For the first time in perhaps three years, I went running "at altitude" today. What this means is that I ran in a location that happens to sit at a critically high level of altitude. In my case, this was Denver, Colorado, which sits at about 5,430 feet above sea level.
I grew up in an area that was about 4,500 feet above sea level, but have lived at much lower altitudes for the better part of the last ten years. Thus, I have not done much in the way of "altitude training" since I was in my early twenties. Being able to have this experience again brought back all kinds of memories: Memories of side aches, of dry-mouth, of burning lungs and burning muscles, and so on. It was a trip down memory lane.
Those who have only ever lived in places of high altitude have little-to-no insight into low altitude training. Those who have only ever lived in places of low altitude have little-to-no insight into high altitude training. It is only a small subset of us who have experienced both kinds of training in significant proportions. Hence, in the interest of sharing some lessons learned, and in hopes that this information will aide those of you who have trained in one set of conditions and suddenly find yourself in another, I would like to discuss how altitude affects running.
First, The Basics
The general idea here is as follows: The higher the altitude, the less dense the atmosphere is. What this means is that those of us who live and train at higher altitudes must attempt to perform the same activities with less oxygen.
To compensate for life at higher altitudes, the human body develops a higher density of hemoglobin in the blood stream. Hemoglobin, roughly speaking, is a protein contained in red blood cells whose job is to transport oxygen to human cells for use in respiration, i.e. for aerobic energy. The more oxygen available in the air, the less hemoglobin is necessary. Oxygen is so plentiful that each breath brings in a large amount of oxygen, which can then be easily transported into the cells and respirated into energy. The less oxygen in the air, the more the body will attempt to transport oxygen as efficiently as possible. Every morsel counts, thus the body produces a great deal of hemoglobin to absorb every morsel of oxygen and transport it into the cells.
The truth is, it's not density of oxygen that matters so much as it is hemoglobin. As a result, many competitive endurance athletes will spend a large part of their training regimen exercising in places of high altitude so that their bodies will produce more hemoglobin. When they finally descend to sea level and compete in a race, their bodies will have an above-average level of hemoglobin and will therefore be capable of producing more cellular energy for the same number of "breaths."
A Brief Word On "Cheating"
Incidentally, this is also what "blood doping" is. Some athletes will train at high altitudes, and then donate blood to themselves. The high-hemoglobin blood is kept on ice until such time as the athlete is ready for sea-level competition. At that point, they receive a blood transfusion consisting of their own, high-hemoglobin blood. They receive all the benefits of their time at high altitude, even if they have not recently trained at altitude. Most sports governing bodies consider this cheating. I would remark, however, that it is only cheating if it involves a blood transfusion. There is nothing "illegal" about training at altitude two weeks before the competition, but the end result is the same as a blood transfusion. Same athlete, same workouts, same competition. The only difference is the time period between the initial descent and the race day.
Similarly, an athlete (Lance Armstrong, for example) may choose to inject himself with EPO, which is a synthetic hormone that enhances hemoglobin production. Its therapeutic use is to facilitate the healing process for those people who have neutropenia, i.e. low white blood cell levels. For the most part, this is chemotherapy patients. An added side-effect is that additional hemoglobin are also produced. The impact on an athlete is no different than spending a couple of weeks at a high altitude, which I reiterate is perfectly "legal." But taking an injection that results in exactly the same physiological response is considered cheating.
I will leave the ethical discussion to my readers.
Running At Different Altitudes
From the above discussion, it should be clear that training at high altitudes results in higher blood-hemoglobin levels. While this is the object "of interest" with respect to high-altitude training, it is far from being the whole story. What's interesting to me is the fact that running at higher and lower altitudes simply feels different and demands a different approach to training.
That is to say, a person's lungs have to do a lot more work at higher altitudes than they do at lower ones. While this may seem relatively straightforward, the physical sensations involved are remarkably different.
