The reason doing an activity at high altitude is difficult is because our bodies get starved of oxygen. Contrary to popular belief, the percentage of oxygen in the air doesn’t change significantly with altitude. This is all to do with pressure.

The higher from sea level we are, the lower the atmospheric pressure. The atmospheric pressure determines the density of the air, therefore in effect the higher you go the less air there is to breath. So although the percentage of oxygen doesn’t change, the number of oxygen molecules available to breath reduces the higher you climb.

AltitudeTable % saturation

Altitude (meters)
Altitude (feet)
Effective Oxygen %


To compensate this need of oxygen the body adapt different processes:

  • From when we reach a higher altitude: We increase our ventilation. So consequently we increase the CO2 production: Increases body acidity, this is regulated by the kidneys ( regulation of o2 and brain). So to have not a kidneys problem and stop this regulation of Co2 is important to drink a lot (6L/ day) or don’t lose water (breath warm- humid). If we stop pissing means that we have a kidney problem.
  • 24h after reach the altitude: We have an EPO production to increase the red cells, to increase the transport of O2.
  • 7 days: We can see an increase in the hematocrit and the effects of blood acclimatization
  • 3 weeks / 400h: Hif 1 (diffusion O2 to muscles) Enzyme and diffusion acclimatization. All our body can do in acclimatization is done.

Is important to think that the SatO2 (Oxygen Saturation) decreases when we are sleeping (we breath less, our body is on a resting mode), so the body reacts worth at altitude, It will take 3-4h after wake up to come back to our normal SatO2 level. So think about this time when it will be hard/bad to do an activity or go higher up. In terms of acclimatization, the best way to recover in altitude is not sleeping but on an awake rest.

To increase the SatO2, we can do hyperventilation’s with a big amplitude, or find a method to have (breathe) Co2 during the sleep.

In the terrain it seems that 5500m is the maximum altitude where we can make a complete acclimatization (higher than that we consume more than we can recover), and we can refer to some experiences of high altitude exploits after an acclimatization “only” at this altitude: Messner in Everest solo (August 1980) and Lorettan and Troillet in Holbein Couloir (Everest, August 1986) did not climb higher than 6000m during the acclimatization but spend around 2 months around 5000- 6000m.


The classical acclimatisation is to go up 500m maximum per day and rest there to acclimatize before going up again. This is a long acclimatisation period with the advantage of being fairly secure but with the consequence of lots of fatigue due to the high altitude “sleeping”. The acclimatisation happens during the exposition at the altitude, because we spend a great amount of time at this altitude.

We can also acclimate in a THSL form. Training high and sleeping low. That means to go as high as it feels ok and down to sleep the lowest possible. This can be 1000-2000 or even more depending the physical capacities and pre-acclimatisation of the climber. With this our sleep will be great and we can fully (or almost) recover for the next day, and our shape will keep higher during a longer period than with a classical acclimatisation. Here the acclimatisation happens when we’re back down and the body is adpating to the stimuli recived some hours before.

The benefits of a THSL acclimatisation are the great recovery and the mantain of the performance levels, but they are also disadvantages. First the fact that to climb to a higher altitude than the one we’re already acclimatized we play with the fact that the negative effects to altitude (Edemas, MAM…) arrive with a delay of +- 8h after the exposition, what means that we need to climb fast and go down fast before this effects arrive, but if for some reason (weather, technical difficulties, problem, physical capacities) we’re not fast enought the consequences can be fatal. We need to also note that even if we have touched an altitude the amount of time spent at this altitude will not be sufficient to fully acclimatize at this altitude, but lower, so in the ascent we need to take this into account too.

For a lower 8000m summit some believe that it is necesary (or very recomended) to spend a night at 7500m, and for a high 8000m (8400-8800m) at 7900/8000m. To limit the probability of Edema on the climb if it takes longer than expected. It is also possible to do a THSL strategy touching one or several times this altitudes without sleeping to start the acclimatisation but knowing that during our climb above this altitude we need to move quickly.

Here some profiles of acclimatisations:

Kilian Jornet: I believe the Cho Oyu – Everest Expedition in 2017 was my best acclimatization profile: HERE



The body can have a memory, if we have experienced an altitude before, the body can adapt mechanisms in a faster / more efficient way. That doesn’t mean that we will not have problems in altitude if we have been there before. Every time we go in altitude we will need to acclimatize and everybody can have problems (MAM, Edema) in altitude some time.

The altitude where we train / live will make a difference, a pre-acclimatization. If one has been training at 4000m during some month, probably we will be able to go straight to 5000m and climb 6000m summits in a short period of time. If we live at sea level, this period will be longer, and we will need to take more progressive. We can considerate that the altitude to reach without any effect is around the altitude we are (living – training) + 1000m.

A good shape, aerobic training will be good to assimilate the first stages of acclimatization but is not because we are more fit that we will acclimatize faster / better.

