Performance and metabolic benefits after sleeping in a high-altitude tent
Well ... I decided to answer those questions through a personal study designed to recapitulate the standard performance high altitude protocol (ref. [1]) and extend it by one more month. In this post, I will try to describe the process, what I experienced and what really changed in my physiology throughout a 13-week long experiment. To give you a sense of the magnitude of this study, it entailed tracking and analyzing over 5,000 data points for 90+ days. The data collection included most physiological parameters previously reported in scientific literature that change with high altitude exposure.
To make things exciting and get rid of the thrilling anticipation, I will jump right in the conclusions first, and then walk you through step-by-step on how I set up this study, how I personally adapted and felt during the nights in the high altitude tent and during the days outside of it, how I came up with the facts and observations, and more importantly, if I - at the end of the day - believe this truthfully improved my health and performance.
This study went on for 13 wks including 2 wks sleeping at sea-level (Pre-Altitude), 8 wks sleeping in a high-altitude tent (at 11,000ft, following a first wk of acclimatization) and 3 wks sleeping back at sea-level (Post-Altitude) - Fig.5. While keeping my lifestyle habits the same i.e., there were no significant week-to-week changes in training volume and intensity as well as no significant changes in sleep, stress and diet/GI health as you can see below (Fig. 1) ...
[Note: I did reduce my weight-lifting hours as the season progressed but at the same time, I spent more hours outside running and kayaking - making my overall net load steady throughout]
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| Fig.1 No significant changes in any of the lifestyle metrics measured daily during the 13wk study (metrics include: training volume, training load (see ref. [2]), activity, sleep, stress and GI health) - p-value > 0.05 Wilcoxon test |
... turns out that sleeping at 11,000ft (for an average of ~8.5hrs/night) and training at sea-level (for a total average of ~1.7hrs/day 6 days a week) for 8 wks had the following effects on my body:
- Key blood markers related to performance increased: Hematocrit and Hemoglobin reached a personal all-time high after week 5 of sleeping at high-altitude and maintained higher values than sea-level two weeks post high-altitude (Fig. 2 and Table 2).
- Electrolyte content and DHEA-S increased: Electrolyte content (Potassium, Sodium and Calcium) along with DHEA-S (the major sex pro-hormone) increased when comparing average values before and after sleeping at high-altitude for 8 weeks (Fig. 2 and Table 2).
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- Lipid content improved: Lipid trends showed higher HDL (good cholesterol), lower LDL (bad cholesterol), and lower total cholesterol and triglycerides comparing average values before and after sleeping at high-altitude for 8 weeks (Fig. 2 and Table 2).
- Metabolic markers improved: Glucose was lower when comparing average values before and after sleeping at high-altitude for 8 weeks (Fig. 2 and Table 2).
[Note: HbA1c was slightly higher but within normal ranges]
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| Fig. 2. Seven comprehensive blood tests and the trends of their blood markers during the 13 week study (2 before, 3 during, 2 after sleeping at high-altitude). Notable increase in HMC (Hematocrit), HMG (Hemoglobin), Potassium, Sodium, Calcium, HDL, and DHEA-S, and decrease in LDL, TG and Glucose. |
- Body weight and fat mass significantly decreased: Fat mass and body weight were measured daily by two independent body scales on the market and showed the same trend of significant decrease from weeks 4-5 of high altitude sleep onwards, and maintained that trend 2 weeks post-altitude (Fig.3).
[Note: A slight drop in body water and muscle mass can be seen during that time but the decrease did not occur at consistently significant levels]
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| Fig. 3. Significant decrease in body fat mass after week 3 and significant decrease in body weight after week 5 of sleeping at the high-altitude tent [* p-value < 0.05 **p-value < 0.005 Wilcoxon test]. Slight drop in muscle mass and body water but not at consistent significant levels [daily measures using Withings Body+ scale] |
- Gut health improved: By measuring precise bacterial DNA content and activity in my gut with an at-home test, before and during the high-altitude tent study, it was found that high-altitude improved my digestion and immunity, lowered my gut inflammation, dysbiosis and intestinal permeability (Table 1).
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| Table 1: Metrics calculated from the bacterial DNA content and activity associated with gut health were improved after sleeping at high-altitude: digestion, inflammation, gut dysbiosis, immunity and intestinal permeability [metrics provided by Thorne's Gut Health DNA test] |
- Younger by more than 1 year: By comparing the differences in biological and chronological ages (delta) before and after high altitude, taking average values, it was found that sleeping in the high altitude tent made me younger by more than 1 year! It also improved individual organ ages (blood age, metabolic age, lipid and liver ages - Table 2).
[DELTA post - DELTA pre = -4.95 - (-)3.7 = -1.25 younger by 1.25yrs, see Table 2 below].
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| Table 2. Changes in biological age and organ ages as well as changes in key blood biomarkers throughout the 13wk high-altitude study [blood test and metrics calculated using the at-home test kit of Thorne's Biological Age test] |
- Potential Performance increase reported in ~2weeks post-high-altitude: I experienced feelings of increased energy and vitality during my workouts in two different days during the second week post high-altitude exposure. Coincidentally, at the same week (wk 12, Fig.4), there were significantly higher RMSSD values measured (RMSSD values of heart rate variability reflect parasympathetic nervous system activity; increased values possibly indicate better recovery).
