Your Resting Heart Rate Is Talking. Are You Listening?
Flotti's take: that little number your watch records while you sleep is the cheapest, most reliable early warning system in all of sports science.
Let me tell you about my favourite number. It's not your pace. It's not your training load. It's not even your Fitness score. It's your resting heart rate — that quiet little beat your watch measures while you're asleep, before your ego wakes up and starts making bad decisions.
The overnight truth detector
Your resting heart rate (RHR) is measured while you sleep — usually the lowest value your watch records overnight. It strips away stress, caffeine, excitement, and ego. What’s left is a raw signal of how your body is actually doing.
The absolute number matters less than your personal trend. A resting HR of 55 means something very different for a 25-year-old runner than a 50-year-old cyclist. What matters is: is it higher than your normal?
Your "normal" RHR is the average over the last 30 days. A single reading 2-3 beats above normal? Noise. Three or more days trending upward? That's a signal. Pay attention.
What an elevated RHR means
When your resting heart rate rises above your baseline, something is stressing your body. The tricky part: it doesn’t tell you what. It could be:
- Accumulated training fatigue — you’ve been hammering it all week
- Coming down with something — your immune system is fighting before you feel symptoms
- Poor sleep — even one bad night shows up the next morning
- Alcohol — yes, those two beers at dinner are visible in your overnight data
- Life stress — work, travel, emotional load. Your heart doesn’t distinguish between types of stress
Your RHR has been 4 beats above baseline for three days. Fatigue is high, sleep was short on Monday and Tuesday, and you ran hard yesterday. I don't know which one is the culprit — probably all of them. But I know today isn't the day for intervals. Easy or rest.
The 48-hour early warning
Here’s why I love this metric: RHR rises before you feel bad. It’s an early warning system. By the time you feel the heavy legs, the scratchy throat, the “I just can’t be bothered” — your resting heart rate was already telling you two days ago.
I’ve seen it again and again in the data. Athlete pushes through despite elevated RHR. Gets sick three days later. Misses a week. If they’d taken two easy days when the number first spiked, they’d have lost two days instead of seven.
Ignoring an elevated RHR for three days and pushing through costs you more training time than just backing off for a day or two. The maths is simple. The ego makes it complicated.
What about HRV?
Heart rate variability (HRV) gets a lot of hype. It measures the variation between heartbeats — higher is generally better, meaning your nervous system is relaxed and adaptable.
HRV is useful but noisier than RHR. It fluctuates more day to day, it’s harder to establish a reliable baseline, and different watches measure it differently. Some athletes swear by it. Others find it inconsistent.
My take?
Use both if your watch tracks them. But if you only look at one number each morning, make it resting heart rate. It's simpler, more stable, and I've found it more predictive for your training decisions. HRV is the fancy version of the same signal.
| Metric | Stability | Actionability | Watch support |
|---|---|---|---|
| Resting HR | High — steady baseline | High — clear signals | Universal |
| HRV | Medium — noisy day-to-day | Medium — needs context | Varies by device |
How I use it
Every morning when your watch syncs, I check your RHR against your 30-day average. If it’s elevated, I factor that into my recommendations. Not as the only input — I combine it with your training load, sleep data, and recent workout intensity.
But it’s the first thing I look at. Before the training plan. Before the Fitness score. Before anything.
RHR at 47 this morning — right on your baseline. Sleep was 7.5 hours, Fatigue is manageable. Green light. Let's do that tempo session.
Make it a habit: check your RHR before you check your training plan. If the number is up, adjust the plan — not the other way around. The plan serves you, not the other way around.
The quiet metric
RHR won’t impress anyone at the pub. “My resting heart rate was 48 this morning” isn’t a conversation starter. But it might be the most honest feedback loop you have as an athlete.
Your pace can lie (downhill, tailwind, fresh legs). Your perceived effort can lie (adrenaline, caffeine, good music). Your resting heart rate doesn’t lie. It just tells you the truth, every morning, while you sleep.
Listen to it.
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