You regularly hit your weekly exercise goals (Active Zone Minutes, anyone?), log your physical activity with exercise modes on your Fitbit watch, and pay attention to your sleep patterns with Fitbit’s advanced sleep tools. You know that your Fitbit tracker or smartwatch can help you dial into key metrics, like your resting heart rate—and you may have even improved yours last year, like many other Fitbit users. But did you know that heart rate isn’t the only important metric to track when it comes to your well-being, heart, and overall health? 

Your Heart Rate Variability, or HRV, can tell you even more about how your body is handling physical strain, and, if you experience a significant drop, whether your body is showing potential signs of the onset of illness. Keep reading to find out how—and why it’s so important.

Heart rate variability is the time between your heartbeats, and it can change from night to night. For example, your heart rate may be telling you that your heart is beating at 60 beats per minute, but that doesn’t mean it’s beating once every second. 

To get a little more technical than we usually do, the actual variance in time between heartbeats—down to milliseconds—is the variability. Calculated during deep sleep, HRV can be used as a measure of recovery. According to the Harvard Health blog, measuring it can tell you about your physical resilience and ability to perform at high levels—i.e., how readily your body can transition from rest to activity and back. 

Harvard Health tells us that your HRV is controlled by a part of the body called the autonomic nervous system (ANS). Essentially, your ANS regulates normal bodily functions like heart rate, of course, but also things like breathing, blood pressure, digestion, and more. It is divided into the sympathetic and the parasympathetic nervous systems, or as you might know them—”fight-or-flight” (sympathetic) versus “rest and digest” (parasympathetic) responses.

If your ANS is functioning normally (balanced between “fight- or-flight” and “rest and digest” modes), it receives all kinds of information from the region of your brain called the hypothalamus, and you won’t even notice as it keeps your body working day in and day out. It’s when the balance in your ANS is disrupted that your body’s fight-or-flight mode may overcompensate, resulting in a lower HRV.

In general, a higher average HRV is linked to greater overall health and fitness. A significant drop in your HRV can have many causes, including a poor night’s sleep, physical strain, diet, or being emotionally or physically stressed. 

Again, a significant drop in your HRV may mean that your body is in fight-or-flight mode, so look to see if your HRV has been trending downward over multiple nights. You could also just be in a normal recovery phase after some intense workouts! 

But, if that’s the case, you guessed it—your lower HRV is letting you know that your body is in need of rest. You may want to consider prioritizing recovery to bounce back from potential overtraining, lack of sleep, hormonal changes, psychological stress, and more. 

Your HRV trends are available in the Fitbit app on Fitbit Sense, Versa 2 and 3, Charge 4, Inspire 2, and Luxe devices. You’ll want to pay special attention to the days that your HRV is out of your personal range, specifically on low days. 

Interested in learning more? Check out the Health Metrics dashboard.¹