Note: This feature was previously available on APEX 2/APEX 2 Pro/VERTIX 2/VERTIX 2S. The HRV Index has now been replaced by the Wellness Check feature, with more watch models supporting this feature. Unlike the HRV Index, Wellness Check displays HRV as raw data (rMSSD), allowing you to better track and understand your wellness journey.
You can read more about Wellness Check for on-demand HRV measurements here.
You can also read more about automatic HRV monitoring and assessment here.
What is HRV?
By definition, heart rate variability or HRV is a measurement of the variance between sequences of consecutive heartbeats. For example, suppose your heart is beating at 60 beats per minute. Despite how that sounds, this does not mean that your heart is beating exactly once per second. There may be instances where there are 1.2 seconds between beats, then 0.8 seconds, 1.1 seconds, and so on. In fact, when it comes to HRV the greater the variance between individual beats of your heart, the more likely it is that your body is adequately recovered.
As accessibility to HRV measurement devices has become commonplace for many individuals, it continues to be proven time and time again that HRV is an accurate and practical measurement to evaluate the status of your autonomic nervous system (ANS). The autonomic nervous system consists of two branches, the sympathetic and parasympathetic nervous systems. The sympathetic nervous system is commonly referred to commonly as the "fight or flight" branch, while the parasympathetic is known for being the "rest and digest" branch of the autonomic nervous system. The two branches of the autonomic nervous system influence one another and vary in their overall impact on the status of your autonomic nervous system.
How is HRV Measured?
Compatible COROS watches apply the rMSSD method to get an accurate HRV measurement which is then input into our unique HRV Index algorithm to provide a personalized and easy-to-understand metric displaying the current status of your body's response to external factors.
Recording your HRV Index
To receive your HRV Index, you will do so through the HRV measurement tool. To access this tool, hold the back button to access your toolbox. From there, scroll until you see the HRV Test. This will start the HRV measurement, follow the on-screen prompts in order to record your HRV Index. During the 30-second HRV measurement, please stay seated and maintain a static, upright posture throughout the entire process, keeping both your body and watch still. Try to not speak or move if at all possible.
In addition, here are a few best practice tips to ensure the accuracy of your HRV readings.
1. We recommend taking your HRV measurement between 4:00-10:00 in the morning
2. After waking up, sit still or calmly for about 5 minutes prior to taking the measurement
3. HRV is an easily influenced metric that can be altered by anything from answering emails to eating breakfast or even brushing your teeth. Please try and avoid measuring your HRV directly after completing any similar activities to gain the most accurate measurement.
4. Try and ensure that measurements are taken at or around the same time and with the same sitting posture every day, mitigating any "bias" from external factors. This makes the trend view of your HRV Index an "apples to apples" comparison to ensure the highest degree of accuracy.
Affected by biological rhythms, HRV will fluctuate greatly throughout the day. For this reason, it is important to reiterate the HRV measurement should be taken at or near the same time every day for comparison purposes. Comparing HRV indexes taken at different times or after different activities provides little to no valuable feedback. Following the Best Practice tips for your HRV measurements is the best way to attain a valuable, practical, and accurate HRV Index score each day.
HRV Index Explained
The HRV index is a value ranging from 1 to 100, indicating the current status of your physical and mental stress on your autonomic nervous system. The Index score is a proprietary evaluation model which may include but is not limited to, your previous 7 days of HRV measurements.
To summarize, the higher the value, the more relaxed or "ready" your body and nervous system are compared to your personal average. Here is a guideline for what your HRV Index score means:
81-100 (superior) Ready for peak performance.
51-80 (high) Ready for hard training.
21-50 (medium) Ready for moderate training.
1-20 (low) Limit intensity, focus on recovery.
The first 3 days that you use the HRV index tool, the HRV Index provided from your COROS watch is based on publicly available demographic data. After the 3rd day, the HRV index will be completely customized to your personal baseline. The more HRV measurements recorded, the more accurate the HRV Index becomes as it updates the evaluation model to your personal physiology.
