Most of us think of our hearts beating like a metronome. Sure, the tempo speeds up during a workout and slows down when we’re just on the couch, but we picture it to be a pretty steady machine.

But the truth is that there’s a little bit of time difference between each beat—what’s called heart rate variability (HRV). While your heart rate tells you how many times your ticker is beating per minute, your HRV is the fluctuation in the amount of time in between each heartbeat.

Although a normal adult HRV can range anywhere from 20 to 200 milliseconds, according to Oura Ring, a higher number typically indicates greater fitness and solid recovery. Lower numbers, on the other hand, could be a sign of current or future health problems—they point to your autonomic nervous system possibly being stuck in stressed-out fight-or-flight mode.

Either way, these fluctuations are so minimal (just fractions of a second) that they can only be detected with a special device. But just like almost any health stat you might want to track these days, there’s an app for it. I wanted to see how my workouts were affecting the stress levels of my body in real time, so I recently decided to use Elite HRV to analyze my heart rate and HRV during my workouts with Well+Good’s fitness videos on YouTube. And let me tell you: It feels like having my own little lab in the comfort of my home—or the gym, or outside.

Before starting a workout, I’ll put on my Polar H9 chest strap monitor, since chest straps are known to be the most reliable tool when it comes to tracking your heart. (Although fitness watches like Apple Watch or Whoop do measure HRV by shining a low-level light through your skin to read fluctuations in blood flow, that technique isn’t as accurate as having electrodes on your chest tracking your heart’s electrical activity.) Then I put my phone right on my tripod stand so that I can easily see my stats live during the workout.

Once I start moving, the info from my chest strap gets sent to the app, and I can watch how my heart rate and HRV are affected throughout my training session right on my phone screen. If I keep the chest strap on for longer, I can also see what both look like before and after my workouts, giving me a helpful baseline.

At the same time as I’m watching my HRV, I can also turn on the custom breathing pacer that suggests the ideal breathing pace for the exercises I’m doing. It plays an inhale and exhale sound (or a cue that actually says “inhale” and “exhale”) to match my breath to, and also shows a flower or circle that expands and contracts as a visual cue. The idea is that following it can condition you to better control your breathing—particularly during high intensity training when you might otherwise start panting. This is useful because, as Leada Malek, DPT, CSCS, SCS, a board-certified sports specialist in San Francisco, previously told Well+Good, faster, shorter breaths can increase our pain response, while regulating our breath can down-shift our nervous system, making us feel more calm and controlled.

What’s cool is that I can immediately see she’s right when I use the biofeedback tool that lets you track the effects of deep breathing (or meditation) on your HRV. During a workout, I’ll notice that following the suggested breathing pace improves my HRV. When you’re not in the middle of a workout, you can also try the app’s separate biofeedback exercises for specific health conditions like anxiety, training yourself how to breathe when you’re feeling anxious, for instance.

Although the app is free, I upgraded to a “personal pro” membership for $8.00 a month to get access to a personal pro dashboard where I can easily see a graph of how my HRV is trending over the course of a workout video, or even over the last week or month.

Coaches and trainers can go one step further: If they decide to set up a team dashboard, they’ll gain insights into how anyone in their class or on their team who’s using Elite HRV is responding to the workouts. The live feedback allows them to immediately see if the session is allowing everyone to hit their heart rate goals so that they can dial up or dial down the intensity in real time. Afterward, they can use this info to help strategize for the next training session.

Another helpful feature? The day after each workout, I can check in on how my body is doing with a morning readiness read. To track my recovery and long-term progress, a color indicator lights up like a traffic light. Green means go, go, go for that tough workout! Yellow means proceed with caution: Maybe stick to a walking workout or a low-intensity cardio dance class. Red means stop, drop, and let my body rest. Following these recommendations helps me make the most of where my body is at each day, keeping me from overtraining.

Sure, I’m mainly working out with free, publicly available videos on Well+Good’s YouTube channel. But Elite HRV makes the experience personalized for my body. I’m able to fine-tune the details to make each workout work for me so I can see real results—and in real time.

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