Any hope for altitude compensation based on our location/elevation for races?

Does anyone know if the Zwift team has any plans on accounting for the lower power output that happens at altitude so that those of us doing Zwift races who live at high altitudes have a chance to race without a handicap?

I live in Boulder, CO at 5,300 ft. The power reduction here compared to sea level is between 10% and 15%, depending on which study you’re looking at.

When I race in Zwift, I’m at a big disadvantage over someone who’s on their trainer at sea level.

A lot of people in the Zwift community get rightly upset about people who are weight doping, but to those of us who live at higher altitudes, everyone who rides on their trainer at sea level are essentially oxygen doping compared to those of us who have much less dense oxygen to breath.

There is only one old archived thread on this in the forum here: Altitude Compensation?

Does anyone know if there are plans for the speed calculations in Zwift to account for our physical, in real life location altitude so that those of us at higher altitudes get an appropriately calculated added amount of speed so that we are on a level playing field with people who ride at sea level?

I am not an expert on this subject, I read a few papers on this topic so I can understand it a bit more. But what I don’t see in this papers is what is the impact if you live at altitude. I understand going from high to low altitude will give you an advantage. I have personal experience of that.

But living at attitude you are used to the environment and your body get custom to training and performing at altitude. So when you move to lower altitude your have an advantage, but once your body get use to the change your performance will return to original levels.

So I think there need to be a lot more studies on how living permanently at altitude impact performance.

Zwift could be used to test this. Look at segment times of Racers at altitude vs those at sea level. So if someone is looking to do some research this should be a good topic.


I can see the argument, but it’s also introducing yet another variable that has to be verified for anyone to claim to be riding “legitimately”.

If you live at altitude, aren’t you already adapted to it? I thought that was the fundamental reason for people training in the mountains then going back to compete at lower altitudes, because the adaptations provide a performance benefit.


Hi guys. Yes, indeed, I’m acclimatized to the altitude here, but there’s still a decrease in power output and FTP once your body is acclimatized.

If I were to drive down to sea level in one day, then get on my trainer, I would have about 10% more power just because of the greater oxygen density.

I know this because I’ve tested it multiple times.

If you’re interested, take a quick peek at this study:

Here’s the bottom line conclusion from that study: “The bottom line of that portion of my blog post was that as the altitude increases aerobic function decreases and so FTP decreases. And as you acclimate to a new, higher altitude your aerobic function and FTP improve, but they never attain the level you would have at a lower altitude.”

Once your body is acclimatized to altitude, there is still around a 5% loss of power because of lower oxygen density (based on this particular study.) I’ve seen other studies that show the power loss after acclimatization is greater than 5%.

I do agree that this would add another variable to confirm for zwift riders…their location and altitude, but in my mind it would be worth it. My Garmin can read altitude. Maybe that could be the confirmation needed…the garmin data of altitude.

All these studies is done with cyclist moving from one elevation to another. But I have not seen a study comparing people born and living at altitude.

From Joe Friel:
If you arrived a few weeks early allowing your body to fully adapt that loss of performance would theoretically and gradually shrink to about 5%. Looks like this is a theoretical value, and he talk about a few weeks. what happen after 5 years.

I do agree there is a difference when moving from one to the other.

Now with zwift it could be interesting to see the top segment times of racers on different elevation.

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That would be interesting to see the top segment times cross referenced with elevation data.

From my experience and those of my teammates, even after acclimatizing for a few weeks, our power stays consistently higher at sea level and consistently lower at altitude.

But it would be good to find a study that shows that data, rather than studies that talk about what happens right after athletes move from one elevation to another.

I’ll keep researching to see if there’s studies that back up my personal experience of the power difference after acclimatization. :slight_smile:

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It could be one of those things like an HRM that riders might or might not have; but for people who don’t already have a head unit that can relay altitude it’s a significant additional cost. So it’d be unreasonable to make it mandatory I think. No reason it couldn’t be displayed along with height and weight on Zwift Power though.

I appreciate what you’re saying regarding power loss. I don’t know if it’s significant or not, and I must admit it’s not something that had ever crossed my mind as being a variable between Zwifters. It’s an interesting aspect to consider though, for sure.

Same but For Dummies?

Thanks heaps for these charts, Jonathan. I’m aware of the complex interactions between oxygen density, power output, and air density, but wasn’t aware of the exact degree those factors balance out to increase overall speed when moving through air is involved. So that first chart is really cool to see, even if it’s not applicable to my question with regard to power loss as a result of altitude when zwifting, because air density doesn’t come into play with zwift.

