Your heart normally beats between 60 and 90 beats per minute. If you’re athletic and in top physical shape, your heart rate may be slower, as low as 50 beats-per-minute. That’s your heart rate – but what is heart rate variability? It’s the time that elapses between each beat of your heart. When you measure heart rate variability, you quantify how much the time between each heartbeat varies.
Why is this important? Heart rate variability is an indicator of overall cardiovascular health as well as how much physical or psychological stress your body is under. You can measure heart rate variability and use it as an indicator of whether you’re overtraining and whether you need to dial back your training and give your body more time to recover. First, let’s look at heart rate variability means physiologically and what kind of information it can give you.
Heart Rate Variability and Your Nervous System
Your heart rate is controlled by your autonomic (or automatic) nervous system. Your autonomic nervous system has two components: the sympathetic and parasympathetic divisions. The sympathetic nervous system is sometimes called the “fight or flight” component because it’s activated during times of stress and during exercise. It’s the sympathetic nervous system that speeds up your heart rate. In contrast, the parasympathetic division is the “digest and relax” division of your autonomic nervous system. It’s active when you’re in a resting or in a relaxed state or after a meal. The job of the parasympathetic nervous system is to slow your heart rate down.
A healthy nervous system can respond quickly to changes in the environment. When it senses danger, it can activate your sympathetic nervous system at lightning speed and bring it back down after the danger has passed. A resilient nervous system that can react quickly bodes well for your health. One marker of nervous system resilience is heart rate variability. In other words, more heart rate variability is a sign of a healthy, balanced nervous system. Greater heart rate variability also means your parasympathetic nervous system predominates over your sympathetic nervous system. That’s what you want. You don’t want your sympathetic nervous system to gain the upper hand since that’s the part of your autonomic nervous system turned on during times of stress.
What does this have to do with exercise training? A decrease in heart rate variability can be a sign that you’re overtraining too. It’s an indicator that your body needs more recovery time. To use heart rate variability to screen for overtraining, you’ll first need to measure your heart rate variability each morning for a week or two to establish your baseline. Then, you look for deviations from the baseline as an indicator that you’re pushing your body too hard and not giving it enough time to recover.
How Do You Measure Heart Rate Variability?
You can measure heart rate variability using an electrocardiogram, a machine that traces the electrical activity in your heart. Of course, you have to attach electrodes to your chest and that’s not very practical. As an alternative, a heart rate monitor along with a heart rate variability heart rate app available online gives you this capability as well. If you download one of these apps, the best time to measure is first thing in the morning before you get out of bed.
When you measure heart rate variability, be aware that degree of hydration, the temperature of the room, humidity, medications, whether or not you’ve had caffeine, stress, and your general mood can impact the results. You can reduce the effect of these variables by measuring first thing in the morning before getting out of bed.
Do You Really Need to Measure Heart Rate Variability?
Heart rate variability provides you with helpful information about how your body is responding to your training schedule. If you see a drop in heart rate variability, ask yourself whether you’re training too hard or too often or whether stress could be playing a role in the decline.
Another rough measure of whether you’re pushing your body beyond its ability to adapt is your heart rate first thing in the morning. If your heart rate is higher than it is normally when you awaken, you may be pushing yourself too hard. As with heart rate variability, simply check your heart rate before getting out of bed in the morning. Establish a baseline. If your heart rate rises 5 beats per minute or more, you’re probably not taking enough recovery time between workouts. When your resting heart rate is up first thing in the morning, it suggests your sympathetic nervous system has gained the upper hand.
A Marker for a Healthy Heart
Good heart rate variability isn’t just useful for monitoring for overtraining, cardiologists use it as a marker for heart health. You find greater heart rate variability in healthy hearts, whereas low variability is linked with a greater risk of cardiac death and all-cause mortality, especially in the elderly. What this shows is how important your autonomic nervous system is for heart health.
How might low heart rate variability trigger a heart attack? One theory is that an imbalanced autonomic nervous system may trigger inflammation. As you know, inflammation is linked with a variety of health problems, including heart disease. When the inner walls of blood vessels become inflamed, the risk of a clot forming rises in an artery, including the coronary arteries that supply blood to the heart. A clot can, in turn, lead to reduce blood flow to the heart and damage it.
The Bottom Line
Heart rate variability is a marker of excess stress on your body, either mental or physical. If you work out, it’s also a sign that your body needs recovery time. Longer term, high heart rate variability is an indicator of a healthier heart. Is it worth investing in a heart rate monitor and app? If you enjoy the constant feedback that monitoring offers, it might be worthwhile. As an alternative, use your first-morning heart rate to monitor for excessive fatigue or overtraining. It’s not as sensitive as heart rate variability, so you may not pick up on the fact that you’re overtraining as early. Still, it, too, is useful.
References:
Circulation. 1994 Aug;90(2):878-83.
Competitor.com. “Think You’re Overtraining? Check Your Pulse”
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