You know your easy runs should be easy. The 80/20 research is clear. But “easy” isn’t a pace. It’s not a heart rate number. It’s a feeling — and that feeling is surprisingly hard to pin down when you’re actually out there running.
Your watch says 9:15 pace. Your heart rate monitor says 142 bpm. Your body says “this is fine.” Are you running easy? Maybe. It depends on a dozen variables that change every single day. The right tool for measuring effort depends on what you’re trying to do, what equipment you have, and how honest you are with yourself.
The Three Tools
Pace: What You’re Doing
Pace tells you how fast you’re moving. That’s it. It doesn’t tell you how hard you’re working.
The same 9:00 pace could be a relaxed cruise on a cool October morning or a suffer-fest in August humidity. It could feel effortless on flat ground and brutal on a hilly route. It could be easy when you’re rested and borderline hard after a bad night’s sleep.
Pace is useful for race-specific workouts where you need to practice running at a specific speed. If your goal marathon pace is 9:30, you need to practice running 9:30. For that, pace is the right metric.
But for easy runs, pace is the wrong tool. It doesn’t adjust for anything — not heat, not wind, not fatigue, not the hill you’re climbing, not the fact that you slept four hours. If you lock onto a pace target for your easy runs, you will inevitably run too hard on bad days and too easy on good days. Neither is ideal.
Heart Rate: What It’s Costing You
Heart rate measures your cardiovascular response to effort. Unlike pace, it reflects what’s happening inside your body, not just how fast your legs are moving.
For easy running, your heart rate should generally stay in the range of 60-75% of your maximum heart rate. This corresponds roughly to “Zone 2” in most training models — the aerobic zone where you’re building your endurance engine without accumulating significant fatigue.
Heart rate is excellent at one specific job: preventing you from running easy days too fast. If you set a heart rate ceiling and stay under it, you can’t accidentally drift into moderate intensity. This is why many coaches use heart rate zones for easy and long runs.
But heart rate has real limitations:
The lag problem. Heart rate takes 15-30 seconds to respond to changes in effort. This makes it nearly useless for interval workouts, where you might be running hard for 60 seconds. By the time your heart rate catches up, the interval is half over.
Daily variability. Your heart rate at the same pace can vary by 5-10 beats per minute depending on factors that have nothing to do with fitness: how well you slept, how hydrated you are, whether you had coffee, ambient temperature, stress levels, where you are in your menstrual cycle, even the time of day. A heart rate of 145 might be easy on Monday and moderate on Thursday — at the exact same pace.
Cardiac drift. During any run longer than about 45 minutes, your heart rate will gradually rise even if you hold a steady pace. Your core temperature increases, blood gets redirected to the skin for cooling, stroke volume drops, and heart rate climbs to compensate. A typical drift is 5-15 beats per minute over an hour. This means your heart rate in the second half of a long run doesn’t mean the same thing as the same heart rate in the first mile.
The max heart rate problem. Heart rate zones are based on your maximum heart rate, and most people don’t know theirs accurately. The old “220 minus your age” formula has a standard deviation of ±10-12 beats per minute. A 40-year-old’s true max heart rate could be anywhere from 168 to 192. If your zones are based on the wrong max, every zone is shifted — and your “easy” ceiling might actually be moderate, or vice versa.
The more accurate formula from Tanaka and colleagues — 208 minus 0.7 times your age — is better, but still has individual variation. The only way to know your true max is a maximal effort test, and most recreational runners haven’t done one.
RPE: What It Feels Like
Rate of Perceived Exertion is the simplest tool: a 1-10 scale of how hard the effort feels.
| RPE | What It Feels Like | Running Context |
|---|---|---|
| 1-2 | Barely moving | Walking, warmup |
| 3-4 | Easy. Full conversation. | Easy runs, long runs |
| 5 | Moderate. Sentences get shorter. | Upper easy / low moderate |
| 6-7 | Hard. A few words at a time. | Tempo, threshold |
| 8-9 | Very hard. Can barely speak. | Intervals, race effort |
| 10 | Maximum. Cannot sustain. | Sprint finish, all-out |
Easy running is RPE 3-4. The defining characteristic: you can talk in full, multi-sentence paragraphs without gasping between words. Not short phrases. Not “yeah… I’m… fine.” Actual conversation. If you’re running alone, you should be able to recite a paragraph out loud or sing a few lines of a song.
