The Endure EQ by Excel Endurance

The Endure EQ Vol. 023 | How to improve your threshold with heavy domain training

publishedabout 1 month ago
4 min read

Hello Reader,

Welcome back to The Endure EQ.

The next 4 editions of The Endure EQ are going to dive into each of the major aspects of building your endurance engine.

If you missed last weeks volume you might want to head back and read about building your aerobic base.

This will be a helpful starting point before we talk heavy domain training.

How to improve your threshold with heavy domain training

Heavy domain of training

The heavy domain of training marks the start of unstable physiology.

Meaning that the body has to work a lot harder to maintain your forward motion than in the moderate domain.

When we think about training in this domain there are 2 zones that you should be looking to do work in:

  • Zone 3 (Tempo)
  • Zone 4 (Threshold)

These are your moderate-hard and fast sessions accordingly.

The heavy domain is marked by above lactate threshold but bellow critical power or speed.

There are 2 big mistakes we want to avoid with this zone:

  1. Never training in this zone.
  2. Training too much in this zone.

You need work in all the zones in order to build your endurance engine.

But it can be hard to define the limits of these zones.

Once you find them you can tailor your training towards specific race goals.

Why do we need to work in the heavy domain?

Your heavy domain falls around your racing intensity.

Depending on what race you are doing you are going to bounce around this zone while racing. Short course falling near the upper range and long course falling at the lower range.

There are 2 big reasons that we want to train here:

  1. Specific adaptations for racing.
  2. Increasing metabolic fitness.

Both of these are important when considering your overall endurance engine.

Specific racing adaptations

Because this is your ‘racing zone’ you want to get really comfortable doing work here.

The adaptations that we gain raise the power the you can sustain for longer periods of time. This increase your room to train and makes it more comfortable to do work. This domain and racing are also mentally taxing so by doing work here we are build specific mental endurance to sustain this level of effort in your races.

Because the ultimate goal is to be able to race longer and faster.

Increasing metabolic fitness

The gains that we see in this zone all come from changing your metabolic fitness.

Your metabolic fitness is best thought of as your ability to use lactate as a fuel source.

One of the hallmarks of heavy domain training is the presence of lactate in the blood. We want you to be able to both do more work before an increase in lactate and be able to use that lactate as a fuel source. We use the lactate thresholds to define this zone but they are also a good predictor of racing performance.

The better you can use lactate the better your metabolic fitness and the faster you can likely race.

The bottomline for heavy domain work is this:

Improve the metabolic fitness of your muscles and raise the power that you can sustain while racing.

How do you train in the heavy domain?

Here is my simple framework for training in the heavy domain:

Let’s break down each aspect.

Identify the boundaries of heavy domain

As with all specific training you need benchmarks from your fitness testing to know where these zones lie.

Test regularly so that as you increase your metabolic and physical fitness you are still training in the proper zone.

The top of the heavy domain is around your FTP/CP/CS. So, your 20 min power/run test will help guide the threshold ranges.

We can use a percentage of your threshold to estimate tempo zone work.

Accumulate enough time in these zones

When it comes to your overall training prescription you want to get enough time in this zone. There is too much and too little for most athletes.

And this is highly specific.

A good starting point is limiting your heavy and severe domain work to less than 20% of your overall training.

If you’re worried about doing too much in this zone just add more moderate work it will pay off in the long-run.

Anchor tempo and threshold with effort markers

Here is the EE Zones with effort markers:

Helpful to guide your training.

Tempo Training

  • Sustainable efforts for 10-30 mins
  • Focused effort that requires mental work to stay there
  • Around RPE 5-6

Threshold or CP/CS training

  • Fast interval work (5-10 mins in length)
  • When in this zone, above CP/CS you will fade, bellow it you can sustain.
  • Around RPE 7

Limit to 1 stimulus at a time.

With these zones (and the next few we will cover) it’s best to focus your training blocks around one stimulus at time.

The bulk of your training will always be endurance and moderate domain work.

But you will tailor the block with specific intensity work.

You can include some of the other upper zones as maintenance making the primary goal being your block focus.

Workout examples

  • TempoRun:
    • 10 min endurance/warm-up
    • 5 min tempo
    • 5 min endurance
    • Repeat 1-5 times
    • 5 min cool-down
  • TempoBike:
    • 30 min endurance/warm-up
    • 20 min tempo
    • 5 min endurance
    • Repeat 1-4 times
    • 10 min cool down
  • IntervalRun
    • 10 min endurance/warm-up
    • 2 min threshold
    • 2 min endurance
    • Repeat 4-8 times
    • 5 min cool-down
  • IntervalBike
    • 30 min endurance/warm-up
    • 5 min threshold
    • 5 min endurance
    • Repeat 3-6 times
    • 10 min cool down


  • You need work in all the zones in order to build your endurance engine.
  • Heavy domain work aims to improve the metabolic fitness of your muscles and raise the power that you can sustain while racing.
  • Look to add enough work in this zone to develop your engine.

Thank you for being here!

- Chandler

When you’re ready here are 3 ways that Excel Endurance by Chandler Scott can help you:

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