This is an excerpt from Daniels' Running Formula-3rd Edition.
When we attempt to analyze how any type of training affects performance in any sport, it is important to understand what demands running places on the human body. Is speed of greatest importance, or strength and power, or is it endurance that is primary in the sport in question? No doubt being at altitude affects the body in a few different ways, and the following points are worthy of consideration.
- Performance in low-speed endurance events (e.g., running events that last more than about 2 minutes) is slower at altitude than at sea level. Relatively speaking, running over medium and long distances involves slow movement against air resistance, and the slight benefit a runner gains by moving through the less dense air at altitude does not make up for the loss in aerobic power caused by lower amounts of oxygen being delivered by the blood to the exercising muscles.
- Performance in high-speed events, as in the case of sprinters, whether of short duration or prolonged, benefits from the less dense air encountered at altitude. In other words, the reduced air resistance more than makes up for the reduced pressure of oxygen.
- With acclimatization to altitude (2 or more weeks), performance at altitude will improve in endurance events. I have seen some runners, after 3 weeks of acclimatization, race a mile at altitude more than 10 seconds faster than they were able to perform upon initial altitude exposure. You must remember, however, that some improvement comes though just learning how to run a race under altitude conditions.
- Regardless of the length of time available for altitude acclimatization, low-speed endurance performance will never reach that which can be achieved at sea level.
- In addition, some researchers have reported that sea-level performance will (or may) improve as a result of altitude training. Consider the following situation, one that I and, I am sure, other researchers have encountered: A group of runners have just finished a spring semester in college, where they have been studying for final exams; the weather is 90 degrees and 80 percent humidity. We take them to altitude, where it is 80 degrees and 10 percent humidity, and they have nothing to do but eat, sleep, and train, and upon return to sea level they run a new personal best time in a 5K race. Man, that altitude sure is the answer, isn't it? Was it being at altitude or all the other things that changed during this time?
Relative to racing at altitude, there are two types of acclimatization that take place with training at altitude (as mentioned in point 3); one is a physiological acclimatization and one a competitive acclimatization. A big difference between these two types of acclimatization is that the physiological benefits, such as learning to ventilate larger amounts of air, are lost after some time back at sea level, and much of the competitive benefits are not lost, even after some weeks or months back at sea level.
In other words, once you have gone through the process of learning how to race at altitude, that will stay with you fairly permanently; you tend to remember how best to race in this environment. You could compare this to learning to race a new distance. A 5K race is a fair bit different for a miler, but after running a few 5K races, the runner will have adjusted to competing at this distance.
I should clarify that in this discussion about altitude training and racing, I am referring to moderate altitude, which is generally considered altitudes between 1,200 and 2,500 meters, which are in the range of about 4,000 to 8,000 feet above sea level. Most of my studies and training of athletes at altitude have been at elevations of about 2,130 to 2,255 meters (7,000 to 7,400 feet). There's no question that 7,000 feet imposes almost double the stress than does 5,000 feet because the real problems with altitude don't begin until about 3,000 feet above sea level, so going from 5,000 to 7,000 is about the same as going from sea level to 5,000.
Upon arrival at altitude, one's aerobic capacity (V∙O2max) is reduced by about 12 to 16 percent, but a runner's performance is affected by only about 6 to 8 percent. This happens because the “cost” (aerobic demand) of running is less at altitude compared to sea level, as a result of the less dense air against which you are running. So you lose some in aerobic power but gain some back in running economy.