Your watch says your HRV was 52 last night. Is that good?
Honestly: nobody can tell you. Not from that number alone. An HRV of 52 is a strong morning for one runner and a warning sign for another, because heart rate variability only means something compared to your own recent readings. A page that answers “is 52 good?” with an age chart is answering a different question — how you compare to strangers, not how recovered you are today.
What you can do is turn that number into a daily training decision using a method you can inspect, run yourself, and check against your own results. Here is the whole protocol in three lines:
- Green — today’s HRV is inside or above your normal 7-day range: run the planned session, hard days included.
- Amber — modestly below your normal range: keep the session, cut the intensity or volume.
- Red — well below your range, or several low mornings in a row: recovery work or rest.
The rest of this guide shows you how to build the baseline those branches depend on, how to classify a morning, what to do on borderline days, and the specific situations where the number lies to you. It won’t diagnose anything, and it won’t tell you which wearable to buy.
What HRV actually measures
Heart rate variability is the variation in time between individual heartbeats, measured in milliseconds. It is not your heart rate. A heart beating 60 times a minute doesn’t tick once per second like a metronome; the gaps vary, and the size of that variation is the signal.
The variation comes from your autonomic nervous system, which has two branches. The sympathetic branch mobilises you for effort and stress. The parasympathetic branch handles rest and recovery. When the parasympathetic side is active, the gaps between beats vary more, so HRV rises. Under accumulated stress, from training or anything else, variation shrinks.
The metric behind most of the research in this guide is RMSSD (you’ll sometimes see lnRMSSD, the same metric on a log scale); your watch may report that or a related measure under the single label “HRV”. You don’t need the math. You need the practical reading: HRV above your own normal usually means you’re recovered; below your normal usually means your body is still dealing with something: training load, poor sleep, illness, stress. That framing, deviation from a personal baseline rather than comparison to other people, is the one used in the recent review of HRV monitoring for athletes in Sensors, and it’s the foundation of everything below.
What you need before any of this works
Three prerequisites, in order:
A device that records overnight HRV. If you sleep in an Apple Watch, a recent Garmin, an Oura ring, or a Whoop, you almost certainly have this already. No single brand is required, and you do not need to buy anything new.
Access to the number each morning. On an Apple Watch, HRV lands in Apple Health (Browse → Heart → Heart Rate Variability). Garmin is the awkward one: it keeps HRV inside Garmin Connect and doesn’t sync it to Apple Health automatically, so if you want it there you’ll need the workaround covered in our guide to getting Garmin HRV into Apple Health.
Seven consecutive mornings of patience. The protocol starts working after your first full baseline week, not on day one. That’s not a product limitation; it’s what the measurement requires, as the next step explains.
One warning before you start: readings are only comparable when the conditions are. Overnight measurements are actually good for this, because a narrative review of HRV in strength and conditioning notes that most commercially available wearables measure HRV during slow-wave (deep) sleep precisely to minimise the noise that daytime movement creates. Sleep in roughly your usual way, and let the watch do its thing.
Step 1: Build your seven-day baseline
The Sensors review is direct about this: to interpret daily HRV appropriately, athletes must first establish a stable personal baseline, which means collecting daily HRV for at least 7 consecutive days under consistent conditions.
So, for one week:
- Wear the device to bed every night.
- Each morning, note the overnight HRV reading. A notes app or spreadsheet is fine.
- Change nothing else on purpose. Train normally, sleep normally. You’re measuring your normal, not optimising it yet.
After seven mornings, compute two things:
- Your baseline: the average of the seven readings.
- Your normal range: the lowest and highest of those seven readings.
Check before moving on: you can state your 7-day average and your week’s low and high. If you can’t, keep collecting. If a night was clearly abnormal (heavy drinking, a fever), extend the week rather than letting it distort the range; you’ll see why in the failure-modes section.
Keep updating the average as you go. Your baseline should always reflect the most recent week or so of readings, because your normal drifts with fitness, season, and life.
Step 2: Read this morning against your own numbers
Now the daily part. Each morning, compare today’s reading to your baseline and range, and classify the day:
- Green. Today is inside your normal range, or above it. Recovery looks normal.