The second chart confirms several of the studies I’ve read about. There is power loss the higher you are in altitude, and after thinking more on it since I posted the original comment in this thread, I feel pretty certain that the power loss is sustained for riders at higher altitude even after weeks of acclimatization.

I’ll dig into the post you linked to soon. Thanks again for posting this data. :slight_smile:

You’re welcome. I would absolutely agree that there is always a power loss at altitude. That is just my acceptance of how my body functioned for about 2.5 years living between 5000-7000 ft. My fitness is much less but my power is about the same now that I live at 800 ft.

The variability for that loss is determined by too many physiological factors for me to talk out of my rear end here on what that estimated number is. The best I can do is to suggest previously published data and say it depends.

The first chart is irrelevant for Zwift, as you say, but it’s some cool info for IRL.

Indeed. The first chart is awesome for planning out which velodrome to use for setting the hour record, which is something I’d like to take a crack at in the next few years (hour record for my old guy age group, that is. :slight_smile:

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My phone and computer both know where I am. It shouldn’t be difficult to use one or the other to verify location and elevation, and apply a power adjustment for altitude.

Location is the easy part (although it can be faked), the question I have is what is the adjustment that need to be made.

There is a lot of studies dealing with traveling and acclimation to different altitude.

I don’t see any studies that show what the power difference is for someone living at altitude vs someone living at sea level.

The blue line in Johnathan’s second chart shows exactly this.

Good luck! keep us in the loop. I’ve thought about going for the American record but don’t have the fitness or the capital at the moment. I’m not sure I want to dedicate enough resources to dethrone Zirbel, but I think it is very possible until Lambie decides to take a crack at it. My wife though, I think if she would have any interest, she could take a crack at the women’s hour record.

My advice would be the spend as much time at the race altitude as possible leading up to the event. At least 5 weeks prior (7-10 easy days, final training block/adaptation, final taper and race prep) or fly in the day before and hope you have good travel legs.

Second piece of advice would be to not leave any bits of low hanging fruits available. I look at some of the masters competitions and I am amazed at the free speed that I can see them giving away due to equipment choice alone.

That is for someone that acclimating going from one altitude to another. But that is weeks of acclimation not years or forever.

I take “acclimatized” to mean that no further meaningful changes are occurring.

I read the study and it was a few weeks, can’t recall what they defined as “acclimatized”. I will check again, I don’t have it here right now.

don’t get me wrong, as I said before this sound like a good thing, I just don’t think we have valid data, yet.

Great discussion and one in which I have a vested interest and often deal with since I live and Zwift in both Breckenridge, CO where our primary house is at 9,750’ (2,972m), and in Denver where we have a condo at 5,295’ (1,614m). Note that Denver is almost exactly half way elevation-wise between sea level and our home in Breckenridge.

I have lived here for 17 years, so believe I’m as acclimated as anyone here. Granted, everyone is different physiologically, I’m a sample size of one, and an old “one” (72) at that. Nevertheless, here are some of my observations, Alpe du Zwift average power & time during steady very hard efforts and locational FTPs:

Power (from a Quarq PM) and time up Alpe du Zwift:

  • in Houston (sea level) Feb 2019 - 242w avg, 55:22 minutes
  • in Denver (5,295’, 1,614m) Nov 2018 - 226w avg 58:48 minutes
  • in Breckenridge (9,750’, 2,972m) - June 2019 - 206w avg, 1:04:23 hours

If I assume sea level is 100%, my average hour power in Denver is at 93.4% of sea level, and 85.1% in Breckenridge. These percentages fall almost perfectly on the blue Bassett, etal (Acclimatized Athlete) curve Johnathan posted above. In fact, these percentage power adjustments are almost exactly those I see in Training Peaks WKO4’s calculation of my “Elevation Corrected Power” (effective sea level power) for my IRL workouts at altitude.

I also use these percentages (or the inverse of them) to adjust my FTP and training ranges for Breck, Denver and sea level (235 in Denver, 215 in Breckenridge, 255 at sea level). I’ve found that doing so results in my HR being in the same bpm range for Tempo/Sweet Spot, Steady State/Threshold or Climbing Repeat efforts regardless of location.

As I said, this is only one person’s observational experience but I have no doubt that altitude has a physiological and sustainable power impact regardless of how long one has had to acclimate. It gets better and easier but the gains taper off over 6 weeks or less and living up here is NEVER like living at sea level.

It’s breathtaking up here in the mountains - figuratively and literally!