A hurried example would be as follows: When I was growing up and running regularly, I got a side-ache perhaps two or three times per week. In contrast, running at sea level for the past ten years, I may have developed a side-ache two or three times across the entire decade. That the lungs must do more work at higher altitudes is a bald fact, but the depth and length of a person's breathing has an enormous impact on the cadence of a person's running stride.
To push oneself into a sprint at high altitudes means to virtually deplete oneself of one's oxygen levels on a cellular basis. As soon as a person reaches the pace of a sprint, every muscle burns to a degree that many low-altitude runners have never experienced. On top of that, there is no use attempting to compensate with heavier breathing. Where one expects a breath to be, there is only an empty croak. It is an extremely odd sensation indeed to gasp for air, but to have nothing there to fill one's lungs. This is what it means to run at a high altitude.
Of course, if this is all you ever know about running, you will hardly notice it. I myself hardly noticed it for the first two decades of my life. There was nothing to which to compare. I had never run at lower altitudes.
Then, one day, I had the opportunity to run at sea level. I had heard many stories about how much easier it is to run at low altitudes. I expected to triumphantly glide at a mind-bogglingly fast pace, seemingly without effort. Imagine my shock when I discovered that my running pace was nearly identical to what I would have run at high altitudes! What went wrong?
This brings me to low-altitude running. As should be clear by now, running at various altitudes simply has a different feel. As aforementioned, high-altitude running feels as though one is constantly gasping for breath, almost as if the wind has been knocked out of you. Running at low altitudes does not magically become easy. One's muscles must still push equally as hard to reach the same pace. We would logically expect this to be the case, but due to the folklore surrounding altitudes, some runners - myself included - expect some sort of disproportionate ease at which sea-level running can take place.
It doesn't work that way. Running a 4:00 mile at sea level requires exactly the same muscular effort as a 4:00 mile at altitude. The difference is that, where a running acclimated to high altitudes would ordinarily expect that pace to result in a particular amount of "gasping for air," this does not occur at sea level. It takes an even higher level of "muscular effort" to result in the same amount of "gasping for air."
Thus, a high-altitude runner who finds himself at sea level can "afford" to push himself to a faster pace without that effort "costing" the accustomed level of "gasping."
I use quotation marks here because what I am describing is a physical sensation ill-suited to verbal description. Another way to look at it is to consider your own "normal running pace." You go out for a run at the usual pace, and you fall into a rhythm. Your breathing matches up with your strides at a given ratio. If you happen to be accustomed to sea-level running, then when you find yourself at a higher altitude, you will go running at the same speed, and your body will feel identical, but for one difference: You'll be gasping for air. Your muscles will not feel any different. Your awareness of your own pace will not feel any different. The difference will be centralized in your lungs.
Similarly, a runner accustomed to high altitude training will often forget how hard he can push himself during a sea-level outing, because his muscles and cadence will feel the same. The only difference is that his lungs will be taking smaller, shallower breaths. To achieve the same kind of workout he is used to, he must push himself toward a faster pace.
I will further add that his leg muscles might not necessarily be up for the challenge. The key point here is that there is no automatic "benefit" to running at sea-level, even if one is acclimatized to higher altitudes. Training at high altitudes will improve the shape your lungs are in. Training at low altitudes will improve the shape your other muscles are in. Ideally, an athlete will build up both sets of muscles, but of course that is easier said than done.
The point I have tried to make here is that both low-altitude and high-altitude training confers certain benefits.
It may surprise those of us who are accustomed to high altitudes how much harder we can push at sea level without feeling the same level of fatigue and muscle-burning; but in order to enjoy that benefit, we must actually push to that degree. Many don't realize that they have to push to see the difference.
Similarly, those of us who have been fully acclimated to lower altitudes will be shocked to discover how badly their lungs and muscles burn during a high-altitude run. Their muscles may be fully ready to undertake severe punishment, but if their lungs are not used to gasping for air the way high-altitude runners can, they will find high-altitude running extremely daunting.
Hopefully this verbal synopsis of the matter proves useful to you the next time you change altitude and go for a run.