Heart rate variability has lately gained the attention of many people looking to track, understand and optimize their recovery and readiness. Heart rate variability or HRV is something you can track with Wahoo, Oura ring, Vitalmonitor, but what is HRV all about and why should we care?
HRV stands for Heart Rate Variability. Researchers and physiologists have been tracking and utilizing HRV for decades because it’s a useful indicator of several health-related issues (more about these later), but only lately has it grabbed the attention of athletes, coaches, biohackers and the general public.
A healthy heart beat contains healthy irregularities. Even if your heart rate is, say, 60 beats per minute, that doesn’t mean that your heart beats once every second – or at one-second intervals like a clock.
Rather, there is variation among the intervals between your heartbeats. The interval between your successive heartbeats can be, for example, 0.85 seconds between some two succeeding beats and 1.35 seconds between some other two.
Even though the difference is measured in parts of seconds, you can actually feel the difference.
Here’s a tip for anyone who wants to experience it: place a finger gently on your neck or wrist and find your pulse. You should feel that the longest intervals take place when you exhale, and the shortest intervals when you inhale.
Why track HRV? The key is the phrase “healthy irregularities” we used in the beginning of the article. The type of variability indicated by HRV is perfectly normal. Actually, it’s desirable.
To understand HRV, we first need to understand our nervous system and heart rate. Heart rate variability can be traced back to our autonomic nervous system.
The autonomic nervous system regulates very important systems in our body, including heart and respiration rate and digestion. The autonomic nervous system has a parasympathetic (rest) and a sympathetic (activation) branch. Heart rate variability is an indicator that both branches are functioning – the parasympathetic in particular.
Intrinsic heart rate is measured in the condition in which neither parasympathetic nor sympathetic regulation is present. When completely blocked from autonomic regulation, a healthy heart contracts at a rate of about 100 beats per minute (the number is individual, however).
Parasympathetic regulation lowers your heart rate from the intrinsic level, giving more room for variability between successive heartbeats. Parasympathetic regulation causes almost immediate changes that affect only a few beats at a time, after which the heart rate returns towards the intrinsic rate. Sympathetic regulation elevates your heart rate from the intrinsic level, and there is less room for variability between successive heartbeats. Sympathetic regulation affects several consecutive heart beats.
Put these together and we can formulate a rule that when the rest-related parasympathetic branch is active and the sympathetic branch is inactive, your heart rate is lower and HRV higher. Factors such as stress can lead to the withdrawal of parasympathetic activity, or activation of sympathetic branch even when you are resting, both leading to elevated heart rate and lowered HRV.