Tip · Oxygen

Sleeping at (simulated) altitude

Q: How much does altitude training really achieve?

The most robust figure comes from a meta-analysis with raw data from 17 studies: about 1.1 % increase in hemoglobin mass per 100 hours of altitude exposure, and after altitude about 3.3 % above baseline for up to 20 days. On the performance side, elite runners improved by 1.1 % over 3,000 m. In elite sport that is a lot, in everyday life it is little.

Q: Are mountain weekends enough?

According to the dose recommendations, no. Less than 12 to 14 hours daily over less than two weeks, under 200 hours in total, is considered probably insufficient; more than 14 hours daily over three to four weeks is recommended, that is, more than 300 hours. A weekend at 1,800 m provides about 40 hours of exposure at the lower stimulus threshold.

Q: Does an altitude tent work just like real altitude?

The developer group’s practical review says natural and simulated altitude could produce comparable increases in red cell mass and endurance performance with sufficient exposure time. The only double-blind, placebo-controlled study with normobaric hypoxia, however, found no difference from placebo in hemoglobin mass, VO2max or time-trial performance after four weeks of 16 hours daily at 3,000 m.

Q: Is it true that many people do not respond at all?

Yes. In the classic study, 39 runners were retrospectively divided into 17 responders and 15 non-responders. Non-responders no longer showed elevated EPO levels after 14 days and had no increase in either red cell mass or VO2max. The 95 % prediction interval for the individual hemoglobin response after 300 hours ranges from 1.1 to 6 %.

Q: Why do you have to train low?

Because training quality suffers at altitude. In the original study, VO2max and red cell mass rose equally in both altitude groups, but the 5,000 m time improved only in those who trained low. Non-responders were significantly slower in intervals at altitude and achieved a lower oxygen uptake in doing so.

Q: Do I need an iron value beforehand?

Yes, that is the only preparation explicitly required in the practical literature. With serum ferritin below 20 µg/l in women and below 30 µg/l in men, an altitude-induced increase in hemoglobin mass is minimal. Normalization two to three weeks before the start and continuation throughout the entire altitude exposure are recommended.

Altitude stress stimulates EPO and red blood cells.

Sleeping high and training low is one of the few biohacking methods with a randomized original study and a dose you can recalculate: about 1.1 % hemoglobin mass per 100 hours. Here is what follows from it — and what the two best-controlled studies found.

In short

Hemoglobin mass rises under altitude exposure by about 1.1 % per 100 hours, and after altitude it remains about 3.3 % above baseline for up to 20 days. In the original study, however, the 5,000 m time improved only in the group that slept high and trained low. The dose is measured in hours: more than 14 hours daily over three to four weeks is recommended, that is, more than 300 hours. Individual variation is large, and the two best-controlled studies found no effect at all. Without adequate iron status, blood formation does not work anyway.

What lies behind it

The reduced partial pressure of oxygen stabilizes the hypoxia-inducible factor, the kidney releases more erythropoietin, and over weeks the red cell mass grows. In elite runners, the EPO level was nearly doubled 20 hours after ascent (from 8.5 ± 0.5 to 16.2 ± 1.0 IU/ml), and hemoglobin concentration rose by 1 g/dl over the camp.

The second part of the principle is just as important: training takes place low, because at altitude interval speed drops. In the original study, VO2max and red cell mass rose equally in both altitude groups; the 5,000 m time improved only in the high-low group.

The dose is time

The most robust quantitative statement comes from a meta-analysis with raw data from 17 studies: about 1.1 % increase in hemoglobin mass per 100 hours, for classic altitude training as well as for Live High Train Low. After altitude, the value stayed about 3.3 % above baseline for up to 20 days.

From this follows the dose recommendation of the developer group: less than 12 to 14 hours per day over less than two weeks, under 200 hours in total, is probably too little; more than 14 hours over three to four weeks, that is, more than 300 hours, is better suited. Three weeks with eight hours per night are not the same as three weeks with 16.

How large the variation really is

The most honest number in the meta-analysis is not the mean but the prediction interval: for an athlete’s true response after 300 hours, it ranges from 1.1 to 6 %. The analytical measurement error is about 2 %. Anyone who measures once cannot distinguish a small real effect from noise.

The same pattern at the performance level: 39 collegiate runners, women and men, were retrospectively divided into 17 responders and 15 non-responders; in the non-responders, EPO was no longer elevated after 14 days, and neither red cell mass nor VO2max increased. The often-quoted figure of “one third” belongs to a different finding: among elite runners, one third ran a personal best after the altitude camp.

