Testing for Aerobic Decoupling

Is testing for decoupling in other zones like Sweetspot or threshold worth anything? Can it help you understand what your one hour or two hour power might be… anything like this?

Did 2x50min efforts today, maybe around Sweetspot/threshold but power was consistent on both. Can I use the numbers on intervals to earn anything? The numbers for D on it are all over the place, no clue what it means. some are - numbers too.

Yes!, if you measure a constant effort. Say 90min SST or 60min THR. Cheers.

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Crap, I bottled it. Was going to go for longer effort, like just do the whole ride at Sweetspot, but bailed. Did 50min then 10 rest, then 50min again.


Very rare I do anything like that recently, all been POL Z1 or Z3. Suppose could have another go in a week or two if the data is useful…

I guess you could compare the NP/HR of each interval and track progress there.

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How would you interpret the D numbers on the intervals? Some are positive and some are negative.,

Joe Friel to my knowledge is the coach that introduced aerobic decoupling to a wider audience. There are still some 10+ year old blog posts discussing application. Originally he used it to determine when it was time to progress from early base (zone2 riding) to adding tempo and sweet spot.

I use it after taking a break. Look for decoupling to drop below 5% on 2 to 3 hour rides. Then I stop using it for anything, however I do keep reviewing it all season.

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NP/HR can only give you a positive number.

I mean more the Decoupling numbers on Intervals. I don’t have a guide on how to interpret them… might have to look for this Joe Friel post @bbarrera has seen.

Sorry, really need to learn to do this stuff myself… but totally new to working with decoupling and I’m kinda just bored and looking for a new plaything with it. See the D values in the two 50min blocks, they have different values, some are - numbers.

Intervals actually breaks the intervals 50/50 so I have 4 decoupling values over the two efforts.

Interval 1

Interval 2

Second interval is crazy, goes from 4.1% to minus 2.1%!

Can I read something from that?

Hmm, intervals.icu wrongly identified your long 50 minute efforts as three separate efforts? Surprised it didn’t break the second 50 minute effort into 4. That’s what I see.

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Ah yes, the break in the second one is when I went through a mini roundabout… was literally just a few seconds I slowed and stopped pedalling… didn’t think it would cause any problems for it.

Use that route a lot, its excellent and flat, just has that one bit that you need to chill for. I go up and down it… so usually twice I hit that bit.

Drag the edge of the interval, where it breaks, to the end of each 50 minute segment that will give you two 50 minute intervals.

So for the first one the end of the 18:53 interval drag it to the end of the 50 minutes (around 1 hour 10 at a guess)
The mouse pointer changes to an arrow when you grab the edge. Hold down your mouse key and pull/scroll to the right.

Edit: It has split the intervals because you reduced power enough for it to detect and consider it the end of the interval, stopped pedalling or it lost cadence readings for some reason.

If you struggle to use your mouse to edit the intervals you can change the interval in the table, see screen shot

Personally I find it easier to use the mouse.


Not really… the average power was 2 watts less but HR didnt rise hence the negative.

Adjust / Set your intervals correctly. Even without doing this you can see there is no drift… the actual D number doesnt tell you anything much. I’m guessing its around 1.x, maybe low 2.x

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Ah that’s cool thanks! Now I have 155bpm 5.2% and 157bpm 2.1%. Can I know use it to make interpretations of any kind?

I was correct with my guess of low 2.x then :wink:

So, what does it tell us?

The first interval has a higher decoupling value.

This is because you are not pre-fatigued / warmed up and during the interval you are holding the same power but your HR is ramping up for the first few minutes / quarter (HR lag) while your body reaches an equilibrium. Cardiac output moves to match the work done; heat increases until it reaches a point where is being dispersed in equal measure etc. Basically, it is because you are warming up during the beginning of the interval, HR rises power stays the same. If you just look at the last 30 ish minutes its about the same as interval two.

The second interval is a lower ‘D’ value as you are pre-fatigued and warmed up, this results in your HR hitting a plateau much earlier in the interval, there is no further drift. It suggests these intervals were ‘comfortably’ decoupling wise within your capability.

Your data shows why it is important to consider the context, decoupling can be very misleading if you do not (without thinking about it someone might assume interval 1 wasn’t as good as interval 2, this isn’t the case). There are plenty of reasons to question its usefulness. Although if you understand the limitations, it can be kind of useful in certain circumstances.

PS. 2x 50’ @ 293w with no (next to no) decoupling, I hate you and are never providing you any useful feedback again. :wink:


Wow that’s amazing. Was expecting a one-liner like, ‘can’t tell you anything’ go do 90min intervals (which I really didn’t want to hear).

