I would say that above 1000m you start to see some differences, very slightly though. From 1500m on the differences are more noticeable.

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"Yeah, no one likes a smartass, but we all like stars" - Thom Yorke


smartasscoach.tri-oeiras.com

After living at sea level (San Diego) for a couple years and moving to Flagstaff, AZ (7000ft) I can tell you that it is MUCH less that 7000ft. When I first got here it felt like I was having an asthma attach and was getting spit out the back of rides during accelerations. I felt fine as long as the intensity was not too high but at race intensities I felt a big difference. I agree with the 1000m (a little over 3000ft for the metricly challenged) you start to see it and 1500m it is noticeable, but from what I understand everyone is different.

FWIW: I've seen a couple people have some serious symptoms of High Altitude Plumonary Edema (HAPE) when they take too big a jump in altitude. If you are heading up above 8-10,000ft there can be more serious problems than not catching your breath.

"The concentration of oxygen at sea level is about 21% and the barometric pressure averages 760 mmHg. As altitude increases, the concentration remains the same but the number of oxygen molecules per breath is reduced. At 12,000 feet (3,658 meters) the barometric pressure is only 483 mmHg, so there are roughly 40% fewer oxygen molecules per breath. In order to properly oxygenate the body, your breathing rate (even while at rest) has to increase. This extra ventilation increases the oxygen content in the blood, but not to sea level concentrations. Since the amount of oxygen required for activity is the same, the body must adjust to having less oxygen. In addition, for reasons not entirely understood, high altitude and lower air pressure causes fluid to leak from the capillaries which can cause fluid build-up in both the lungs and the brain (HAPE). Continuing to higher altitudes without proper acclimatization can lead to potentially serious, even life-threatening illnesses."

Pete

I live and train in Detroit, and raced in Boulder, CO last summer. I could tell that ther was not as much air on the coarse as I needed. That said it was worse on the third and fourth days after arrival (I raced on the day after I got there).

If you are planning on going up make sure that you are in good shape to begin with, and then try not to go anerobic. Once in debt you will find it very hard to recover.

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This is your life, and it's ending one minute at a time. - Fight Club
Industry Brat.

I am in Boulder and the common train of thought is that it takes about a month for the body to completely adjust (make more red blood cells) if you are coming from sea level. We do a Boulder to MT Evans ride twice a year (14K ft summit, highest paved road in the US) and there is NO AIR up there.

I guess that means I can eat twinkies and drink fat tire all winter and go sub 9 @ IMAZ right?

Reactions to changes in altitude are very individual and have nothing to do with fitness. Sometimes those who are fit push too hard and do worse. Take it easy, stay hydrated and you will adjust in a few days. Racing shape will take longer and you will never be as fast up high, but soon you will feel great at altitude. I live at 7000 feet and spend a lot of time between 10k and 12k. When you return to sea level, you will really enjoy the benefits. Conventional wisdom now for elite training is to live and sleep at altitude and do your intervals at low altitude where greater intensity is possible.