Unlock your potential: Understand and utilize training intensity zones

Unlock your potential: Understand and utilize training intensity zones

Key takeaways
This article will examine training intensity zones for you as an endurance athlete. What they are, how to measure them, and how to implement the framework.

Also, unlock your full potential and optimize your workouts with our free training intensity tools. Download our test protocols and zone calculator to accurately measure your functional threshold and define your individual training zones.

Measuring training intensity can seem confusing and unnecessary for non-professional athletes. Still, it is a crucial aspect of your training. Understanding the concepts of training intensity zones helps you optimize your workouts and ultimately improve your performance.

When reading this article, keep in mind that the purpose of endurance training is simple – to discover your functional threshold, improve its level, and the time you can operate at that level.

Though the terminology may seem daunting, the underlying ideas of training intensity are easy to grasp – so let us demystify it!

What is the functional threshold?

Functional threshold refers to the highest intensity you can sustain for a prolonged period, typically one hour. And it is sport-specific.

The functional threshold is often used to measure an individual’s fitness and is a key component of endurance sports training and performance.
Knowing your functional threshold allows you to design a training plan and each session to target specific areas of improvement.
When training to improve the functional threshold, you would typically use higher-intensity interval training, commonly known as threshold training.

Like any other performance metric, the functional threshold change over time and should be reassessed (tested for) periodically to track progress and adjust your training as necessary.

To emphasize its importance, we regularly test for all disciplines and calibrate your individual training zones in all our training programs.

How do I measure training intensity?

Download our free test protocols and zone calculator to accurately measure your functional threshold and define your individual training zones.

Training intensity can be measured in several ways:

Perceived effort – A relative measure that can be used for all sports.
Pace – A speed measure usually used for swimming and running.
Power – A measure mainly for cycling.
Heart rate – Traditionally used with cycling and running.

The best method to measure training intensity will depend on the activity you participate in and your available equipment. Let us continue by exploring each measurement and its pros and cons.

Perceived effort

The perceived effort, also known as the Rate of Perceived Exertion (RPE), is a self-assessed and subjective measure of how hard an individual feels working during physical activity. It is typically measured on a scale of 1 to 10, with 1 being the least and 10 being the maximum effort.

The RPE scale is a simple and accessible tool that can be used to monitor training intensity and progress. Unlike other measures of training intensity, such as heart rate or power output, the perceived effort can be easily assessed without any special equipment. And it can be used in various settings, including at home, in the gym, or outdoors.


The main advantage of RPE is that it is an individualized measure, considering your current fitness level, how you feel that day, and how you respond to different types of exercise.

RPE is a practical measurement when training in different environments, as a heart rate monitor may not work correctly at high altitudes or in extreme temperatures.

Another benefit is that it does not depend on external gadgets, making it very convenient for a beginner without all the gear.


One potential disadvantage of the perceived effort is that your psychological state and external factors like fatigue, hydration, stress, and sleep can influence it. That is why it is important not to rely solely on RPE as the only measure of training intensity. Instead, use it with other metrics such as heart rate, power output, or pace.

Additionally, RPE is a self-reported measure; thus, the accuracy of the results may be affected by your ability to gauge your own exertion level. In some cases, athletes may overestimate or underestimate their own exertion, which can impact the accuracy of the data.


Without getting too technical, the pace is another way to describe the speed in training and racing.

Speed is notated as the distance over time, as in kilometers per hour (km/h) or miles per hour (mi/h).
The pace is the other way around. It refers to time over distance and is usually measured in units such as minutes per mile.

For example, a runner may have a pace of 8 minutes per mile, meaning it takes 8 minutes to run one mile. Or you swim in 2:15 minutes per 100 meters.

Pace zones are typically calculated as a percentage of your personal best performance for a given distance or based on your threshold pace. More on this later.


The foremost benefit of using pace zones is that they can provide a clear, specific, and measurable target for training.