What is well supported

The original study is still the cleanest work on the method: 39 trained competitive runners, women and men, a four-week training camp, randomized to three groups of 13 each — living at 2,500 m and training at 1,250 m, living and training at 2,500 m, living and training at 150 m. Both altitude groups increased VO2max by 5 %, proportional to the 9 % increase in red cell mass (r = 0.37; p < 0.05); the control group did not. The 5,000 m time improved only in the high-low group. It also works in elite runners, albeit modestly: 14 men and 8 women improved their 3,000 m time by 1.1 % after 27 days (95 % CI 0.3–1.9 %).

What the studies show

The original study (Levine and Stray-Gundersen 1997)

39 trained runners (27 men, 12 women), randomized to three groups of 13 each. The primary performance measure was a 5,000 m time trial. VO2max plus 5 % in both altitude groups, red cell mass plus 9 %, but performance improvement only with high-low (13.4 ± 10 s). This cleanly separates physiological adaptation and performance.

The dose meta-analysis (Gore et al. 2013)

Meta-analysis based on raw data from 17 studies that determined hemoglobin mass with the optimized carbon monoxide rebreathing method. It rose during exposure by about 1.1 % per 100 hours and remained about 3.3 % above baseline for up to 20 days after altitude. The 95 % prediction interval for the individual response after 300 hours ranges from 1.1 to 6 %.

The only double-blind placebo study (Siebenmann et al. 2012)

16 endurance cyclists trained for eight weeks below 1,200 m and spent 16 hours daily for four weeks in rooms with normal air (placebo, n = 6) or normobaric hypoxia equivalent to 3,000 m (n = 10); participants did not know their group assignment. Hemoglobin mass, VO2max and mean power in a simulated 26.15 km time trial remained unchanged in both groups.

Where the number comes from — and where it does not

The two best-controlled studies found nothing. Four weeks of 16 hours daily of normobaric hypoxia at the 3,000 m level changed neither hemoglobin mass nor VO2max nor time-trial performance. And at real altitude a controlled study came out the same way: 26 nights at 2,207 m with 16.7 ± 0.5 hours of daily exposure produced no effect on erythropoietin, reticulocytes, hemoglobin mass, VO2max or 3,000 m running performance in 19 cross-country skiers, women and men. This dose lies exactly in the range of what altitude tents offer. All positive studies are unblinded, and altitude training has a large expectation effect.

The meta-analyses also contradict each other on VO2max: an analysis of 13 studies with 276 participants found no effect (SMD −0.13; 95 % CI −1.21 to 0.96; p = 0.68), another of 17 publications found a clear one (SMD 0.67; 95 % CI 0.35–1.00; p < 0.001).

How to do it

The key figures from the developer group’s practical review: below 1,800 m, altitude may not provide a sufficient stimulus; above 3,000 m, the potential to impair recovery increases. Duration: under 200 hours too little, over 300 hours better suited. Iron is a prerequisite: with serum ferritin below 20 µg/l in women and below 30 µg/l in men, an altitude-induced increase is minimal; iron status should be normalized two to three weeks beforehand.

In the studies it looked like this: four weeks of living at 2,500 m and training at 1,250 m. Mountain weekends do not achieve this — 1,800 m is the lower limit, and a weekend provides about 40 hours of exposure.

Safety

The recommended sleeping altitude lies below the critical threshold for altitude sickness, and that is the decisive point. In a study of 1,370 mountaineers in the Western Alps, the prevalence on the day of ascent was 5.8 % at 2,850 m and 2.1 % at 3,050 m, but 14.8 % at 3,650 m and 21.9 % at 4,559 m. At a sleeping altitude of 2,000 to 2,500 m it is therefore rare. The second point is sleep: in a nocturnal study of 37 healthy people, the apnea-hypopnea index at 3,400 m was 40.3 ± 33.0 in men and 2.4 ± 2.8 in women; at sea level, all had a normal breathing pattern. The higher the tent is set, the more likely sleep suffers — over weeks a real counter-effect. People with untreated sleep apnea, coronary heart disease, heart failure, pulmonary hypertension, sickle cell disease or severe anemia, pregnant women and children should be cautious.

BK-Score Supported, with caveats

Human evidence		6
Mechanism		8
Safety data		6
Hype gap		5
Track record of use		8

The “live high, train low” principle is well studied in competitive sport, and the EPO response is measurable. For altitude tents, the only placebo-controlled study with normobaric hypoxia found no effect at all, and a controlled study at real altitude also came up empty. In the classic responder analysis, 15 of 32 classified runners were non-responders.

What is rated is the state of knowledge, not the effect. “Safety data 9” means well studied – not harmless.
Subjective assessment by Biohacking Kompakt based on published scoring rules – not a scientific rating and not a medical recommendation. Rules and all ratings (German)

Frequently asked questions about sleeping at (simulated) altitude

How much does altitude training really achieve?