I have some decent data from the other side, racing a few IM's at sea level and going up to race at altitude.

My sea level IM's are done at 180-185W and then this is followed by runs in the 4:0x range (a good day is under 4)
At Tahoe it was pretty cold on loop 1, so I kind of had to overbike at sea level wattage just to warm up. I was cold for the first 2 hours when it was in the high 30'sF. Once I warmed up on loop2, knowing I can't ride at sea level wattage, I dialed it back to 160W. My final average was 170W (ride time was 5:39 which was solid on that course). I thought I was being really conservative, but the last 20K felt really tough at that wattage even though I was still passing many people. Over to the run, I ran with sea level perceived exertion and ended up running 4:28. YIKES....I never even walked a step. I was just that slow on the run. I was still 9th in my age group, so not a bad day at altitude.

Also 3.5 weeks before Tahoe I did an altitude power test while climbing Passo di Stelvio in Italy. I have done several half IM's at 215W so I set out to climb it at 215W all the way. Start is 4500 ft, end is 9000 ft. I do 2:30 rides at 215 and back it up with solid runs, so holding 215W should be no big deal for a 100 min climb. And it wasn't until I got over 6500 ft, when the perceived exertion at 215W started going through the roof. In the final 2500 feet leading up to 9000 ft, 215W felt like holding 100% FTP. This was really informative and gave me an early window into the impact on my wattage and perceived exertion racing at 6400 ft at Tahoe since my body would not be ready for altitude (I showed up at Tahoe on Saturday before the race).

Dev

Given interindividual differences, it is always going to be a bit of a guess. Your best bet would therefore be to rely on software that takes such physiological differences into account.

I think the difference usually ranges from 5-10%, but it is probably determined by what system is the limiting factor for your FTP. For example if you have smaller lung capacity compared to the volume of blood your heart can pump.

I find that I can put out about 7-8% more power at sea-level and I live at 5100 ft. My lung capacity is 120% that of a normal person my size, but I was told that my heart's ability to pump blood is what limits my VO2 max. I would guess that if lung capacity is your limiting factor, then you might be closer to the 10% improvement.

Andrew, could you point us to the software. I may do IM Boulder next year which should be around 1000 ft lower than Tahoe, so hoping to be hammered a bit less than Tahoe.

Lung capacity has nothing to do with it.

Glad you asked! ;)

http://home.trainingpeaks.com/products/wko4

(Charts w/ my new, more individualized approach to correcting for the effects of elevation should be posted to the Chart Exchange in the next week or so. In the interim, some examples can be seen here: http://home.trainingpeaks.com/...orrected-power-chart)

Try having one lung removed and see if it affects your FTP.

A study here might be of interest.

http://tf.hu/...009/08/82-Degens.pdf

Lung function declines with age but it would seem training doesn't improve lung function. Training will no doubt improve function of diaphragm etc but it doesn't seem to,affect the lungs themselves.

What I would like someone to explain is this;

Why is it that we become breathless and lose control of our breathing and are unable to talk and are forced to slow down sooner or later if we are putting out power above FTP or running above threshold pace even though our lungs are breathing in more than enough oxygen?

Why do we feel so out of breath if our lungs are taking in enough oxygen and exhaling enough carbon dioxide?

Perhaps it's just the easiest way to cause us to slow down when the muscles are not getting the required oxygen?

In short, if it isn't our lung capacity / function which is the limiting factor why does it feel that it is?

It seems our perceived exertion feels it's the lungs not getting enough oxygen when in fact they are, we just can't transport it to the muscles. So why do we gasp air when it isn't what we need?

It seems our breathing is the major feedback system between the exercising muscles and the brain. We feel the urge to breath deeper and faster if out heart is unable to pump enough blood fast enough to the working muscles. We feel the same urge if our heart is able to pump enough blood but our blood does not have enough red cells. We feel the same urge if our muscles are unable to take in enough oxygen even if it is available in the blood.

We do feel pain from the muscles as well, but the overriding discomfort is our breathing. Unless we have heart problems we don't feel pain from the heart no matter how desperate our breathing. We don't feel our heart increasing its rate or stroke volume but we immediately feel our breathing increase. Yet we know that our lungs are breathing in more than enough oxygen, there is no real point in breathing deeper and faster yet the urge to do so is so great we must.

Is there a way of controlling breathing and limiting the discomfort so we can continue at a faster pace for longer?

It's all very well saying that the lungs are not the limiting factor, but breathing discomfort certainly is. How do we minimise it?