Power adjusted for altitude

[david]

Intervals.icu can now plot power adjusted for altitude (tx @John_Peters_endura.f ) using the unacclimatised (1-7 days at altitude) and acclimatised (several weeks at altitude) formula from Bassett et al. Here I have plotted power & power adjusted for altitude (acclimatised and not) on Alpe D’Huez. I didn’t pace it quite as badly as I thought!

Click “Charts” to add these:

If you want to see all 3 together click Charts → Paste and copy in this code for the custom chart:

{
  "id": "ccc0d26339",
  "name": "Alt Adjusted Power",
  "height": 120,
  "yAxisLabel": null,
  "yAxisMin": null,
  "yAxisMax": null,
  "y2AxisLabel": null,
  "y2AxisMin": null,
  "y2AxisMax": null,
  "plots": [
    {
      "id": 1,
      "text": "Power",
      "color": "#6633cc",
      "extras": [],
      "legend": false,
      "stream": "watts",
      "transform": "avg_60s",
      "areaOpacity": 0.05,
      "lineOpacity": 0.7
    },
    {
      "stream": "watts_alt_acc",
      "color": "#ff00ff",
      "text": "w:alt acc",
      "areaOpacity": 0,
      "lineOpacity": 0.7,
      "legend": true,
      "transform": "avg_60s",
      "id": 2,
      "extras": []
    },
    {
      "stream": "watts_alt",
      "color": "#24a122",
      "text": "w:alt",
      "areaOpacity": 0,
      "lineOpacity": 0.7,
      "legend": true,
      "transform": "avg_60s",
      "id": 3,
      "extras": []
    }
  ],
  "legendPos": "topLeft"
}

Alex's Cycle Blog

[Tito]

Awesome David! Very useful for people like me who are changing the altitude frequently!!! I was doing this math manually…

Thanks !!!

[Nicolas_Dricot]

Very nice! Thanks David! Do you think you could also add this as a “field” so we can easily get a look at corrected power for specific intervals? That’d be very useful to complement this chart.

[Eric_Mittelstaedt]

This is great for folks like me who live/ride in the 7-10k/ft elevation world the vast majority of the time and ‘rough-estimate’ and dream what it’d be like to be riding at sea-level at times Quick question though - shouldn’t the acclimatized estimate be higher than the un-acclimatized estimate? Looking at this, it would indicate so:

and experience would tell me that people who end up coming up to altitude from sea-level suffer with their power output/vo2max in their first few days.

[Nicolas_Dricot]

The acclimatised and non-acclimatised power estimates are trying to give you an equivalent power that you’d have done at sea level. Therefore, if you are acclimatised, you will suffer less from altitude as your graph shows (power reduction as a %age is lower) than if you are non-acclimatised. The equivalent power at sea level is then lower if you are acclimatised.

[Eric_Mittelstaedt]

Ahh right - I was inverting expectations based on the actual chart, but the implementation makes sense (duh). It’s still early and on a first cup of joe

[david]

I added the interval fields. You need to re-analyze or make a dummy edit to existing activities to see them.

[Nicolas_Dricot]

Awesome, that was quick! Thanks again.

[Xavier_Hipolito_Marg]

Thank you, as always!

[Jean-Michel_Lachance]

Very cool feature !

[Martial_Pottier]

Wonderful, thank you David! Do you know why it is not “working” on some activities such as Intervals.icu?

the values are shown if I manually select an interval, but it is not appearing on intervals set on the activity, only “w” is shown, without any value.

Edit: It seems to be solved

[david]

Yes you need to make a small edit to one of your intervals (or add one) to get the rest to be re-analyzed.

[Tito]

Hi David,

Is it possible to add a field (maybe customized) to know the equivalent average power not only at the sea level but instead at a specific altitude in meters? (based on the % of power at the sea level and Bassett formula)

Would be useful to know how much power could be estimated for an event or race at a specific altitude or for indoor activities when we travel to different altitude place…

Thanks a lot!

Fabian.

[david]

I think that will need to wait until custom fields are implemented. I am not sure how to fit it into the UI.

[Mike_Hardy]

Sorry for using necromancy on an oooold thread, but I just discovered intervals.icu (amazing work here, truly! but you know that) and had one question related to altitude estimates. I’m at 2500m/8500ft normally but I ride in Zwift which provides virtual altitudes that have no bearing on my reality of course. So altitude adjustment for these workouts is desired but not possible.

Would it be possible to say for a ride “this ride was virtual and was conducted at 2500m, use that for altitude adjusted power estimation”. Or even to have a profile setting where you could say “I’m at 2500m, use that for all virtual rides”? Then of course I guess you’d want that to be set over time periods so if you travel you could move it (I could dream up features all day ;-). The MVP would be to just set it directly in a virtual activity though, for me.

Even if the idea is a non-starter, really impressed by the site. Cheers

[Ben]

Makes sense.

If David doesn’t implement this directly then it will still be possible in the upcoming custom activity charts feature and should be pretty easy to implement as it’s just multiplying the power stream by a constant.

[Mike_Hardy]

That would certainly bring things closer (and in fact, as a sometimes-lazy programmer myself I’m tempted to argue it’s “good enough” really) but if you go up the Alpe du Zwift then you’ll get 9500m elevation or so at the top which isn’t correct either as in reality the activity is at an unvarying altitude the entire time.

I’ll keep my eye out for custom activity charts though - thank you!

[david]

I have added altitude to Actions → Fix Data under the activity timeline chart. You can use this to adjust the altitude trace.

[Mike_Hardy]

Well that did the trick perfectly! Thank you very much. You’ve more than earned my support, I’ll go set that up to make sure I buy you a coffee equivalent irl

[Nick_van_Dyke]

Sorry for another necro - thank you for this chart option! It really simplifies activity comparisons. Would it be possible to extend altitude-adjusted power to the Power/Duration curve, and the “Compare” charts like Power vs HR?

I’m about to move to a location that’s 5000 feet higher than where I’ve trained the past three years. Even after acclimatizing, the ~5% hit to FTP will make it difficult to directly compare my progression to past years’ numbers.

I also foresee hitting power-related PRs when then traveling to race at sea level, which would have the same effect of muddying comparisons.