- Amber. Today is modestly below the bottom of your normal range. Something is off, but one soft reading is not a crisis.
- Red. Today is far below your range, or this is the second or third low morning in a row. Your body is telling you it hasn’t absorbed the load yet.
Where exactly amber ends and red begins is a judgment call, and it’s honest to say the research reviewed here doesn’t hand you a universal cut-off. The Sensors review warns that single-time-point HRV measures are highly susceptible to transient fluctuations from daily stressors, sleep disruption, environment, and measurement inconsistency, which is why this protocol never reacts strongly to one number: one low morning is amber at worst, and red requires either a dramatic drop or a pattern.
A note on the pleasant surprise: a morning far above your range is not automatically a super-compensation day. Often it’s noise. And in one specific population, highly trained endurance athletes, research reviewed in the strength-and-conditioning paper found HRV sometimes fails to fall, or even paradoxically rises, during overtraining. Treat an unusual spike as “interesting, watch the trend,” not as license to double the session.
Check before moving on: today has a colour. You can say why.
Step 3: Pick today’s session
The classification maps to an action:
| Today is | What to do | What that looks like |
|---|---|---|
| Green | Run the planned session, including hard ones | Intervals, tempo, heavy lifting, long run: whatever the plan says |
| Amber | Keep the session, shrink it | Same workout type at reduced intensity, or fewer sets/reps/kilometres |
| Red | Recovery work or rest | Easy walk, mobility, light spin, or a full day off |
The borderline rule. When you genuinely can’t tell, with today sitting right at the edge of your range, don’t ask HRV to settle it alone. The strength-and-conditioning review’s guidance is that falling HRV can flag overreaching, but in aerobic athletes it may not be sensitive enough on its own and is best used alongside secondary markers. So consult three cheap ones: last night’s sleep duration, your resting heart rate versus its usual value, and how you actually feel. Two or more pointing down: treat the day as amber.
A note for lifters. The same review reports that increasing resistance-training load produces a prolonged reduction in HRV, with suppressed readings and reduced performance still measurable 48 hours after a session, resolving only after a multi-day recovery in some athletes. Recovery time also varies genuinely between individuals. A low reading the morning after heavy squats is your body doing exactly what the literature says it does. That’s amber logic, not red-alert logic, unless it persists.
A worked week (hypothetical). Numbers below are invented to make the method concrete; they are not a case study. Maja, a recreational runner, logs her baseline week: 48, 52, 50, 55, 47, 51, 49. Average 50, range 47–55.
- Monday: HRV 53. Inside range → green. She runs her planned intervals.
- Tuesday: HRV 45. Two below her range floor → amber. Tempo run becomes a shorter, easier tempo.
- Wednesday: HRV 49. Back in range → green. Normal easy run.
- Thursday: HRV 38, after a stressful work deadline and short sleep. Far below range → red. She swaps the hill session for a walk.
- Friday: HRV 46. Slightly below range, but sleep was good and RHR is normal → borderline, secondary markers say fine. She treats it as amber and lifts light.
- Weekend: 50 and 54 → green. Long run goes ahead as planned.
One hard session moved, one shrunk, nothing skipped that didn’t need skipping. That’s the protocol working: small, boring adjustments, made early.
Step 4: Verify it over weeks, not mornings
Single days are noisy; the signal is in the trend. After three or four weeks, look back and ask:
- Is your baseline stable or gently rising as training progresses? That’s consistent with absorbing your load.
- Are red days rare and explainable (a race, a terrible night, illness)?
- Did sessions you adjusted on amber days feel better than forcing them would have?
There’s real evidence this style of training holds up. The Sensors review cites randomized work on HRV-guided endurance training, notably Kiviniemi and colleagues’ 2007 trial, in which runners whose hard days were scheduled by daily HRV improved at least as much as runners following a predefined plan. We won’t quote effect sizes here because we couldn’t verify the full paper’s numbers directly, but the direction of the finding is why this approach is taken seriously in the literature rather than being a wearable-marketing invention.
