How slow should your easy runs be?

How slow is an easy run, in numbers?

Easy running stays below your first threshold. That threshold is the point where lactate in your blood starts to climb. Below it, the effort feels steady and you can still talk.

Lab tests show how slow that is. Finnish researchers tested 165 recreational runners on a treadmill. The first threshold came at 65.7% of each runner's top speed in the test on average. That is about two thirds of top speed.^[1] Their heart rate at that speed was already 80.7% of max.^[1] So easy running can feel slow next to your fastest running.

The speed itself changes from runner to runner. Breathing tests on a treadmill found the top of easy at very different speeds in more than 1,000 adults.^[2] The least-trained women reached it at 7.2 km/h on average. That is about 13:25 per mile. The most-trained men reached it at 11.8 km/h, or about 8:11 per mile.^[2]

One pace cannot fit all of those runners. One pace also cannot fit you on every day, as the next sections show. Heart rate can follow you, because it moves with the effort your body is making. Start with your own Easy band.

Why does heat slow your easy pace?

Heat makes the same pace harder. Your heart rate climbs faster on a hot day, and the page on Zone 2 running that feels too slow shows by how much. That higher heart rate reflects a real change in the body.

Lafrenz and colleagues had 10 trained men ride at one steady effort in a 95°F room and in a 72°F room. The men drank to replace their sweat in both rooms.^[3] Between minute 15 and minute 45 in the heat, the most oxygen the men could use fell by 15%. In the cool room it showed no clear drop.^[3] So in the heat the same workload became a bigger share of what their bodies could do.

A review of this research reached the same conclusion. In the heat, the higher heart rate reflects a harder effort for the body.^[4] That is why heart rate makes a good guide on a hot day. Your pace stays the same, and the run gets harder. Slowing down to hold your heart rate keeps the run easy.

Water loss adds to the climb. Montain and Coyle had eight trained cyclists ride for two hours in a warm room four separate times. Each time they drank a different amount. Across the four rides, they lost between 1.1% and 4.2% of their body weight.^[5] Their heart rate rose in step with the water they lost.^[5] Drinking on a long, hot easy run helps limit that climb.

Why does heart rate climb late in a long run?

Heart rate drift is a slow climb in heart rate while your pace stays the same. It starts after about 10 minutes of steady moderate exercise.^[4] The longer the run, the more time drift has to build.

A huge study shows how far it can go. Smyth and colleagues looked at heart rate and speed from 82,303 marathons. On average, heart rate for a given speed was 16% higher from 35 to 40 km than from 5 to 10 km.^[6] The climb first showed up about 25 km into the race.^[6]

Runners drifted by very different amounts. About a third of them drifted only a little, and that group finished faster on average.^[6]

Hold the heart rate on a long easy run and let the pace drop. A slower final half hour at the same heart rate is still an easy run.

What do hills do to your easy pace?

Hills change how much work each step takes. Minetti and colleagues measured 10 runners on a treadmill at many slopes.^[7] Uphill, the energy for each meter rose with the slope. On the steepest slope they tested, it was more than five times the flat value.^[7] Your heart rate climbs with that work, so your pace drops on the way up.

Downhill is where the pace comes back. On a 20% downhill slope, running took about half the energy of flat running.^[7] So the same easy heart rate often comes with a faster pace on the way down.

Steeper is not always easier. On the steepest downhill slope in the study, running took more energy for each meter than flat running.^[7] A very steep descent can raise your heart rate too.

Steep climbs are a good place to walk. On the steepest uphill slope, walking took a little less energy than running.^[7] A walk up a steep hill can keep the whole run easy.

How does the talk test work?

The talk test is a simple easy-run check. Persinger and colleagues found that the point where talking first became hard came almost exactly at the first breathing threshold.^[8]

Comfortable talking can still run a little high. Quinn and Coons had 15 young adults read a passage aloud on a treadmill. While reading still felt comfortable, their heart rate averaged 82% of max.^[9] Their effort rating was about 12 on a scale from 6 to 20. In that study the comfortable-talking point came above the first breathing threshold.^[9]

So the talk test works best as a second check. When your heart rate and your breathing disagree, follow the one that tells you to slow down.

Here is the test on the road. Say a full sentence out loud. If the words come easily and your heart rate is in your Easy band, you are running easy. If talking takes effort, you are at the top of easy or just past it, so slow down a step.

Where is the top of your Easy band drawn?

The top of Easy comes from blood tests on runners. Nuuttila and colleagues found the first threshold at 78.9% of max heart rate for men and 83.6% for women.^[1] Easy ends at 79% of your max for men and 83% for women. When sex is not given, Easy ends at 80%. How Diastra draws your bands covers the breathing-test studies that point the same way.

Say your max is 185. Easy then runs from 111 to 146 beats a minute for a man and from 111 to 153 for a woman.

An average edge still misses some runners. At 80% of max, 57 of every 100 runners in the blood-test study were below their first threshold and 43 were above it.^[1] So your own line could be lower than the top of your band. If the top of Easy feels hard, run slower and let the talk test decide.

How do you run an easy run by heart rate?

1. Start slower than feels right. Heart rate lags behind your legs. It makes about two thirds of a change within about a minute of a change in speed.^[10] Give it a few minutes to settle before you judge the pace.
2. Keep your heart rate under the top of Easy. When it crosses the line, slow down or walk until it settles back into your band.
3. Slow down in the heat. A hot day raises your heart rate at your usual pace, so your easy pace drops with it.
4. Let the pace drop late in a long run. Hold the heart rate as drift sets in.
5. Walk the steep hills. A walk keeps the climb easy.
6. Use the talk test as a second check. A full sentence should come out easily.
7. Judge progress over weeks. One run can be off for many reasons. Compare your pace at the same heart rate on the same route across many runs.

Most of a polarized or a pyramidal week is easy running, and polarized training compares the two. To check where your watch draws its lines, see heart rate zones on Apple Watch.

What Diastra does with easy runs

Diastra draws your Easy band from your own max heart rate. It finds that max in the workouts your Apple Watch saved in Apple Health, in a guided test or in a number you type, and it tells you which one it used. The top of Easy is split by sex. During a run, the watch taps your wrist when you drift out of your band. Diastra credits only the minutes that held in Easy, at whatever pace the day allowed. Over the weeks Diastra shows whether your training is working.