# Impact of Altitude on Power



## redlizard (Jul 26, 2007)

No doubt this has been asked before, but I didn't have much luck on a search.....

Is there any generally accepted rule of thumb on how altitude impacts power output? For example, if someone averages 250 watts at sea level, would it be 20% lower at 5000' elevation? 10% lower?

I'm asking because I live/train at about 6500' and have a pretty decent watts/kg at around 3.75, but my threshold is pretty wimpy compared to you 300+ watt guys.

Put another way, would my output and watts/kg be appreciably higher at sea level? If so, any way of estimating?


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## iliveonnitro (Feb 19, 2006)

Since you are acclimated, you lose about 8% at 6500ft.

For acclimated athletes, in % of zero elevation power:
y = -1.12x^2 - 1.90x + 99.9 (R^2 = 0.973)

where x=elevation in km.

Source:
Bassett, D.R. Jr., C.R. Kyle, L. Passfield, J.P. Broker, and E.R. Burke. Comparing cycling world hour records, 1967-1996: modeling with empirical data. Medicine and Science in Sports and Exercise 31:1665-76, 1999.


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## redlizard (Jul 26, 2007)

Thanks, Nitro. I was hoping for 10%, but I can live with 8%. Based on that, I cleared 4.0 w/kg today. Not bad for a runner with pencil thin legs, I guess.


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## Sherpa23 (Nov 5, 2001)

The formula Nitro posted is the right formula. 

For all intents and purposes, you should go by your altitude wattage. I know it probably seems a little unfair but the problem is that when you go to sea level, while in some ways you would be able to do 8% more power, your legs probably can't deal with the additional power over an extended period until there is an adaption to the increased workload.

When I go to sea level for a race, I usually try to meter my efforts at the start of a race because what happens is that you can sort of overwhelm your legs with the additional power and basically have no legs for the late parts of a race when you need them. Even though the rest of your system can handle it, your legs are still used to altitude power and not always ready for sea level power.


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## spiffomatic (Jan 28, 2010)

I hope the thread hijack isn't minded, but along similar lines, I've been looking for some guidance re: altitude. Living at 8k' and training there and 5k' mostly, but about 25% of the time down at sea level for work. Racing 5k' and above. Have access to gym equipment bikes at S.L., but can make a good workout out of it if need be. Given the opportunity to make some more aerobic watts down there, what could be the best use of that time? Sherpa, based on what you've said, maybe short power-oriented work could be the most effective - or would threshold work and sustained power higher than I could otherwise maintain be best?

Thanks, and again, sorry for jumping in!


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## Sherpa23 (Nov 5, 2001)

spiffomatic said:


> I hope the thread hijack isn't minded, but along similar lines, I've been looking for some guidance re: altitude. Living at 8k' and training there and 5k' mostly, but about 25% of the time down at sea level for work. Racing 5k' and above. Have access to gym equipment bikes at S.L., but can make a good workout out of it if need be. Given the opportunity to make some more aerobic watts down there, what could be the best use of that time? Sherpa, based on what you've said, maybe short power-oriented work could be the most effective - or would threshold work and sustained power higher than I could otherwise maintain be best?
> 
> Thanks, and again, sorry for jumping in!


You have the right idea. If you can do 25% of your workouts at sea level, you should do power-oriented intervals to build your body's ability to produce that additional power when in an oxygen-rich environment. What exactly those intervals should be, I don't know. Some of the coaches here are more qualified to answer that than I am. Generally speaking, they range from things like 30 second intervals to 10 minute intervals. With an exercise bike, though, the shorter ones might be hard.

One thing that I do recommend is that you don't focus on intervals that focus on recovery (like 1 min on, 1 min off) but rather intervals that you can go all out on with good recovery in between. The focus is on the power, in this case.

HTH.


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## iliveonnitro (Feb 19, 2006)

Sherpa23 said:


> You have the right idea. If you can do 25% of your workouts at sea level, you should do power-oriented intervals to build your body's ability to produce that additional power when in an oxygen-rich environment. What exactly those intervals should be, I don't know. Some of the coaches here are more qualified to answer that than I am. Generally speaking, they range from things like 30 second intervals to 10 minute intervals. With an exercise bike, though, the shorter ones might be hard.
> 
> One thing that I do recommend is that you don't focus on intervals that focus on recovery (like 1 min on, 1 min off) but rather intervals that you can go all out on with good recovery in between. The focus is on the power, in this case.
> 
> HTH.


Live high, train low.


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## Tlaloc (May 12, 2005)

*???*



iliveonnitro said:


> For acclimated athletes, in % of zero elevation power:
> y = -1.12x^2 - 1.90x + 99.9 (R^2 = 0.973)
> 
> where x=elevation in km.


That equation as you write it is incomprehensible:

What is y? - All terms should be defined.

What's with the terms in parentheses:
What is R? All terms should be defined.
In math and programming, the standard precedence of operators would require the expression in parentheses to be multiplied by the 99.9 but it couldn't contain an equals sign.

If I assume that y = percentage of sea-lever power, ignore the parenthetical expression the result seems to make sense. Is the parenthetical expression a red herring?

In other words do you mean:

y = -1.12x^2 - 1.90x + 99.9

where:
x = elevation in km.
y = power at altitude


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## iliveonnitro (Feb 19, 2006)

Tlaloc said:


> That equation as you write it is incomprehensible:
> 
> What is y? - All terms should be defined.
> 
> ...


I suppose it's a bit academic, but it is far from incomprehensible. In fact, you understood it mostly. The R^2 value is a coefficient of determination. In other words, the formula is not applicable up to ~5% of the time.

So, y = *percent* of power held at zero altitude and x = elevation in km.

for 6500ft = 1.981km
y = -1.12(1.981)^2 - 1.90(1.981) + 99.9
y = 91.74 % of your zero-altitude power
or, 100-91.74 = 8.26% loss of power at elevation.

The formula is different if you are not acclimated to the elevation.


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## asgelle (Apr 21, 2003)

Tlaloc said:


> That equation as you write it is incomprehensible:...


http://opinionator.blogs.nytimes.com/2010/01/31/from-fish-to-infinity/
fish,fish,fish,fish,fish,fish


Also, note the full citation was included. If anyone couldn't follow the equation, the original explanation was referenced. There was no point rewriting it here.


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