Does wearing a face mask while exercising lead to inhaling dangerously high levels of carbon dioxide or dangerously low levels of oxygen?

Last updated: February 20, 2022
The single study in this list that examines this question found that the answer is no. A single study is often not sufficient to draw a conclusion so we encourage you to refer to this study merely as food for thought.

Chart summary of 1 study examining this question

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Total studies in list: 1
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The impact of face masks on performance and physiological outcomes during exercise: a systematic review and meta-analysis
"Face masks are promoted for preventing spread of viruses; however, wearing a mask during exercise might increase CO2 rebreathing, decrease arterial oxygenation, and decrease exercise performance. A systematic review and meta-analysis was conducted on the impact of wearing a mask during exercise. Data sources included SPORTDiscus, PubMed, and Medline. Eligibility criteria included all study designs comparing surgical, N95, or cloth masks to a no mask condition during any type of exercise where exercise performance and/or physiological parameters were evaluated. Healthy and clinical participants were included. Mean differences (MD) or standardized mean differences (SMD) with 95% confidence intervals were calculated and pooled effects assessed. Twenty-two studies involving 1573 participants (620 females, 953 males) were included. Surgical, or N95 masks did not impact exercise performance (SMD −0.05 [−0.16, 0.07] and −0.16 [−0.54, 0.22], respectively) but increased ratings of perceived exertion (SMD 0.33 [0.09, 0.58] and 0.61 [0.23, 0.99]) and dyspnea (SMD 0.6 [0.3, 0.9] for all masks). End-tidal CO2 (MD 3.3 [1.0, 5.6] and 3.7 [3.0, 4.4] mm Hg), and heart rate (MD 2 [0,4] beats/min with N95 masks) slightly increased. Face masks can be worn during exercise with no influences on performance and minimal impacts on physiological variables. PROSPERO registration: CRD42020224988."
Keely A. Shaw,
2021 Applied Physiology, Nutrition, and Metabolism