Applying the HRV index
While measuring HRV is straightforward, interpreting and taking action towards the data oftentimes is not quite so simple. HRV readings are typically used in a fitness and training lens, however, HRV is often influenced by a large number of external factors. The list of lifestyle, genetic, and training factors which play into your personal HRV measurement is limitless, but some of the most common factors are physical exercise, muscular stress, mental stress, diet, caffeine consumption, illness, drugs, and more.
Generally speaking, a high HRV index means that the parasympathetic nervous system is more active, and vice versa. When the parasympathetic nervous system is more active, this indicates that the body is currently in a state of relaxation. When the sympathetic nervous system is more active, this indicates that the body is currently in a state of tension, excitement, or fatigue.
While it is easy to become highly focused on what your HRV Index score is on any given morning, the trend view or macro view of your HRV Index tends to be a more valuable way to interpret the data. For example, waking up to a low index score between 1-20 does not mean that it is absolutely necessary to take a rest day, but if your HRV Index is showing a stable decline over a stretch of a few days, this might be a sign that you are overreaching in training or you are under heavy stress. On the flip side, multiple days of high HRV Index scores could be an indicator that your body is recovering quickly and showing improved physical fitness or overall well-being.
Maintaining an Accurate HRV Index
There can be great differences in HRV from one person to another as it is a highly individualized measurement based on your unique physiology. As you take more HRV measurements every morning, your COROS watch will learn more about your physiology to produce the most accurate HRV index/evaluation model. Your COROS watch will determine your HRV index based on your demographic reference values at the beginning. Once you have completed 3 days of morning HRV measurements, the HRV index algorithm will give you a result based on your personal physiology that will become more and more accurate as more measurements are taken. It is also important to note that allowing other individuals to measure their HRV on your watch will interfere/skew with the evaluation model making it less accurate, which is why we recommend limiting this tool to personal use.
What causes changes in HRV?
Just as HRV is a personalized measurement, what might increase or decrease one's HRV Index can vary greatly from person to person. Generally speaking, here is a list of common factors that you may try to include in your daily routine to see if they help improve your HRV Index:
Increasing hydration, quality sleep, adequate recovery time, diet changes, sauna sessions, stretching, ice baths, cold showers, meditation, breathwork, blue light blockers, sleep masks, and more!
Factors that most often lead to HRV decreases may include but are not limited to: alcohol consumption, an irregular sleep schedule, work/life stress, heavy training load, changes to exercise methods (aerobic to anaerobic, vice versa), and many more.
When it comes to improving your HRV Index, it is most important to "listen" to your own body. Taking into consideration all external factors to try and figure out what helps you most!
Using the HRV Index for Training
The HRV index can be used as a supplementary indicator of fitness level to compensate for the impact of other factors outside of training load. As discussed before, a high HRV index is typically a sign of good recovery and "readiness" to train hard.
If your body does not feel fully recovered and but your morning HRV index has returned to near your average level, this can be a good sign that the body is adjusting HRV for your body to recover faster. In addition, the sooner your HRV returns to normal levels after exercise also may be a sign that your body is recovering well.
The trend of your HRV Index score will likely be incredibly insightful towards your body's training and stress adaptation, however, it is important to remember that the HRV Index should be used as another tool in your training toolbox. Using the HRV Index as the sole determinant of how you should train every day will likely not produce the most beneficial results.
Why do I feel tired when the HRV index is high?
If your HRV index returns to a normal level, it usually means the nervous system is fully recovered and relaxed. However, if your body feels very tired despite a high HRV index, this might be a sign that the body has been overtrained and the level of parasympathetic nerve activity needs to be improved to allow the body to quickly recover from fatigue, which is a self-repair mechanism of the body.
Why is the ECG waveform inverted?
Please make sure that you are wearing the watch on the same wrist as specified in your settings. If you are wearing the watch on your left wrist during the HRV measurement, but the settings indicate right wrist, the waveform will appear inverted or upside down. The inversion of the waveform will not affect the index or measurement, but it is still recommended that the watch is worn on the same wrist as in the watch settings.
HRV Index Disclaimer
The HRV index obtained by HRV measurement is for reference only and cannot diagnose any medical conditions.