The One HRV Trend That Actually Matters (Hint: It's Not Today's Score)
Estimated read time: 4.2 minutes (about as long as it takes to decide whether that red HRV score means you should skip your workout, spoiler: probably not🤔)
Hey Performance Nerds! Jonah here. 🤓
Most runners I talk to are using HRV wrong. They see a red score, skip workouts, and three weeks later wonder why race day felt so hard.
Here's what you'll learn today:
The actual physiology of HRV (and why your readiness score misses the point)
The decision table for when HRV matters vs when to ignore it
How I measure and interpret HRV (not what the app tells you)
(Augie has never checked his HRV. He also never skips a workout. Coincidence? Probably not.)
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🔬 What HRV Actually Measures (And What It Doesn't)
Your heart doesn’t beat like a metronome. There’s natural variation between beats, measured in milliseconds.
HRV measures that variation. It reflects how stressed or recovered you are.
Your nervous system runs on two modes:
Parasympathetic: rest, digest, adapt
Sympathetic: stress, fight, train
HRV reflects which system is dominating.
High HRV = lots of variation between beats. Parasympathetic dominant. Usually means relaxed and adaptable.
A sudden spike well above your baseline can reflect rebound or recovery processes, not peak readiness.
Low HRV = less variation between beats. Sympathetic dominant. Something is adding load.
There's no universal "good" number. Elite athletes might sit at 80ms. You might be 35ms. Neither is better.
What matters is YOUR baseline. A stable HRV within your range is good. A trend below or above YOUR normal is the signal worth noticing.
Short-term drops in HRV during hard training are often expected. You’re supposed to be in a stress state when the goal is adaptation.
In one study, runners’ HRV dropped 41% during a 3-week overload, then rebounded 46% during recovery. They got faster.
The key isn’t the drop, it’s the rebound. Suppression that bounces back is adaptation. Suppression that lingers is a signal to adjust.
⚠️ Why Your Watch Gets This Wrong
Watches hide their math. Your "readiness score" blends HRV with sleep, strain, and other inputs.
How they calculate it? The company won't tell you.
In one analysis:
HRV explained ~56% of WHOOP Recovery
HRV explained <5% of Oura Readiness
Same red score. Completely different meaning.
That’s why raw HRV trends beat black-box scores.
🗺️ The Decision Table: When to Listen vs When to Ignore
HRV is most useful at the trend level, not day-to-day. Individual responses vary.
HRV Signal | What It Likely Means | What I Do |
|---|---|---|
Single-day drop | Noise from sleep, stress, alcohol, travel | Ignore. Train as planned. |
HRV normal during hard training | Stress is being absorbed | Continue. This is the goal. |
7–14 day HRV downtrend during hard training | Stress accumulating faster than adaptation | Keep training, reduce intensity for 24–72 hours. |
Low HRV + poor performance + feel terrible | Maladaptation or non-training stress overload | Adjust plan. Deload or reduce intensity. |
Low HRV but I feel good and train well | Algorithm or non-limiting stress | Train. |
HRV rebounds during deload | Recovery systems working | Green light to reload. |
HRV doesn’t tell me what to do. It helps confirm whether the plan is working.
Life Stress Hits Harder Than Training
HRV can't tell where stress comes from. It's a total stress barometer.
In a dataset of about 9 million HRV measurements:
Stressor | Typical HRV Impact |
|---|---|
High-intensity training | Modest suppression |
High alcohol intake | 2-3x larger suppression |
Acute illness | 2-3x larger suppression |
When your HRV is low, the question isn't "should I skip training?"
The question is: "What's adding stress to the system?"
Check sleep quality, alcohol in the past 48 hours, travel, work stress, and signs of illness before blaming yesterday's tempo run.
🔧 How I Actually Use HRV
My philosophy: raw signal over black-box scores. Consistency over complexity.
The Protocol
Parameter | What I Do |
|---|---|
Timing | Morning, immediately on waking |
Position | Sit up, same position every day |
Duration | About 1 minute recording |
Device | Same device always |
App | HRV4Training (shows raw numbers, no black-box scores) |
I measure HRV seated in the morning because it’s more sensitive to training stress. Overnight HRV can look great while adaptation is quietly falling behind.
Inconsistent measurement = useless data.
HRV only becomes useful after several weeks of consistent measurement establish your baseline, from there I look at short trends around that range.
The Daily Check I Run
How do I feel right now? (This is #1. Always.)
How hard was yesterday's session?
