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*Dr. Bill Misner, Ph.D.


The "Plans of Mice and Men" are often spoiled when altitude sickness spins its entangling web over an outing, converting an anticipated adventure into a time-standing-still convalescence. Nearly half of all travelers ascending rapidly to altitudes of 8,000 to 14,000 ft. experience unexpected headache, malaise, or decreased appetite. This is a milder form of "Mountain Sickness;" resolving treatment is rest, hydration, analgesics (e.g. ibuprofen), and definitively refraining from alcohol.

Oxygen content at sea level is 21% at a barometric pressure averaging 760 mm Hg, but as altitude increases to 12,000 feet (3,658 meters) the barometric pressure drops to 480 mm Hg, but the number of oxygen molecules per breath is reduced as the oxygen pressure drops [40% less oxygen molecules per breath.] Proper oxygenation requires breathing rate to increase. Extra breaths increase the blood-oxygen content, but never to sea level values. Since the amount of oxygen required for energy is the similar, the body must adjust to having less oxygen. High altitude and lower air pressure forces fluid to leak from the capillaries which can cause fluid build-up in both the lungs and the brain.

Continuing to higher altitudes without proper acclimatization can lead to potentially serious, life-threatening illnesses. Severe forms of Altitude-Induced illness may be life threatening because of pulmonary or cerebral edema. Severe forms are characterized by severe shortness of breath, cough, severe headache, confusion, or hallucinations. This may progress to coma or death, and is regarded as a medical emergency. Immediate descent to lower altitude, administration of oxygen, and medical attention are required.

If you experience these symptoms do not go to higher altitudes. Prescription medication taken in advance may prevent this illness...Headaches should be treated with acetazolamide, rather than simple painkillers. Acetazolamide alters the acidity of the blood and stimulates an increase in breathing rate. This prescription drug is a diuretic, so be prepared to produce more urine than usual while you are taking the drug. In other words hydrate, hydrate, and hydrate!

With increased fluid loss at altitude, electrolyte capsules should also be considered for reducing systemic imbalances in urinary or perspiration induced electrolyte losses. All individuals who once experience mountain sickness are at risk during future trips and should always seek medical advice. Some athletes report a degree of moderate success from using a device called a "Gamow Bag" as soon as the symptoms begin.

Jane Wilson Howarth's descriptive book theoretically implies that this sickness is very complex and still not well understood. She claims acute mountain sickness (AMS) is caused by a failure of the body's biochemistry to maintain the correct balance of acid and alkaline in the blood which in turn is necessary to control breathing and crucial fluid balance in the body. The acid/alkali balance is normally controlled by the concentration of carbon dioxide in the blood; thus the body's drive to breathe is controlled by build up of carbon dioxide (rather than a deficit of oxygen). At sea level this ensures that you breathe in enough oxygen, but at altitude, carbon dioxide is more soluble and the amount in the blood needs to be higher before its concentration is high enough to stimulate a higher breathing rate. You need to breathe faster at altitude so that you can take in enough oxygen from the thinner air. Despite this, the carbon dioxide drive to breathe initially lags behind the body's need for oxygen. When oxygen supplies to the brain are not maintained, headaches and confusion may begin. The headache is a sign that the brain is swelling slightly. After a few days at altitude, other longer-term mechanisms switch in. These are enzyme and hormone changes, which allow the breathing rate to settle to a slower rate again. This is called adaptive acclimatization. [1]

In general the higher the altitude the longer it takes to adapt. Understanding the adaptation process and the things that you can do to "help it go away" will make for a less taxing transition. A number of physiologic changes occur to allow for acclimatization at high altitude. These can be divided into immediate, which take place over several days, and long term, which requires weeks to a few months.

The first thing that happens is your respiratory rate and heart rates speed up. This occurs both at rest and during sub-max. exercise. This helps offset the lower partial pressure of oxygen. You will not be able to reach your maximal oxygen uptake [VO2 Max], so don't get frustrated. The faster breathing rate changes your acid-base balance and this takes a longer to correct. How much do I lack and how long will it take to correct?


The underlying problem with high altitude (>2000 m) is that there is less oxygen and while this may not be that threatening to individuals at rest it does pose a challenge to athletes. Of course for the pure anaerobic events no adaptation is required so this discussion is necessarily focused on endurance training and competition. Being fit gives no guaranteed protection. But indeed, the fitter you are, the faster you can ascend and the more likely you are to suffer from mountain sickness. Athlete who are trying to prove themselves most often get into trouble while fit middle-aged women athletes appear to be best adapted, using a moderate rate of ascent. Sharkey reported research suggesting altitude limitations on exercise rates were based on barometric pressure-PO2 in air-PO2 in lungs-arterial O2 saturation:

-0-  .......................100%
6500 ft. .................. 90%
14100 ft. ................ 75%
23000 ft. ................ 50%


