Your heart doesn’t beat like a metronome
Most people think that the heart beats with regularity, like a metronome. When your heart rate is 60 beats per minute, your heart beats once every second, right? Not exactly. At rest, your heartbeat is nothing like a metronome, the time between individual beats changes fluidly. It can be anywhere between 0,9 seconds and 1,1 seconds in the given example. Even though it’s not a perceptible difference, we can measure it. This is exactly what heart rate variability is all about – it’s a measure of the variation in time between each heartbeat.
Why is your heart rate so variable?
Your heart rate is controlled by your autonomic nervous system as it responds to the demands placed on your body. There are two main components to it – the sympathetic and the parasympathetic nervous system. They are each other’s opposites.
• Sympathetic nervous system – This component helps your body activate its “fight or flight” response. Its activity increases when you’re stressed, in danger or physically active. The sympathetic nervous system causes your heart to beat faster.
• Parasympathetic nervous system – This component activates your “rest and digest” response, which relaxes your body after physical activity or stress. The parasympathetic nervous system causes your heartbeat to slow down.
A balanced nervous system receives commands from both the sympathetic and parasympathetic components, which results in heart rate variability. This means that high HRV is generally a good thing. When either of the systems dominates, your heart rate starts to resemble a metronome as the variability goes away, this usually signals a problem.
HRV is very individual
The problem with HRV is that it’s a very sensitive metric. It fluctuates throughout the day, from one day to the next, and most of all, from one person to another. Younger people tend to have higher HRV than older people. Elite athletes usually have greater HRV than amateurs – interestingly, endurance athletes like cyclists typically have higher HRV than strength-based athletes. But all of these trends go out the window when you look at individuals. You may well find a highly trained pro who will have a lower HRV than a sedentary person. This means that when you measure your HRV, you can’t simply look up some recommended values. You have to track your HRV consistently to find out what are “healthy” or “concerning” HRV values for you.
Look for the trends in your HRV
Tracking HRV can be confusing at first, you see values jumping up and down from day to day and even more so hour to hour. This is completely normal, as you know, your heart constantly receives commands to slow down or speed up depending on which component of the nervous system is more active. The trick to getting valuable information from HRV is to look for long-term trends.
When you start a new training plan or get back into cycling after a long break, you should be seeing an increase in HRV numbers over weeks and months. Similarly, if you notice that your HRV keeps going down for a few days straight, it may be a sign of training too much, not sleeping well or getting sick. There is much more you can learn from tracking your HRV, especially along with other metrics. We will look at that later in the series. The next article will be all about how to best track your HRV.