Power/HR in Z2 metric

[david]

Intervals.icu now calculates power / HR for time spent in heart rate Z2 for each ride. This is the average watts / average heart rate for the parts of the ride done in HR zone 2 (aerobic or endurance). The ride is split up into 1 minute sections adjusted for HR lag. Only minutes in HR Z2 with cadence between 85 and 100 and little decoupling* are kept. The power/HR Z2 ratio is the average of these minutes and an indicator of aerobic fitness.

You can add this as a plot to a custom chart. If I look back on 2 years of my data the times when power / HR Z2 has been highest are also when I have had my highest eFTP.

• I still need to implement the “little decoupling” filter.

[Wojciech_Marszalkows]

@david

cadence between 85 and 100

I usually drive in Z2 at 70-80 rpm It doesn’t work for me
I need to change my pedaling technique

[Cyclopaat]

60 - 70 rpm here - I have a 55 chain ring and only use the 11-14 on the cassette

[david]

Oh wow. Didn’t expect that. The cadence filter is supposed to filter out coasting, cadence drills and so on. Not monster mashers.

[Michael_Webber]

I’m in the same boat: 85 rpm is about where I sit in Z2.
Perhaps use a power filter instead? I mean, define Z2 by HR as you have done, but then filter by [say] watts > 50%FTP rather than cadence? That gets rid of coasting.
It is almost true that whatever cadence range you select as a filter, there will be people who regularly ride outside it. Perhaps just drop this and advise people to bear it in mind when interpreting the results?

[Filip_Radkovic]

Same here, I’m usually around 75 in a chill Z2 ride, 85 seems to be my sweetspot for sweetspot stuff, 90 for threshold, 90+ for above threshold and 95+ for racing, where I tend to spin more at all intensities for some reason, adrenaline maybe. I’ve also noticed it changes a bit over time. I’d like to think I’ve gained some more muscular endurance this year which enables me to be more comfortable in lower cadences/more torque than previously, while I’m still able to spin when needed, but that’s just what I like to tell myself, maybe it’s bollocks

[david]

I am working on this. My data is very messy without the cadence filter. I will try a cadence window related to the mean for the Z2 parts of the ride to chuck out the outliers.

[Wojciech_Marszalkows]

Maybe insert cadence filter configuration?

[david]

I could but its better if I can come up with something that “just works”. I think filtering based on cadence of the ride in Z2 HR will do the trick. If you normally ride at 80 rpm it will use say 75-90 as the range etc.

[Michael_Webber]

@david

I will try a cadence window related to the mean for the Z2 parts of the ride to chuck out the outliers.

Clever pants! So what’s your thinking here – +/-10 per cent? Is that wide enough? I suppose that we are talking about Z2, so that might be enough.

[Cyclopaat]

Wassup with Z2 anyway? I only spend 26% of my rides in Z1-Z2, so even if that’s more than 50% Z2, it’s still (way) less than 25% of the total…

[Bogdan_Rylski]

I guess my zone discipline pays off, this was a ride from last sunday. I just upped my FTP so I’m still getting the feeling of my new power zones.

[Cyclopaat]

Is usually end up with something like this…

[david]

It now finds the median cadence of the Z2 HR data points and keeps those within 0.92 and 1.15 of that. I will deploy that tomorrow morning to recalculate everyones stuff. Its a reasonable match for eFTP for me for the last 2 years and nice because you don’t even have to do max efforts for this, just ride easy Z2 and you can figure out how fit you are!

[david]

I also added CSV download of the HR lag adjusted power vs HR minutes for an activity:

start,secs,movingSecs,watts,bpm,ratio,cadence
0,60,56,147,115,1.28,43
60,60,36,168,126,1.33,63
183,60,60,118,112,1.05,61
243,60,60,140,111,1.26,60
303,60,60,158,116,1.36,83
...

[Bogdan_Rylski]

Out of curiosity, would it change the graph at all if you switched the zone filter to power? Thus plotting Pw/HR for time spent in power Z2.

[david]

Probably not much unless your power zones have changed i.e. FTP changed. The big advantage of using HR zones as a base is that they generally don’t change during a season.

[Cyclopaat]

They do as you fatigue (too much) in which case HR is either lower or higher than normal.

[Matteo_Saul]

This is very cool. One thing I thought of and maybe it’s already factored in or doesn’t matter, but sometimes the entire ride is Zone 2, and sometimes the majority of the ride is 1 hour intervals with .5-1 hour zone 2. I find that Zone 2 heart rate after an interval session to be higher than just plain zone 2. Does this matter? Would looking at only complete zone 2 rides show a better indication of fitness increase?

[Cyclopaat]

@Matteo_Saul

Does this matter?

No. You will fatigue more during the intervals, after which it is not uncommon to end up with a slightly higher than normal HR, compared to Z2 only activities.