Additionally, pace zones are a useful measure of intensity in sports where heart rate monitoring may be unreliable, such as swimming or running in hot weather.

The pace is also helpful in tracking progress over time by comparing current pacing with previous training sessions or races.


One weakness of pace is that it can be affected by external factors such as terrain, weather, and altitude. For example, suppose you are trail running. Then it is challenging to keep a certain pace due to the topography, making heart rate a better way to keep track of your effort.

Another disadvantage is that it may be affected by equipment, for example, when running on a treadmill. In that case, the pace may be affected by the calibration of the treadmill, making it less reliable as a measure.


The power measurement, as measured by a power meter, is particularly well-established in cycling. It provides a real-time measure of the work being done by you, allowing for precise and accurate measurement of training intensity.

When using a power meter to measure training intensity, you can set specific power-based training zones, much like heart rate or pace zones. These power zones are typically based on a percentage of your functional threshold power (FTP).

1Active recovery, power output lower than 55% FTP
2Endurance, power output between 56-75% FTP
3Tempo, power output between 76-90% FTP
4Threshold, power output between 91-105% FTP
5Interval, power output above 105% FTP
In this table we show a standard set of power-based training zones.


Power meters usually provide additional information such as cadence, pedal stroke, and power distribution which can be used to analyze and improve technique.

Again, the power measurement is most applicable in cycling and other power-based sports, as it is based on the amount of energy (work) you produce.


Power meters are less applicable in other sports, such as running or swimming, as there is no direct measure of power output. However, power meters are now becoming available for running. Still, as of writing this article, they are less common and may not be as accurate as in cycling.

Heart rate

Heart rate is the most common tool to measure training intensity in endurance sports.

The heart rate measurement is based on the principle that as exercise intensity increases, so does heart rate. Therefore, by monitoring heart rate during your training, you ensure you are training at the appropriate intensity to meet specific goals.


Heart rate is relatively easy to measure and can be done with a heart rate monitor or a simple manual pulse check.

Today, all smartwatches can show this variable, which makes it very accessible.

Additionally, it provides a measure of overall cardiovascular fitness and recovery status. In this context, it can give you an insight into how you are responding to training and external stressors.


Unfortunately, heart rate can be affected by several factors, such as stress, hydration, sleep, and medications, which may cause variations in the heart rate measurements. It is also less reliable in some environmental conditions, such as extreme temperatures, altitude, or high humidity.

Furthermore, the measurement is not as precise as the power output in cycling. The heart rate measurement is lagging as it estimates the energy used and is not an exact measure of the work.

We suggest you use more than one way to measure your training intensity. And be aware of possible biases and external factors that may affect the results.

How do I test for my functional threshold?

To understand your functional threshold, you need to conduct so-called threshold tests. Unfortunately, no magical test will define your threshold for all sports. For example, in swimming, you will not be able to get the same pulse as in running or biking. And your power on the bike does not apply to your running.

Therefore, you need to do sports-specific tests. And in all our training programs for triathlon and swimrun, we regularly test for all disciplines and calibrate your individual training zones.

In the table below, you can find the measures we use in each sport.

CyclingHeart rate or power
RunningHeart rate or pace

When you are about to test, it is vital to have a good test routine. And conduct your tests under controlled conditions, preferably with the help of a coach or a friend. Also, use the same equipment and method, and try to mimic the last time testing situation. So that you can repeat your test in a couple of weeks and analyze the result in the context of the earlier tests.

Standard threshold tests

Download our free test protocols and zone calculator to accurately measure your functional threshold and define your individual training zones.

The table below suggests some threshold tests commonly used to define your functional threshold in swimming, cycling, and running.

Swimming3x300m intervals: Swim (and calculate the average pace) 3x300m, completing it as quickly as possible.


1000/1500m time trial: Swim 1000m or 1500m at a steady pace to complete it in the fastest time possible.
Cycling20-minute time trial: Ride as hard as possible for 20 minutes and measure the power output, distance, or average speed.


