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What is the Aerobic Threshold?

Updated: Apr 2, 2021

The Aerobic Threshold (AeT) is an important ceiling for endurance athletes. It marks the uppermost exercise limit before when energy is dominated by the anaerobic system (glycogen/carbs/sugars).

The aerobic threshold is usually set at the top of Zone 2. It is also referred to as LT1/VT1. LT1/VT1 is the first lactate/ventilatory turn point where lactate rises above baseline levels. Lactate acid is produced as exercise intensity increases and carbohydrate combustion increases. The harder you exercise the more carbohydrate you use to fuel your effort.

The figure below shows where the Aerobic Threshold sits in relation to a 6 zone model.

The AeT sits right at the top of Zone 2. When training at this intensity energy is mainly provided through fat metabolism with smaller contribution coming from carbohydrates. AS intensity of exercise increases so does carbohydrate metabolism shown below. Note this is an example of an athlete after an INSCYD metabolic test. Fat and Carbohyrate metablism is unique and individual, the results presented below may be different for you.

The main benefits to training below AeT and in particular in Zone 2 are:

  • You burn fat

    • You are primarily using Type 1 slow twitch muscles. These fibres mostly fuel themselves with stored fat

  • You build more mitochondria

    • The majority of your muscle energy comes from the mitochondria

    • Devoting time to Zone 2 training will stimulate mitochondria growth and help you become a better fat burner

    • Better fat burning means glycogen sparing

  • You become more metabolically flexible

    • A big base enables you to be switch between fuel sources (fats and carbs) at different intensities

  • Clear lactate faster

    • Lactate is a by product of the breakdown of carbohydrate during exercise

    • It is produced at higher rates as intensity increases

    • Lactate is used as a fuel source in other cells

    • Lactate is cleared out of fast twitch muscle fibres into the slow twitch muscle fibres by a process known as mitochondrial lactate oxidation

    • Once in the slow twitch muscle fibres lactate is re-sued as energy

Building a big aerobic base and training in Zone 2 has many advantages. Over the last number of years the ‘no pain, no gain’ mantra has been popular. If exercise intensity is not hard then you are not training hard enough. It can be common in athletes who may have highly fine tuned top end anaerobic capacities but underdeveloped aerobic capacity/base.

This is known as Aerobic Deficiency Syndrome (ADS), first coined by Dr. Phil Maffatone in the 1980s

But what is ADS?

Don’t be alarmed it is not some life threatening condition. ADS is the result of a poorly functioning aerobic system.

For short events such as 5K, 10K and all the way up to half marathon you run these events close to or at your Anaerobic Threshold. The pace you can hold at your Anaerobic Threshold is key for these events. If you try to push above this threshold you will blow up.

Similarly, if you extend out the duration of your event to 3+ hours (marathon, Ironman or 70.3) then your Aerobic Threshold is critical for performance. For long distance events your Aerobic Threshold is a key determinant of success. If you push above the Aerobic Threshold for these events you run the risk of hitting the wall.

Athletes who have a well developed aerobic system have an aerobic threshold pretty close to their anaerobic threshold, within 10%. It is one of the reasons the elite athletes can put out those super quick times. The figure below gives an example of an athlete with a well developed aerobic threshold. Their aerobic threshold is within 10% of their anaerobic threshold.

An athlete with ADS will have a very different profile shown below.

This athlete may feel fit and strong and be able to push through to high numbers for short durations. But for an event lasting more than 3+ hours the athlete will be forced to slow down, if they spend a lot of time above their Aerobic Threshold.

They most likely fall into the trap of training moderately hard all the time.

The Aerobic Threshold can be trained and improved. Moving the Aerobic Threshold or raising the aerobic ceiling closer to the Anaerobic Threshold should be the goal for every endurance athlete.

This will involve Zone 2 training and avoiding Zone 3 or moderate intensity. Be patient and build your aerobic base, then add intensity.

You will reap the benefits of all the advantages of having a high Aerobic Threshold mention above.

If you would like to determine you AeT and Fat and Carbohydrate combustion rates book for INSCYD test today

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