Who this is for?
This is for people who want to understand HRV without becoming ruled by it.
There’s a lot of noise around HRV right now. It shows up on watches, rings, apps, dashboards — often with a colour, a score, and very little explanation.
For some people it becomes helpful. For others, it becomes another thing to worry about first thing in the morning. So let’s slow this right down and strip it back. HRV isn’t magic. It’s not a performance score.
And it’s definitely not a measure of your worth as a human. HRV can be a useful stress and recovery signal — if you understand what it’s actually measuring, how to measure it properly, and how to act on it. This article will walk you through:
- What HRV actually is
- How HRV is measured
- What the numbers mean (and don’t mean)
- How you can influence HRV
- How I personally use HRV now — and going forward
No hype. No fear. Just context.
What Is Heart Rate Variability (HRV)?
Heart Rate Variability (HRV) refers to the variation in time between each heartbeat. It’s not about how fast your heart is beating — it’s about how flexible the timing is between beats.
Even at the same heart rate, a healthy heart doesn’t beat like a metronome. The gaps between beats subtly speed up and slow down, especially at rest.
Variation is normal, but a higher reading is not always better. Signal errors and irregular heart rhythms can also increase measured variability. In simple terms:
- HRV within your usual range can be one sign that you are coping with your current demands
- HRV below your usual range can prompt a check of sleep, training, illness and other stresses; it does not identify a cause
But to really understand HRV, we need to look one layer deeper — at your nervous system controlling your heart.
The Autonomic Nervous System (ANS): The Real Driver of HRV
HRV reflects influences on the timing of your heartbeats, including your autonomic nervous system (ANS) — the part of your nervous system that runs automatically, without conscious thought.
This is the part of your nervous system that connects your brain to most of your internal organs. Your ANS regulates many of the body’s most important systems, including:
- Heart rate
- Breathing
- Digestion
- Blood pressure
- Stress responses
💡 It’s your body’s internal control system, constantly helping you respond to what’s happening around you.
Where does the autonomic nervous system fit in the overall structure of the nervous system?
Your overall nervous system includes two main subsystems:
- Central nervous system: This includes your brain (your retina and optic nerve in your eyes are considered part of your brain, structure-wise) and spinal cord.
- Peripheral nervous system: This includes every part of your nervous system that isn’t your brain and spinal cord.
The Two Branches of the ANS (The fun part!)
Your autonomic nervous system has two main branches that are always communicating with your heart.
Parasympathetic Nervous System (PNS) – “Rest and Digest”
This is the calming, recovery-focused side. When parasympathetic activity is higher:
- Heart rate slows
- Digestion improves
- Repair and recovery processes increase
- There’s more space between heartbeats
At rest, common HRV measures such as RMSSD are particularly sensitive to parasympathetic influence. This is a useful association, not a score for every body function listed above. Patterns in HRV may provide context about:
- Good recovery
- Aerobic fitness
- Greater stress resilience
Sympathetic Nervous System (SNS) – “Fight or Flight”
This is the stress and action side. When sympathetic activity is higher:
- Heart rate increases
- Breathing becomes faster and shallower
- Energy is mobilised
- There’s less space between heartbeats
HRV may fall during stress, but it does not directly measure sympathetic activity. Lower HRV is commonly seen with:
- Psychological stress
- Poor sleep
- Illness
- Heavy training blocks
- Travel and disruption
This isn’t “bad” — it’s necessary for performance and survival. Problems arise when the system stays here too long.
What HRV can tell us about the nervous system
Your heart has its own pacemaker, influenced by the autonomic nervous system and breathing, among other factors. Common resting measures such as RMSSD mainly reflect changes in cardiac parasympathetic influence. HRV is not a direct measurement of the balance between the two branches, and it cannot tell you exactly where stress is coming from. RMSSD and SDNN are commonly expressed in milliseconds (ms). They describe variability in different ways, so the numbers should not be treated as interchangeable.
For a practical explanation, see Marco Altini’s guide to HRV measures.
HRV Is Personal
There is no universal “good” or “bad” HRV number. HRV is:
- Highly individual
- Sensitive to daily and seasonal change
- Influenced by sleep, stress, training, illness, hormones, and life
Some people have very steady HRV. Others fluctuate more. Both can be healthy. The only meaningful comparison is:
You vs you, over time
How Do We Measure HRV?
HRV is extremely sensitive — which is why both the measurement method and consistent conditions matter.
ECG, chest straps and optical sensors
An electrocardiogram (ECG) is the reference method for recording the heart’s electrical activity. A validated chest strap that supplies reliable beat-to-beat intervals can be a practical option for a resting HRV measurement. Chest straps still need good electrode contact and a suitable recording method. Movement, poor contact and irregular beats can affect the result. They are not interchangeable with a clinical ECG examination.