When to stop trusting the protocol: if your HRV declines week over week despite easier training, or you feel persistently unwell, stop adjusting workouts and talk to a doctor. A trend that won’t recover is a medical question, not a programming question.
When HRV lies to you
This is the section HRV guides tend to skip, and it’s where naive HRV training goes wrong.
Single readings are noise-prone. One number reflects last night’s environment, a disrupted sleep, or a measurement quirk as easily as it reflects recovery. Never make a big decision on one reading.
Alcohol distorts the whole night. In a 2025 study in Nutrients that tracked drinkers with smartwatches, a fixed moderate dose (40 g of alcohol per day for women, 60 g for men, over three days) raised nocturnal resting heart rate significantly, from 63.6 to 66.6 bpm on average (p < 0.001). The authors discuss suppressed vagal activity showing up as reduced HRV, though the study’s measured outcome was heart rate. Practically: the morning after drinking, expect your overnight numbers to look worse, and don’t count that reading toward your baseline.
Illness and life stress move it too. HRV responds to total load on your system. A looming deadline or an incoming cold can drop your reading with zero training involved. The reading isn’t wrong; you really are less ready. But the cause matters for what you do next.
In highly trained endurance athletes, overtraining can hide. As covered in Step 2: studies reviewed in the strength-and-conditioning literature found some overloaded endurance athletes showed no HRV drop, or a paradoxical rise. If you’re a high-volume endurance athlete, a reassuring HRV does not overrule mounting fatigue, falling performance, and rising resting heart rate.
RMSSD has limits. RMSSD mainly tracks parasympathetic activity; the Sensors review notes its capacity to reflect the full autonomic picture, especially when sympathetic activation dominates, is limited. Another reason the borderline rule uses secondary markers instead of treating HRV as an oracle.
Raising your baseline HRV
Different question from the rest of this guide, and a shorter answer than the internet suggests. Three levers have solid evidence behind them:
Sleep 7+ hours. The AASM/SRS consensus statement recommends adults sleep 7 or more hours per night on a regular basis, with shorter sleep linked to impaired performance among many other outcomes. We’ve covered how much sleep recovery actually takes in more depth.
Drink less alcohol. The Nutrients smartwatch study above showed even a fixed moderate dose measurably elevated nocturnal heart rate over three days. Fewer drinking nights means fewer distorted recovery nights.
Manage training load sensibly. The strength-and-conditioning review’s whole premise: load suppresses HRV until it’s absorbed. Progress gradually and respect recovery days, and your baseline gets the chance to climb.
That’s the list. No supplements, no gadgets, no twelve hacks.
Quick answers
What’s a good HRV for my age? Comparing yourself to an age table is the wrong move. One high-authority medical page prints “normal” ranges by decade without citing a source for them, then advises in the same article that you follow your own individual trend instead. Take the second half of that advice. The research framing is baseline-first: at least 7 consecutive days of your own data, then deviation from your normal. Your 7-day average is your “good.”
Is 37 a low HRV? Only your baseline can say. For someone whose normal range is 45–55, a 37 is a red morning. For someone whose baseline is 37, it’s a green Tuesday. Same number, opposite meanings — which is exactly why this guide made you build a baseline before interpreting anything.
One way to run this every morning
Everything above works with a notes app and thirty seconds of arithmetic, and it always will. If you’d rather not do the arithmetic, this is the part where we mention that we built an app for it.
Readiness Coach is our iOS app, and it runs exactly the method in this guide: it reads your overnight HRV, resting heart rate, and sleep from Apple Health, compares each against your personal baseline (never a population chart), and produces one morning readiness score. The weighting is published, not proprietary: 45% recovery, 40% sleep, 15% stress, with a 7-day calibration week to establish your baselines — the same seven mornings you’d collect by hand in Step 1. The full breakdown is in our readiness score explainer, so you can check the math against this article. The core daily score is free, and new accounts get the first week fully unlocked.
If that sounds useful, it’s on the App Store. If not, the protocol above is yours either way.
Readiness Coach is a general-wellness app. Nothing here, in the app or in this article, is medical advice, and neither can diagnose or treat any condition. For persistent unexplained changes in your heart data or how you feel, see a healthcare professional.