Zone 3 – Tempo or moderate aerobic effort

First off what is it – This is an effort where it starts to feel and be a little more uncomfortable. An effort that you could hold for roughly a half marathon in duration. They tend to build lactate acid at a higher rate of zone 2 but not as high as zone 4 sessions therefore you can have slightly longer intervals and recovery pretty quickly from them. So dial into what the effort is, they aren’t threshold efforts that are really challenging but a way of building a higher lactate tolerance

How do we measure it

RPE – 6-7 – Uncomfortably comfortable eg half marathon feel

% THR Bike – 84-94

% FTP Bike – 76-90

% THR Run – 90-94

Why has Zone 3 got a bad name or referred to as the grey zone

Zone 3 is often called the grey zone and stated not to train in it as it can detrimental to the progress fitness. The simple fact is over a number of years athletes have been training the majority of there sessions at too higher intensity (zone 3) not really knowing or not trusting that actually the effort is lower for light aerobic and long term fitness. Knowing when to use this session or intensity can be a huge benefit

Using this zone as the main frame of training is training the wrong fuelling system and builds up fatigue/lactate acid much quicker than zone 2 effort, therefore leaving an athlete not feeling great over long periods of time

How do we use this training zone

Knowing how to use this zone has huge benefit. We use it in events very often so why wouldn’t we train it

these efforts are generally longer reps in all phases of training but become a little more frequent or longer in duration in a certain session as you progress through the phases


PREP Phase 2-4 intervals of  6-10 mins with 3 mins recovery

BUILD Phase 3-5 intervals of 6-10 mins or 2-3intervals of 10-15 mins with 3 mins recovery

SHARPENING Phase 4-6 intervals of 6-10 mins or 3-5 intervals of 10-15 with 3 mins recovery


Key Points

Zone 3 is a great way to work with slightly higher levels of lactate acid without and being able to recover/flush it out quicker

It activates higher levels of muscle fibres

We start to burn more carb as fuel rather than fat, so we don’t want it to be the main part of your training

Your doing endurance sports that most of us are last well over an hour, this is a great way to learn about pacing or a cruise speed that works in events that are around half marathon/half IM distance







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