• Kerry Sutton

Are You Training Too Fast?

It’s a commonly held belief that when you go out running you need to run fast and hard, sweat buckets, and pant like a dog for a session to be ‘worth it’. The reasoning being that training fast brings more rapid improvement. That’s true. But that improvement is limited and plateaus fast.

The trick is to focus first on your aerobic base which can be steadily improved for years. Long easy distance is the name of the game, and hopefully this article will persuade you why.


The Metabolic Pyramid


When we run there’s a point at which the body starts to work harder and lactate begins accumulating in the muscles. This point is called the Aerobic Threshold (AeT).

Lactate is a byproduct generated by the cells when producing energy at higher intensities. Annoyingly, when it builds-up faster than we can remove it, it basically stops our muscles working and causes exhaustion.

Now the finer details are a little more complicated, but we can think about it like this. If we train the regions above AeT we get fast results, but they’re also very limited—ultimately lactate is still accumulating.

Alternatively, if we train the region below AeT (essentially the aerobic system), improvement is slow but virtually infinite—one of the main reasons why ultra-athletes peak so late in life. And what’s more, by expanding our aerobic capacity we stay lactate-less even at faster speeds, meaning that those paces become entirely sustainable (or at least until our legs fall apart…!).

Even for the elites, aerobic training makes up 60-70% of their training. Even 800m runners with their speedy sub-2min races, are doing over 50% of their training here, usually with years of aerobic base building already behind them.

For most of us, we should be looking at much more like 80-100%. Look at it as an opportunity. You have years of base building improvement ready to exploit!


To train the aerobic system you need to be running below AeT. But unless you have a metabolic testing lab handy, that’s not particularly helpful. Below are a few rough guidelines.

The key point is that AeT is relative dependent on your training history and aerobic fitness, so specific time and pace guidelines aren’t remotely useful. Everyone is different.


Here’s an easy formula to estimate you’re AeT (you can read more here: https://philmaffetone.com/180-formula/).

Subtract your age from 180 and then: • -10 for any current major illness/injury recovery or regular medication • -5 for a history of regular illnesses, training regression or if just getting back into it all • +5 if you’re sitting on two or more years of consistent training with visible improvement

Then aim to keep your heart rate under that number.

If you can, get yourself a chest heart rate monitor: in-built watch readings are often inaccurate.


For most people, when you’re running too fast to speak full sentences, AeT is long behind you. So as long as you’re able to hold conversation, or talk out loud to yourself as I like to do (don’t judge me…), then you’re in the right zone. Holding your breath for five seconds is another useful test.


For us non-elites, the ability to breathe through our noses can also correspond well with AeT, though if you’re up there with the professionals it tends not to be so accurate.


Aerobic training can feel VERY slow to begin with—you may even be walking. This is where that saying comes in: ‘Trust the Process!’

It’s easy to look at the training paces of elites and aim for those. But remember that training is relative. To them, 7-minute miles aren’t all that fast—in fact they’re comfortably under AeT. But if we attempted to replicate that we’d be redlining well into lactate territory: a sure recipe for overtraining and injury.

First we need to catch up! So get out there, kill your ego, and start enjoying those long, easy miles.


You can’t go wrong if you keep things simple: 80-90% below AeT, and the rest you can play with. But if you’re interested, there are masses of resources out there on heart rate and optimising your aerobic training.

If I had one recommendation it’s the outstanding book: Training for the Uphill Athlete (Steve House, Scott Johnston & Kílian Jornet).

"You only need to spend a few minutes with Kerry to feel how passionate and dedicated she is to sport and running in particular. Her ultra marathon successes are an inspiration. I’d be happy to recommend her".
Sharron Davis - MBE, Olympic Medalist

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