Key Points
Intermittent hypoxia improves cardio-autonomic function and exercise tolerance
There are several ways to achieve intermittent hypoxia and receive benefits, including prolonged hypoxic exposure, intermittent hypoxic exposure, and intermittent hypoxic training
Intermittent hypoxia is beneficial in sedentary and clinical populations
The Breathing Diabetic Summary
I love review papers because they summarize the key findings from the scientific literature in an easy to follow manner. Therefore, anytime I find a review study on a subject of interest, I dive right in.
This one was unique because it looked at the effects of simulated altitude on non-athletic, sedentary, and clinical populations. Most studies on simulated altitude involve elite performers, so it was interesting seeing a review paper focusing on more “everyday” people.
Using different search criteria, they identified 26 studies that have looked at intermittent hypoxia in the abovementioned populations. Within those 26 studies, they then identified 3 different methods of achieving intermittent hypoxia:
Prolonged hypoxic exposure (PHE): Continuous hypoxic interval, such as “live high, train low”.
Intermittent hypoxic exposure (IHE): Short intervals (5-10 min) of hypoxic:normoxic exposure.
Intermittent hypoxic training (IHT): Exercising in hypoxia.
For our purposes, IHE and IHT are the only practical methods for achieving hypoxia via breath holds. However, the results for PHE will also be included for completeness (and, maybe one day altitude tents will be affordable!).
Here, I’ll summarize the benefits they found for each method of hypoxia.
IHE:
Reduced systemic stress
Improved heart rate variability
Improved autonomic balance
Reduced blood pressure
Greater exercise tolerance
Longer time to exhaustion while exercising
Hematological results were mixed. Some studies showed increased red blood cells, others didn’t.
PHE:
Improved lung ventilation
Improved submaximal exercise performance
Improved blood lipid profile
Improved blood flow to the heart
IHT:
Increased aerobic capacity
Increased fat burning
Increased mitochondrial density
Improved autonomic balance
With respect to PHE, the research suggested that at least 1 hour of 12% O2 for 2 weeks would provide the greatest benefits without side effects. They did not provide recommendations for IHE or IHT.
However, a 2014 review study showed that 3-15 episodes of 9-16% O2 is the therapeutic range for IHE. This corresponds to blood O2 saturations of approximately 82-95%.
Also, from a practical perspective, we know that we can perform walking breath holds to achieve mild IHT. Essentially, we combine the IHE protocol with walking.
Overall, this paper suggests that intermittent hypoxia has many benefits in sedentary, non-athletic, and clinical populations, including improved cardiovascular and autonomic function and increased exercise capacity.
It also showed that there are several ways to achieve those benefits: Prolonged exposure, intermittent exposure, or exposure during exercise.
I recommend that you find a modality that fits you or your client’s lifestyle that can be practiced consistently.
Abstract from Paper
BACKGROUND: The reportedly beneficial improvements in an athlete's physical performance following altitude training may have merit for individuals struggling to meet physical activity guidelines.
AIM: To review the effectiveness of simulated altitude training methodologies at improving cardiovascular health in sedentary and clinical cohorts.
METHODS: Articles were selected from Science Direct, PubMed, and Google Scholar databases using a combination of the following search terms anywhere in the article: "intermittent hypoxia," "intermittent hypoxic," "normobaric hypoxia," or "altitude," and a participant descriptor including the following: "sedentary," "untrained," or "inactive."
RESULTS: 1015 articles were returned, of which 26 studies were accepted (4 clinical cohorts, 22 studies used sedentary participants). Simulated altitude methodologies included prolonged hypoxic exposure (PHE: continuous hypoxic interval), intermittent hypoxic exposure (IHE: 5-10 minutes hypoxic:normoxic intervals), and intermittent hypoxic training (IHT: exercising in hypoxia).
CONCLUSIONS: In a clinical cohort, PHE for 3-4 hours at 2700-4200 m for 2-3 weeks may improve blood lipid profile, myocardial perfusion, and exercise capacity, while 3 weeks of IHE treatment may improve baroreflex sensitivity and heart rate variability. In the sedentary population, IHE was most likely to improve submaximal exercise tolerance, time to exhaustion, and heart rate variability. Hematological adaptations were unclear. Typically, a 4-week intervention of 1-hour-long PHE intervals 5 days a week, at a fraction of inspired oxygen (FIO2) of 0.15, was beneficial for pulmonary ventilation, submaximal exercise, and maximum oxygen consumption ([Formula: see text]O2max), but an FIO2 of 0.12 reduced hyperemic response and antioxidative capacity. While IHT may be beneficial for increased lipid metabolism in the short term, it is unlikely to confer any additional advantage over normoxic exercise over the long term. IHT may improve vascular health and autonomic balance.
Journal Reference:
Lizamore CA, Hamlin MJ. The Use of Simulated Altitude Techniques for Beneficial Cardiovascular Health Outcomes in Nonathletic, Sedentary, and Clinical Populations: A Literature Review. High Alt Med Biol. 2017;18(4):305-321.