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Understanding HRV Status on Your Garmin Device
What is Heart Rate Variability?
Heart rate variability (HRV) is a physiological phenomenon that can be recorded, analyzed, and interpreted to help understand how your body is navigating the challenges of life and environment.
Specifically, HRV refers to the ever-changing length of time between consecutive heartbeats. When your heart is beating at 60 beats per minute, the beats are not evenly spaced one second apart. Look closely and you will see that some beats are slightly less than one second apart and others are a little bit more than one second apart. This irregularity is perfectly normal and healthy.
These slight changes between heartbeats can be easily documented with an accurate recording device and are typically measured in milliseconds. Without physiological knowledge and analytic methods, however, the HRV phenomenon would simply be a list of numbers.
Statistical analysis can reveal meaningful patterns in large amounts of data. RMSSD is a standard statistical measure of HRV. It represents the root mean square of successive differences between normal heartbeats for a given set of heartbeat data. This way of looking at HRV data is widely used by physiologists and exercise scientists to investigate topics like the impact of training loads and recovery processes.
Luckily, you do not need to be an expert in physiology or statistical analysis to benefit from HRV-based insight. A wealth of information exists on the subject, however, if you do want to explore further.
Why does HRV provide such valuable insight? The activity of your heart is regulated by your autonomic nervous system, which adjusts a wide variety of physiological systems in response to situational demands. This means that changes in how your heart beats from one moment to the next can be used as a window through which activity occurring within your autonomic nervous system can be seen.
In general, higher HRV is associated with parasympathetic dominance within your autonomic nervous system, a sign that your body is in rest-and-digest mode. On the other hand, a lower HRV is typically associated with elevated sympathetic activity within your autonomic nervous system, an indication of stress or fight-or-flight response.
How Your Compatible Garmin Watch Measures HRV
Data used to calculate your HRV is recorded by the Elevate HR sensor located on the back of your watch. This sensor uses reflected light to detect pulse wave blood flow as it is pumped by your heart and pushed through your veins. This means that technically your device is looking at pulse rate variability which effectively reflects heart rate variability in the context of this analysis and usage scenario.
Compatible Garmin devices calculate HRV continuously while you are sleeping. When you wake up, you can view your average HRV calculated using data from the entire sleep period. You can also review a chart that shows how your HRV changed while you were asleep based on analysis of 5-minute time windows.
This offers a significant advantage compared to other methods that measure HRV during only part of the night, during specific sleep stages, or involve testing at specific times of the day.
Because HRV is a statistical measure, differences in the timing and duration of the measurement affect the results. This makes it a challenge to make apples-to-apple comparisons between HRV measurements produced with alternative protocols and different devices.
Interpreting HRV and Why Your Personal Baseline Matters
You will be able to see your average HRV and overnight trends as soon as you start using your device. Simply wear your device to bed and the analysis automatically occurs. What you will missing at first is meaningful context for interpreting your results.
When it comes to making sense of any HRV metric, everything starts from you. A normal, healthy degree of variability for you is not necessarily the same as for someone else. Some people have naturally higher ranges of variation while others tend to exhibit less variability. And that is not all, what is normal for you also changes over time.
Your own personal history, then, is the single-most meaningful frame of reference for interpreting HRV data. Given this fact, documenting your personally normal range of HRV values is a necessary first step in making your HRV data actionable.
This takes time. In practice, it means that you need to routinely wear your Garmin device overnight for around three weeks before HRV status becomes fully active. While three weeks is the minimum amount of time needed to gauge your personal baseline, the analysis can utilize a few months of data to strengthen and validate your baseline range when that amount of data is available.
Key concept: Your HRV baseline is a range of values (e.g., 33-45 milliseconds) derived from your measurement history that represent a normal degree of variability for you personally. Your baseline is the lens through which future HRV measurements can be meaningfully interpreted.
Once your baseline range is identified, your overnight HRV is used to enhance insight from other Garmin features. These other features include your current Training Status and daily Training Readiness assessments on compatible devices.
Your baseline HRV range is not static and will shift over time. You may notice, for example, that your normal range of variability is lower after an extended training period compared to when you are in peak condition. Normal HRV ranges also typically decline with age.
Navigating the HRV Status Widget
As mentioned, the HRV status widget on your device offers more than just one perspective for monitoring your situation. The primary view reveals your current HRV status. Your status can be balanced, unbalanced, low or poor. At the bottom of the first screen, you can see your average HRV measured during the previous night.
Scroll down and you will again be able to see last night’s average HRV, but with additional context. This is where you will find your highest HRV recorded for any 5-minute period during the night. You will also discover a chart that shows how your HRV changed during the night.
The final screen shows your current 7-day average HRV and a plot of average overnight HRV values recorded over the past 7-day period.
HRV Status: Balanced, Unbalanced, Low, and Poor
When your HRV status is balanced, it means that your 7-day average HRV is within your personal baseline range. A balanced HRV status typically indicates your body maintaining homeostasis, a dynamic biological equilibrium associated with optional functioning.
An unbalanced HRV status means your current 7-day-average HRV is outside of your personal baseline range. Note that an unbalanced HRV status can be either higher or slightly lower than your baseline.
Given that higher HRV values are typically associated with parasympathetic dominance within your autonomic nervous system, it is easy to assume that higher is always better from the perspective of good recovery. This is not always the case. Mounting evidence shows a relationship between abnormally high HRV values relative to your personal baseline and functional overreach (overtraining), especially when that overreach is achieved through large amounts of low-intensity physical activity. In these situations, your parasympathetic system is working hyperactively towards the goal of reestablishing homeostasis.
If your 7-day average HRV drops significantly below your baseline, your HRV status is reclassified from unbalanced to low.
Your personal baseline is dynamic and changes slowly over time following trends in your normal overnight HRV values. If your personal baseline drops below age-based standards associated with good health, then your HRV status is classified as poor. When this happens, your baseline range is no longer displayed. This is to avoid scenarios where your HRV might be considered both balanced and below healthy norms.