On December 23, 2025, Sivert Guttorm Bakken, a 27-year-old Norwegian biathlete and European champion, was found dead in his hotel room at Passo di Lavazè in northern Italy, 1808 m above the sea level.

Reports that he was using an elevation training mask (ETM) set to simulate an altitude of about 7000 m have raised clinically relevant questions about cumulative hypoxic exposure, which have not been validated in scientific literature.

Bakken’s medical history may be relevant to the circumstances of his death, although autopsy findings are still pending. In May 2022, he developed pericarditis following a third dose of a COVID vaccine; the condition forced him to suspend competitive activity for nearly 2 years.

Taken together, a prior cardiac condition, the use of a commercial hypoxic device, and the occurrence of sudden death raise clinically important questions regarding the cardiovascular safety of these devices. The case highlights a potential gap in evidence regarding their use in athletes with preexisting heart disease and underscores the need for clearer guidance, medical supervision, and further research into the physiologic effects of extreme or combined hypoxic exposure.

How Hypoxic Masks Work

ETMs are commercial devices marketed as tools to simulate altitude training by reducing oxygen (O₂) intake. However, scientific literature highlighted a fundamental difference in mechanisms of action of these masks. Real altitude induces hypobaric hypoxia by reducing the partial pressure of atmospheric O₂, and ETMs work by mechanically resisting airflow without altering the composition of inspired gases.

“Athletes around the world have used altitude training for years using multiple methodologies, depending on where they live and where they train, in the pursuit of maximizing athletic performance. The potential benefits of altitude training are based on adaptive physiological responses, which compensate for the relative lack of [O₂] in the air, on the muscular, blood, cardiovascular, respiratory, hormonal, metabolic, and nervous systems. Since altitude training is not easily available, strategies have been developed in recent years to make simulated altitude training generate effects similar to those of real altitude training,” wrote the authors on the use of ETMs; the authors were led by Diego Fernández-Lázaro, an assistant professor in the Department of Cellular Biology, Genetics, Histology, and Pharmacology at the University of Valladolid in Valladolid, Spain.

A 2016 study reported that during prolonged submaximal exercise — defined as 20 minutes at 60% of maximal O₂ uptake (VO₂max) — performed while wearing an ETM, the modest hypoxemia observed was primarily attributable to two mechanisms: a reduction in the respiratory rate caused by the valve system and rebreathing of carbon dioxide accumulated within the ETM’s dead space. The authors concluded that wearing an ETM during endurance exercise causes modest hypoxemia but is well tolerated overall.

Other researchers have examined ETMs in different sports. A 2021 study found that during an incremental cycling test with an ETM set to 2743 m, O₂ saturation (SpO₂) decreased by only 1.5% compared with control conditions at maximal intensity. In contrast, at comparable real altitudes of 2500-3000 m, SpO₂ typically falls from approximately 97%-95% to 89%-90%, representing a substantially greater reduction than that produced by the mask.

“The failure to significantly observe [O₂] desaturation and changes in hematological variables suggests that the ETM works more like an inspiratory muscle training device than a simulator of altitude,” wrote the authors in a review published in the Journal of Sports Science and Medicine.

Cardiac Risks

A study published in 2019 evaluated the cardiovascular effects of ETM use in 15 healthy adults during cycling at 70% VO₂max under randomized, controlled conditions. Investigators observed significant alterations in autonomic nervous system function, including higher resting systolic blood pressure, elevated heart rate during postexercise recovery, shortened interbeat intervals during recovery, and reduced sympathovagal balance, expressed as the natural logarithm of the low-frequency to high-frequency (LF/HF) ratio.

This finding is clinically relevant. A reduction in the LF/HF ratio reflects delayed parasympathetic reactivation after physical stress, indicating prolonged sympathetic predominance. The authors concluded that “the ETM induces modest hypoxemia but does not affect heart rate variability during cycling in healthy adults,” while noting that autonomic changes were observed.

The study also reported a significant increase in perceived respiratory effort (P < .001) with the use of an ETM, supporting reports of subjective discomfort that could affect adherence and potentially provoke stress responses in susceptible individuals.

