Maximise Your HIIT Sessions With The Latest Scientific Performance Test.

Science to the rescue!

High-Intensity Interval Training (HIIT) can provide you with an incredible bang for your buck in time spent training, but only when it’s performed correctly and to your unique needs. When getting ready to do your HIIT session, the first question that’s probably going to come to mind is ‘what pace (min/km or min/mile) should I run this interval at?’


What pace should you run your HIIT session at?

You’ve maybe went to a club session, and your coach tells you to run this interval at your ‘10k pace’, or your ‘5k pace’. You’re probably doing some mental mathematics as you read this, recalling your fastest 10k or 5k race, and determining what average running pace that you ran it at….Got it yet? Ultimately, what you’re doing here is guessing. You’re guessing what running pace is going to be best for you today based on a race that you did maybe 6 months ago. Can you see the problem yet?


The problem?

1) This information is based on your fitness levels some time ago that are NOT specific to your unique needs today

2) This method has NO physiological justification. The net result? You going out too hard and ‘blowing up’, having to stop the session early. Or going too easy, leading to an ineffective training session wasting your time and your time is precious.  


Should you determine your interval pace by functional speed?

A time-trial effort, no matter how long it may be to determine your ‘functional speed’ is a convenient but entirely arbitrary definition that is devoid of physiological meaning. Don’t get me wrong, if you were to re-test your ‘functional speed’ after a training block (3-4 weeks) and run a pace that was faster than your previous effort, this would be an indication of positive improvement. There is, however, nothing more ‘special’ about 60 minutes of exercise compared to, for example, 65 minutes, 44 minutes, or 23 minutes. To fully customitse your HIIT sessions to your unique needs, you should instead use a scientific performance test. Specifically, the one considered to be the gold-standard by the experts of the world to determine your critical speed (your threshold) [1].


How to use a scientific performance test to fully customise your HIIT sessions.


As you begin to consider scientific performance testing, your mind is likely cast to a high-performance laboratory. For many runners just like you, access to such facilities is likely impossible owing to various logistical and/or financial constraints. You’re, however, in luck! To determine what has been most recently redefined to be the ‘gold standard’ marker of your maximal metabolic steady state by Dr. Andrew Jones (the physiologist behind the Nike 2 hour project and Paula Radcliffe’s success) [1,2]. All you need is a 400m athletics track (or a flat stretch of road) and a GPS watch. Armed with this, you can determine your critical speed (threshold) and D’ (anaerobic capacity) by 3 minutes of all-out running. A test that is not the alternative to the gold standard in the lab, it is the GOLD standard [1,2].

What is critical speed and why should you use it to fully customise your HIIT sessions and more?

Critical speed marks the boundary between two very discrete exercise domains of exercise intensity, specifically your ‘heavy’ (yellow zone) and ‘severe’ (red zone) intensity domain. Translation? For your VO2 max HIIT sessions to be optimal, they need to place you in the ‘severe’ (red zone) intensity domain upon every interval, placing you at the limits of your physiological tolerance. Specifically, increasing the levels of lactate in your blood above your lactate turnpoint 2, driving your oxygen uptake to at or near your VO2max and your heart rate at or near it’s max [3]. This can only be achieved when running for long enough in your ‘severe’ intensity domain, and to do this effectively during your HIIT sessions you need to know your critical speed. A parameter you should aim to improve in view of it’s ability to predict race performance [4].


By testing your critical speed at the end of every training block you can objectively determine if your training plan is helping you run faster, taking the guesswork out. If this has not improved, it’s time to make changes to your training plan. In the words of the great Albert Einstein The definition of insanity is doing the same thing over and over again but expecting different results.’


(1) Jones AM, Burnley M, Black MI, et al. The maximal metabolic steady state: redefining the ‘gold standard’. Physiol Rep 2019;7:e14098.

(2) Craig JC, Vanhatalo A, Burnley M, et al. Critical Power: Possibly the Most Important Fatigue Threshold in Exercise Physiology. Muscle Exerc Physiol 2019;:42–3. 

(3) Åstrand I, Åstrand P-O, Christensen EH, et al. Myohemoglobin as an Oxygen-Store in Man. Acta Physiol Scand 1960;48:454–60. 

(4) Pettitt RW, Jamnick N, Clark IE. 3-Min all-out exercise test for running. Int J Sports Med 2012;33:426–31. 


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