The changes observed after a week cause the oxygen content of arterial blood to increase significantly above values observed immediately upon arrival at altitude.
Following this adaptation of decreasing plasma volume is an increase in red cell mass. Through responses initiated by the body, reduced arterial oxygen pressure stimulates an increase in the total number of red blood cells.
For example, a healthy, high-altitude native may have a red blood cell count that is 50 percent greater than a native sea level dweller. These two adaptations to altitude have an effect that translates into a large increase in the blood's capacity to transport oxygen at rest and during exercise.
Speed and Power at Altitude
Having lots of red blood cells that flood the body with oxygen-carrying capability sounds great, right? People ought to be aerobic animals after they adapt to altitude.
But here's the bad news: When exposed to higher altitudes, it's nearly impossible for athletes to train at the same intensity as they were able to train while at sea level.
In other words, if you are a lowlander capable of averaging 20 mph for a 40 km time trial, at a heart rate of 175 beats per minute and a perceived exertion of 17 on the Borg Scale (breathing hard), your average speed (assuming a duplicate course profile) could be decreased by 5 to 10 percent for the same heart rate and perceived exertion when exposed to even moderate altitudes. This means your speed will decrease by 2 mph, which is quite a reduction.
What if people who already live at high altitude travel to sea level? Is there an automatic gain in speed? That's a good question, and there's no easy answer.
Since people living at a higher altitude are not able to train at the same intensity levels they would train at as lowlanders, they have not trained their bodies to perform at higher speeds. Unproven by science, perhaps the highlanders don't have the neuromuscular programming, in addition to the metabolic speeds, necessary to cycle fast at sea level.
How long is it before the benefits of high altitude disappear when that athlete travels to race at sea level? Estimates for an athlete to lose the maximum benefits of their native, high-altitude adaptations are in the six- to eight-week range.
Up NextIn Part II
we'll look at utilizing altitude to improve race performance.