You voted, and heart rate training won. There was so much good research here that I'm splitting it into two parts. This week is about using your data to make daily decisions. Next week, we'll get more specific on training zones and paces based on what you tell me you want to know. Before we get into it, three quick definitions. Heart rate variability, or HRV, measures the tiny variation in time between your heartbeats, a sign of how recovered your nervous system is. Resting heart rate is exactly what it sounds like, your heart rate first thing in the morning before you get up. Well-being score is just a simple daily check-in, how's your sleep, fatigue, soreness, and stress.
ARTICLE BELOW:
The Research
Worth knowing upfront, this is a cycling study, not running. The specific results won't transfer over directly. But the system of thinking behind it applies to any endurance sport.
Researchers ran a 40-day study on 28 experienced cyclists. The first 9 days established each person's own baseline. The remaining 31 days is where it got interesting, participants were split into three groups, and their morning data actually started driving daily training calls. One group used HRV alone. One added a simple well-being check. One added resting heart rate on top of that. Every morning, the numbers decided whether that day was a hard day, an easy day, or a rest day.
What They Found
The research suggests these are the key takeaways
The HRV-only group showed less significant performance improvement across the study
The group combining HRV, well-being, and resting heart rate saw the biggest, most consistent gains, including meaningful jumps in 5-minute power (roughly 311 to 338 watts on average) and 20-minute power (roughly 261 to 285 watts)
Across all three groups, the metrics that improved were shorter, harder efforts, 1-minute, 5-minute, and 20-minute power, along with functional threshold power. These are similar findings to other studies in cyclists and runners where training based on HRV shows enhanced performance.
One number in isolation may not be enough. Combining a few simple daily inputs showed greater improvements in performance metrics
🟡 Promising results, but a small sample and this only applies to cycling performance directly.
Here's exactly how they used the numbers
This is the part I think is most useful, so let me lay it out plainly.
During the 9-day baseline, everyone just tracked their morning HRV (using a watch wearable), resting heart rate (using a watch wearable), and well-being without changing anything. That gave each person their own personal average to compare against going forward, not some generic number that applies to everyone.
From day 10 on, each morning's reading got compared to a rolling reference point, roughly, that person's own recent average minus their normal day-to-day swing. If today's number came in below that line, it counted as a real dip, not just noise.
Here's the actual decision logic:
If HRV came in below the reference line, the day got downgraded from hard to easy
If well-being also came in low that same morning, the day got downgraded again, so an easy day became a full rest day
The group using all three markers ran the same logic, but adjusted HRV mathematically using resting heart rate first, which helped separate a genuine dip from normal day-to-day fluctuation
Two guardrails applied no matter what the numbers said. First, after two hard days in a row, the next day had to be easy, period. Second, no more than roughly 9 training days in a row before a forced rest day.
One important detail. This system only ever downgrades a session. A great morning reading didn't mean go harder than planned, it just meant proceed with the day you already had scheduled. The numbers protect you on bad days, they don't push you on good ones.
What This Means For You
This is something I already do myself. If I wake up feeling less recovered, and my HRV backs that up, that's a day I'll skip a hard run even if it was on the calendar. My nervous system is telling me it's not ready. Sometimes I'll notice my sleep score wasn't great and my resting heart rate is elevated, and I'll ask myself, am I getting sick? Am I not recovered? That's enough to make me adjust before I dig myself into a hole.
Seeing this study validated something I was already doing. And that's really the point here. We are all experiments of one. A single training plan applied to everyone will fit some people and fail others. The best plans change day to day based on the inputs you actually have that day.
This ties directly to the injury research we covered a few weeks ago. A big part of staying healthy is catching the warning signs early instead of pushing through them. This gives you a structured way to do exactly that.
🏆 How To Apply It
Track your resting heart rate and a simple daily well-being check (sleep, fatigue, soreness, stress) alongside HRV if your watch gives you one
Compare today's numbers to your own recent average, not some generic target. What's normal for you is what matters
If your numbers are down from your normal baseline, downgrade the day one notch. A hard day becomes easy. An easy day becomes an easier/shorter easy day, OR a full rest day
This isn't permission to push harder than planned on a good day. It only works in one direction, protecting you on the days your body needs it
Build in guardrails no matter what the numbers say. Don't stack too many hard days in a row, and make sure a true rest day shows up regularly
This isn't about disregarding what your body is telling you and grinding through the old no pain, no gain mindset. We've seen time and time again that approach doesn't hold up. Use your data. Hold yourself accountable to it, not just to the schedule you wrote three weeks ago.
Next week, I'll get more specific on how to actually use heart rate to guide the sessions themselves. Before then, I want to know where you're starting from.
-Keep running happy, healthy, and strong
Spencer
Know a runner who would love some more evidence based feedback. Share the link HERE. and don’t forget to remind them they might have to double opt in :)