Dr. Rhonda Patrick: You were talking about heart rate variability, or HRV. Before we came on camera, we were discussing markers of recovery that people might measure with a wearable device.

Dr. Andy Galpin: Yep.

Dr. Rhonda Patrick: You said that the subjective measure of how a person feels wins.

Dr. Andy Galpin: Yep.

Dr. Rhonda Patrick: That seems to be the case with almost everything. If you ask how hard someone is working, you could look at their heart rate or ask about their perceived exertion. Perceived exertion often wins.

Dr. Benjamin Levine was on the podcast and argued that HRV is extremely variable. He sees variation of plus or minus 25% depending on factors such as the time of day and breathing. He likes to use resting heart rate measured first thing in the morning as a marker of recovery. If a person's resting heart rate is higher than expected, it could indicate that they are entering nonfunctional overreaching. I want to talk about overtraining.

Dr. Andy Galpin: Nice use of the term, by the way. Good dig.

Dr. Rhonda Patrick: Thank you.

Dr. Andy Galpin: That's good.

Dr. Rhonda Patrick: What do you think about HRV when people can follow a consistent measurement protocol? They might measure at the same time of day, use the same posture, and control their breathing before the measurement.

Dr. Andy Galpin: The measures you described are related to respiratory physiology. There are many ways to measure readiness, performance, fatigue, or load management, depending on which part of the spectrum we are discussing. Some are performance-based. HRV and resting heart rate are on the respiratory-physiology side, so we can stay there.

We more commonly use respiratory rate, and we can also look at something such as carbon dioxide tolerance. We will set those aside for a moment and focus on HRV and resting heart rate.

Resting heart rate is a useful sign if conditions are stable. If it becomes elevated by more than about three to five beats per minute for more than a couple of days, that is a good sign that something is happening. In this case, it is not a good thing. As you said, an increase generally indicates that the person is getting overcooked from too much training, total stress or allostatic load, or something similar.

Dr. Rhonda Patrick: Not enough recovery.

Dr. Andy Galpin: Not enough recovery, not enough calories, or something else is happening. The problem is that resting heart rate is very insensitive. It can take weeks for that change to appear. By the time resting heart rate changes, the person can be far into the problem. We should have seen it weeks earlier.

Dr. Rhonda Patrick: Does that apply even to resting heart rate measured first thing in the morning?

Dr. Andy Galpin: One hundred percent.

Dr. Rhonda Patrick: Yeah.

Dr. Andy Galpin: You might not see a change in first-thing-in-the-morning resting heart rate until a person has been having problems for a long time.

People prefer HRV because it is more sensitive. Like resting heart rate, it is nonspecific, so it does not tell you exactly what is happening. But the variability Dr. Levine mentioned can also be useful after you establish a person's standard deviation and learn how much they normally fluctuate.

Some people's nervous systems are very stable, and others are less stable. The width of a person's normal daily HRV range can reveal what is happening in the system. Because HRV is sensitive, it can show changes quickly.

A common mistake is looking at the absolute HRV score. If I said your resting heart rate is 100 beats per minute, you know that is probably bad. If I said your HRV is 100, however, you would not know what it means without knowing the device and conditions. Resting heart rate is generally clearer and easier to define as good or bad. HRV is a moving target. It is more sensitive, but it must be interpreted relative to the person.

After establishing a person's normal standard deviation, a shift of more than one, and especially two, standard deviations for more than a couple of days suggests that something is happening. You will see that pattern well before the problem causes changes in resting heart rate.

You do not want to overreact to one day. Imagine that a device usually shows an HRV score of 70. Some people remain between 65 and 75, so their standard deviation might be five milliseconds. Other people normally have a standard deviation of 20.

Dr. Rhonda Patrick: How do they establish their normal standard deviation?

Dr. Andy Galpin: Measure for 30 days.

Dr. Rhonda Patrick: Thirty days.

Dr. Andy Galpin: Measure for 30 days.

Dr. Rhonda Patrick: Try to keep things stable and take the average. Most trackers give people these numbers anyway.

Dr. Andy Galpin: If a value is outside the standard deviation for one day, I do not care much. If the pattern continues for three or more days, I pay more attention. I typically look for at least five days of a continual pattern in one direction or the other. Something is happening.

