What Is HRV? Your Nervous System's Real-Time Report Card

Heart rate variability reveals how well your nervous system adapts to stress, and research links higher HRV to lower mortality risk. Here's what HRV actually measures, what your numbers mean, and 3 protocols to improve it starting today.

Your heart doesn't beat like a metronome. Even at a steady 60 beats per minute, the time between each beat varies slightly. That variation, measured in milliseconds, is your heart rate variability.

Dr. Andy Galpin, exercise physiologist at Cal State Fullerton, puts it simply: "Your heart rate, let's say your resting heart rate is 60 beats per minute, it doesn't actually beat 60 times in exactly one minute evenly. There's variation in the timing between beats. At times of extremely high stress you will be very rhythmic: beat, beat, beat, beat, beat. A high HRV indicates a lot of variation meaning you're pretty recovered. A low HRV meaning there's not a lot of variation means you're probably pretty stressed."

Here's the thing: this tiny variation tells a much bigger story than your heart rate alone. It's a direct window into your autonomic nervous system's state.

Why Variability Is Actually Good

The counterintuitive part trips people up. More variation equals better health. Less variation signals stress. I was skeptical too when I first heard this.

Think of it this way. A rigid, metronomic heartbeat means your body is locked into one gear. It can't adapt. A variable heartbeat means your nervous system can shift gears fluidly, responding to whatever life throws at you.

As researchers Fred Shaffer and J.P. Ginsberg note, "A healthy heart is not a metronome." I find that phrase useful when explaining HRV to skeptics. Your heart should dance, not march.

HRV reflects the constant push and pull between two branches of your autonomic nervous system. The sympathetic branch accelerates your heart rate. The parasympathetic branch applies the brakes.

When both branches work together smoothly, your heart rate varies naturally. When stress dominates, the sympathetic system takes over and that variation disappears. Your heart locks into a rigid pattern.

This is why HRV serves as such a reliable stress marker. It captures nervous system balance in real time. Which is wild when you think about it: a few milliseconds of timing difference tells you whether your body is in recovery mode or fight-or-flight.

The Vagus Nerve's Role

The vagus nerve is the main communication highway between your brain and heart. It carries parasympathetic signals that slow your heart rate and increase variability.

Dr. Andrew Huberman, neuroscientist at Stanford, explains the mechanism: "The deceleration of heart rate that goes from the vagus motor pathway to the sinoatrial node is the basis of what's called HRV or Heart Rate Variability."

Strong vagal tone means strong parasympathetic influence. That translates directly to higher HRV. Weak vagal tone leaves the sympathetic system unchecked, and your HRV drops.

So I dug into this and found something I didn't expect: you can directly strengthen vagal tone with simple breathing protocols. More on that below.

Typical adult HRV ranges from below 20 to over 200 milliseconds. That's a massive spread, which is why comparing your HRV to someone else's means almost nothing.

Age matters significantly. According to WHOOP data, 20 to 25 year-olds average 55-105ms. By ages 60-65, that range drops to 25-45ms. The most dramatic decrease occurs between the second and third decades of life.

For 24-hour SDNN measurements, the medical thresholds are clearer. Below 50ms is considered unhealthy. Between 50-100ms is compromised. Above 100ms is healthy, and those in this range show 5.3 times lower mortality risk. That's not nothing.

Look, I recommend focusing on your personal baseline rather than population averages. Your HRV today matters only in relation to your HRV last week.

Why Your HRV Changes Day to Day

A single low reading means nothing. Let me be direct: tracking day-to-day fluctuations will drive you crazy if you take each number seriously.

Dr. Andy Galpin offers a practical rule: "If your recovery score is in the tanks for more than 7 days, that's when we start paying attention. A single bad day or even a few days could just be normal fluctuation from life stress, poor sleep, or a hard workout."

One drinking session can suppress your HRV for up to five days. A bad night of sleep will tank tomorrow's reading. These are normal responses, not emergencies.

The 7-day rule keeps you sane. Single days mean nothing. A week-long pattern means something.

Dr. Galpin recommends taking your HRV for at least a month before using that value to make any changes. This baseline period matters because HRV fluctuates so much from normal life.

My approach: one subjective measure plus one objective measure. How do I feel? What does my HRV say? When they align, I trust the signal. When they conflict, I dig deeper.

