Podcast, Science and Physiology

Altitude training with prof. Grégoire Millet | EP#258

 November 2, 2020

By  Mikael Eriksson


Gregoire Millet

Professor Grégoire Millet is one of the world's foremost researchers in the field of altitude training and hypoxic training. He combines his academic prowess with a background as an elite triathlete and coach, and is therefore in a perfect position to not just do the science, but actually apply it in the real world. In this episode, we discuss all things altitude training, plus general training principles from a few of the world's best athletes that prof. Millet has worked with and published data from.

In this Episode you'll learn about:

  • What happens physiologically when training at altitude or in hypoxic conditions
  • The potential performance gains from altitude training, and how everybody can be a responder
  • How to structure altitude training to maximise the performance benefits
  • New(ish) paradigms in altitude training: Live high-train low and high, and Repeated Sprint training in Hypoxia (RSH)
  • Living at altitude year round
  • Altitude champers and tents
  • Dissecting the performances of Martin Fourcade (the most successful biathlete of the last decade, and the most successful French Olympian of all time) and Kilian Jornet (mountaineer, trail and mountain runner, summited Mount Everest twice in a week without supplemental oxygen)

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What happens physiologically when training and racing on altitude

05:00 -

  • The following mechanisms applies to the so-called ”train-high-live-high” strategy:
  • The physiological adaptions that occur from training and residing on high altitude is to the greatest extent related to the body’s oxygen transporting capacity.

    All stages of the transport chain of oxygen seem to be affected of the altitude, and hence physiological adaptions correspondingly occur at all stages as well.

    However, the most central part of the body’s ability to transport oxygen is hemoglobin, an oxygen binding molecule in the blood.

    The most important adaptions to high altitude is therefore related to hemoglobin.

    Hemoglobin can be measured through blood samples, either as the concentration (normally) of hemoglobin or the total amount of hemoglobin in the body (considerably more technical to test), which is out of most interest.
  • When we are at altitude, the barometric pressure is considerably lower compared to sea level, and this makes it harder for the oxygen to diffuse from the alveoli in the lungs to the capillaries in the lungs (where the gas exchange in the lungs appear).

    This leads in turn to an increased breathing rate (reflects a good sensitivity for the changed environment in the athlete) in order to increase the pressure in the alveoli so that the oxygen easier will diffuse from air to blood, the increased breathing rate also leads to an increased carbon-dioxide ventilation and thus lower levels of carbo-dioxide in the blood (hypocapnia).

    The body detects this hypocapnia (as well as a lower arterial pressure of oxygen), which will induce several changes in the blood composition.

    One such change is an altered buffert capacity in regards to the acid-base regulation of the body, the amount of bicarbonate in the blood, which is an important part of the aid-base regulation buffert system is reduced, which in turn leads to diuresis (increased urine production).

    Consequently, another clear symptom of an athlete being responsive (reacts to chemical alterations in the blood) to a high altitude environment is that he or she needs to run more frequently to the toilet and pee.
  • The greatest physiological adaptation that will be seen from a high altitude training camp is an increased total mass of hemoglobin.

    To put things into context, a poorly-moderately trained adult male typically have a VO2max of around 45 ml oxygen/min/kg, while some of the highest recorded endurance athletes have recorded VO2max:s of just above 90 ml oxygen/min/kg.

    These athletes also display twice as high total mass of hemoglobin as their poorly-moderately trained counterparts, indicating that this is a parameter that corresponds extremely well to VO2max, and in the next step to endurance performance in general.
  • Typically, 100h @ optimal altitude will lead to a 1 % increase in total hemoglobin mass.

    In 3-4 weeks, this will lead to a 3-4 % increase in hemoglobin mass (in athletes who responds well to residing and training on high altitude).

    The gains in performance will, however, typically not be equally big since VO2max is only part of performance.

    However, there are clear indicatives that altitude training could also lead to a better work economy, and improve performance due to that factor as well.

    Optimal altitude is for most people between 2300-2500m as this altitude is sufficient to induce powerful physiological responses, but will not affect the sleep quality too much as well as training quality can be fairly maintained.

Training at altitude

28:10 -

  • Generally, one needs to be at altitude for at least 18 days but preferably 3-4 weeks to see any meaningful adaptions.
  • It is crucial that the intensity must be decreased to compensate for the lower VO2max one exhibits at altitude.

    Generally, VO2max decreases by 6-7 % per 1000m of altitude and the intensity should hence be modified accordingly (same percentage of reduction in running velocity and cycling power).
  • During the acclimatization phase (between 3-10 days depending on previous experience from altitude training) one must maintain aerobic training (low intensity), strength training and sprints (in order to maintain neurological adaptions).

    It is essential to keep the intensity low during the acclimatization phase because if the intensity goes up too much, this could alter the pH level in the blood, which in turn inhibits many of the adaptive processes, such as the production of EPO, which signals to the body to create more red blood cells and with that more hemoglobin.

