Sleep Health Average HRV

The normal range of the average HRV (heart rate variability) during sleep stages of ordinary healthy adults is usually in the 40-100ms range. The higher the value, the stronger the autonomic nervous regulation ability and the better the quality of sleep recovery. However, this indicator varies greatly among individuals, and cross-population comparisons have no practical significance. It only has reference value for the dynamic changes in the individual's long-term baseline.

A while ago, I helped a friend who works in Internet operations adjust his sleep. He just bought a new smart watch. The first thing he did when he woke up every day was to check his sleep report. He saw that the average sleep HRV of his colleagues in the same department was generally above 70, but he himself was stuck at around 45 all year round. He was so frightened that he thought he was going to die suddenly. He suffered from insomnia for three consecutive days, and the value dropped even more. I checked his monitoring data for the past three months and discovered that he has maintained the habit of long-distance running three times a week all year round. His resting heart rate has been stable at around 42. His own autonomic nervous system baseline is different from that of his colleagues who have been sedentary. He is simply not happy with the comparison. To put it bluntly, HRV is the degree of change in the time difference between two heartbeats. When you are awake, you have to deal with work and stress, your sympathetic nerves are tight, and your heartbeat rhythm is steady, so the difference is small. ； When sleeping, the parasympathetic nerves are on duty for repair, and the heartbeat will speed up and slow down according to the body's condition. The greater the difference, the higher the HRV will naturally be. For people born with a low basal heart rate, the value will be lower than that of ordinary people. Coupled with the influence of age, basic diseases, and long-term exercise habits, the difference between people can even be more than 50ms. There is no unified "excellent line" at all.

Interestingly, regarding the application of sleep HRV, the clinical and consumer electronics circles have completely different attitudes. The sleep department of regular hospitals has not yet included average sleep HRV in the diagnostic criteria. After all, there are too many interfering factors - smoking a cigarette before going to bed, drinking half a glass of iced Americano in the afternoon, falling asleep emotionally after an argument with a partner, or even being woken up by a mosquito in the middle of the night. The value of the day may drop by 20%. Looking at the data alone cannot explain the problem at all. It can at most be used as an auxiliary reference item for autonomic nervous function. To truly judge sleep problems, polysomnography is still needed. However, the consumer electronics industry has spent a lot of money on HRV algorithm optimization in recent years. Garmin, Apple, and domestic smart watch manufacturers can now even separate the HRV values ​​​​in different stages of deep sleep, light sleep, and REM, and provide users with sleep adjustments and exercise suggestions. I have been using Garmin watches for nearly two years, and I have indeed found that as long as I drank milk tea after 6 pm the day before, the HRV of the day's deep sleep will drop by at least 15ms, and I will be groggy when I wake up. The corresponding relationship is ridiculously accurate.

There is a lot of quarrel over this indicator in the fitness circle now. One school of thought says that sleep HRV should be used as a hard target for training. As long as the value of the day is more than 20% lower than the personal baseline, and resolutely avoid heavy weight training, it can perfectly avoid the pitfalls of overtraining. ； The other group thinks that it is completely metaphysics. Ordinary people exercise for relaxation. Staring at the numbers every day only puts a burden on themselves. Occasionally, the numbers drop for a day or two. It is not a big deal. I have been trying it myself for more than half a year, and I think it is really useful to use this as a reference if you are an athlete preparing for a competition, or if you have been training hard recently. I once increased the intensity of leg training for a week in a row, and my HRV dropped by almost 30%. I didn't take it seriously. Then I strained my hamstring muscle during the next training session, which took almost a month to heal. ； But if you only train three or four times a week, each time for only one hour of aerobic and strength training, you don’t have to worry about this number. Your body’s feeling of being really tired is much more accurate than a watch.

When I was working on a project last year, I only slept 5-6 hours a day for two consecutive weeks, and my average sleep HRV dropped from the usual early 60s to 32. During that time, I was really tired when I woke up, irritable at every turn, and my hands shook when I touched a cup. After the project ended, I took three days off. I did nothing every day. When I was sleepy and woke up, I was in a daze. On the third day, the measurement value returned to 58. I didn't go to the doctor. To put it bluntly, this indicator is a health signal light that you can understand. It only lights up once in a while. If you don’t panic, first recall whether you have had any crazy living habits recently, and you will come back after adjusting. If it is 30% lower than your own baseline for more than two consecutive weeks, and is also accompanied by problems such as tiredness after sleeping for 8 hours, early awakening, and palpitation, it is not too late to go to the hospital for examination.

Oh, by the way, the HRV values ​​measured by different brands of equipment may be very different. The accuracy of the photoelectric watch is definitely not as good as the medical ECG belt. If you really care about the accuracy of the value, don’t change the brand of equipment to measure back and forth. Just use the same equipment for long-term tracking and see the changing trend. There is no need to worry about the absolute value.

In fact, in the final analysis, no matter how good the average HRV value is during sleep, it is not as real as feeling refreshed when you wake up in the morning. Numbers are dead, but people are alive. Don’t let the value on a watch hijack your sleep. That would be putting the cart before the horse, right?