PACE VS POWER - RUNNING Z4 | 80/20 Endurance

# PACE VS POWER – RUNNING Z4

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• #15891
MatCat
Participant

I noticed Pace Zone4 is 102%-115% of Threshold Pace, while Power Zone4 is 103%-120% of rFTP.

Now, Threshold pace should be pretty much = FTP, so why this % difference?

5% is quite a lot

#15901

Hi MatCat.

The relationship between true physiological intensity and the fact that HR, Pace and Power are distinct intensity metrics, means that the percentages for each zones are slightly different.

Your Threshold pace, and rFTP are actually a measure of your Lactate threshold – so threshold pace is not going to be exactly the same as your rFTP % wise. Power is the most reliable measure of your LT as it is not impacted by external factors such as weather, terrain and excitability the way HR and Pace are.
Hope that was a helpful explanation.

#15909
David Warden
Keymaster

Mattia, thanks for using our plans. This is just the nature of the difference between Pace, Power and HR. Note that HR is only 102-105% of LTHR. FTP, Threshold Pace, and LTHR are simply vastly different ways to measure intensity and the zone %s just won’t line up. Sort of like using C and F to measure temperature. Why is room temperature 33% of boiling point when using F, but just 20% of boiling point when using C (and room temperature of 79% boiling point when using Kelvin!)? Both are the exact same temperature, but you can’t compare the % each lands on a different scale. Regarding running at 115% of rFTP for your zone 4 intervals and getting killed, consider running at just 105% instead which is just as valid a Zone 4 interval as 115%.

David

#15910
MatCat
Participant

Thanks, I’d like to dig deeper in this:

Both rFTP and Threshold pace test, according to the book, can be running all-out for 20mins and then taking 95% of that value.
This gets me two values which are interchangeable: in stryd I can see the relation between pace and power and it’s linear. So 10% increase in power = 10% increase in pace and so on.

To be more specific with an example – my latest test gave me a Threshold pace of 4:49min/km and rFTP of 292W. Now, 120% of my rFTP is 350W; if I throw this value in the stryd race calculator I see it equals a pace of 4:00min/km (which is also 120% of 4:49min/km as the relation is linear, as I mentioned).

So, according to POWER, my upper Z4 limit would make me run at 350W and 4:00min/km.

But the upper limit of Z4 according to the calculator based on pace would be 4:14min/km (and around 333W). Which is a HUGE difference.

I don’t know, maybe this linear relation between pace and power it’s just something specific to myself and other people have different ratio? But for me it certainly doesn’t work as I was definitely overexerting myself doing RAn at 115%-116% of my FTP.

#15919
tedc
Participant

This is a pretty interesting topic to me. I do all of my runs with Stryd power as the zone method. I am curious what the basis (presumably scientific research reports), or origin story, is for the Pace and Power zones. Maybe that would help to understand why they are different.

#15925
David Warden
Keymaster

There is not a linear relationship between Pace and Power, neither in terms of outcome:output, nor in terms of the zone scale. Pace and Power are also not interchangeable, at least not in the way discussed here.

The C and F temperature scale example, used earlier in this thread, warrants revisiting. From freezing to boiling, F is a 212-unit scale and C is a 100-unit scale. Both measure the same “intensity” but an increase of 10 units in one is not a parallel increase in the other. Note the same issue with the Pace and Power zones. Pace is a 55-unit scale (60-115%), and Power is a 70-unit scale (50-120%). Therefore, an increase in 1 unit one one will never equal the same intensity of a 1-unit increase in the other. I mean, I can chart F and C using F on the Y-axis and C on the X-axis and give you a “line” but that is not “linear” the way it might be presented by Stryd.

On the former outcome:output issue, Pace is an outcome, a result. Power is an output. The two are not linear. Outcome outside of a perfectly efficient system (which the human body is not) will never match output, you will always lose efficiency. Therefore, a 10% increase in power (output) will be something less than a 10% increase in speed (outcome).

Therefore, Pace and Power are not interchangeable, at least on a 1:1 % of threshold pace and power. They can be interchangeable in that you can choose to use Pace or Power at any moment in your workout, but the % of threshold will never be the same between the two for a given intensity (just like C and F will never line up for the same temperature above freezing).

@MatCat
, I think we can solve this problem much quicker by having you provide your exact Pace and Power numbers from your 20-minute test. It also seems that perhaps the root cause here is trying to combine the Stryd system and the 80/20 system. Imagine Stryd did not exist. What is the conflict that remains?

@Tedc
, Pace and Power zones are different because Pace and Power and HR and RPE and MAF and Friel and Cogan and CTS and USAT and USAC zones are different. If you are asking why 80/20 Pace Zone 4 happens to be 102-115% and Power Zone 4 happens to be 103-120%, see Chapter 20 of the book Triathlon Science for the basis of our zones.

David

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