    As the athlete gets more and more acclimatized to the altitude the training intensity could carefully be raised, but it is important to monitor the training intensity diligently throughout the entire altitude training camp.
  • One way to monitor altitude acclimatization is by the oxygen saturation of the blood (percentage of hemoglobin molecules that are oxygenated, i.e. carries oxygen molecules).

    At sea level the saturation is 98 % and during the first days at around 2500m altitude this percentage could drop to 87-88 %.

    From this level, one should expect a daily increase in saturation up to maybe 93-94 % where it usually stabilizes (it will never reach 98 % on altitude).

    If an athlete is doing too intense training too early, then typically the saturation will drop the following day.
  • Another good way to monitor altitude acclimatization is by the athlete’s state of hydration, which can be monitored by weighing the athlete every day and/or by looking at the concentration of the urine.

    When at altitude, one looses more fluids by two different mechanisms, the first one being by an altered chemical balance in the blood, which induces diuresis (explained above) and the other one being due to the increased ventilation rate (as we breath, water vapor is breathed out).

    If an athlete reaches a too severe state of dehydration, this can also impact the acclimatization process.
  • A third way of monitoring the acclimatization is by measuring heart rate variability (HRV) daily, which should stabilize during the acclimatization period.

    Further, it is also crucial to monitor the HR during sleep.

Training after the acclimatization phase

39:15 -

  • Generally, one can maintain a high training volume when training at altitude, but there are certain aspects one needs to take into consideration even when training at fairly low intensity.

    The first one being to make sure to stay hydrated as one looses more fluids on altitude and the other one is that the body tends to consume more carbohydrates when exercising at altitude, creating a greater risk for hypoglycemia, hence one must make some nutritional changes (increase the carbohydrate intake) in order to compensate for this.
  • In terms of intensity training, the intensity needs to be adjusted for the altitude as well as the current stage of adaption.

    The before mentioned rule of 6-7 % decrease in VO2max per 1000m altitude applies to non-adapted athletes, as the athlete adapts to the altitude, this % decrease in VO2max will be less but will never be the same as on sea level.

    So for instance, at 2000m altitude, the decrease in VO2max is at start of a training camp typically around 15 %, however, after a week or so, this percentage would be closer to 9 % and by the end of the training camp (3-4 weeks) down to 5 %, which it basically will never get lower than.
  • I would also recommend athletes to not conduct high intensity sessions to the same extent as they do on sea level because of longer recovery time and a greater demand for carbohydrates (more difficult to replenish glycogen stores post session).

    One also needs to take longer recovery between intervals during the session itself.

Individual responses to altitude training

43:45 -

  • To be honest, I don’t think there exists competently non-responders to altitude training, but different people exhibit different chemo sensibility (reactions to alterations in the chemical blood composition induced by altitude), which plays an important role to how they will repsond to altitude training.

    To start with, one must check iron levels before going to an altitude training camp, because if the iron stores are low, then the body won’t be able to increase the production of hemoglobin and hence no respons will be yielded.

    Different people also will need different altitudes in order for the body to react in the desired way, if the altitude is too high or too low, no physiological adaptions will occur.

    One way to get an idea of what degree of altitude an athlete will need to live and train at in roder to get a sought after physiological response is to check the oxygen saturation by the end of a VO2max test performed at sea level, if the saturation is severely affected by the end of the test, then this indicates that the athlete should not go as high as 2300-2500m altitude, which is typically recommended.

Post altitude training

48:25 -

  • Plenty of research has been conducted on when one gets a performance peak following a high altitude training camp, the current consensus within in the field is the following:

    As soon as day 2-3 post altitude training one is likely to get a good performance, but this is practically very difficult to capitalize on.

    After this, a period of poor performance is likely to occur as one needs to readapt to sea level breathing patterns and biomechanics.

    The reason for why (primarily running) biomechanics is hypothesized to be influenced in a negative way by altitude is because one cannot run at the same velocity due to lower VO2max at altitude, and that is one would need a readapting phase to sea level running biomechanics, however, new research suggests that this is not the case (a soon to be published study suggests that altitude is not detrimental to running biomechanics as previously hypothesized).

    However, it has also been suggested that one also is likely to get good performances between day 5-6 post altitude camp.

    After 2 weeks to up to 3-4 weeks back at sea level, one is rather certain to get a good performance as the hematological adaption processes from the altitude almost certainly have reached its full potential, leading to a peak in VO2max.

    During this period, athletes also display their best work economy, hence the increased performance seen in this period originates from both a peak in VO2max as well as improved work economy induced by the altitude training.


57:00 -

  • In recent years it has been suggested that one might combine ”the best of two worlds”, by living at fairly high altitude but train at lower altitude.

    In theory, one would then get the hematological responses from living at altitude and simultaneously maintain a higher training quality (intensity).
  • Personally I do believe that this strategy could be very effective if it is being applied in the right way.