The signal is nonspecific, so there will be noise. I see that as a feature rather than a downside because it prompts questions. Did the person change something in their food, sleep, or environment? Many factors can affect HRV.

We use HRV a fair amount. Some people become so obsessed with the numbers that we take the measurement away and ask them how they feel. That is related to the variability problem Dr. Levine described.

I recently worked with a client in his 40s who sold a company early in life and has a lot of money. He surfs, and everything we measure looks fantastic. He has been in the program for about a year and a half and is very consistent, but he cannot get the HRV score out of his mind. He keeps thinking it is down when the value is actually normal for him.

Technology companies also change their algorithms frequently, so commercial HRV scores can change. If a person is using commercial HRV data, Dr. Levine is right that they should be skeptical and avoid overinterpreting it.

A consistent change in resting heart rate means something. It is unlikely to be an accident. One day of different HRV data could mean nothing and could be irrelevant to what a person is doing, but that does not make HRV a bad marker. When used appropriately, it gives us a lot of information.

We also find value in applications such as biofeedback training, where we can develop more resilience in the nervous system and observe it objectively. We can ask whether someone can calm themselves down and then look for the change in their physiology. If the HRV data do not move, that helps us decide what we want the person to do next. HRV therefore has value beyond being a single ultimate recovery marker.

In my opinion, respiratory rate is even better for recovery monitoring. Changes in respiratory rate can occur well before changes in resting heart rate, and breathing rate can influence both resting heart rate and HRV. If a person starts breathing more, something is happening.

Laura Bloomfield published interesting work that measured resting heart rate, sleep, HRV, and other variables in relation to stress. In her second study, a one-beat-per-minute increase in resting heart rate corresponded to about a 1% to 2% increase in the likelihood of moderate-to-high stress. A one-breath-per-minute increase in respiratory rate corresponded to about a 20% to 30% increase. Respiratory rate flagged the change much earlier. Resting heart rate did not reveal much, but HRV and especially respiratory rate changed sharply.

If someone's normal overnight respiratory rate is 12 breaths per minute and it rises to 14, I think something is happening. If it remains at 14 for two days, the person might become sick the next day, might already be sick, or might have another stressor. When we coach people, I do not want to wait six weeks to notice a problem. I want to ask immediately what is happening. In our experience, HRV and respiratory rate change well before resting heart rate.

Dr. Rhonda Patrick: How accurate are devices that measure respiratory rate?

Dr. Andy Galpin: It depends on the device. Accuracy decreases when measurement moves to the wrist or hand. A chest strap is better. When accuracy matters in our sleep testing, we place a device directly on the chest. We measure respiratory rate, the amplitude of the change in the chest, and its direct movement. Outside of that context, respiratory rate is fairly easy to measure.

Dr. Rhonda Patrick: If someone is doing this at home, would they wear a strap while sleeping?

Dr. Andy Galpin: They can, or they can wear a watch.

Dr. Rhonda Patrick: You lose accuracy with a watch.

Dr. Andy Galpin: A watch is generally okay for respiratory rate. Accuracy decreases more for HRV. Respiratory rate is relatively easy for a tracker to detect, but HRV is trickier.

Dr. Rhonda Patrick: You mentioned studies showing that respiratory rate is very sensitive to stress. That includes more than psychological stress, correct?

Dr. Andy Galpin: Correct. It can respond to exercise or any type of stress on the body, including nutritional and environmental stress.

A few years ago, several devices began providing early COVID flags. The NFL and NBA used them, including a system that I think used Oura. We had many professional athletes using these tools. I will give Laura credit because the alerts were quite good. We would receive an alert suggesting that someone had COVID even when the athlete had no signs or symptoms.

Dr. Rhonda Patrick: Then the person's temperature might rise a few days later.

Dr. Andy Galpin: The algorithm combined respiratory rate, body temperature, and several other measures. It was released publicly last year.

Dr. Rhonda Patrick: My friend Dr. Ashley Mason was involved in studies of that system.

Dr. Andy Galpin: It was fantastic. I did not analyze the data or read the papers, but it was accurate for our athletes. We sometimes had a day to prepare because we knew an illness was developing.

Those measures can be sensitive. Even a wearable on the finger produced data that were useful enough to suggest that a person might become sick the next day. Changes can reflect psychological stress, nutrition, a bacterial or viral infection, environmental exposure, allergens, and many other factors that make people breathe faster.