Wrist wearables use optical sensors to detect the pulse. These estimates can be useful, especially at rest or during sleep, but device fit, movement and signal processing affect accuracy. The Polar H10 is one example of a chest strap used with compatible HRV apps. There is also a long-term independent review if you want to understand the practicalities.
Active vs Passive Measurement
A deliberate resting measurement:
- You initiate it
- You are still (lying or seated)
- Follow the validated recording length used by your app, often 1–5 minutes
- Ideally first thing in the morning
Passive measurement:
- Collected automatically
- Often during sleep
- Sometimes during quiet daytime moments
Overnight HRV can contribute to daily decisions and longer-term trends when interpreted consistently and alongside how you feel. Morning and overnight measurements are different protocols: do not combine them as though they are the same baseline.
How Apple, Garmin and HRV apps differ
Different devices use different recording windows, filtering and calculations. Keep comparisons within the same device and measurement method wherever possible.
Apple Watch
Apple Health reports HRV using SDNN, the standard deviation of normal-to-normal beat intervals. These are sampled measurements, not a continuous clinical ECG. Recording conditions and the length of the sample affect interpretation. Source: Apple HealthKit: heart rate variability SDNN.
Garmin
On compatible watches, Garmin’s HRV Status uses overnight readings and compares recent patterns with your personal baseline. Device features vary. Garmin also reports RMSSD and SDRR in its separate Health Snapshot feature. Read Garmin’s HRV Status guidance and Health Snapshot explanation.
HRV4Training
HRV4Training supports deliberate resting measurements, including compatible phone-camera and external-sensor methods. Follow its current device guidance and use a consistent routine. Its recovery score is derived from RMSSD, so it is not directly comparable with a raw SDNN value. See the app’s measurement guidance and validation research.
What Do the Numbers Mean?
There is no universal “good” or “bad” HRV. What matters is:
- Your baseline
- Your normal range of variation
- How quickly you recover back to baseline
One low day = information Several low days = a pattern Large changes can reflect physiology, measurement conditions or signal error. Check the context before interpreting them. Trends tell the story. Single days are just sentences.
This illustration is a simplified reminder to look at context. A large swing is not proof of stress: measurement error and other physiological changes can also affect HRV.
How Can You Influence HRV?
HRV can be influenced in two ways:
Acute (short-term)
These can change how you feel and may affect a reading in the moment:
- Slow nasal breathing with longer exhales
- Awareness of stress and tension
- Light movement (walking, mobility)
Chronic (long-term)
These support health and recovery over time, although an increase in baseline HRV is not guaranteed:
- Appropriate strength and aerobic activity
- Adjusting training using your plan, symptoms, recovery and readiness together
- Managing total training + life load
- Prioritising sleep
- Fuelling consistently (carbs + protein)
- Reducing unnecessary background stress
- Thinking in weeks, months, not days
How I Use HRV (Now and Going Forward)
I use HRV as one signal among many, not a verdict.
What I pay attention to:
- Consistent measurement
- Baseline and trends
- Context: sleep, mood, energy, hunger, stress and my growing interest in relaxed, comfortable breathing.
The chart below is from November–December 2025. At that time, my displayed baseline was 101–117 ms. I travelled for work in France from 10–12 December 2025, and the change in my HRV coincided with that disruption. It was useful context, rather than proof that travel caused the change. I was out of routine. My sleep, my nutrition, my Pillars — none of them were stable.
A personal note on cold immersion
I’ve used cold immersion and found that it makes me focus on breathing and staying calm. That is a personal observation, not evidence that cold water reliably improves HRV or recovery. Cold water also places an acute demand on the body. It is not needed to use HRV well, and I do not recommend it simply to change a score. Anyone considering it should understand cold-water risks and seek individual advice where relevant.
What I don’t chase:
- Perfect scores
- Daily highs
- Other people’s numbers (Very important – Because we are terrible for comparison)
Low HRV doesn’t mean “don’t train”. It means train with intent, not ego. Wearables give numbers. Reflection gives meaning.
💡 My Reflections: HRV, Stress, and the Three Pillars We Work On at Pillars
HRV can provide context about your response to stress. Not just training stress. Not just physical stress. But life stress. And this is where HRV becomes really useful — not as a number to chase, but as a prompt to zoom out and ask a better question:
Where is stress coming from, and what actually needs my attention right now?
