What is RPE and why should all runners use it?

Exhausted muscular sportsman pouring water on head after running in sunny day in park

I love a bit of tech and embrace the role it plays in enhancing the precision of running, but I always use the most basic method to measure intensity: rate of perceived effort (RPE).

The simplicity of RPE is its strong point. It’s nothing more than a scale of how hard you feel you’re running. There’s no numbers or algorithms, and it doesn’t need any equipment – just your ability to gauge effort.

It’s also much easier to plan and follow workouts when using RPE and it’s a more effective metric, too. So what’s wrong with going by heart rate?

Heart rate isn’t a good training tool

Your heart rate isn’t an accurate way of gauging intensity. The numbers on your watch aren’t precise – especially if you don’t use a chest strap – and the figures aren’t a direct measure of the work being done.

There’s also many factors that can affect your heart rate, such as fatigue, hydration and caffeine, to give just a few examples.

Another disadvantage of using heart rate to measure intensity is something called “cardiac drift.” This is the upward rise of your heart rate over a workout and is especially noticeable during an interval session.

Example of cardiac drift during an running interval session. The heart rate increases with each interval, but the pace remains stable.
Example of cardiac drift during an interval session (reps 4-6)

If you’re running by heart rate and told to maintain the same range for each interval, the likelihood is that you’ll complete the first one at a faster pace than the rest. This is because your heart rate increases with each effort, so while it seems you’re on target, you don’t realise your workload is actually falling. As a result, the session loses some of its effectiveness.

In my experience, training by heart rate is more problematic than going by feel. By all means use it after the fact in your training analysis, but keep in mind the factors that confound it.

The RPE scale

RPE is nothing more than a gauge of how hard you feel during exercise and is measured on a 1-to-10 scale.

1Sitting downNormalNormal
2-4Easy runComfortableConversational
5-6Moderate runIncreased3-4 sentences
7-8Hard runSomewhat rapid1-2 sentences
8-9Very hard runDeep and rapid5-6 words
9-10Extremely hard runBreathlessOne word

Using the above as reference, a recovery run or jog would score between 3 and 4. A pace you could maintain forever (ultra runner territory) would be about 5, a steady tempo run is 7, while an all-out interval session would peak at 9 or 10.

So why RPE?

RPE is easy to understand and is also a great indicator of how you’re performing, both now and over time.

When you’re fresh and bopping along at 8:30 min/mile it might seem easy. When you’re tired, you may feel like you need to put more effort in to achieve the same pace. A higher RPE is a sign to recognise you’re fatigued and considering backing off.

RPE also allows you to easily monitor your progress. At the start of marathon training, for example, a long run at 9:00 min/mile may feel taxing and you’d rate it 6 or 7 on the RPE scale. After several weeks of training, the same run over the same distance may feel easier, presenting the opportunity to up the pace.

I base all my running and coaching on RPE. If not for the reasons above, but for the fact everything else is largely irrelevant when it comes to race day. As renowned ultra running coach Jason Koop puts it:

“When you are scrambling up a 25 percent grade in a cold thunderstorm at 10,000 feet above sea level, 65 miles into a 100-mile ultramarathon, what heart rate would define lactate threshold pace? What minute-per-mile should a midpack ultrarunner aim for in that scenario?”

Jason Koop – Training Essentials for Ultrarunning

A little tongue-in-cheek, but he makes the case for RPE. It’s the only reliable measurement that accurately captures both a runner’s state and intensity.

Picture of Dan Cross

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