The Running Series · No.02
Effort, Pace, and Heart Rate
How to Actually Gauge Intensity
Picture a Saturday in late July. It is 82 degrees with the kind of humidity Chicago specializes in, and your plan says eight miles easy at 9:30 pace. You head out and hit 9:30, and by mile five your heart rate is sitting where it usually sits during a tempo run, your breathing has gone ragged, and you finish the run genuinely cooked.
Technically you did the workout as written. You also converted an easy day into a hard one without meaning to, which means the real session you had planned for tomorrow is now compromised before you have even started it.
This is the fundamental issue with training by pace. Pace is an output rather than an input, the end result of your current fitness interacting with heat, humidity, wind, terrain, sleep, stress, hydration, and whatever training you did over the previous few days. When you lock a pace in as your target, every one of those variables quietly gets absorbed as additional effort you never planned for. Effort, on the other hand, is the thing you actually control, and it is what your body is responding to anyway.
The short version
- Pace is an output, not an input. Heat, sleep, and stress all get absorbed into it as effort you never planned for.
- The talk test is the best free tool. Full sentences means easy, short phrases means threshold, a word or two means intervals.
- RPE rates how hard it feels right now, which is exactly why it stays honest on a bad day.
- Treat heart rate as a second opinion. It lags, it drifts, and its zones are often simply wrong.
The talk test
This is the most reliable field tool available to any runner, and it costs nothing. The idea is simply to notice how much you can say while running.
If you can hold full sentences without gasping, you are in the easy or recovery range. If you are down to short phrases of a few words, you are somewhere around threshold. One or two words at a time means you are into interval territory, and if you cannot speak at all, you are working harder than almost any workout should require.
There is a real reason this works rather than it being a rough guess. Speaking requires you to control your exhalation, and that control degrades in a fairly predictable relationship with how much air you need to move. The points where your speech starts breaking down happen to line up closely with the physiological thresholds coaches actually care about, so a very crude test ends up tracking meaningful markers surprisingly well.
A habit worth building is to say a full sentence out loud somewhere in the middle of every easy run. If you cannot manage it, slow down. It takes about five seconds and it protects the rest of your week.
RPE
RPE is a rating from 1 to 10 of how hard the effort feels right now, which is different from how hard it is supposed to feel or how hard the same pace felt last Tuesday.
Easy running sits around 3 to 4, recovery around 2 to 3, threshold around 6 to 7, and intervals around 8 to 9. A 10 would be an all-out sprint, which almost never has a place in marathon training.
The word doing the most work in that description is "now," because RPE is useful precisely because it accounts for everything your body knows about its own current state, including the parts a watch has no access to. On a day when you slept badly or ran hard the day before, a genuine 4 will be slower than it was last week, and that is the system working correctly rather than evidence of a bad run.
Heart rate
Heart rate data is useful, but it also gets misread more often than almost any other metric, so there are a few things worth understanding before you lean on it.
It lags behind you
Heart rate takes something like 30 to 60 seconds to catch up to a change in effort, so during a three-minute interval it will be inaccurate for the first third of every repetition. If you chase a target number at the start of a rep, you will almost always go out too hard.
It drifts on long runs
Your rate climbs over a long run even when pace and effort stay perfectly steady. This is cardiac drift, driven mainly by fluid loss and rising core temperature reducing how much blood your heart moves per beat. A higher number late in a long run is normal and does not mean you faded.
Life moves it around
Heat, humidity, caffeine, poor sleep, illness, and general life stress all affect it, and on a hot day the same effort might sit 10 to 15 beats higher than usual.
Your zones may be wrong
Most zone charts are built from the old formula of 220 minus your age, which carries an error range of roughly 10 to 12 beats in either direction for any given person. If the max is off, every zone underneath it is off as well.
The practical approach is to treat heart rate as a second opinion rather than the final word. When it disagrees with your perceived effort on a particular day, effort should generally win. Where the data genuinely shines is in trends across weeks and months, not in interpreting any single run.
Where pace does belong
Pace earns its keep in race-pace workouts and in the race itself. Once you have a goal and a date, the number matters a great deal, because a race is run against a clock and you need to know what that specific number feels like when your legs are already tired.
Outside of that, pace works better as a record of what happened than as a target you chase. Look at it afterward, and try not to run to it.
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