Howarth suggests, "The only way to avoid it is to allow plenty of time for acclimatization and if you notice any symptoms, stop or at least slow down the ascent. A recommended safe rate of ascent is to take several days to reach 3500m(11,000 ft), and then a further week to reach 5500m (18,000ft). This is an average ascent or a rate of about 300m per day, but take rest days and pace yourself according to the slowest member of the party. Even at this rate, not everyone will be able to go high. Many people are too impatient to ascend at this rate, or it may be that accommodation or terrain make it difficult to slow down."[1]

There exists a wide variation between how one individual responds to altitude stress and another reacts unfavorably. Moderate-altitude living (2,500 m), combined with low-altitude training (1,250 m) (i.e., live high - train low), results in a significantly greater improvement in maximal O2 uptake (VO2 max) and performance over equivalent sea-level training. To determine what factors contributed to this variability, 39 collegiate runners (27 men, 12 women) were retrospectively divided into 17 responders and 15 nonresponders to altitude training on the basis of the change in sea-level 5,000-m run time determined before and after 28 days of living at moderate altitude and training at either low or moderate altitude. Responders displayed a significantly larger increase in erythropoietin (EPO) concentration after 30 hours at altitude compared with nonresponders. After 14 days at altitude, EPO was still elevated in responders but was not significantly different from sea-level values in nonresponders. The EPO response led to a significant increase in total red cell volume and O2 max in responders; in contrast, nonresponders did not show a difference in total red cell volume or O2 max after altitude training. Nonresponders demonstrated a significant slowing of interval-training velocity at altitude and thus achieved a smaller O2 consumption during those intervals, compared with responders. The acute increases in EPO and O2 max were significantly higher in the prospective cohort of responders, compared with nonresponders, to altitude training.

After a 28-day altitude training camp, a significant improvement in 5,000-m run performance is, in part, dependent on:
(1) Living at a high enough altitude to achieve a large acute increase in EPO, sufficient to increase the total red cell volume and O2 max, and
(2) Training at a low enough altitude to maintain interval training velocity and O2 volume near sea-level values
(3) How then do you "UP" your EPO?

WHAT IF YOUR EPO EFFICIENCY IS ADAPTIVELY LOW OR REACTIVELY SLOW? If you are one of the unfortunates whose EPO is not where it would enable you to readily adapt, then a long term processes may be your best approach. Long term changes with gradual altitude exposure are:

(A)-Decrease in maximum cardiac output a decreased maximum heart rate
(B)-Increased number of red blood cells
(C)-Excretion of base via the kidneys to restore acid-base balance (Unfortunately, the net result is less tolerance for lactic acid)
(D)-A chemical change within red blood cells that makes them more efficient at unloading oxygen to the tissues
(E)-An increase in the number of mitochondria and oxidative enzymes


DIET - A high carbohydrate, low salt diet allows for better adaptation and less risk of "mountain sickness". Some people experience significant decline in appetite and the resulting loss of muscle mass may hinder performance. Iron is used to make hemoglobin and the demand for making more red blood cells may require low iron supplementation--especially in women or vegetarians.

FLUIDS - Because mountain air is cool and dry you can lose a lot of water, be sure to maintain adequate hydration. Electrolytes should be added in moderate dose proportionate to increased fluid intake and loss.

AVOID ALCOHOL - It is best to avoid alcohol consumption during the acclimatization period, since it appears to increase the risk of "mountain sickness".

EXERCISE - Rate of exercise must be kept slow and easy until adaptation occurs. Pushing too hard may increase your risk of overtraining, dehydration, or injury. As noted above some people lacking the operant EPO levels do not adapt as well as others. There is not one workout protocol that works for everyone--just like at sea level. Log the perceived rate of fatigue [not timed distances], during workout and at rest, morning resting heart rate, weight, and mood. Correlate this with the intensity of your workouts and to help mold a flexible routine that is right for you. Keep the rate moderate or easy will support adaptive cellular mechanisms faster than "pushing the envelope" to the limit.


The body's adaptation to high altitude helps significantly but doesn't fully compensate for the general lack of oxygen. There is a drop of 2% in VO2 Max for every 300 meters elevation above 1500 meters, even after allowing for full acclimatization. To fully appreciate this realize that there aren't any world record times at high altitudes. Think about this for a moment. The air density and wind resistance is much lower. Wind resistance is the cyclist's biggest barrier to speed. If all other factors were equal, then there would be faster times at higher altitudes. Because there aren't, meaning that something else must have decreased. That something is the engine -- the human oxygen engine --telling us to slow down while it changes its cellular response to an oxygen-deprived environment.


[1]-Howarth JW, BUGS, BITES, AND BOWELS, Cadogan Books, London. 2nd edition (August 1999), 90-96.

[2]-Sharkey BJ, PHYSIOLOGY OF FITNESS, Human Kinetics Publishers, Inc., Champaign, Ill., 1984: 196.

[3]-J Appl Physiol Vol. 85, Issue 4, 1448-1456, October 1998.

[4]-Assistance appreciated, courtesy of Dr. Mark A. Jenkins, M.D. @:


Outdoor Action Guide to High Altitude: Acclimatization and Illnesses

*Dr. Bill Misner Ph.D.
Director of Research & Product Development

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