RPE’s superpower is that it accounts for everything simultaneously. Heat, fatigue, sleep quality, stress, altitude, hills, wind, caffeine, hydration, how your legs feel from yesterday’s workout — RPE integrates all of it into a single honest signal. Your body is remarkably good at knowing how hard it’s working, even when the external numbers are confusing.
The research supports this. Scherr and colleagues found strong correlations between RPE and physiological markers of intensity: heart rate (r = 0.74) and blood lactate concentration (r = 0.83). Carl Foster’s work on session RPE showed that a single post-workout effort rating captures training load as accurately as more complex heart rate-based methods. Gunnar Borg, who developed the foundational RPE scale, demonstrated decades ago that perceived effort tracks closely with objective measures of physiological stress.
RPE does have one limitation: calibration takes practice. New runners often underrate easy efforts (“that felt too slow to count as exercise”) and overrate hard ones. It takes a couple of weeks of conscious practice to develop an accurate internal scale. But once calibrated, RPE is the most versatile and honest effort tool you have — and it costs nothing.
The Decision Ladder
So which tool should you use? It depends on the workout.
For easy runs: Use the talk test (a practical version of RPE). Can you speak in full sentences? You’re in the right zone. If you can’t, slow down — regardless of what your watch says. If you have a heart rate monitor, a Zone 2 ceiling is a useful secondary check to prevent drift.
For quality sessions: Use pace when the workout calls for a specific speed (race-pace intervals, goal-pace tempo runs). Use RPE when the workout calls for an effort level (threshold feel, “comfortably hard,” hard but controlled).
When they conflict: Trust RPE. If your watch says you’re in Zone 2 but the run feels moderate, your body is probably right — maybe you slept poorly, maybe it’s hotter than your watch accounts for, maybe yesterday’s workout left more fatigue than expected. Slow down. If your pace is “too slow” but the effort feels easy and your breathing is relaxed, you’re fine. The pace isn’t wrong — the conditions just made the same effort cost different today.
This isn’t a feel-good platitude. It’s how the physiology works. Your body integrates hundreds of signals — many of which no watch can measure — into the single feeling of “how hard is this.” When that feeling disagrees with an external number, the external number is the one that’s missing information.
What “Easy” Feels Like (The Real Test)
Forget the numbers for a minute. Here’s what a properly easy run feels like:
- You could maintain this effort for a very long time — maybe not forever, but you’re not counting down the minutes.
- Your breathing is rhythmic and relaxed. You’re not consciously managing it.
- You can talk. Really talk. Tell a story. Explain something complicated. Not just “yeah” between breaths.
- Your legs are working but not straining. There’s no burn, no heaviness, no sense of pushing.
- At the end, you feel like you could do it again. Not exhausted. Not needing the couch. Ready for tomorrow.
And here’s the part that trips people up: this might feel too easy. Especially if you’re used to running every run at moderate effort, a properly easy run can feel like you’re not doing anything. That feeling is normal, and it’s wrong. Your body is adapting at easy effort — building mitochondria, expanding capillary networks, improving fat oxidation, increasing cardiac efficiency. The adaptations just don’t announce themselves with heavy breathing and sore legs.
Why Pacewright Uses RPE
Pacewright calculates your training load as duration (minutes) multiplied by RPE (1-10). A 45-minute easy run at RPE 3 produces a training load of 135. A 45-minute tempo run at RPE 7 produces 315. Same time, very different stress.
This is a deliberate design choice. Duration × RPE works for every runner — with or without a GPS watch, with or without a heart rate monitor, in any conditions. It captures the actual physiological cost of a session in a way that duration alone or distance alone cannot.
When your plan says “easy run,” the target is RPE 3-4. Not a pace. Not a heart rate zone. An effort level that your body determines in real time based on everything it knows about how you feel today. On a cool, rested morning, that might be 9:00 pace. On a hot, tired afternoon, it might be 10:15. Both are the same workout — the same effort, the same training stimulus, the same adaptation — even though the numbers on your watch look different.
Your watch measures what happened. RPE measures what it cost. For easy running, the cost is what matters.