    However, the best strategy would probably be to combine ”train-high-live-high and ”train-low-live-low”, for instance by starting an altitude training camp by living and training high and then as the key event approaches one can do more and more training at lower altitude.

Repeated sprints in hypoxia (RSH)

1:00:30 -

  • This is a training strategy, which includes repeated high intensity sprints in a hypoxic environment (either at altitude or in an artificial hypoxic environment).

    The mechanisms behind why this type of training seems to be particularly effective have nothing to do with a hematological response, but is instead believed to be mediated by special signal cascades induced by high intensity in combination with hypoxia, and seems to be able to improve fatigue resistance (mainly acute) in the muscles.

    This mainly has applications for sports where attacks or sprints occur frequently (and hence to some extent in short course triathlon where the pace is rather uneven throughout the race).

    For olympic distance triathletes a RSH session could include 3-4 sets of 4-6reps of 10s sprints with 20s of recovery.

”Train-low-live-high and train high”

1:05:10 -

  • This training strategy includes residing at high altitude, while completing most training sessions at lower altitude, however, the training is also combined with RSH sessions 2-3 times per week (can even be done during the acclimatization phase.

Living at altitude

1:07:30 -

  • For people living all year around at altitude, I think it is important for these athletes to do training camp at sea level in order to execute some really high quality training.

    I don’t think it is desirable to stay on altitude all year around, but it is probably extremely beneficial to stay most of the year at altitude and during some periods of times come down to sea level for training and/or racing, much like the African runners do.

    The same recommendations on when to go back to sea level for a race (at sea level) applies for people living at altitude as the athletes being on altitude training camps.

Altitude tents and chambers

1:10:00 -

  • There are different types of altitude tents or chambers, some of them works by regulating the barometric pressure (as in real altitude) and some works by lowering the percentage of oxygen in the air within the tent or chamber.

    The conditions in these artificial environments as well as the physiological responses do differ from real altitude in some ways, but a recently published study that investigated the hematological response found no significant differences between real altitude and artificially created altitude environments.

Case studies of top endurance athletes

1:15:45 -

  • Over the years, I have had the great benefits of taking part of some of the world’s best endurance athletes’ training, among them Killian Journet (ultra running), Romain Bardet (cycling) and Martin Fourcade (biathlon).

    In many features, these athletes express great similarities despite being involved in different sports.

    One such parameter is altitude, all these athletes have been conducting training on altitude during extensive periods of their training.

    There is an ongoing discussion that athletes who already express very high VO2max and/or total mass of hemoglobin, will not benefit from altitude training, but in my opinion this is not the case, even these athletes could get a 1-2 % performance gain from altitude training, which at their level could be the difference between a podium position and being outside of the top ten finishers.
  • In our case study of Martin Fourcade, our main findings were that the more polarized his training was, the better he seemed to perform.

    We also investigated the link between heart rate variability (HRV) and performance and found a strong correlation here as well, hence, I encourage all athletes to monitor their HRV daily, and particularly during critical phases of the training (i.e. when being on altitude, increasing training load, making dietary changes etc.).
  • Killian Journet is an athlete who implemented the ”live high-train-low and train high” (by living and sleeping in an altitude tent) strategy in his training with good respons.
  • Finally I would like to emphasize that altitude training can be a very effective training tool, and if well monitored it could be extremely effective (it can help you achieve those extra 3-4 % of performance gains).

    However, poorly executed training on altitude could instead be detrimental to performance.

Final advices

1:24:00 -

  • My first advice in regards to altitude training is to monitor responses in form of saturation, hydration, HRV, fatigue, nutrition, etc. in a very accurate way when going on an altitude training camp (especially during the acclimatization phase).
  • My second advise it to monitor post altitude responses (mainly subjective scores such as feeling and perceived fatigue) to determine what can be the best timing for performance post an altitude training camp in the future.
  • My third message is that altitude training is a very complex training method that every athlete and coach needs to develop an individual strategy in regards to, which can only be done by experience.
  • A final advice not related to altitude training is to implement a polarized training approach and monitor your HRV.

Rapid fire questions

1:26:10 -

  • What is your favorite book, blog or resource related to endurance sport? I have to favorite books, ”Endure” by Alex Hutchinson and ”How bad do you want it?” by Matt Fitzgerald.
  • What is a personal habit that has helped you achieve success? Hard work! Not to be discouraged by failure.
  • Who is somebody that you look up to or have inspired you? I am very impressed by Killian Journet, both by his physical performances and the way he shares his training data as well as his life style and personality.


Mikael Eriksson

I am a full-time triathlon coach, founder of Scientific Triathlon, and host of the top-rated podcast That Triathlon Show. I am from Finland but live in Lisbon, Portugal.

Please contact me if you have feedback on the podcast or want to make suggestions for improvement or send in a question for a Q&A episode.

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