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| Fig.4. Daily RMSSD values of heart rate variability measured in 2min recordings upon awaking [ns: not-significant; * p-value < 0.05 (Wilcoxon test); data provided by EliteHRV app using PolarH10 heart rate monitor] |
All these physiology data showed that sleeping in the high-altitude tent improved my health and performance but how did the whole process actually make me feel?
Did I tolerate the tent? How was it like during my days and nights of sleeping at high-altitude?
Did it make me feel any better after I returned at sea-level?
As we saw earlier, this study went on for 13 wks including 2 wks sleeping at sea-level (Pre-Altitude), 8 wks sleeping in a high-altitude tent (at 11,000ft following the first wk of acclimatization) and 3 wks sleeping back at sea-level (Post-Altitude) - Fig.5.
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| Fig. 5. High altitude tent study overview and timeline |
Blood tests were done with the Biological Age test before (2 tests), during (3 tests) and after (2 tests) sleeping in the high altitude tent. Two DNA Gut Health tests were also done before and during the high altitude sleep period - Fig.6.
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| Fig. 6. High altitude tent study schematic showing the timeline of the Biological Age test and DNA Gut Health test |
On a daily basis, data were collected for the following categories: Sleep, Training and Lifestyle (using the Polar Vantage M and self-reported values); SpO2 (blood oxygen saturation) and HR (heart rate) in real time during sleep (using the Wellue O2 ring); Room and Tent temperature and humidity upon awakening (using a digital thermometer); HRV (heart rate variability) metrics in 2min measurements upon awaking every morning (using the EliteHRV app and the PolarH10 hear rate monitor); morning blood pressure before breakfast (using MMIZOO portable blood pressure device); Body weight & composition before breakfast (using the Wellue and Withings Body+ scales) - Fig.7.
The high-altitude tent was rented from MileHighTraining.com.
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The tent itself is pretty simple, similar to a camping tent. It wraps over and around your bed mattress and it is super easy to assemble and dis-assemble. When on, a generator pumps high-concentration nitrogen air at a steady rate into the tent with a simple tube that feeds into the tent through a small zipped area/corner of the tent. The generator is not very quiet so it is worth getting a pair of simple but good earplugs if you want a better experience overnight and minimal acclimatization time. It only took me a couple of days to get used to this new environment.
Here is a quick video of how you get the tent assembled and hooked to the generator:
My acclimatization week went super smooth and I had zero issues falling asleep and staying asleep in the tent. I spent the first week at increasing altitude levels day-by-day as: 4,000ft, 5,000ft, 7,000ft, 9,000ft, 10,000ft, 11,000ft, 11,000ft. Following this acclimatization week, I spent the remaining 7 weeks at 11,000ft. After that, I went down and stayed at sea-level for 3 weeks.
[Note: the standard performance protocol recommend 1 week of acclimatization, 3 weeks of high altitude, 2 weeks of post-altitude at sea-level (ref. [1]). I decided to extend the high-altitude exposure by one more month to monitor the effects on my body for both 1-month and 2-month periods and determine my personal optimal stay at high-altitude to achieve maximum benefits].
I had no headaches or changes in appetite during the entire time of high altitude exposure. However, I did notice that as the altitude increased, I would wake up feeling more lethargic and my energy levels would take a bit more to kick in compared to a normal at-seal-level morning. To combat that brain fog, I just added an extra cup of coffee with breakfast and worked well. In terms of training and recovery, during the first couple of weeks, I noticed that some days I would feel more tired than others .. but there was no real pattern here, I believe this was just part of the adaptation process.
Overall, it took me about 2 weeks to fully adapt to my new routine. Things that were expected to see during the adaptation process were: a drop in my overnight blood oxygen saturation levels as well as an increase of my overnight heart rate; changes in my autonomic nervous system reflecting changes in the sympathovagal balance (see Figs. 4,8,9 as well as ref. [3]); and metabolic changes with altered blood lipid levels, glucose and HbA1c (Fig. 2) followed by significant decreases in body weight and fat mass (Fig. 3).
As a side note, it is interesting to see that my lipid values (TC, TG, LDL) increased while in high-altitude but decreased at lower than pre-altitude values after I returned to sea-level. This aligns with the biological changes reported to take place within the fat cells of the body: hypoxia is known to enhance lipolysis in cells and release free fatty acids into circulation - hence this temporary lipid increase in my blood lipid levels but decrease in my body fat mass (see ref. [4]).
