Nicholas B. Tiller

The blog that unifies scientific skepticism, critical-thinking, health & fitness, and the exercise sciences

  • Nicholas B. Tiller Ph.D.

#42: No, it's not dangerous to exercise with a facemask

Two recent review articles, published in the Annals of the American Thoracic Society and the Journal of Cardiopulmonary Rehabilitation and Prevention state, quite unequivocally, that exercising with a facemask evokes no detrimental effect on health or performance.

This is an important conclusion given that both the CDC and WHO strongly recommend the use of facemasks to slow the transmission of the COVID-19 virus. Facemasks should especially be worn during “aerosol-generating procedures” like exercise during which the individual generates tiny respiratory particles that are sufficiently small and light to remain suspended in the air for long periods, travel beyond 6 ft from the source patient, and penetrate or circumnavigate surgical masks. Aerosols are distinct from respiratory “droplets” which fall the ground before traveling particularly far.

These new insights on facemasks contradict the major premise of a June 2020 article featured in the “Health and Medicine” category of The Conversation which argued that “it could be dangerous to exercise with a facemask on”. After contacting The Conversation to highlight the new research, they refused to retract their article and it remains online. Not only that, but the article itself is scientifically flawed and wildly speculative. Let me briefly elaborate.

The piece suggested that exercising with a facemask could potentially “reduce oxygen levels” and that “a mask makes it harder to inhale the quantity of air needed to perform at the highest levels”. In support, the author performed a single-subject exercise test on a treadmill during which a facemask was worn underneath full fencing equipment. A sample line from a standard gas analyzer was taped to the cheek of the researcher to record oxygen and carbon dioxide levels; the main finding was that low-intensity exercise with a facemask reduced oxygen concentration to 17%.

There are so many flaws in the piece that I found it difficult to organize my thoughts. Nevertheless, below is a summary of the major points highlighted in my correspondence with The Conversation.

First, to support the major premise that facemasks could be dangerous to exercisers, the article cited a news report of two Chinese youths who sadly died during exercise while wearing facemasks. However, there is no direct evidence linking facemasks to the cause of death, and no autopsy was performed. The statement is, therefore, wildly speculative.

Second, the researcher described a single-subject experiment to test the effect of a facemask on “oxygen levels”. Anybody with a cursory understanding of the scientific method appreciates that single-subject studies do not generate data from which inferences can be drawn. Irrespective of the findings, it is irresponsible to use this as the basis for a mainstream article that is likely to reach many thousands of readers.

Third, there are technical issues regarding the experiment. The researcher stated that wearing a facemask reduced her oxygen levels to 17%. Yet, the setup described in the article (and also pictured) shows the sample line of the gas analyzer taped to the side of the researcher’s face. This measurement is prone to error because the mask may result in some degree of expired gas accumulating around the face resulting in decreased oxygen being measured. But the reading from the sample line does not measure the oxygen content of the air being inhaled, nor the air being absorbed by the lungs, and is even further removed from oxygen levels in the blood. There is absolutely no evidence that gas exchange was affected during the test.

Finally, the test, for reasons still unknown, was conducted while wearing fencing kit, which obviously does not reflect the exercising conditions of most individuals. It certainly doesn’t represent the potential detrimental effects of a cloth mask.

Why am I writing about this? Because the potential consequences of such false messaging could be profound. Millions of people exercise everyday, sometimes in fairly close proximity to others, and these aerosol-generating procedures put people at risk. It is crucial that appropriate precautions are taken to protect all involved. The article published in The Conversation made dangerously misinformed claims that contradicted advice from professional bodies and undermined the collective response to controlling the COVID-19 pandemic. Moreover, it has since been contradicted by published data. It likely had important public health implications.

And yet, the article remains online. The last email to me from The Conversation read:

“…at this stage, I don't see a reason to retract the article or to publish a correction, but thank you for getting in touch with your concerns. Best regards. If you have faith in facts, please donate to support The Conversation”

Their article has so far been shared over 11,000 times. Media fear-mongering 1 – 0 Science.