You know your numbers. You know your FTP, your threshold heart rate, exactly where your zone 2 ceiling sits on the bike. You have probably spent years defending that ceiling against every group ride that tried to drag you over it.
Then you start running, and you do the obvious thing: you strap on the heart rate monitor, set the same zones, and go. Ten minutes in, your heart rate is 15 beats over your cycling zone 2 ceiling and you are barely jogging. So you slow down. Then you slow down again. Eventually you are shuffling along at a pace that feels like nothing, staring at a number that still says tempo.
Here is what nobody tells you when you take up running as a cyclist: your heart rate zones do not transfer between sports. Not approximately, not with a quick mental adjustment on the fly. The physiology of running produces genuinely different heart rate behaviour, and if you port your cycling zones across, you will either run your easy runs too slow to be useful or convince yourself that easy running is impossible. Same engine, same athlete, different numbers.
The good news: this is completely fixable, and fixing it takes one field test and a bit of honesty about effort.
Why your heart rate runs higher on the run
At any given perceived effort, heart rate during running sits roughly 5 to 15 beats per minute higher than during cycling. That is not a fitness problem or a sign you are "bad at running." It is three pieces of physiology stacking on top of each other.
More muscle mass is working. On the bike, the work is concentrated in your legs, and even there the recruitment is limited to a fairly narrow pattern around the pedal stroke. Running recruits the full chain — glutes, hamstrings, calves and feet doing things cycling never asks of them, plus your trunk stabilising every stride and your arms driving the rhythm. More working muscle means more oxygen demand, which means more cardiac output, which means a higher heart rate at the same subjective effort.
Running is weight-bearing. On the bike, the saddle carries most of your body weight and the frame carries the rest. On a run, you carry all of it, and you lift it — every stride launches your entire mass airborne and absorbs the landing. That vertical work is metabolically expensive in a way that simply does not exist on a bicycle.
Oxygen uptake kinetics are faster. When you start running, your oxygen consumption climbs to meet the demand more quickly than it does on the bike. The cardiovascular response arrives sooner and settles higher. This is one reason a run feels "on" from the first minutes in a way an easy spin never does.
Stack those together and the result is predictable: the heart rate that means genuine zone 2 on your bike means something slower than zone 2 on a run — and the run heart rate that feels like zone 2 would read as tempo by your cycling numbers.
The 10bpm rule is a starting point, not a law
You will find a tidy rule all over triathlon forums: your running threshold heart rate is about 10bpm higher than your cycling threshold, so add 10 to your bike zones and away you go.
As a first estimate, fine. As a law, no.
The actual gap between your cycling and running heart rates depends on your individual physiology and — this is the part that catches cyclists — your training status in each sport. A well-trained cyclist who has barely run since school is exactly the person for whom the rule breaks down most. Years of riding have built a cardiovascular engine that is enormous relative to your running-specific durability, and your running economy is poor, so the heart rate cost of even slow running is inflated. Some riders see a 5-beat gap. Some see 20. The same rider can see the gap shrink over months as their running economy improves and the metabolic cost of each stride comes down.
So use 10bpm the way you would use a mate's guess at your FTP: a place to start, not a number to defend. Seed your running zones with it if you like, then confirm against the two tools that actually settle the question — a field test and your own perception of effort.
RPE is the common currency
Stephen Seiler, the sports scientist behind the 80/20 framing that most of us build our training around, has made this point for years: elite endurance athletes across sports regulate intensity primarily by feel, with the devices as a check rather than a master. And feel is the one measure that travels between cycling and running without conversion.
Zone 2 is zone 2 in both sports when you define it by perception:
- Roughly 3-4 out of 10 effort.
- Fully conversational — complete sentences, not gasped fragments.
- Nasal breathing just about possible, if not exactly comfortable.
If you can hold a proper conversation while running, you are in the right place, whatever the strap says. If you can only manage short phrases, you have drifted into tempo, whatever the strap says. The talk test is crude, unglamorous, and more reliable across sports than any borrowed heart rate number.
We covered how RPE, power and heart rate interact on the bike in the RPE and power guide, and the same hierarchy applies here — with one substitution. On the bike, power is your objective anchor. On the run, pace plays that role, with the caveat that hills, heat and wind corrupt pace far more than they corrupt power. Heart rate, in both sports, is the lagging, context-dependent signal: useful for confirming trends, poor at dictating the next five minutes.
Cardiac drift: why your heart rate lies to you late in a run
There is a second reason to be suspicious of heart rate as your primary running control, and it gets worse the longer you go.
