The What, Why and How of the Anaerobic Threshold

As runners become more invested in their own running and are looking for ways to enhance their running performance, the term “threshold” training will often come up. Many people may know this term and are aware of its perceived importance, however the specifics often get lost in translation. By the end of this blog, we hope you have an understanding as to what your anaerobic threshold is, how you can measure it and how you can use it to effectively train towards your next PB!


What is the Anaerobic Threshold?


Firstly, to understand our threshold (AT), we need to understand how the body uses energy when we run. Aerobic energy is simply energy that is derived from oxygen (O2). When we run, our body is breathing in O2 from the environment and taking it to working muscles via the lungs and bloodstream. The muscles then use this O2 for energy and put out carbon dioxide (CO2) as a waste product that we can then breath out. This is a very sustainable activity as there is plenty of O2 to breath in and the body has an effective method of expelling the CO2. As our exercise intensity, and subsequent demand for energy, increases, the body will continue this cycle of breathing in O2 and breathing out CO2. If we keep increasing our exercise intensity (running faster) then eventually there is a point when the body can no longer supply the energy required through O2 alone. This is where the anaerobic energy system comes in. As your O2 demand approaches its maximum capacity, the body will begin to supply energy through anaerobic sources (the details of which are beyond the scope of this blog). The advantage of anaerobic energy is that it can be supplied to the body extremely quickly, essentially topping up the energy demand that cannot be supplied by O2. The disadvantage is that the waste product of anaerobic energy, hydrogen ions (H+), cannot be dispelled as easily as CO2 (the waste product of aerobic energy).  When we use anaerobic energy, lactic acid is the initial waste product that immediately breaks down into lactate and H+. The H+ are our primary concern as when they accumulate, they create an acidic (low pH) environment in both the working muscles and the bloodstream. When the pH drops significantly, muscle function is impaired and performance is compromised. Anyone who has tried to run near their best pace for more than 30s will know the feeling! Now, without getting too complicated, a key point to understand is that to clear the H+, we need to combine them with O2. But remember we are already using all our O2 to fuel our aerobic energy. So until we reduce the intensity of our run to a point at which there is now O2 to spare, we will continue accumulating H+ and our pace will not be sustainable.


Our AT can now be defined as the point at which H+ are being produced in the muscle at the same rate at which they were being cleared into the blood. If we begin accumulating H+, we are above our anaerobic threshold.


Understanding where our threshold training sits in relation to our other aerobic zones in crucial to making sustainable improvements to your running performance

Why Should We Improve Our Anaerobic Threshold?

For runners of all levels, improving their AT is a significant predictor to distance running performance. For runners targeting distance events (>3000m) almost all of the gains in performance will derive from improving the capacity or efficiency of the aerobic system. To justify this, we must remember the proportions at which each energy system contributes to our running. If we run at our best pace for 45s, we derive ~50% of the energy from both aerobic and anaerobic sources. Going up to 2min sees us use 65% aerobic/35% anaerobic and 4min will see us use 80% aerobic/20% anaerobic. So with the time it takes to run events of 5km, 10km, 21km or 42km, our primary concerns for increasing performance lies with our aerobic system. Remember our AT is the point at which we go from being sustainable with our aerobic energy demands, to unsustainable. So if we can raise our AT (run at a faster pace for the same H+ production) our aerobic performance ceiling is increased and our distance running performance can improve significantly.

 Measuring our Anaerobic Threshold

Now we know what is the AT is, we need to be aware at which running intensity the AT occurs. The gold standard for AT testing is a lactate threshold test. This test is typically performed on a treadmill and involves gradually increasing your running pace to find the point at which the AT occurs. Whilst the H+ are the measure of the AT, they are very difficult to measure in the muscle. So a far more effective method is to measure the concurrent level of lactate in the blood. Most runners will find their AT correlates very closely with a measure of 4mMol of lactate in their blood. A graduated treadmill test that measures blood lactate can then identify the pace and heart rate (HR) that leads to this 4mMol blood lactate measure. Find out more HERE


