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Why your perfect 20 minute FTP test is setting imperfect zones

You only have to see the fright on their face, or hear the sharp intake of air, when whispers of an upcoming test reach a rider. Why now? Why me! When a word like 'test' is spoken, 'pass' and 'fail' quickly infiltrate an athlete's psyche.

Performance tests have many forms and guises and, truthfully, we prefer to deploy them in disguise. There are methods to assess progress which can be completed on the fly and behind the scenes.

The benchmark field test for setting zones, the classic 20-minute test, is often difficult to extrapolate from training or racing data, unless the rider is a Time Trial specialist and regularly racing. It is a test most of us have done and recognise... but could the perfect 20-minute effort actually turn out to be more damaging than useful?

Pushing to the limit in FTP test
FTP - Full gas

Setting the scene

By far the most popular zonal system with power (watts) is the seven-zone system developed by Dr Andrew Coogan and Hunter Allen, popularised by their books and it's close alignment with Training Peaks.

The testing protocol they suggest is one that locates a threshold referred to as Functional Threshold Power (FTP) – the average power you can sustain for one hour.

For the purpose of time – and misery – saving, the effort to obtain the threshold is reduced to 20 minutes, with a few caveats and calculations.

As a field test, whilst never directly quoted as such by Coogan and Allen, this threshold is designed to supply a useable marker similar to the Anaerobic Threshold (AnT), which is located by lab-based lactate profiling of an athlete's blood. Both are pivotal in setting accurate and useable training zones to improve and refine fitness.

Anaerobic cheat codes

A one hour effort is predominantly aerobic in nature and whilst anaerobic energy is in use and available, its impact will be minimal. That can't be said for the reduced 20 minute effort, where a stronger anaerobic rider can get a 'head start' on the watts before blowing their anaerobic budget!

This is why the protocol requires an anaerobic effort prior to the 20 minutes: to give a fair reflection of aerobic power and find the point where we start to use glycogen at a higher rate. If the mission is to accurately find this point, corrupting the data it lies within makes little sense.

Living with your results

Imagine a scenario where you set your FTP at 320w after completing a 20 minute test. During the test you thrashed-out 400w for the first four minutes before hanging on to the end, because your strong-suit is anaerobic efforts. In reality, your FTP could be 300w.

A 20w difference. No problem, right? I'll be training harder!

That's not entirely true. You are missing-out on the ability to pin-point when you are training sub-threshold – where you can boost your threshold number from below. The consequences will see you persuading the body to use inefficient fuel sources, limiting your improvements.

This is unnecessarily draining on you and the balance of anaerobic and aerobic work becomes harder to keep track of.

Runaway train

The AnT number is otherwise known as Maximal Lactate Steady State (MLSS), as blood lactate is steady and cleared at the same rate it's generated.

This is a balancing act, whereby blood lactate floats at approximately 4.0mmol/L (AT4) and does not increase given a steady workload. Working at AT4 in a sustained manner is a fundamental training tool for increasing threshold power.

If the threshold is set too high – even 20w too high – lactate will continue to increase and one of two things will happen. We will either unwittingly train the wrong system, or will have to reduce the wattage to allow lactate to clear before pushing it up again. There is much to be gained from this, as it's effectively a set of 'over/under' efforts or 'lactate criss-cross' – but it would be nice to be capable of the planned sustained threshold set.

Measure twice, cut once

Another key concern for finding our number is that we produce our personal best. WHAT?! That's the whole idea?

No, not unless you want every subsequent day - that you might well have tapered for - to be abject misery. A reality where every zone feels uncomfortable and you routinely find yourself cracking mid-way through intervals.

The fix is to be realistic and assess the increase, or decrease. Set your zones half-way between the pre-test number and the new mark. Then, in a few weeks, carry-out another test to confirm the results.

The worst outcome will see you training well within your true zones and able to complete efforts with relative ease. You ARE allowed to add extra intervals if you feel you have more in the tank!

Save your best for Sundays

Having outlined why taking your all-time best 20 minute power and using it to set training zones is not the best idea... there is a place for the metric.

Your 20 minute peak power still provides an important performance marker and one you can use for assessing your progress year-to-year and, dare I say, as a comparison to your competitors!

But, when they ask, tell those competitors the lower number. Save a surprise for the road...

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