What does HRV say relative to my normal range?
Perception leads. HRV confirms.
When all three align, the signal is strong. When they conflict, I trust how I feel over what the app says.
The question: Am I absorbing training stress, or just accumulating it?
What I Pay Attention To
7 day HRV trends relative to my own baseline, not single days
HRV during hard blocks
Hard training + HRV stays normal = I’m absorbing load, continue
Hard training, I feel off, + HRV trending down = stress accumulating, adjust intensity
HRV paired with resting HR
Both moving the same direction = real signal
HRV during deloads
Should rebound. If it doesn’t, something else is driving stress
Mismatch between HRV and how I feel
HRV low + feel great = train
HRV low + feel terrible = investigate and adjust
Life stress confirmed by HRV
Poor sleep, travel, illness, work stress → HRV down → training is not the problem
Life stress confirmed by HRV trends (sick, deadline, travel → feel off → HRV down → adjust)
If HRV says "recovered" but I feel terrible, something's off. If HRV says "stressed" but I feel great, I train.
What I Actively Ignore
One-day drops
HRV race week
HRV that contradicts how I feel and how I'm performing
A quick credit where it’s due: much of how I think about HRV is shaped by the work of Marco Altini.
His app, HRV4Training, is what I use to view raw HRV without black-box scores, and it’s where you can find more detail on the exact morning measurement approach I follow.
🎯 Practical Takeaways
HRV is a stress barometer, not a training commandment
Trends matter. Single days don’t. Look at 7–14 day patterns.
Suppressed HRV during hard training might be expected, not a warning.
Trust yourself over the algorithm. Feeling > app.
Consistency beats precision. Same time, same position, same device.
Hard training + HRV stays normal = I’m absorbing load, continue
Hard training, I feel off, + HRV trending down = stress accumulating, adjust intensity
Bottom line: Use HRV to ask better questions, not to cancel workouts.
✅ 48-Hour Action Checklist
[ ] Stop reacting to single-day HRV changes
[ ] Screenshot your last 7 days of HRV data
[ ] Compare trends to sleep, fueling, and training load
[ ] Decide how HRV will (and won’t) influence your next training block
[ ] If HRV creates more anxiety than clarity, delete the app
💬 One last thing before you go.
After the NFL, I wasn't sure if obsessing over performance science still mattered, until I started helping this community.
Your training goals? They brought that fire back.
So if you're stuck, second-guessing something, or just want to share how training's going, hit reply. I read every message and I'm here to help however I can.
Jonah & Augie
Are You a True Running Nerd? Prove it.. 🧐
Welcome to the prove you’re a nerd section. Each week, I ask a question about a common running science myth.
Answer correctly, and you’ll be entered into a weekly raffle to win a package of Jonah’s favorite supplements.
What’s the primary reason modern PEBA-based foams improve running economy in “super shoes”?
Last Week’s Results: Built for the Long Haul 🧬🏃♂️
Endurance running looks smooth on the surface, but this question revealed how well people understand what’s actually doing the work over 26.2 miles.
The correct answer?
A. Slow-twitch fibers are more fatigue-resistant and energy-efficient, while fast-twitch fibers produce more force but fatigue faster 🧬🏃♂️ ✅
Slow-twitch (Type I) fibers are built for aerobic work. They’re packed with mitochondria, capillaries, and aerobic enzymes, which lets them produce force repeatedly at a lower energy cost. That efficiency is why they dominate at marathon pace.
Fast-twitch (Type II) fibers can generate more force, but they burn through fuel faster and fatigue more quickly, making them less economical for steady endurance running.
That doesn’t mean fast-twitch fibers disappear in long races. As fatigue builds, they’re gradually recruited to help maintain pace, but they do the job at a much higher metabolic cost.
Here’s how the votes shook out:
🟩 A. Slow-twitch fibers are more fatigue-resistant and energy-efficient 🧬🏃♂️ – 242 ✅
⬜️ B. Fast-twitch fibers use more oxygen but generate less force 🫁⬇️ – 9
⬜️ C. Slow-twitch fibers rely mainly on glycogen, while fast-twitch burn fat 🍞🥑 – 5
🟨 D. Fast-twitch fibers are only recruited at sprint speeds 🚫⚡ – 14
Bottom line?
Marathon performance is built on fibers that can produce force cheaply for hours. The better your aerobic training, the longer your slow-twitch fibers carry the load, and the later you’re forced to call in the expensive fast-twitch help.