Whilst we have the ability to run over or above our AT, the resultant increase in anaerobic demand often leads to an increased recovery time for a reduced aerobic benefit from the session

 Estimates can also be made of your AT through a practical running session. At Front Runner Sports, we will often perform what’s known as a Critical Velocity (Vcr) test to assist runners in finding their AT. Due to the accumulation of H+, we know it is impossible to run at a pace exceeding your AT for >30min. So running at your best effort for 30min with the aim to cover the maximum possible distance in this time, will give an accurate estimate of your AT. The resulting average pace and/or HR that you sustained for this 30min is known as your Vcr. If a runner has put in their best effort over 30min, we expect a small amount of H+ accumulation at the end of the run. So to derive your AT pace from the Vcr testing, we recommend taking 97% of the pace you were able to run for the 30min. For example if your Vcr pace = 5min/km = 12km/h, then your AT = 12 x 0.97 = 11.64km/h = 5.09min/km

Training at Your Anaerobic Threshold

 Once you have a pace or HR that correlates with your AT, we can set about training to improve it! We know that the most effective way to improve our AT is to train on or slightly beneath our AT, not above it. As the body does not like an acidic environment, regularly going close to the point of H+ accumulation (but not over it) gives the body the stimulus it needs to enhance the aerobic capacity within the muscles (again, the specifics of which are beyond the scope of this blog) to improve the capacity at which O2 can be used as a fuel source.

How long you can spend at your AT is a reflection of your current conditioning to AT training as well as your muscular endurance. However, most regular runners should find that in training, they should be able to run for ~20min (either continuous or in long intervals) at their AT when working reasonably hard. To continue to improve your AT, we need to gradually increase the amount of time we spend running at your AT. This could be achieved by having less recovery between AT intervals or spending more time at your AT. But importantly, you should not run quicker than your AT, as we lose the aerobic stimulus required to get maximum aerobic adaptation.

As you become more competent, some runners can aim to spend up to 30min at their AT. If you can achieve this, then it would be recommend to re-test your AT to quantify the improvement you have seen. Some example sessions can be seen below:

Recreational Runner

  • 3 x 7min @ AT with 3min of walk/light jog recovery (R)
  • 2 x 10min @ AT with 3min walk/light jog R
  • 1 x 15min @ AT

 Serious Recreational Runner

  • 3 x 8min @ AT with 90s easy jog R
  • 2 x 12min @ AT with 2min easy jog R
  • 1 x 20min @ AT

 Advanced Runner

  • 3 x 10min @ AT with 90s steady jog R
  • 2 x 15min @ AT with 2min steady jog R
  • 1 x 25min @ AT

Finding a consistent and uninterrupted section of running trail is perfect for AT training

 The 3 principles of progressive overload can be applied to threshold training to improve the aerobic stimulus the session will provide:

Firstly, make the run more continuous. E.g. Instead of running 3 x 8min @ AT, run 2 x 12min @ AT. Both will stimulate the body for 24min at your AT, but a more consistent application of the training stress will make the run more difficult.

  • Secondly, a more active and shorter recovery. Typically threshold intervals should be separated by 90s – 3min of active recovery, depending on your current level of conditioning to the training. If you find you need more recovery, you will likely be exceeding your AT pace. As you train more regularly at your AT, you will find your time to recover and feel comfortable again will reduce. So initially take less time (e.g. from 3min to 2min to 90s) then try to make the recovery more active (e.g. from a walk to a light jog, to a steady jog).
  • Lastly, increase the time period you spend at your AT. If you can aim to get up to 25-30min of running at your AT, you will see a nice improvement in your AT pace when you re-test.

We trust you now have a greater understanding as to what the AT is and how you can use this knowledge to improve your running. If you wish to know more about this topic, or anything to do with your running training, please get in touch with our expert coaching team who are ready to assist you towards your next running goal! Please email or see our website.

Running Regards,

Front Runner Coaching Team





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