Health / Expert Advice

What Exactly Is Heart Rate Variability Training?

How to get the most out of this innovative training metric

If you haven’t heard of heart rate variability training, it’s worth it to your workouts to learn a bit more. It seems like heart rate variability is the next big thing in wearable fitness data—and there’s good reason for the hype. With hyper-accurate detection of the time between heartbeats, HRV monitors and corresponding training apps open up a new world of possibilities for intuitive training—one that’s informed by your physical state, not the other way around. Here to explain how to make the data work for you is Simon Wegerif, director of ithlete, an app that tracks heart rate variability.

Why Monitoring Heart Rate Variability Matters

Knowing and monitoring your resting heart rate is generally good health advice. But it’s only part of the story your ticker has to tell. “Counter to what you might expect, your heart is actually not beating with a metronomic regularity,” Wegerif says. “In fact, variability in the heart rate is very healthy.”

That’s because the variability in your heart rate reflects the current state of your body. The more variability, the better your physical condition, Wegerif explains. “If your body is very stressed, then there’s very little variability in beat-to-beat heart rate,” he says. “But if your body is relaxed and aerobically fit and healthy, then you’ll get a lot of variability from your heart rate.”

Therefore, the heart’s ability to vary the duration of time between beats is indicative of its ability to reflect changes in the rest of the body. That means you’re ready to work. If your exercise schedule involves HIIT routines, for instance, a high variability reading in the morning means you’re clear to crush the gym. It doesn’t mean that your condition can’t change later in the day, though. “With convenient HRV monitoring, you’re taking a snapshot of the autonomic nervous system, which is basically valleyed for the time you’re taking the snapshot,” Wegerif says. A stressful day at work may alter your heart rate variability before a post-work run or gym session. So factor the day’s impact on your body into your morning variability metric.

How Heart Rate Variability Integrates Into Your Training

Professional athletes use heart rate variability to schedule workouts around high variability readings and rest players who have low variability. Wegerif says one English Premier League team orders a medical inquiry for players with unexplained drops in heart rate variability. But most of us don’t have the time to schedule around a daily readout. Still, this method affords users the ability to push the envelope with confidence.

Athletes who periodize their training (such as a marathoner in a base-building phase) do so knowing they’ll go into periods of constant low energy due to the high training load. Such phases are a gamble. Go hard and win fitness, but go too hard and risk burnout or illness. “Endurance athletes are known for being very hard on themselves, and there’s a danger of nonfunctional overreaching,” Wegerif says. It’s hard to tell whether overreaching is functional (in that it ultimately elevates your fitness) or nonfunctional while you’re doing it. But monitoring your HRV means you’ll know when you’re healthy enough to stay on the gas. You’ll also know when you’re running on fumes.

HRV apps do the work for you.

Rather than leave you to interpret the figures, HRV apps, such as Wegerif’s, set parameters within a designated amount of standard deviations from your baseline reading. The baseline is essentially a moving average of your daily HRV snapshots from a period of weeks, Wegerif explains. “We give people a green light as long as they’re within an acceptable range around their baseline,” he says. “Then, of course, they can still choose the workout they want to do that day.”

A yellow reading on Wegerif’s app indicates subpar recovery and suggests a rest, and a red reading means you should probably skip the day’s workout. Over a period of weeks and months, improvements in cardiovascular fitness will move the baseline HRV up, reflecting improvements in overall health.

What else can heart rate variability predict?

HRV is a reflection of the overall load on your body. Therefore, an unexplained low variability may be indicative of an impending illness—perhaps one brought on by a high training load. “On the road toward overtraining, you weaken the immune system. So you make yourself more likely to contract upper respiratory infections, coughs, and colds,” Wegerif says.

Carefully monitoring heart rate variability while attempting to hold constant life’s variables—changes to diet, sleep, work, and exercise—can tell us a lot about how our bodies react to certain stimuli. But the technique does have limits. One misconception is that HRV can tell you how your gut feels about the sandwich you ate for lunch. “[HRV] is sensitive to hydration status and the state of the digestive system,” Wegerif says. “There [are] a lot of conflicting things going on when the digestive system is mobilized.”

Start Training with Heart Rate Variability

You’ll need to download an HRV app and connect it to a heart rate monitor. Not all monitors are created equal, and your smartwatch isn’t going to be as accurate as a purpose-built device. “EKG is the gold standard for measuring HRV,” Wegerif says. “You’re measuring the time between every heartbeat very precisely, to a resolution of about two out of 1,000 milliseconds. It’s really quite an accurate measurement.”

In order to get reliable data, a chest-mounted or fingertip heart rate monitor with EKG technology is your best bet. Although, Wegerif says developments in wearable-enabled clothing with sewn-in sensors also looks promising.

Apple claims the company is developing EKG technology small enough for the Apple Watch. However, the current model, along with the rest of the wrist-mounted wearable market, sacrifice accuracy for size. They use photoplethysmography to take snapshots of the autonomic nervous system. However, they rely on algorithms that are susceptible to motion and changes in the amount of blood in the skin at the time of measurement. A less accurate measurement means your metric could read more standard deviations from the baseline than it actually is. So keep that in mind if you’re not using an EKG-enabled device.

Be Consistent

Take your measurement at the same time each morning, Wegerif advises, and do it first thing. You’re allowed to use the bathroom, but that’s it. Eating or drinking beforehand throws off the reading, as does stress. “You need to do it without checking a bunch of tweets or anything that would give you mental stress,” he says. Particularly fit people will want to take the reading standing up. A strong parasympathetic vagal tone interferes with a reading taken from a supine position, Wegerif explains.

Using an app that charts HRV over weeks and months, examine your training peaks and valleys. Employ the data to empower smarter training cycles. “Try to get a little bit scientific with it,” Wegerif says. “Try changing one thing at a time, and see what you learn about yourself.

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