Hold a genuinely constant effort — same pace, flat road, steady conditions — and your heart rate will still climb 10 to 20 beats over 30 to 60 minutes. This is cardiac drift. As you warm up and sweat, plasma volume drops, so each heartbeat pumps slightly less blood, so the heart beats faster to maintain the same output. Add heat and dehydration and the drift steepens. Nothing about your effort has changed. The number has.
Drift happens on the bike too, but running amplifies it — more heat production per minute, more of your body working, often less airflow than you get at 30kph on a bike. The practical consequence: if you run to a hard heart rate ceiling, drift will force you to slow down continuously through the back half of a run, until you are moving too slowly to get the stimulus you came for. The effort that started as zone 2 is still zone 2 at minute 50, even though the number on your wrist has crept 15 beats higher.
The fix is the same one experienced runners use: set your effort by pace and RPE in the first 15 minutes, when heart rate is trustworthy, then hold that effort and let heart rate do what it does. Review the number afterwards, don't chase it in the moment.
How to set your running zones properly
Enough theory. Here is the practical setup, in the order I would do it.
Weeks 1-4: run entirely by feel. If you are new to running, your first weeks are about tendons and bones, not calibration — the first 5K plan covers that progression. Run at a conversational effort, walk when the conversation gets hard, and ignore heart rate completely except as data to look at afterwards. A field test in week one of running would only injure you and tell you about a body that will not exist in two months.
Once you can run 30-40 minutes continuously: do a field test. The classic protocol is the 30-minute solo time trial. After a thorough warm-up, run 30 minutes at the hardest effort you can sustain evenly — no sprint finish, no fade. Your average heart rate for the final 20 minutes is a solid estimate of your running threshold heart rate (LTHR). Do it alone, because company drags you into a race, and on a flat, uninterrupted route.
Build your running zones from that number. Using the standard five-zone model, zone 2 sits at roughly 85-89% of running LTHR — the same percentages you would use on the bike, applied to the running-specific anchor. The percentages transfer between sports. The anchor does not. If you want the full walkthrough of how zone 2 is derived and why the definitions vary, the zone 2 heart rate explainer and the heart rate vs power vs RPE guide cover it for the bike; the logic is identical on the run.
Re-test every 8-12 weeks. Your running economy will improve fast in the first months — cyclists bring a big engine to a new chassis, and the chassis adapts. As it does, the pace at every heart rate improves, and the gap between your cycling and running zones can narrow. The zones you set in month one are not the zones of month six.
The mistakes that make easy runs too hard
Three errors show up over and over when cyclists add running, and they all come from trusting the wrong number.
Running to cycling zones. Covered above, but worth repeating because it cuts both ways. Cap your runs at your bike zone 2 ceiling and you will train slower than your true easy range. Judge your runs by bike numbers and conclude "I can't run easy" and you will either give up or decide zones don't apply to running. They apply. They are just different zones.
Racing the pace instead of holding the effort. Cyclists are competitive, and pace is right there on the watch. But your zone 2 running pace as a new runner is genuinely slow — often slower than feels dignified, sometimes including walking on hills. Iñigo San Millán, who built zone 2 protocols for Tadej Pogačar, makes the same point about the bike: the athletes who benefit most are the ones willing to go slow enough. On the run, "slow enough" is slower than you think.
Treating drift as a signal to slow down. If your heart rate has crept 12 beats over an hour at steady effort in warm weather, that is cardiac drift, not a fitness collapse and not a reason to walk. Check your breathing and your ability to talk. If they still say easy, it is still easy.
Two sports, one engine, two sets of numbers
The engine you built on the bike transfers to running better than almost any other sport — we covered how much of the fitness carries across in the fitness transfer piece. What does not transfer is the calibration. Heart rate is a readout of the whole system under a specific mechanical load, and running is a different mechanical load.
So: separate zones per sport, set from a sport-specific field test. RPE as the currency between them — conversational, 3-4 out of 10, in both. Pace and power as the objective anchors in their respective sports. Heart rate as the auditor that reviews the books afterwards, not the manager that runs the day.
Get that hierarchy right and your easy runs finally become what they are supposed to be: easy, repeatable, and the foundation for everything else. Slot them into your week alongside the riding using the weekly schedule guide, and if you want your run fuelling sorted before your long runs stretch past the hour, the fuelling differences piece is the companion read.
And if you want a second set of eyes on your zones — bike or run — the Roadman community on Skool is where those conversations happen every week.