Performance Effects in Doubt

Contrary to commercial claims of performance enhancement, one of the studies documented acute adverse effects during resistance training. In a study involving 20 recreational weight lifters, the use of an ETM was associated with a significant reduction in peak movement velocity during squats and bench press, lower postexercise lactate concentrations, and decreased self-reported alertness and task focus. The dropout rate was 12%, with 3 of 25 participants withdrawing because of dizziness, anxiety, and marked discomfort.

The concurrent reduction in movement velocity and lactate production suggests diminished recruitment of fast-twitch muscle fibers, likely because the participants focused on controlling breathing rather than executing movement efficiently. The authors concluded: “Wearing the ETM during bouts of resistance training did not hinder the ability to achieve desired training volumes during the resistance training session. However, wearing the ETM does seem to attenuate the ability to maintain working velocity during training bouts and negatively influence ratings of alertness and focus for task.”

Doping or Not

“This is a tragic situation with many unresolved questions” said Acting Secretary General of the Norwegian Biathlon Association Emilie Nordskar in a press release.

In May 2006, the World Anti-Doping Agency (WADA) evaluated whether to prohibit the use of artificial hypoxic devices, including hypobaric chambers, altitude tents, and masks. The discussion centered on three criteria: whether such devices provided meaningful performance advantages, whether prolonged use posed unacceptable medical risk, and whether their use violated the fundamental ethical principles of sports.

Tom Murray, a bioethicist and former chair of the ethics panel associated with the WADA, argued in favor of a ban by characterizing hypoxic devices as “passive technology,” saying, “The athlete does nothing more than enter a room, put on a mask, and flip a switch.” This position underscored the distinction between active training and passive technological manipulation of the physiologic environment.

The scientific response was swift. A total of 76 physicians, bioethicists, and scientists, led by Benjamin D. Levine, MD, professor in the Department of Internal Medicine, UT Southwestern Medical Center, Dallas, signed an open letter opposing the ban, arguing that “Biologically, physiologically, functionally — there’s no difference between real altitude and these artificial hypoxic environments.”

Dick Pound, then president of the WADA, announced the decision on September 16, 2006. “The biggest item for discussion was whether we should put on the list of prohibited methods artificially hypoxic conditions and the consensus — in fact the overwhelming consensus of our health, medicine, and research committees — was that, at this time, it was not appropriate to do so,” he said.

Currently, neither the WADA nor international federations classify hypoxic devices as doping devices. Some countries, including Italy and Norway, have enforced national restrictions, creating a complex regulatory environment.

In Bakken’s case, the Norwegian Biathlon Association explained that it was “not currently aware of the circumstances surrounding Sivert’s acquisition and use of this mask,” raising concerns about direct-to-consumer marketing of such devices without medical oversight.

Risk Factors

This case also raises concerns about hypoxic device use in athletes with a history of inflammatory cardiac disease. In May 2022, Bakken developed pericarditis after a third dose of a COVID vaccine, an adverse effect recognized as rare by the European Medicines Agency for mRNA vaccines. The estimated incidence ranges from 1 in 10,000 to 1 in 25,000 among young males, with higher rates reported after the second dose.

Even after apparent clinical resolution, pericarditis may lead to subclinical symptoms including pericardial thickening, focal adhesions, and reduced cardiac compliance. These changes can impair ventricular filling, particularly during acute hemodynamic stress, such as intense exercise at altitude.

ETMs impose inspiratory and expiratory resistance, increasing the O₂ consumption of respiratory muscles. Studies on similar devices have documented a 15%-25% increase in the effort required for breathing (respiratory work). Consequently, during maximal physical exertion, the elevated demand for O₂ by the respiratory system may compromise the amount of O₂ available for delivery to the heart muscle (myocardium), potentially limiting the overall performance or causing stress to the cardiovascular system.

According to VG, one of Norway’s largest national daily newspapers in Norway and widely read across Scandinavia, Bakken set a mask to simulate an altitude of 7000 m, well above the levels evaluated in published studies, which typically range from 2743 m to 3658 m.

Currently, no causal relationship has been established between the use of an ETM, Bakken’s cardiac history, and his death. Autopsy findings will be necessary to clarify the cause of death and the sequence of events.

This story was translated from Univadis Italy, part of the Medscape Professional Network.