At Pillars Nutrition, we don’t look at stress as one thing. We look at it through three main Pillars of stress
Pillar 1: Home 🏡
This is everything that loves you — and everything you love. Family. Friends. Relationships. Community. This pillar can be deeply supportive… and also deeply demanding. When interpreting HRV, it is worth considering:
- Emotional load
- Responsibility
- Conflict
- Even positive stress (weddings, holidays, big life moments)
A strong home pillar doesn’t mean “no stress”. It means support, connection, and enough space to recover.
Pillar 2: Work 🏢
Work is an interesting one. In theory, wouldn’t it be great not to have to work? But in practice, most of us need purpose, routine, challenge, and stimulation. Work can:
- Give structure
- Create meaning
- Drive growth
But it can also:
- Bleed into everything
- Remove boundaries
- Quietly dominate recovery time
Work stress is part of the context I consider when reviewing HRV. A reading cannot diagnose burnout or tell us whether work is the cause.
Pillar 3: Yourself (the one we work on the most) 🥰
This is the pillar that supports the other two. And it’s the one most people neglect. This is about:
- Putting yourself first without guilt
- Understanding your needs
- Prioritising recovery, movement, nutrition, sleep, and boundaries
When this pillar is strong:
- Home becomes easier to manage
- Work becomes more sustainable
When it’s weak, the other two start to wobble. At Pillars, we spend a lot of time helping people rebuild this pillar, because it’s the one you actually have the most influence over.
Why We Look Beyond Just HRV
HRV is powerful — but it’s not used in isolation. Alongside HRV, we monitor:
- Mood
- Energy levels
- Hunger
- Sleep quality
- Steps
- The 3 Pillars (Home – Work, and Self)
Because numbers without context don’t change behaviour. Reflection does. That end-of-day pause — logging, noticing, checking in — isn’t admin. It’s you paying attention to yourself. We use tailored reflection fields in Cronometer to support these conversations.
Why I look at HRV alongside resting heart rate
HRV has become a useful part of my own reflection, but resting heart rate still matters. They describe different aspects of the same system and can change together or separately. Neither is guaranteed to warn you before illness, fatigue or a drop in performance. I look at both alongside sleep, mood, energy, symptoms and training. A reassuring score should never override feeling unwell.
The Bigger Picture
HRV isn’t about doing less. It’s about doing the right thing, at the right time, often enough. At Pillars, I use HRV as:
- A conversation starter
- A pattern-spotting tool
- A way to support better decisions
Not as a scorecard. Not as a judgement. Your body is always talking. HRV just gives it a microphone. And when you listen — within the context of home, work, and yourself — you don’t just train better. You live better! ❤️
About this guide
This guide is for general education and coaching context, not a diagnostic tool or a medical prescription. Persistent symptoms or concerns about your heart rhythm need medical assessment. Do not use an HRV reading to decide whether symptoms are safe to ignore.
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📚 Further Reading (Open Links)
For those who want to go deeper into the science and practical application of HRV, stress, and recovery, the following resources are well-respected, evidence-based, and genuinely useful. I also highly recommend the work of Marco Altini, whose approach to HRV is grounded, practical, and refreshingly free from hype.
- 🌐 Website: https://www.marcoaltini.com
- ✉️ Substack: https://marcoaltini.substack.com/
🎧 Recommended Watch / Listen
For a deeper, more applied understanding of HRV, stress, and the nervous system, these are excellent starting points.
1. Podcast: Dr Andy Galpin — HRV, Stress, and Training Readiness
Andy Galpin consistently explains HRV in a practical, coach-friendly way, particularly around nervous system regulation, recovery, and performance decision-making. 👉 https://performpodcast.com
2. Podcast: Peter Attia — HRV, VO₂ Max, Longevity & Recovery
Peter Attia regularly discusses HRV in the context of healthspan, stress load, and long-term adaptation — particularly how HRV fits alongside other metrics rather than replacing them. 👉 https://peterattiamd.com/podcast/
3. YouTube: Dr Stacey Sims — Women, Hormones, Stress & Recovery
Dr Sims’ work is essential when discussing HRV in women, especially around:
- Menstrual cycle variability
- Perimenopause
- Stress tolerance
- Recovery expectations
Her perspective is critical for interpreting HRV with context rather than rigid rules. 👉 https://www.youtube.com/watch?v=kVjTtdtwYOM
4. Podcast: Joel Jamieson — HRV, Conditioning & Stress
Joel Jamieson is one of the original voices in applying HRV to training and recovery. His work is particularly strong on:
- Stress vs recovery balance
- Why HRV predicts cost, not performance
- How to avoid misusing HRV data
More from Pillars
Want support bringing food, training and recovery habits together? Explore nutrition and lifestyle coaching with Tim, in Oswestry or online across Shropshire. Book a free conversation or browse our free nutrition guides.