The value of training to heart rate

Here's something I want you to sit with for a second: your pace is lying to you.

Not always. Not maliciously. But on any given run, the number on your watch is being shaped by about a dozen things that have nothing to do with your fitness. The wind. The heat. Whether you slept well. Whether you ate enough yesterday. Whether the route has more climb than you remembered. Your pace is the output of all of those variables stacked on top of each other — and then you're using it to judge how fit you are.

Heart rate, on the other hand, is just you. It's your body telling you, in real time (well almost, there is a bit of lag but we can get to that!), how hard it's actually working.

That's the whole argument, really. Everything else in this post is just the detail.

Why Pace Lies (And Heart Rate Doesn't)

Cast your mind back to a run that felt genuinely hard — harder than expected for the effort you were putting in. Maybe it was warm. Maybe you'd had a disrupted week. Maybe you were grinding into a headwind for the back half. Your watch will show you a pace that looks slow, and if you're anything like most runners I work with, your brain starts to fill in the narrative: I'm getting worse. I'm losing fitness. Something's wrong.

Nothing is wrong. The conditions changed. Your pace reflected that. Your heart rate, if you'd been watching it, would have told a very different story — probably sitting exactly where it should be, showing you an honest picture of the effort you were putting out.

This is what I love about heart rate training. When you run to a target zone rather than a target pace, all of those external variables stop mattering in the way they used to. Running uphill? You slow down naturally to keep your heart rate in check. Headwind on the way out? Same. Hot July afternoon — and we've written about how heat affects your running specifically — your easy pace might be thirty or forty seconds a mile slower than usual, and that's completely fine, because you're still training at the right intensity.

Even a tailwind is accounted for. You'll run a little faster than usual and your heart rate will tell you if you've strayed too hard. It's honest in both directions.

The Frustration Loop — And How to Break It

There's a pattern I see with runners that heart rate training fixes almost immediately.

Runner has a good session. Uploads the data. Feels great. Runner goes out the next day, conditions are slightly different, runs two seconds per mile slower. Uploads the data. Concludes they're getting worse. Goes out the day after that to prove they're still fit. Runs too hard. Gets tired. Gets frustrated. Repeat.

If any of that sounds familiar, you're not alone. I've had this conversation more times than I can count. The problem isn't the running — it's the measuring stick. Pace is a terrible measuring stick on any individual run, because it's contaminated by everything around it.

Here's the alternative. Your session calls for Zone 2 — let's say a heart rate of 140 to 150. You go out, you come back, your average is 143. Done. Session complete. Tick it off. Yes, you might notice the pace was a bit slower than last week — but that's not the point of the session. The point of the session is to stress a specific physiological system at the right intensity. You did that. Move on.

That shift — from pace to effort as the primary metric — is genuinely one of the most useful things I can help a runner make.

What Heart Rate Training Actually Gives You

Beyond fixing the frustration loop, training to heart rate does a few things that are harder to get any other way.

It makes your sessions specific to you. Everyone's heart works slightly differently. The zones we calculate for you are based on your data, not a generic formula. That matters, because the generic formulas are often wildly off — and we'll go into exactly why in the next post in this series.

It gives you early warning signals. When a runner's easy-pace heart rate starts creeping up over successive sessions, that tells me something before they've even mentioned feeling tired. They might be accumulating fatigue. They might be coming down with something. Heart rate catches it early. Similarly, a failure to get the heart rate up to expected levels on a hard session can be a sign of overtraining — the body protecting itself. Pace alone won't show you that.

It tracks progress in a genuinely useful way. After a few weeks of consistent training, you'll start running faster for the same heart rate. That's real fitness improvement — measurable, unambiguous, and deeply satisfying when you notice it happening.

Where It Gets Complicated (Because I Won't Pretend It's Perfect)

Heart rate training has a few quirks worth knowing before you start, because they catch people out.

The first is cardiac lag — the fact that your heart rate doesn't respond instantly to a change in effort. If you go from walking to sprinting, your heart rate will take 30 to 60 seconds to catch up with what your legs are already doing. On short repetitions of a minute or two, you might not even reach your target zone until the rep is almost over. That's normal. It doesn't mean you haven't worked hard.

The second is high-intensity zones. For Zone 5 — genuinely maximal efforts — heart rate becomes less useful as the primary guide, simply because of that lag. For short, fast reps like kilometre repeats at 10K pace, I'll use heart rate but also using pace to guide us to the right place. The key is making sure effort isn't drifting too far above what 10K should feel like. As the session goes on and the body warms up, the zones align more naturally.

The third is the need for patience — and this one I can't emphasise enough. Heart rate training asks you to trust the process over weeks and months, not days. The runners who bail after a fortnight because the paces feel slow are the same ones who miss the moment — usually around week six or eight — when something quietly clicks and the easy runs start feeling genuinely easy and getting faster. That payoff is real. But you have to earn it.

The fourth is you need accurate data. Look at the spread in this graph. Athletes of the same age with max heart rates varying by 20, 30, even 40 beats per minute. The 220-minus-age formula picks one point in the middle and pretends it applies to everyone. If your actual max is at the high end of that range, the formula will set your zones too low and you'll be under-working every session. If it's at the low end, you'll be training too hard and wondering why you're always tired. Either way, you're not training to your physiology — you're training to a guess. This is why we never use generic calculations to set your zones. The data needs to be yours.

Graph showing the 220-age calculation for a group of athletes

The Commitment It Requires

Here's the honest bit. Heart rate training only works if you actually follow it — not just on the days when the numbers look good.

The most common mistake I see is runners who train to heart rate on their easy days but abandon it the moment things get hard or the pace feels slow. What you end up with is heart rate training on the runs you were going to take easy anyway, and pace-chasing on everything else. That's not the same thing.

The whole point is that the zones shape all of the training, and the sessions are designed to interact with each other.

You'll need a plan to follow. You'll need to trust it. And on the days the pace feels frustratingly slow, you'll need to remind yourself that slow and correct beats fast and wrong every single time.

You might also need a decent heart rate monitor — and we'd always recommend a chest strap over a wrist sensor for accuracy, particularly for intervals and anything above Zone 2. But we'll come to all of that in the next post.

Up Next in Heart Rate Month

This post is about why — why heart rate gives you an honest picture that pace can't. But knowing the why isn't much use without the how.

Next up: Getting Heart Rate Training Right — where we cover how to actually find your zones, the methods that work, the ones that don't, and the mistakes most runners make when they start out.

And at the end of the month, we'll be introducing something in the Full Potential app that makes all of this considerably easier to put into practice. More on that soon.

Thinking about an autumn race? If you want heart rate training built properly into your plan from the start, drop me a line. We'll build a block that gets you to the start line fit, fresh and ready to run your best. Book a coaching package →

#Training #HeartRate #EffortLevels #Garmin #UnderstandingSessions