Most wearables now track HRV automatically during sleep. That's enough for most people. You don't need lab-grade equipment to benefit from HRV insights.

The Week-Over-Week Rule

Compare Monday to Monday, not Monday to Tuesday. Same-day comparison accounts for your weekly rhythm.

Your Tuesday HRV might always run lower because of your Monday workout. Your Friday might always spike because you sleep in on Thursdays. These patterns are unique to you.

I've found that week-over-week comparison eliminates most false alarms. If this Monday's HRV is 15% below last Monday, that's worth investigating. If it's 15% below Sunday, that's probably just your normal pattern.

HRV goes beyond a simple wellness metric. The mortality data is striking: SDNN measurements above 100ms correlate with 5.3 times lower mortality risk compared to those below 50ms. Kind of insane when you realize this is just measuring the timing between heartbeats.

Dr. Andy Galpin explains why HRV outperforms simpler metrics: "HRV is a better recovery marker than resting heart rate alone because what you're trying to do is measure the balance of parasympathetic and sympathetic nervous system activity. HRV captures both sides of that equation."

Resting heart rate only tells you how fast your heart is beating. Understanding what is HRV gives you insight into how flexibly your nervous system is operating. That flexibility predicts health outcomes far better than speed alone.

Improving HRV comes down to strengthening vagal tone. The following protocols target that directly.

The Extended Exhale Protocol

Dr. Andrew Huberman shares what I consider the most actionable HRV intervention: "One of the best ways to improve your HRV, both in sleep and in wakeful states, which takes a very minimum of effort and is rarely if ever discussed, is simply throughout the day, I would say 10, 15, or maybe even 20 times per day, any time you remember to, just exhale."

That's it. Just extend your exhale. Not complex breathing patterns. Not hour-long meditation sessions. Simply exhale fully, 10-20 times throughout your day.

This works because exhaling activates the parasympathetic branch. Each extended exhale strengthens vagal tone slightly. Over time, those small activations compound.

If you're like me and won't remember to do this throughout the day, NSDR tracks guide this exact exhale pattern. I put one on before a meeting or when I need to downshift, and the pacing handles itself.

Sleep and Recovery Practices

Here's what surprised me: daytime breathing practices improve nighttime HRV. The vagal strengthening carries over into sleep.

Hydration also plays a role. The general guideline is approximately one ounce of water per pound of bodyweight daily. Dehydration stresses the cardiovascular system and suppresses HRV.

Using NSDR as a pre-sleep downshift protocol helps transition your nervous system from sympathetic dominance to parasympathetic recovery. The state change before sleep sets up better HRV throughout the night.

The Cold Exposure Paradox

Cold exposure presents an interesting pattern. During cold immersion, HRV actually drops. Your nervous system registers the cold as stress and responds accordingly.

But wait, it gets better. Measurements at 15-180 minutes after cold exposure show HRV rising above baseline. The recovery overshoot seems to strengthen the parasympathetic response.

I mention this because the immediate response can mislead you. If you check HRV during or right after cold exposure, you'll see worse numbers. The benefit shows up in the recovery window.

Now that you understand what is HRV and how it works, here are the most common questions.

What is a good HRV for my age?

When learning what is HRV, this is the first question most people ask. For adults ages 20-25, average HRV ranges from 55-105ms. By ages 60-65, that drops to 25-45ms. But your personal baseline matters more than population averages. Track your own numbers for a month before drawing conclusions.

Is 70 a good HRV?

For most adults, 70ms falls within the healthy range. But context matters. If your baseline is 90ms, a reading of 70ms suggests you're under stress. If your baseline is 50ms, 70ms means you're well-recovered. Always compare to your own history.

What is the fastest way to increase HRV?

Extended exhales work within days. The protocol is simple: 10-20 times daily, consciously extend your exhale. This directly activates the parasympathetic system and strengthens vagal tone. Paced breathing at 4.5-7.5 breaths per minute targets the optimal frequency for HRV improvement.

How long does it take to improve HRV?

Many people report measurable changes within a few weeks of consistent practice. Dr. Galpin recommends tracking for at least a month to establish a reliable baseline. Real improvements require that baseline context to verify.

Does HRV go down with age?

Yes. The most dramatic decrease occurs between the second and third decades of life. Women tend to have lower SDNN values but higher parasympathetic power. While age-related decline is normal, consistent breathing practices and recovery protocols can maintain HRV better than doing nothing.