A systematic review of previous studies looks not just at established fitness and performance benefits of reduced oxygen consumption during training, but also the wider health benefits.
Review by Assoc Prof Mike Climstein, PhD & Dr Joe Walsh, PhD.
Title: Effects of Intermittent Hypoxia–Hyperoxia on Performance‑ and Health‑Related Outcomes in Humans: A Systematic Review
Authors: Behrendt, T., Bielitzki, R., Behrens, M., Herold, F., & Schega, L. (2022).
Source: Sports Medicine-Open. 8(70):1-28. https://pubmed.ncbi.nlm.nih.gov/35639211/
Introduction: I am quite fortunate that I am still in regular contact with a number of friends from university who were on my lifting team. So, every second year when I would travel to the US to present research at the American College of Sports Medicine (ACSM) National Conference, I would fly over a couple days earlier and visit Brett and his wife Lori in Park City, Utah.
If you’re an avid skier, you will know that Park City is one of the best ski resorts in the Western United States. For sea level non-skiing folks, Park City is at an altitude of just over 2,100 metres. To put this in perspective, at sea level, the amount of oxygen in the air that we breathe (called fractional inspirational oxygen content (FiO2) is 20.9%. At 2,000 metres, this amount of oxygen drops to 16.3%. Now, that’s nowhere near Mt Everest (i.e. over 8,800 metres and an FiO2 of 6.8%) but 2,000 metres is just short of the altitude of Australia’s tallest mountain, Mt Kosciuszko, which is 2,200 metres. You will physiologically feel the difference at 2,000 metres, trust me!
Now, being a surf-loving person, my flight to Park City was from sea-level Sydney, to Los Angeles, also at sea level. Then change planes and a direct flight to Salt Lake City (altitude just over 1,200 metres). Next, a car ride up to Park City, and now I am at over 2,100 metres. What do you do when you get to see your great friends only once every couple of years? That’s right, you warmly accept their invitation to sit in the jacuzzi on their deck while it’s snowing, and drink the fantastic raspberry beer from their local microbrewery. Not long after, I’m starting to get a headache, feeling tired and am aware that my heart rate is up, which is unusual for me. I figure that I’m probably a bit dehydrated from the flight and that rehydrating with beer possibly wasn’t the smartest strategy. My headache continues to worsen, so I hit the Nurofen Plus (which always works when I get migraines), but the next day I’m still not feeling crash hot. I should add here that at this time I have my PhD and deliver lectures on altitude medicine, so I should know what is happening to me.
I arrive at the ACSM national conference in Seattle, which is back to my usual sea level altitude, and tell my professorial colleagues Mark and Kent that my recent encounter with raspberry beer must have really smashed me as I had a bad headache for two days that didn’t resolve until I got to Seattle. Without hesitation, they look at me and Mark sarcastically asks “You really think it was the beer?”, before adding “Clearly you had acute mountain sickness from the altitude in Park City” – and the penny dropped. Looking on the bright side, Kent added “But you probably gained some health benefits from the exposure at altitude”.
Another silver lining emerged from the whole episode: I subsequently published an article on the benefits of hypoxia (low oxygen in the body’s tissues) on cardiometabolic risk factors – and continue to do work in the area today. This leads us to this Research Review by Dr Behrendt and colleagues from Germany, who completed a review of the effects of hypoxia on performance and health benefits.
Let me start by saying the effects of hypoxia exercise training on athletic performance are well-established in the literature: maximal oxygen consumption (i.e. maximal aerobic fitness, VO2max) has been shown to significantly increase by up to 26%, and maximal power has been shown to significantly increase by up to 27%. My interest in Dr. Behrendt’s and colleagues’ paper is the health benefits they identified, and they were quite numerous.