That explains why when I was looking at the two intervals it read to me like something was wrong in interval 1, or like it was harder… penny starting to drop now on what this decoupling stuff means.

I think I’ll do what bb said earlier… maybe use it more on long steady state rides, like 3hours or so, get a feel for base fitness.

Put in some pro-volume 20 hour weeks recently, don’t hate me, hate the free time I’ve had during lockdown :upside_down_face:

Thanks again btw, you and @bbarrera are great here, you guys could write books on this stuff.

And both names start with BB funnily enough :thinking:

@Shrike per my earlier comment I only find real value in using aerobic decoupling after coming back from an off-season break. In 2019 for several reasons I had very little or no cycling during the May-August time period. It took about 6-8 weeks for my decoupling to drop below 5% on a long tempo ride. For example:

  • 2nd week: 17% decoupling on a 2 hour zone2 workout (TR’s Virginia) on trainer
  • 3rd week: 4%, 7%, and 4% decouplings on 2 hour zone2 workout (TR’s Gibbs) on trainer
  • 4th week recovery week for TR’s traditional base
  • 5th week 3% decoupling on 2.25 hour (TR’s Warren)
  • 7th week -3% decoupling outside tempo (only 1 hour tempo of good data)
  • 8th week 0% decoupling on Wed night 1.5 hour zone2 group ride (off the back with another rider) and Fri afternoon 2.25 hours of outside tempo (both rides mid October and temps 90F / 32C)

This was coming back after many months off the bike, and yet the decoupling quickly dropped on 2+ hour workouts inside and outside even with warm temps and I’ll mention my ‘indoor’ trainer is in the garage and I train after work during the heat of the day.

My only advice is to a) toss out the first 20-30 minutes (warmup), and b) toss out any non-steady portions, and c) if you have a X hour event, lets say 5 hour event, then doing a longer steady ride of similar duration and looking at decoupling gives you an indication of aerobic “base fitness” for that duration. Its a simple metric and given your results so far I’d say its of limited value. On the other hand if you had >5% decoupling on 45 or 60 minute zone2 then it would say a lot more.

Hope that helps.


A common theme i see through a lot of comments in this thread is how decoupling is being used. In respect of a single workout, its just a metric and not much can be gleaned from it. It’s usefulness is in tracking it over time and seeing how it changes when you look at workouts of similiar time/intensity over a matter of weeks.
What you should start to see as your aerobic capacity grows is that decoupling is reduced for the same power target.

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Hmm. that may be individual because I haven’t seen that. Here is an older post talking a bit about it:

and the pic from that post

a couple of notes:

  • that is for a segment that started after a 15-25 minute warmup
  • focusing on time period from November 2016 thru April 2017 my aerobic capacity increased substantially in March however I have a December 11th effort at 0.99 IF and -4.3% decoupling

Here are my two ‘worst ever decoupling’ effort on that segment, one happened just 2 days ago:

May 2020:

9.2% decoupling as part of a 3x15 tempo with bursts workout.

April 2021:

8% decoupling on a non-steady state 4x4.5 minute zone5 ‘controlled vo2max’ (not full gas) intervals.

to be honest i’m not sure what i’m meant to make of this data.
You’re comparing decoupling between rides of varying power targets and therefore getting varying decoupling results.

The portion of my comment you quoted excludes the most critical part

the majority of those are at threshold, just mentally ignore the three non-threshold (IF of 0.77, 0.73, 0.84) workouts. Therefore all but three of those rides are basically at or near FTP, and with basically no decoupling. IMHO the data tells a story.

In other words, all but three are:

  • at same relative intensity
  • on the same course and time is relative to the amount of headwind
  • over a period of many months
  • over a period of increasing aerobic capacity (late 2016 lower aerobic capacity compared to March/April 2017)

Putting decoupling into a zone bucket, workout by workout. Workouts with a low VI, say 1.05 or lower, means it was close to a ‘pure’ zone workout for that segment:

my n=1, after establishing basic aerobic fitness my decoupling is usually below 5% on zone2 / zone3 / zone4 workouts. My hypothesis for the negative numbers is that the warmup includes a hard effort a few minutes before the start of the segment, and heart rate settles down over the first few minutes of the segment.

I’ve seen similar trends on other workouts, with a longer warmup and then a long steady tempo effort.

All of that is a long winded explanation with empirical data, that I’ve found little value to using aerobic decoupling as a general purpose metric during a season and across seasons. However it does help me after an off-season break.

Your Mileage May Vary (YMMV).