The Aerobic Threshold and the importance of zone 2 training

The Aerobic Threshold and the importance of zone 2 training

Why is the Aerobic Threshold important?

The aerobic threshold (LT1) is important for endurance athletes because it informs us about your ability to use fats for fuel, and indicates your endurance ability.

A higher aerobic threshold then also means that we will be able to sustain a higher wattage band for many hours (5h).

And this brings me, quiet naturally to the fact, that shifting your threshold upwards makes a lot of sense because long endurance event, such as Ironman, marathon, ultra trail and long distance gravel races will be accomplished just below or at the aerobic threshold. Therefore, improving your first threshold allows you to improve your average poweroutput/pace in these events.

That being said, even endurance events over shorter distances do benefit from a well developed aerobic threshold.

A higher first threshold on the bike for triathletes means that more muscle glycogen can be protected, a key for faster runs in triathlons for example. Your ability to generate power at the end of a long race is important and it depends on your fuel economy. Our most powerful muscle fibre require glycogen to contract.

Furthermore, your ability to oxidise fats efficiently for fuel effects the deflection point of LT2, the anaerobic threshold. This is because a strong aerobic energy development, the ability to use fats, reduces your lactate building rate for a given power output. And so it does make a lot of sense to develop your aerobic threshold (LT1) since it raises your anaerobic threshold (LT2, FTP), too.


This is the reason why endurance athletes devote a lot of their training time to developing or maintaining the aerobic threshold during the pre-season (base) with zone 2 training.

What is Aerobic Threshold Training aka zone 2 training?

Zone 2 is your ‘all day’ pace, an intensity that can generally speaking be sustained for a very long time. It’s ‘easy training’ which means a comfortable, conversational pace.

There are many different ways to determine aerobic threshold or also called LT1, for example via lactate testing – see Hellemans, or best average time trial average heart rate and/or power – see Friel.

And then there is also a fairly easy and effective method to do this, namely to apply subjective perception.

For example: resume an easy pace and slowly increase the intensity of your exercises. Now, you need to pay attention by noting the heart rate where you notice the first deepening of your breath. And that will help to determine aerobic threshold more or less.

This deepening of your breath is caused by your body increasing its demand for oxygen to metabolize (mitochondria) an increase in blood lactate.

The point of deepening is the bottom range of your aerobic zone. The top of your aerobic zone can be estimated by simply adding 10-15 beats per minute to the bottom figure. I’ve done a lot of testing over the years and this method seems to work just fine for Ironman training or Marathon training.