Cardiac Drift/Aerobic Coupling

Having finally got myself a Bluetooth HRM I’ve now done a couple of workouts with it and a little bit of analysis. (I already had an ANT+ HRM but I use TR with an iPad Mini which has the Lightning connector and you can no longer get the 30 pin to Lightning connector so my ANT+ dongle won’t work with the Mini, progress eh?)

First workout was Mount Goode with its fifteen minute intervals close to FTP. Ignoring the initial minute of each interval where my HR ramped up to get to its “steady” rate then my Cardiac Drift for the three intervals sat between 3.4% and 3.9%. That’s well below the 6% drift quoted as the boundary between adapted and non-adapted.

The problem with Mount Goode is that the workout as a whole is too short and at the wrong intensity. Joe Friel in one of his Training Peaks articles reckons that you should use a workout or activity at least two hours in length at Aerobic Threshold (AeT). So today I did Boarstone.

One slight problem: at 15mins the TR app on the iPad froze, no idea why and it’s never done it before. Had to quit the app, restart and resume the workout. Only did it the once. Annoyingly this meant that when the data was exported to Strava and only the first fifteen minutes was exported so I’ve had to work out the aerobic coupling values by hand, OK, via a spreadsheet.

What I ended up with were seven “intervals” with decoupling of: 4.7%; 0.16%; -0.17%; 0%; 0.33%; 0.5%; -2.39%. Yes there are two minus values and a zero in the series. I think it’s safe to say I’m aerobically coupled! Then again I shouldn’t be surprised as I’ve had nearly fifty years of endurance type activity, I’m the archetypal diesel - light the blue touch paper and … wait and watch me plod away.

So the question is: what do I do with it? Joe Friel notes:

When heart rate and pace or speed are coupled (less than 5% decoupling) for the goal duration then aerobic endurance fitness is considered to be optimal and you are ready to move on to the next stage of training-the build period.

Now my goal duration is more like 12hrs riding not three or four but I’m not spending six hours on the trainer as Friel suggests, I’ll just extrapolate the results. I’ve just started the Sustained Power Plan so have implemented that takeaway from the above quote but how else do I use this info? If I notice an upward drift (in the, err, drift) does that indicate overtraining or perhaps the potential onset of illness? It almost seems like an afterthought - “oh we can calculate this …”

Finally, is there a reason TR don’t do the calculation in the workout summary? It’s a much easier calculation than Normalised Power for example, notwithstanding the above comment.

Decoupling as calculated in the article is the first half of the session compared to the last half, not inside an interval, so maybe the numbers will be different when looked at that way?

I know shows decoupling for every interval but I’m not sure it’s of use for ‘short’ intervals (15 minutes may be long enough, but I’m not certain of that one.

Thanks for linking the article though, it enabled me to have another look at today’s ride and get some idea of decoupling!

Doing that gives me a drift of 1.4%. Probably more realistic but still good.

Yeah I’m annoyed, as my interval breakdowns are less than 2% but my workout drift is more like 5%!

I’m now wondering where the line is - what’s long enough, what’s too long etc? I did Vogelsang+1 which is 4 hours, maybe that’s too long for anyone to keep a steady HR?*

*grasping at straws, probably just unfit! :laughing:

EDIT: Just re-read the relevant bit of the article, I’m just unfit :neutral_face:

This is just my feeling, but 4hrs is going to be better measure of this than shorter rides. That being said it is relative as well. For example if you are starting out, a 1hr endurance ride would be good enough to get a measure. And when your decoupling is low enough it’s an indicator that you are ready to move onto longer endurance rides or intensity. For an experienced rider, I doubt 1hr ride would be long enough. From my understanding it’s a measure of whether you are ready to move onto longer durations than you are currently working on.

I also don’t believe this measurement is useful in interval workouts (I ignore it on those types of rides). It’s really meant for steady state endurance rides.

Yeah it’s a tough one, balancing this type of thing (which I can only do really once a week) and using SSB to prep. Just got to trust the process and come in as prepared as you can be I suppose! Maybe 4x4 hour rides a week would improve decoupling, but hopefully say 20w from a good training phase can be as/more useful in the real world.

And it’s all relative. To what your goals are and to how much riding you have done. To get an improvement in endurance and aerobic decoupling, it is never a “set in stone” amount. You mention 4 x 4hr rides per week. That’s if you are already riding a lot. If all you have been doing is 1hr rides, then a few 2-3hr rides will give good improvements. Then eventually as you improve you would have to venture into even longer rides.

It’s very doable, but requires concentration, focus, and control.

Looked up a 5hr outside ride from last summer: 4.5hr @ 120-130bpm; 124HRav.
My CD was high for that ride – too much Z1 time – but HR was steady-ish.

Some of my 4hr rides the past couple of weeks at 60% ftp have been around 3% decoupling. And now some 2-3hr rides at that same intensity show 1%.


(not a flex, but more just an example that it’s not unreasonable)

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