What is HRV? Why is it Important?

Your heartbeat feels pretty steady, right? But even when it’s at a resting average of 60-100 beats per minute, there’s a tiny variation between heartbeats (1). That fluctuation is your heart rate variability (HRV).

HRV is managed by your autonomic nervous system (ANS), which manages things like your heart rate, blood pressure, breathing, and digestion (2). The ANS is divided into two main parts: the sympathetic nervous system (fight-or-flight) and the parasympathetic nervous system (rest-and-digest).

These two systems are always working together, creating the slight variations in the time between heartbeats. The more smoothly your sympathetic system can rev up to handle stress or danger and your parasympathetic system can calm things back down, the higher your HRV. But if those transitions are slower and less responsive, your HRV will be lower.

In healthy adults, the average heart rate variability is 42 milliseconds, with a typical range between 19 and 75 milliseconds (3).

Native Note: Just a quick refresher one millisecond is one-thousandth of a second—so we're talking about tiny differences here.

The gold standard for measuring HRV is an electrocardiogram (ECG or EKG). ECGs use wired sensors attached to your body to record electrical activity in your heart. This lets doctors precisely measure the time between the same point in each heartbeat (4).

To assess some heart conditions, patients can wear a heart monitor outside the doctor’s office for longer periods of time. However, this isn’t a practical way for most people to track their HRV regularly.

This is where wearable devices like smartwatches and chest straps come into play. These devices use a technology called “photoplethysmography”. Basically, they send a pulse of light through your skin to detect changes in blood flow beneath the surface (5). This helps measure your pulse, which is a good stand-in for your heartbeat.

You should note that there's ongoing research looking into how these wearables compare against traditional ECG methods.

In general, a higher HRV is better than a lower one, though there are exceptions (which we’ll get into later).

Research has shown that a lower HRV is linked to an increased risk of disease and even death. In fact, a 2022 review of studies found that low HRV was a strong predictor of higher mortality across different age groups, sexes, and regions (6).

A high HRV usually indicates that your body can handle stress and adapt to changes well. However, in some cases, such as with heart conditions like arrhythmia (irregular heartbeat), a high HRV might be a sign of trouble (7).

The best approach is to monitor your HRV over time and keep an eye out for any significant changes, as they could be early warning signs of health issues.

Your HRV naturally varies over both the short and long term. Here are some key factors that can influence it.

• Genetics: Your genes play a significant role in determining your baseline HRV (8). Genetic variations are what give you a unique autonomic nervous system, resulting in individual differences in HRV patterns. So, you may naturally have a higher or lower HRV.
• Age: HRV generally decreases as you age (9). This decline is typically attributed to various age-related changes in the autonomic nervous system and heart function.
• Biological Sex: On average, females under 30 have a lower HRV than males. However, that gap starts to narrow at 30 and disappears after age 50 (10).
• Hormone Cycles: Changes in HRV during different phases of the menstrual cycle are relatively common due to fluctuations in sex hormones like estrogen and progesterone (11).
• Illness: Heart or lung problems, diabetes, asthma, and viruses like Coronavirus can lower your HRV (12, 13).
• Mental Health: Mental health issues such as depression and anxiety can lower your HRV (14).
• Time of Day: It’s totally normal for HRV to fluctuate during the day, depending on what you’re doing. Typically, your HRV is higher at night, declines slowly before you wake up, and then drops more as you go about your day (15).