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The Triathlete Blueprint newsletter #02-Training Zones explained

Updated: Aug 12

Read time: 5min

By Coach Yan Busset

When it comes to training efficiency, it is crucial that we have a clear understanding of the zones we refer to.

Various zone systems exist within different coaching methods, causing confusion and inconsistency.

Let's explore the terminology to bring more clarity to the concept of zones in training.This way, you will get the best out of your sessions.

As an introduction, I want to specify that the goal of this article is to simplify the concept of zones for beginners, rather than being exhaustive on the topic. The main point is to have a clear common ground in athlete <> coach communication. We could have gone down the rabbit hole of the current state of science in terms of metabolic adaptation, glycolytic capacity, or lactate levels, but today we will keep it simple.

Why do we need zones?

The first benefit of setting intensities by zones is to maximize training session efficiency. You can picture the zone system as a mapping of the ways your body can produce energy. We cut your fitness into slices. You can't improve what you can't measure, so zones are here to serve as graduations of your fitness ruler.

What do we measure?

There are different ways to measure effort. One of the most common ways is heart rate (HR). I like to use HR as cross-reference data, but I prefer not to use it to define zones. HR measurement is not so reliable; many factors will affect it, such as fatigue, temperature, and stress. It's also lagging; it's not a real-time picture of your effort but more like a side effect of it. For biking, my preference goes to power (watts) direct measurement. Power meters are increasingly more reliable and affordable.

For swimming and running, we define the pace at threshold and base the zones calculation on that. And last but not least, I encourage my athletes to learn to self-assess pace by feel. It simplifies the process, using the data to increase self-knowledge but not to be enslaved by it.

How do we measure it?

I tend to prefer using field tests rather than lab testing. A lab test can be more precise in some ways but has limits. They are not so practically repeatable and are less affordable. I like to have the athlete perform the test closest to the race or training conditions. For example, performing the test on a track rather than on a treadmill or with your own bike rather than a lab ergometer will give you results that are relevant to your own setup.

I have changed my testing protocols over the years, weighing the pros and cons of each method, but my current go-to tests are:

For swimming, a CSS (swimming threshold) test, which consists of a 200m and 400m all-out test, which is very simple to execute.

On the bike, depending on the goals and level of the athletes:

A 4-minute + 15-minute all-out test or a classic FTP (Functional Threshold Power) 20-minute all-out test, or sometimes a 30-minute test to limit the margin of error.

On the run, a 1K + 4K all-out test (or 800m + 3K test depending on the athlete's level).

At the training squad I created here in Helsinki, we have the chance to collaborate with David Tilbury-Davis as the High-Performance Manager

of the team. We found that testing at both shorter and longer durations was a good way to map the aerobic efficiency of the athlete. In simple words, to define if the athlete is more of a diesel, petrol-head, or balanced type, as this will affect the way they train.

Additionally, I use an aerobic threshold field test (High Z2 limit) based on a nose-breathing (or talking) ramp-up test (with 3-minute increments). I find this method super efficient for pinpointing the moment when the oxygen consumption increases. When nose breathing is not enough or when you need to shorten your sentences, it's a great indicator of the Z2 ceiling. I complete this assessment with a one-hour steady Z2 for validation. It works like a charm, and teaching my athletes to self-assess the Z2 limit by feel greatly increases the efficiency of their training.

The zone system I use:

Zone 1: Active recovery/Awkwardly easy

Zone 2: Endurance/aerobic threshold,talking long sentences/nose breathing limit

Zone 3: Tempo/Grey Zone

Zone 4: Threshold/anaerobic threshold - Can't talk

Zone 5: Above threshold /Anaerobic, VO2max, neuromuscular power, all-out

In Zone 1, you shouldn't feel drained of your energy while training but rather feel energized by it. It's the best zone for active recovery.

In Zone 2, it's not as easy as Zone 1, but you should still feel that you could last hours at this pace. The celling of Z2 is the Ventilatory threshold 1 (aka VT1)

Zone 3 is the tempo or grey zone (because you shouldn't train too much in it). Age groupers tend to go too fast during endurance sessions, shifting from Zone 2 into Zone 3. In contrast, they don't dare to go fast enough on harder intervals, ending up from Zone 4 or above back into Zone 3. Tempo training is effective but demanding on the system. You need to broaden the spectrum of the zones you train at, or you will end up "racing" every training and becoming a "single-speed" athlete with limited progression margin.

Zone 4 is the anaerobic threshold, the red zone where you can't talk anymore. It's close to what we call in cycling power the FTP (Functional Threshold Power). Theoretically, a well-trained athlete should be able to sustain threshold effort for a maximum of one hour. Another way to say it is that your one-hour all-out best effort will be the pace or power at threshold power.

Zone 5 is above threshold. To simplify, we can call it an "all-out" effort, even though the effort output will depend on the duration. But what you have to keep in mind is that it's basically asking you to go as fast or as hard as possible for the given duration. In other systems, you can see divisions of this Zone 5 into 2 or 3 sub-zones (Z5 & 6 or Z5a, b, and c or Z5, 6, 7): VO2max, anaerobic capacity, neuromuscular power.

Another terminology I use, and that you will hear about, is SST or Sweet Spot Training, especially in biking. It's an intensity between Zone 3 and 4 (usually 88-94% of FTP). It's an interval intensity that targets maximal adaptation benefits (duration vs. intensity).

The vocabulary can change from one sport to another. For example, in swimming, I can refer to paces as easy, endurance, tempo, fast. On the run, you can have easy, marathon pace, 10k pace, etc. But the logic is the same; it's dividing the effort or pace into different levels.

It's important to stay as much as possible in the right zone to maximize the effect of the prescribed workout. Keep in mind that zone limits are not sharp switches ON/OFF; they overlap to some extent. So be precise, but don't stress if you are not hitting the zone precisely.

Your goal as an athlete is to become familiar with the different effort feels of each zone, in order to nuance your pace and maximize training adaptation. With the help of tracking instruments like heart rate monitors, GPS, or power meters, you can pace with precision, but you should also be able to get closer to the right intensity by feel. We could call it developing your inner "science of pacing."


-We divide effort intensities into zones to map your fitness and increase training efficiency.

-Field tests are a good method to define thresholds. Prefer pace and power zones rather than heart rate one.

-I use a 5-zones system: Z1 (active recovery), Z2 (endurance), Z3 (tempo), Z4 (threshold), Z5 (VO2max and above).

-.You can perform a nose-breathing (or talking) ramp-up test to define your Z2 effectively.

-As an athlete, learn to self-assess/ feel the zones and not only rely on external devices.

Thank you for reading and see you next week!


Whenever you’re ready, there are 3 ways I can help you:

1. If you are looking for support for your triathlon journey, I recommend you book a 30min 1on1 video consultation with me here.

2. If you are looking for an online coaching service check here.

3. if you are in the Helsinki area and looking for the best training group check here


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