Should Runners Train by Heart Rate or Pace? Why Neither Tells the Whole Story

Part One: Running by Pace

“Okay gentlemen, we have 40 kilometres… 2 hours 16… that is 3:24 kilometres.”

That’s it. That’s the instruction.

If you’d like to find this masterpiece in running coaching, it’s on Instagram and features a group of elite Kenyan marathoners. I would recommend watching rather than trying.

What it will probably teach you, once you pull your jaw from the floor, is that elite marathoners have an incredible ability to pace. Note the target pace is 3:24/km – not 3:25!

In that session, for that group, pace is the only metric that gets a mention. In fact, the only adjustment that is made for any of the group is:

“Young ones, you are going for 25 to 30 kilometres.”

That’s it.

Run this pace. Run this far. And if you’re not yet ready for that at your age, stop.

So… should you be following this?

100% definitely not.

Not only because you’re not able to run that pace, but because the approach to marathon running does not fit the nature of how you are likely to be running a marathon.

For elite Kenyan runners, the brief is clear. Get to the point where you can run that pace for that distance, or there’s not much chance of winning a major marathon. For the rest of us, the approach is far more nuanced.

Can I Still Train by Pace and Adjust for My Ability?

Well, you could. And actually, there are times when you absolutely should.

The problem isn’t pace itself. The problem is assuming that pace always tells us how hard the body is working – and that distinction matters.

Pace Is an Output, Not a Measure of Physiological Cost

Pace tells us what you are doing. It doesn’t directly tell us what it is costing you to do it.

If you run 5:00/km, you are running at 5:00/km. That much is obvious. But the physiological cost of running at 5:00/km can vary considerably depending on the circumstances.

Run it on a cool, flat morning when you’re fresh and it might feel extremely easy. Run it into a strong headwind, on a hilly route, in 28°C heat with high humidity, after six days of training, and it could feel very different indeed.

The pace hasn’t changed, but the physiological cost clearly has. And that cost will escalate as the session develops. You simply cannot pretend that 5:00/km is the same at the start of that run as it is after 20km.

Why Chasing a Target Pace Can Cause Problems

This is where runners can get themselves into trouble by becoming overly attached to the number on the watch.

Imagine you’ve been prescribed an easy run at 5:15 to 5:40/km. You head out and it’s hot and humid. Assuming you take the first kilometre easy (more on that another day!), you then look to move somewhere into the pace band and find what feels “easy”.

Some days that’ll be 5:15, some days it’ll be 5:40. In fact, a good coach will understand that there’s signal in the part of the band where the athlete finds themselves sitting – but not if the athlete prioritises pace over feel.

And if the conditions are particularly challenging, the important thing is to match the intended effort rather than blindly forcing the pace. That might mean running slower.

The number isn’t the objective. The stimulus is.

When Is Pace Most Useful for Runners?

This is where I think the conversation around pace often becomes unnecessarily polarised. Pace isn’t bad. In certain circumstances, it is probably the most valuable metric you have.

During a race-specific block, particularly during key workouts, pace becomes incredibly important because you are trying to prepare for a very specific performance.

If your goal is to run a sub-3 marathon, you need to know what 4:15/km feels like. Not what 4:15/km feels like for the first two kilometres, when you’re fresh, but what it feels like to run kilometre after kilometre.

How that pace feels when you’re having to hold back early on (and if you don’t feel like you are, it’s not marathon pace – sorry!), what it feels like in the middle kilometres when it starts to require focus, and of course what it feels like at 30km when it really starts to challenge you.

Learning Your Marathon Race Pace

A marathon runner with a very specific goal time in mind needs to become intimately familiar with their goal pace.

They need to be able to feel the rhythm of it, hear the sound of it, respect it and trust it.

This is one of the reasons race-specific training exists. You aren’t simply trying to become fitter. You are trying to develop the ability to produce a particular performance under particular conditions.

So in a race-specific block, pace may be the most valuable metric during your key workouts. At that point, challenges from conditions such as heat, humidity and terrain should also be closely matching your key race – so the previous constraints of pace-based training no longer apply.

Should You Train by Pace, Heart Rate or RPE?

Hopefully you’re already starting to see that the question “Should I train by pace or heart rate?” isn’t really the right question. Or, at the very least, it is incomplete.

The better question is:

“What are we trying to achieve today, and which metric best helps us control that?”

Sometimes that will be pace, sometimes it will be heart rate, sometimes it will be RPE.

And often, the best answer is a combination of all three.

Because both RPE and heart rate have their own set of problems, as we’ll find out in Parts 2 and 3.