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| Fig.8. Time spent at less than 90% SpO2 (blood oxygen saturation levels) during high altitude wks (wk3 - wk10) showed great variability from week to week but it was overall significantly higher than sea-level and it seemed to follow a monthly oscillatory pattern. Minimum heart rate during the night was generally significantly higher during high altitude wks vs. sea-level wks [ns: not-significant; *p-value < 0.05; **p-value < 0.005 Wilcoxon test compared to wk2] |
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| Fig.9. LF/HF ratio of heart rate variability has been proposed as a metric of sympathetic to parasympathetic balance. LF/HF showed a significant decrease during the 8wks of sleeping at high altitude (wk3 - wk10) and then returned almost back to pre-altitude levels during the post-altitude wks (wk11 - wk13), indicating strong ANS (autonomic nervous system) balance changes [ns: not-significant; *p-value < 0.05; **p-value < 0.005; ***p-value < 0.001 Wilcoxon test compared to wk2] |
Looking a bit deeper in the data space ... collapsing all of the 5,000+ data points into their representing single day and using an unsupervised data pattern detection method called PCA (Principal Component Analysis) - a broader pattern emerges! In the PCA plot below (Fig. 10) each dot is a day and represents all metric measurements. You can see then how all data change day to day as the the study progresses (see different aggregation of days/data depending on the status/groups: pre-altitude, acclimatization week, high altitude 1 month, high altitude 2 months and post-altitude).
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| Fig.10. PCA plot of all metrics collapsed in a single dot - day during the 13wk high altitude study. Each dot represents a separate day. The dots are grouped by altitude setting and duration. The size of ellipses represents the 95% confidence interval |
It only makes sense now to ask the question: out of all these data and metrics, which ones are driving the underlying variability of this pattern?
Because by study design, we attempted to keep most parameters steady and introduce only the high-altitude tent as a changing parameter, the altitude setting is obviously the main driver. But excluding the altitude setting, which other parameters play a role?
It turns out that the higher we go up the altitude the lower the overnight SpO (blood oxygen saturation) values and the higher the overnight HR (heart rate) values - as expected (Fig. 11). But in addition, many HRV (heart rate variability) measures also seem to play a role and change, such as time and frequency domains of RMSSD, MeanRR, LF and HF power as well as the LF/HF ratio. What stands out however, is the contribution of the temperature and humidity inside the tent, both of which seem to positively correlate with the altitude setting: the higher the altitude, the higher the temp and humidity inside the tent and the lower the overnight SpO values (Fig. 11).
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The tent does seem to build up higher temperature and humidity compared to the environment outside the tent by an average of ~2.6 F (higher temperature) and ~19% (higher humidity). It is really hard to know what is the cause and effect here. Is it the high altitude setting that drives lower SpO values in my body and thus, higher heart rate, higher respiration rate, which then, builds up heat and humidity in the tent? Is it the material of the tent itself that drives an increase in heat and humidity, which then further drives the variability in SpO values? Or is it simply another reflection of the body's physiological response to high altitude? With the current data it was really difficult to tease out the cause and effect but this observation on its own seems very interesting as it has not been reported in depth before (at least to my knowledge) and it may serve as a new starting point for further research in the area.
In conclusion, I think sleeping in the high altitude tent imposed all expected physiological changes in my body: it increased my blood hematocrit and hemoglobin, improved my metabolic efficiency and gut health, and it gave me a noticeable change in energy levels and sports performance feel 2wks post-altitude. In addition, it seemed to improve my electrolytes, DHEA-S and glucose levels as well as my body composition and recovery - changes that were maintained 2wks post high-altitude. I had no problems or side effects with my sleep and adaptation process at all. The only slightly bothersome effect was a general sluggishness and heavy-feeling during the first morning hours after waking up, which was easily resolved with an extra cup of coffee!
The temp/humidity correlation with SpO values is something that I would like to investigate further in a follow up study but it seemed that it did not affect the end outcome of performance and metabolic benefits (despite the fact that it certainly contributed to a higher variability of the degree of hypoxia in my body by increasing the variability of my overnight SpO values).
Increased temp and humidity inside the tent is something to consider if you are planning to use the tent during the hotter months of the year.
As a last note, it is worth highlighting that this study showed maximum performance benefits after 5-6wks of sleep at high altitude and not after 4wks - as the standard protocol suggests (my data showed highest RMSSD as well as highest HMC and HMG during those weeks, see Fig.4 and Table 2). This is another important point to consider when trying out this product: everybody responds to high altitude differently and may require a personalized protocol in order to receive noticeable benefits. The standard protocol should work for most but max benefits may be achieved after a more personalized protocol gets developed.
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Study Leaders and Contributors:
Science Team
- Loukia Lili, PhD - Sr. director bioinformatics, Thorne HealthTech Inc., study lead
- Nathan Price, PhD - Chief scientific officer, Thorne HealthTech Inc.
Device Support Team
- Wayne Vartabedian - Community engagement, Polar Electro Inc.
- Matt Formato - Director, MileHighTraining, LLC
[1] Millet et al. "Combining Hypoxic Methods for Peak Performance", Sports Medicine 2010; 40 (1): 1-25
[2] Calvert and Bannister "Planning for future performance: implications for long term training", Canadian Journal of Applied Sport science 1980; 5(3): 170-176
[3] Hainsworth et al. "The autonomic nervous system at high-altitude", Clin Auton Res. 2007; 17(1): 13-19
[4] Netzer et al. "Hypoxia, Oxidative Stress and Fat", Biomolecules 2015; 5(2): 1143-1150
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