Methods: To complete this Systematic Review, which is a summary of the existing scientific literature on hypoxia and health, the researchers conducted an electronic search of a number of key databases (i.e. PubMed, Scopus, Web of Science, Cochrane Library) and this identified over 1,000 articles published from 2000 to 2021. The researchers then refined their search to exclude studies relating to animals and certain medical conditions such as sleep apnoea, whereby individuals have long pauses in breathing while sleeping, which results in hypoxia (and requires medical attention).
Additionally, they only included papers that investigated the chronic effects of intermittent hypoxia at rest or intermittent hypoxia combined with exercise. This resulted in a total of eight papers being included in the review.
Results: Of the papers they reported in their review, some involved hypoxia only and others were a combination of exercise and hypoxia. All of the studies involving hypoxia utilised an intermittent protocol, whereby the participants would breathe hypoxic air (i.e. low oxygen concentration) then breathe normoxia air (i.e. normal room air). These cycles of hypoxia and normal room air varied from four to eight cycles lasting two to seven minutes. The studies were conducted over durations of between three and six weeks, with three to five sessions per week. Table 2 in the paper lists the characteristics of all eight studies, good specifics actually.
Two of the studies evaluated cognitive performance, finding that the addition of hypoxia to exercise led to improvements in global cognitive function. Those individuals who performed three weeks of exercise in a hypoxic setting also showed a decrease in circulating biomarkers for Alzheimer’s disease.
With regard to cholesterol levels, a risk factor for cardiovascular disease, there were two studies which reported a reduction in total cholesterol following three weeks of exposure to intermittent hypoxia (9.8% decrease, 5.6mmol to 5.1mmol). In the study by Serebrobska and colleagues that was included in the review, a significant improvement in total cholesterol (-10.5%, 6.3mmol to 5.7mmol) was reported. That same study also found a significant improvement in low-density lipoproteins of 20% (4.2mmol to 3.5mmol).
Another study found a significant (-38%) improvement in the atherogenic index (a comparison of triglyceride cholesterol to high-density lipoprotein cholesterol; essentially bad cholesterol to good cholesterol ratio) in participants with heart disease who completed 5 weeks of hypoxia exposure. With regard to resting blood pressure, one study reported improvements in both systolic (151mmHg reduced to 130mmHg) and diastolic blood pressure (85 mmHg reduced to 73 mmHg) following five weeks of hypoxia exposure. Another study identified only an improvement in diastolic blood pressure (5%, 82mmHg reduced to 78mmHg).
With regard to blood glucose, exposure to hypoxia resulted in a 9.2% improvement in fasting blood glucose (7.1mmol reduced to 6.5mmol). Another study also reported similar findings with an 8.6% improvement in fasting plasma glucose (6.3mmol to 5.8mmol).
Pros: This is a very interesting review and supports the premise of hypoxia having significant, and varied health benefits. However, more work is required in this area to have definitive conclusions and evidence to support the health benefits of intermittent exposure to hypoxia.
This is an interesting area of research for us; in 2013 we published a review on the cardiometabolic benefits of hypoxic training and we reported back then the benefits on fasting blood glucose, resting blood pressure and cholesterol levels (2% to 14% improvements). I am pleased to say we are now continuing work in this area, as although my campus at Southern Cross University is at sea level (and located near some of South East Queensland’s best surf breaks), we are able to conduct hypoxia studies with the use of a hypoxicator (medical device that can provide air similar to that up to 3,000 meters elevation). Watch this space.
Cons: None of the studies reported the desaturation (drops in blood oxygen level) values (i.e., SpO2) from being exposed to hypoxia.
Assoc Prof Mike Climstein, PhD FASMF FACSM FAAESS AEP
Dr Climstein is one of Australia’s leading Accredited Exercise Physiologists. He is a faculty member in Clinical Exercise Physiology, Sport & Exercise Science at Southern Cross University (Gold Coast). firstname.lastname@example.org
Dr Joe Walsh, PhD
Joe has worked in a number of large international research teams with study findings presented around the world. In addition to working in the university sector, he is a director of Sport Science Institute. sportscienceinstitute.com
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