With the increasing popularity of wearable devices such as smartwatches, users have access to more and more health data. Statistics such as resting heart rate, VO2 max, and heart rate variability (HRV) provide valuable references for assessing an individual's health level.
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04-01, 2025However, not all measurement indicators are of equal value. While HRV has long been used by elite athletes to guide training programs, it has also gradually become a "buzzword" among the general public. Matthew Ahmadi, Deputy Director of the Mackenzie Wearables Hub at the University of Sydney, said that HRV has been around in competitive sports for over 20 years.
Dr. Ahmadi pointed out: "HRV has really taken off in the general population in the last decade or so, largely thanks to the increased use of wearable devices." As a leading wearable device brand and the official partner of the Women's Tennis Association, WHOOP has been collecting data on the most consistent factors that improve or harm HRV. Global statistics for 2024 show that getting quality sleep, consuming caffeine, and maintaining a regular wake-up time are most likely to improve HRV, while drinking alcohol, getting sick, and high stress levels can cause HRV values to decline.
So, what exactly does HRV measure? And how can we use it to maximize exercise results? Dr. Ahmadi explained that HRV measures "the variability between heartbeats." The heart does not beat as steadily as a metronome or clock. Therefore, even if your heart rate may be 80 beats per minute, there will be longer or shorter intervals between each heartbeat. The degree of variability of these intervals determines your HRV, with higher values indicating greater variability. Higher values are ideal, indicating that the body is in a state of homeostasis (or balance).
This is because HRV is a window into understanding the autonomic nervous system. The autonomic nervous system consists of two main parts: the parasympathetic nervous system and the sympathetic nervous system. In short, the parasympathetic nervous system is responsible for "rest and digest" processes, while the sympathetic nervous system is responsible for "fight or flight" responses. Ideally, Dr. Ahmadi said, the two are in balance, meaning the body is equally sensitive to both inputs. "The healthier a person's body is, the more able it is to adapt to different stressors, and therefore recover better."
But if your HRV is low, it indicates that one branch of the autonomic nervous system is dominant: "It usually means that your sympathetic nervous system is dominant, so your body is in a state of high alert." The time at which HRV is measured is also crucial for interpreting the results. Dr. Ahmadi said that measuring HRV before going to bed can tell you how well your body has recovered from the day's activities or stressors. "Measuring HRV immediately after waking up can be a good indication of how ready your body is to face the day ahead."
This is the key reason why HRV is superior to other health indicators. A higher HRV not only indicates a higher level of health, but can also be used to determine the intensity of your exercise plan for the day. Kristen Holmes, Chief Scientist at WHOOP, said: "In the field of exercise science, we see HRV as an indicator of 'training readiness.' A higher HRV means more training capacity, while a lower HRV means less endurance and training capacity."
WHOOP uses HRV to determine a user's daily "recovery" score, categorizing it as green, yellow, or red. On green days, WHOOP encourages users to "go all out," while on red days, it recommends "active recovery" activities such as meditation, light walking, or yoga. Many elite athletes similarly use HRV to adjust their exercise plans, and research shows that those who do so can achieve better performance.
WHOOP also collects data on the most common positive and negative influences on HRV. Positive factors include adequate hydration, following a healthy diet, getting quality sleep, and maintaining consistent sleep and wake times. Dr. Holmes said: "This makes it both a great measurement and frustrating. Sometimes it's hard to pinpoint exactly what's causing me to not be able to react and adapt to external stressors in an effective way."
However, there are some consistent factors that lower HRV, the most prominent of which is alcohol consumption. In fact, Dr. Holmes said that alcohol is an "HRV crusher," with 89% of people using the platform reporting a long-term reduction in alcohol intake. "This is because people can directly see the performance cost of their behavior," Holmes said. "Your coach can tell you, 'Hey, alcohol is really bad for your performance,' but until you directly see how it affects your HRV, you're like...wow, I'm a worse version of myself today. It's sobering."
You should avoid comparing your HRV score to those of others. In general, the older you are, the lower your HRV will be, and women tend to have lower average HRV as well. If you want to improve your HRV, both Dr. Ahmadi and Dr. Holmes recommend first establishing a baseline level and then judging any changes based on your own score.
It is also important to note that a low HRV is not always a bad thing. For example, Dr. Ahmadi said that if you start a new exercise program, especially if you previously had a sedentary lifestyle, you should see your HRV decrease. "In the first few weeks, you may see your HRV drop significantly every day," he said. "But ideally, if the program is working as it should, you should start to see your HRV increase in the coming weeks and months, and then gradually decrease as your body adapts to the current program load."
Once your HRV starts to stabilize, it indicates that you are ready to "advance" your program. But if you don't see your HRV improving, then you may need to slow down. "If you see a significant drop, then it's best not to push too hard the next day, because your body is signaling to you that it needs time to recover," he said. "As you adapt to the new training program, your body will adapt, and you will be able to handle higher stress and exercise loads more closely."
