same walk, ignoring my heart rate. When I got home, I felt much, much better and I have been better since. I still pace myself carefully, but keeping my heart rate below that estimated anaerobic threshold does not work well for me. My guess is that my threshold is much higher, probably over 130 bpm.

I also stopped wearing the watch at night, so I no longer even have an overnight HRV or RHR to see. Read more

I am currently using these heart rate zones with my watch.

Zone 5 - 75-100%
Zone 4 - 65-75%
Zone 3 - 55-65%
Zone 2 - 47-55%
Zone 1 - 40-47%

Using those zones and the intensity minutes calculated by the watch give me a rough idea of how much I am physically exerting myself.

Alarms

I have tried using heart rate alarms with both the Visible app and my Garmin watch and I found they don’t help me.

The alarm startles me, I get stressed that I’m doing something wrong, and then I think I start feeling bad. I think the bad feeling is just anxiety. For me it’s better to just monitor how I feel.

Conclusion

I never found my morning resting heart rate 10 bpm high or low, so I don’t know if that is a good indicator of a crash or not. When my watch told my RHR was rising over three days, that was not a good indicator of how I actually felt.

I never found HRV measurements useful. When my watch or Visible told me my HRV was low, that did not correlate well to how I felt and instead just induced anxiety.

Keeping my heart rate below 60% of max heart rate can help me recover from a crash, but if I keep my heart rate that low for many days, then I start to feel terrible. When that happens, I find it difficult to distinguish the terrible feeling from long COVID fatigue and the terrible feeling from not using my body.

I firmly believe that pacing is crucial to recovery. It’s also very easy to imagine myself in a cycle where I feel bad, the watch or app tells me to do less, and that makes me feel worse. I have to be very careful about listening too much to the electronics.