Endurance training zones – intensity in training

Intensity levels of endurance training

Training intensity and how to measure it can often seem like an obscure concept that can only really be done by professional athletes and sports scientists. Questions such as “what is the lactic threshold” – appear to be unnecessarily complicated and not worth worrying about during your endurance training journey. However, they’re actually far simpler, than their complex names suggest and play a vital role in ensuring that you make the most out of your training plan.

In this article, we’re going to examine training zones in endurance sports. What they are, how you can measure them, and what they mean? We will also take a look at how you can implement your knowledge of them into your training schedule.  

This is the fifth in our series of articles on our training philosophy, check out the others here –

  1. Our philosophy
  2. How to start endurance training – define your baseline
  3. Endurance training and racing – finding your goal
  4. Training volume in endurance sports
  5. Endurance training zones – intensity in endurance racing
  6. Endurance training plan – how to periodize training

Functional threshold

The aim of endurance training is simple – to firstly discover your functional threshold, and then improve both the level of it and the period of time that you can operate at it.

So, what is the functional threshold?

Your functional threshold is the maximum amount of hard exercise that you can sustain over a specific period of time (usually an hour). When Usain Bolt runs a 100m sprint he is operating significantly above his functional threshold, forcing his body to create energy anaerobically, which produces lactic acid, eventually meaning that he has to slow down. 

Sprint times are an excellent example of just how difficult it is to maintain hard exercise for long periods of time – the world record for 400m is 43.03 seconds, while the world record for 100m is 9.58 seconds. If you multiply the 100m time by four you get a value of 38.32, showing that even the best athletes in the world, can’t operate at maximum effort for around 40 seconds. 

To be an endurance athlete you have to be able to exercise for a lot longer than 40 seconds. This means that you should forget any notions of going all out, all the time. Instead, you need to discover your personal functional threshold. the intensity of exercise that you can maintain, without having to stop.

How to measure intensity

Training intensity can be measured in the following ways –

  • Perceived effort – A relative measure that can be used for all sports.
  • Tempo – A measure that is usually used for swimming and running.
  • Power – A measure that is used with cycling.
  • Heart rate – A measure that is traditionally used with cycling and running.

Perceived effort

Perceived effort is often measured by the Borg-scale and can be hard to define. It’s a relative measure that allows you to apply a number between 6-20, to the amount of effort it takes you to do a particular activity. The lowest, which would have a rating of 6 would be something like reading a book. Whilst the highest rating of 20, would be something like the final kick in a sprint race. You really can only maintain that effort for a couple of seconds.

However, there are obviously flaws to this, because our perceptions of how difficult something is can often be incorrect. For example, if you are training with a group, it is easier to get dragged into the “group psychosis” and go with the flow of the group. But, if you don’t have a heart rate monitor, tempo or power meter, then this is your best option.


The tempo is measured via the value of speed over a distance. It can be minutes per kilometer in running, time over 100 meters in swimming or kilometers per hour in cycling. This can be a good way of keeping track of your training, but it doesn’t take into account your form on a specific day. 

Imagine that you usually run a 10k in 45 minutes, which gives you a kilometer pace of 4:30 per kilometer. However, on some days, that tempo will be as tough as your usual time splits over a 3k run. You are not suddenly out of shape, but your body is trying to tell you something. Perhaps you have had a bad night’s sleep, are getting sick, or your mind is somewhere else 

We use tempo to measure swim training zones because it is the most reliable way – heart rate monitors are unreliable in water. We call it your T-pace, meaning the amount of time it takes for you to swim 100 meters.


Measuring power is mostly associated with cycling. Though we are seeing a rise of power meters for running, and power meters for swimming exist, but are rare. Your power is measured in watts. Watts is energy over time, fun fact: 1 horsepower is 735 watts. Power helps you to understand the number of calories that you are burning and by measuring the amount of power you produce; you will also gain an insight into how well your cardiovascular system is functioning.

Your Functional Threshold Power (FTP) is the maximum amount of power that your muscles can produce, while still being able to remove lactic acid from them. Your aim is to train at this level for a long period of time, which will eventually increase your FTP. This will allow you to operate at it for longer.

Heart rate

Heart rate is commonly used to measure your functional threshold for running and cycling. Your aim should be to discover your functional threshold heart rate, which is the maximum heart rate that your body can maintain, while still being able to remove lactic acid from your muscles.

Much like FTP with cycling, you then seek to train at (or below) this level for a long period of time, allowing you to travel at faster speeds over longer periods. Remember, you’re aiming to be an endurance athlete, not Usain Bolt, meaning that your functional threshold will be significantly lower, than your maximum all-out speed.

Using tests zones

To understand where your threshold is, you can do tests. And in our training programs, we regularly do tests in all sports. This is because your functional threshold is specific to each sport. That means that you might have a higher one for running, then you do for cycling. 

We take test values from –

  • Swimming – Time/100 meter
  • Cycling – Heart rate or power
  • Running – Heart rate or tempo

There is no magical test that will define your functional threshold for all sports. In swimming, you will not be able to get the same puls as in running or biking. And your power on the bike does not apply to your running. That is why you need to do sports specific tests. 

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

Endurance training zones

Once we have discovered your functional threshold, we will help you break your training down into 5 zones, in each sport, which is defined according to your functional threshold in that sport. We will examine the zones in more detail in a later article, however, as an example for running –

  • Zone 1 – less than 85% of LHTR
  • Zone 2 – 85-89% of LHTR
  • Zone 3 – 90% to 94% of LTHR
  • Zone 4 – 95% to 99% of LTHR   
  • Zone 5 – more than 100% of LTHR

(LTHR – Lactate Threshold Heart Rate)

Training intensity

Most people assume that athletes spend most of their time training in Zone 5 – putting in maximal training effort and reaping huge benefits from it. However, this is totally incorrect – most people should spend little to no time in zone 5, as training in zone 5 for too long, would inevitably lead to burn out or injury. 

You will train in zone 2 for the majority of your training volume, with most athletes spending up to 80% of their training in zone 2. With the remainder divided between zones 3-5. Zone 5 being around 5 – 15 percent depending on where you’re at in your season and your race distance. 

Training in lower zones will give you an effect over the whole spectrum. Training in zone 2 and zone 3 will push your functional threshold upwards. The work done in the lower zones, will widen your range of those zones, and that will help to push your zone 4 upwards. Remember it’s impossible to train in Zone 5 for very long, meaning that the aim of most training programs is to make your scope to go into zone 5 less.  

When doing your training plan, you need to focus on these numbers. If you are unsure about anything in the top end of the zones. We recommend that you focus on zone 2 and zone 4. That will be the most beneficial.

To conclude, your training zones are individual, and not applicable to others. Therefore, you need to keep track of your own progress. Following other people’s training zones, no matter how good they seem, will never help, because your training zones are individual to you.

Do the right thing

We will help you to discover how intense your endurance training should be, allowing you to train smarter.

Sign up, today, for an individualized plan that will allow you to add structure and purpose to your training program.

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