FTP test: A standardized test that is a multiple of the time of the 20-minute time trial.
Running3/5/10km time trial: Run 3, 5, or 10km at a steady pace, as fast as possible.


VO2max test: A lab-based test that involves running at increasing speeds on a treadmill while measuring oxygen uptake.

When you have your test scores, it is time to consider what intensity you should train at.

How to define my training intensity zones?

The easiest way to define your training zones would be to download our free test protocols and zone calculator at the end of this article.

However, break down your training into five intensity zones once you have discovered your functional threshold. Where zone 1 is effortless and zone 5 is challenging.

ZoneThreshold Heart Rate (THR)
1Less than 85% of THR
285-89% of THR
390% to 94% of THR
495% to 99% of THR
5More than 100% of THR
This table shows the training intensity zones based on heart rate for running.

The overall process of determining your training intensity zones is straightforward:

  1. Prepare mentally and set up your gear.
  2. Conduct the sport-specific test and find out your functional threshold.
  3. Use the functional threshold value and calculate your individual training zones.
  4. Update your sports watch and bike computers with the new training zones.
  5. Follow your training plan.
  6. Repeat in 6 weeks (or so).

How to apply training intensity zones?

By now, there should be no doubt that training intensity zones are a valuable tool for designing and adjusting your training plan. Use them to set appropriate training goals, structure your training sessions, monitor your progress, fine-tune your pacing, and consider individual variations.

Let us look more specifically at how you can use it during the training and racing season.

Training intensity for planning

At the beginning of the training season, you should use the concept of training intensity to design your training plan. Then, in the planning phase, figure out your physical and mental strengths and weaknesses and use your intensity zones to set appropriate training goals.

When planning, keep in mind that each zone corresponds to a specific type of training adaptation, such as improving endurance (zone 2), enhancing your muscular endurance (zone 4), or increasing power output (zone 5).

Also, when you structure and build your workouts, design each session to target a specific zone. All to improve your ability to perform in that particular zone. Mix interval training, steady-state training, or a combination of both.

One thing, though – consistency is key.

Training intensity zones are a tool to help you train effectively. But training is not only about the right intensity of the session but also about consistency in the long run. So, following a well-designed training plan that suits you and gradually increases the workload will be the key to your success.

Training intensity in training and racing

Most people assume that athletes should spend most of their time training in zone 5 – putting in maximal training effort to reap the benefits. However, this is totally incorrect – most endurance athletes should spend little to no time in zone 5, as training at this intensity level for too long would inevitably lead to burnout or injury.

Instead, most (around 70%) of your sessions will be dedicated to zone 2 training. The remainder is divided between zone 3-5, depending on where you are in your season and your race distance.

Zone training for Ironman triathlon training
Allocating your Ironman triathlon training hours in the proper intensity zones is vital. Follow the suggested 70-20-10 distribution.

Another great way to use training intensity is to fine-tune your pacing, especially during races or time trials. By understanding the pace or power corresponding to each zone, you can better control your effort and maintain the optimal intensity throughout the activity without becoming un-functional.

If you are on top of this, you will feel it is like cheating.

Training intensity to monitor progress

Today you can find many wearables that gather data about your daily activities. Garmin, Strava, and TrainingPeaks are great examples of online platforms to track and analyze your training.

So upload data like heart rate, power output, or pace from each training session, and use that information to monitor your progress over time. This will allow you to see how your fitness improves so you can adjust your training plan as needed.

Download our free test tools

Defining your training zones can seem overwhelming, but it doesn’t have to be. To make it easy for you, we’ve created free test protocols and a zone calculator that you can download.

With these tools, you’ll be able to accurately measure your functional threshold and determine your individual training zones.

So, download our free test protocols and zone calculator today and take the first step towards reaching your full potential.

Training intensity tools

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