You’re probably familiar with heart rate monitoring during a workout. But there’s a separate marker of the heart’s capacity to endure stress—a measure known as heart rate variability—that might be an even better marker of fitness readiness and fatigue levels.
“Heart rate variability is a measure of stress and recovery within the body, from a physiological standpoint,” says Vincent Luppino, PT, DPT, OCS, a physical therapist at HSS Paramus.
This biomarker, when measured accurately with the help of a heart rate variability tracker, can be used on a daily basis to know if your body is primed for a hard workout or if you need to lower the intensity—or rest.
Your heart rate is a measure of how many times your heart beats within one minute. This can be counted by checking your pulse on your wrist or neck and counting for one minute or by using a heart rate monitor like a fitness watch. An average heart rate for a normal, healthy person is between 60 to 100 beats per minute (BPM) at rest; for an endurance athlete, that number might even drop to 30 to 40 BPM.
Heart rate variability, or HRV, is the measure of the variation in time between heartbeats, measured in milliseconds. For example, sometimes your heart might beat every 1.2 seconds; other times, it might beat at 0.8 seconds. You need a device to measure that variance in timing (more on that below). Ideally, you’d monitor your HRV for two to five minutes to see what your average is.
A longer HRV, with more time between heartbeats, is in general more desirable than a shorter HRV because it shows your body can recover faster from stress and that the heart can resume its normal rate after having been sped up due to exercise, stress, illness or something else. It’s an indicator of how your body handles stress, which includes your training efforts.
If you’re a fan of certain exercise classes, you’ll often hear instructors direct you to a target heart rate. During exercise, a BPM of 120 all the way to 150 is normal during cardio or endurance training.
The gold standard for measuring heart rate variability is an EKG done by a medical professional. After that, the HRV measures within many fitness trackers are thought to be highly reliable at tracking it. Here are some general tips for measurement:
HRV is impacted by a few things, including:
It’s helpful to know your HRV, but only if you know what to do with it. “Take stock of your heart rate variability day to day and notice patterns over time,” suggests Luppino. If you notice a high HRV day, that’s the time to go harder with training. “When I see a lower HRV number on my monitor, I’ll opt for stretching and breathwork to reduce stress and go to bed early that night,” he adds.
Is your HRV a number you should concern yourself with during your workout? Luppino says no. “When I’m working out, I’m not looking at heart rate variability,” he says. “I'm looking at my heart rate to modify what zone I'm in so I can focus on hitting my max heart rate during the training session.”
To improve your HRV, practice managing stress with breathing techniques. Your sympathetic nervous system becomes more active when you’re feeling stressed, causing the heartbeat to quicken and resulting in a lower HRV. Multiple days of recovery and less stress on the body over time will improve your baseline HRV.
To help release some of that stress, Luppino recommends diaphragmatic breathing, which involves focusing on breathing into the diaphragm (a muscle in your belly) to slow the heartbeat. Try this technique, called box breathing: