How to Measure, Use and Improve Your Heart Rate Variability

Lub-dub. Lub-dub. Lub-dub. That’s the rhythmic sound your heart is (hopefully) making during the approximately 100,000 times it beats per day. Many people think the heart beats at a regular tempo like a metronome, but the reality is quite different. The time between each beat, known as the interbeat interval of the heart, is fluid, not fixed. This variation is a remarkable aspect of the heart’s functionality as it adapts to the body’s moment-to-moment needs, impacted by factors such as health status, fitness, physical activity, psychological stress, medication, sleep, and the environment, to name a few.

Doctors have been aware of the so-called Heart Rate Variability (HRV) for at least a century, but only recently has HRV been applied to athletes. In this article, we will discuss what heart rate variability is, how it’s measured, how-to improve it, and how it can be used in exercise. 

Drs. Baraki and Feigenbaum took a deep dive into Heart Rate Variability on Episode 337 of the Barbell Medicine Podcast. Listen below:

Heart rate variability (HRV) is the fluctuation in time intervals between successive heart beats. Heart rate is a separate measurement of how many times the heart beats per minute. A normal resting heart rate is somewhere between 60 to 100 beats per minute (bpm).1 There are special terms for heart rates above (tachycardia) and below this range (bradycardia).  Jargon aside, the time between heart beats gets faster and slower based on a number of different inputs such as the brain, blood pressure, and even your breathing rate. Among the most important inputs to HRV is from the autonomic nervous system.

Heart rate variability is an indirect assessment of autonomic nervous system functioning.2 The autonomic nervous system has two major divisions: 1) the parasympathetic nervous system (rest and digest) and, 2) the sympathetic nervous system (fight or flight). The parasympathetic nervous system’s main functions  at the heart is to slow the heart rate, while sympathetic activity increases heart rate.

Parasympathetic input predominates at rest, typically resulting in a resting heart rate around 70 bpm. When greater blood flow is required, such as during exercise, the sympathetic system’s input goes up in order to increase cardiac output, which is how much blood the heart pumps out per beat. Greater sympathetic activity subsequently increases heart rate, blood pressure, and how much blood is pumped out during each beat. 

In a healthy human heart, there is a dynamic relationship between the two branches, where increased activity in one branch can be associated with increased, decreased, or no change in activity of the other branch. In other words, changes in activity in one branch are not always associated with reciprocal changes in the other branch. After exercise for example, sympathetic activity remains increased while parasympathetic nervous system activity also rises. 3 The net result is a return towards resting heart rate after exercise, e.g. heart rate recovery. 

Overall, it’s best to think of HRV as an assessment of the beat-to-beat variations in heart rate, which serves to fine tune the heart rate to the current needs of the individual.  Further, heart rate variability is an indirect, non-invasive measure of autonomic nervous system functioning.