The anaerobic work can be interesting for altitude. In altitude, we are normally able to keep a pace (slow) but on the moment we want to increase the peace or work in anaerobic for some seconds (sprint), the recovery it will take really long. It will be really hard for our body to eliminate the lactate and the muscles will feel without energy for a long time. Is for that that the anaerobic work before will be interesting, to make the body better on eliminate lactate and on make higher the intensity when we produce lactate. (interesting to do 3’ intervals, 30’’-30’’… or races as Vertical Kilometers)


Captura de pantalla 2015-10-28 a les 20.46.05

Consider the effect of temperature upon pressure altitude. At lower temperature the entire air column is compressed, corresponding to the observation that colder air is denser. Thus a given isosurface (surface of equal pressure) will lie at a lower true altitude in a cold environment compared to a warmer one. In a hot environment, the converse occurs, and a given pressure occurs at a higher true altitude than otherwise.

This effect can be moderately large. During the Antarctic night ground temperatures are common -50° C (-58° F); with even lower temperatures seen every winter at interior stations. These temperatures are roughly 10-15% c
to absolute zero than are the moderate temperatures experienced elsewhere and at other times. The absolute temperature, being reduced by some 10-15%, results in observing the same pressure at a given elevation, as occurs at elevations 10-15% greater under moderate temperatures. Equivalently, for a given elevation, the pressure altitude will be 10-15% higher under Antarctic conditions than for normal temperatures.

At the high-temperature end of the climate spectrum, the effect is smaller because, relative to moderate temperatures, Earth’s hottest surface temperatures deviate by a smaller fraction than do Earth’s lowest temperatures, all fractions calculated using the absolute zero of temperature.

Consider the effect of latitude upon pressure altitude. The acceleration due to gravity g varies with latitude as described below. Then, from Equation (1b) latitude effects pressure altitude via this change in g.

The acceleration due to gravity varies with latitude from two sources. One is the centrifugal pseudo-force owing to Earth’s rotation and amounts to a 0.34% decline in G as one travels from either pole to the equator.

Earth’s departure from a perfect sphere is the second source of variability, with the polar radius less than the equatorial radius by 1 part in 298 – some 21 kilometers. This accounts for an additional fractional decline in G on proceeding from pole to equator.

Air Pressure: The Effects of Altitude, Latitude and Season

by Ward Hobert

A combination of centrifugal force and temperature differences make the troposphere thickest at the equator, 10 to 11 miles. It is only 5 to 6 miles thick at the poles. Due to lower temperatures, the troposphere is denser at the poles, and the net result of all contributing forces and factors is that air pressure is pretty much the same planet-wide at sea level. At high altitudes, this is not true.

Since the air layer over the earth is thinner at the poles, any upward movement from the planet’s surface passes through a greater portion of the air layer than the same movement would accomplish at the equator. Thus, for higher altitudes, air pressure at high latitudes is lower than it is at low latitudes.

We can not quantify this effect until we address seasonality. In the winter the air mass over the poles cools and contracts, and the thickness of the planet’s local atmospheric layer decreases. (Of course, the opposite pole is experiencing summer and its air layer is expanding.) Thus, in winter at high latitudes and high altitudes, air pressure is further depressed.

Now, to quantify: consider the altitude at which air pressure averages 0. 5 atmospheres. On Mt. McKinley, 63: N latitude, this altitude is, on the average, 18,400 feet in mid-summer, and 16,800 feet in mid-winter. In the vicinity of Mt. Everest, 30: N latitude, this altitude is 19,400 feet in mid-summer, and 18,850 feet in mid-winter.

At the summit of McKinley, 20,320 feet actual altitude, the average air pressure in mid-summer is about 0.453 atmospheres, which would correspond to a Himalayan summer altitude of 21,650 feet. In winter the summit pressure for McKinley, 0.420 atm., corresponds to a Himalayan winter altitude of 22,800 feet, and a Himalayan summer altitude of 23,460 feet.

Chimborazo, 20,700 feet actual altitude, is essentially on the equator ( 2: S latitude) and so its summit pressure of about 0.472 atm. does not vary much seasonally.

Most of the information supplied here came from “The World’s Great Mountains: Not the Height You Think”, Terris Moore, American Alpine Journal 16:109, 1968.

For your information:

1 atmosphere = 760 mm Hg = 760 Torrs = 29.92 in. HG = 14.70 psi = 1.013 bars


MAM (Altitude Sickness)

  • head pain – 1
  • nausea – 1
  • appetite loss – 1
  • vomit – 2
  • persistent head pain – 2
  • hight fatigue (not normal) – 3
  • can not pis – 3

If we have some of this symptoms and we add 6 points, we have an acute Altitude Sickness and we should go down and if we have, enter into a hyperbaric caisson.


  • rest dyspnoea
  • dry cough/blood
  • Trouble breathing.
  • Froth and later blood in spit

Take viagra / Adalat / Nifedipine. Go Down, sit upright.  If persist, in 6h we can die.


  • Ataxia
  • Doubled or blurred vision
  • balance problems, Become clumsy
  • hallucination
  • vomit when resting
  • Severe headache

Take corticoids/ dexamethasone/prednisolone – Go Down and not go up again in this expedition,  if persist in 6h we can die.

In case we have a big accident or a edema persist, Amphetamine – Dexamethasone can “give” you some hours of power to go down.

To understand the difference of climbing without supplemental oxygen here is a good study about:

CASE STUDY OF AN ICTUS. due to high Hematocrite / less hydration, the blood became less liquid and it is easy to have vascular problems or ictus.