In the hotel room where Sivert Guttorm Bakken was found lifeless on December 23, 2025 in Lavazé, Italy, investigators also discovered a strange mask covering his face. This training accessory, little known to the general public, immediately aroused questions surrounding this death which shook up biathlon a few days before Christmas.
The 27-year-old Norwegian biathlete suffered from myocarditis, an inflammation of the heart muscle which had already forced him to put his career on hold. No cause and effect link has yet been established between the wearing of this
hypoxic mask and his death, but the Norwegian Biathlon Federation reacted cautiously. Enough to raise questions about this funny mask.
Hypoxic mask: the accessory that aims to imitate altitude
A hypoxic mask is a training mask, often made of neoprene, which covers the nose and mouth and has filters or valves. It seeks to recreate hypoxia, this drop in oxygen concentration in the blood felt around 3,000 or 3,500 meters of altitude. The idea comes from altitude training courses used for a long time by endurance athletes. The “Live High – Train Low” method involves living at 2,100 to 2,500 meters for at least 12 hours a day for at least three weeks, while training lower. This exposure stimulates erythropoietin and red blood cells, which improves oxygen-carrying capacity.
But in practice, these masks do not modify the composition of the air but the way of breathing. Ports partially blocked by valves increase resistance to inhalation and exhalation, forcing the athlete to ventilate harder. Some of the exhaled carbon dioxide can also be re-inhaled. However, “this type of mask creates artificial respiratory resistance and cannot create hypoxia similar to that of altitude (real drop in partial pressure in O2)“, specifies Dr. Gérald Kierzek, emergency physician and medical director of True Medical.
Real risks and very limited benefits for athletes
A study published in 2016 followed 24 moderately trained athletes for six weeks of high-intensity cycling, twice per week, with or without Elevation Training Mask 2.0. Both groups saw their VO2max and maximum power progress in a comparable manner, with only the mask group clearly improving their ventilatory thresholds. For the authors, the ETM “does not seem to act as an altitude simulator, but rather as a respiratory muscle training device“, they write in the Journal of Sports Science and Medicine.
Limited benefits therefore but far from trivial risks. The excessive respiratory stress they cause can lead to CO2 accumulation, compensatory hyperventilation and a risk of overtraining. For people with asthma, high blood pressure or COPD, they can increase the risk of attacks or seizures.
“These devices can cause real risks such as increased ventilatory fatigue, lower blood oxygen levels (O2 saturation at 93-94% vs. 95-100% normal), dizziness, shortness of breath and reduced performance during exercise. In people with asthma, heart disease or beginners, they can aggravate simulated hypoxic symptoms (nausea, headaches, etc.), limit VO2max (maximum quantity of oxygen that the body can use per unit of time) and cause insufficient respiratory muscular adaptation for real benefits. All without significant hematological impact: no significant increase in EPO, capable of increasing endurance and sports performance” alerts Dr. Kierzek.
Hypoxic mask: between training promises and safety questions
For athletes like , this type of mask therefore promises to provide additional stress to the effort without leaving the plain. Manufacturers promote strengthening of respiratory muscles and better endurance, drawing inspiration from the renowned effects of stays at altitude. In fact, studies show limited gains, far from the marketing promises.
Following the death of Sivert Bakken, the Norwegian Biathlon Federation “advises against the use of simulated altitude until more information is available on this matter“, while recalling that “It is up to the athletes to decide whether or not to use a simulated altitude“, she said.
While awaiting the final conclusions, sports authorities point out that simulating altitude is never a trivial gesture, especially for athletes with a medical history.