As soon as the use of an antiviral protective mask is recommended or becomes mandatory in order to reduce the risk of infection, you might wonder what the physiological impacts are during exercise, for example during training sessions.

Is there:
• Hypoxia (decrease in oxygen [O2] concentration in inhaled air)?
• Hypercapnia (increase in carbon dioxide [CO2] concentration in inhaled air)?
• Reduction in hemoglobin O2 saturation?
• A health risk?

Extensive literature review on the subject indicates that only a few research groups have focused on these issues. These studies focuses mainly on submaximal effort, although a scientific report on maximal effort was published in July 2020 (Fikenzer et al.), opening the door to potential new work. However, it should be noted that no research group has focused on high-level athlete populations.

One of the studies focusing on submaximal exercise was conducted by Catalans Pifarré et al. (2020). They took various physiological measurements from eight subjects (including two women), at rest with or without a mask, and during a Ruffier test (21 squats), including:
• Heart rate;
• Concentrations of O2 and CO2 inside the mask;
• Arterial blood O2 saturation.

This study certainly wasn’t perfect: a small number of subjects; no athletes among participants; no information on the types of masks used; tests and measurements performed outdoors, in parks; no standardization of the environment; low exercise intensity (6–8 METs). This work still allows us to get an idea of some of the physiological effects.

The O2 concentration in the mouth at rest, without a mask, was 20.9%. When wearing the mask, this value decreased to 18.3% at rest and 17.8% at the end of the Ruffier test. The CO2 concentration in the mouth was 464 ppm at rest without a mask, 14,162 ppm at rest with a mask and 17,000 ppm post-exercise with a mask. The authors conclude that the use of a mask during exercise is accompanied by mild hypoxia and marked hypercapnia.

As for hemoglobin O2 saturation, it was 97.6% at rest without a mask, but post-exercise with a mask, it was reduced to 92.1%. The authors argue that in some people, this level of hemoglobin O2 saturation can cause discomfort and symptoms. It remains to be seen whether this is also the case for athletes accustomed to high-intensity exercise.

In a more rigorous study, Roberge et al. (2012) showed that in healthy adults (non-athletes), wearing a mask during a one-hour walk at a brisk pace (5.6 km/h) on a treadmill is not accompanied by any physiological reaction significant enough to have clinical consequences (the following were measured: core, cheek and trunk temperature; heart and respiratory rates; perceived effort and thermal stress).

Interestingly, Johnson et al. (1995) observed that in healthy workers (non-athletes), discomfort and ability to work are more affected by mask-wearing in anxious subjects than in non-anxious individuals.

Person et al. (2018) showed that wearing a mask during a six-minute maximal walk test (a common pneumology test) increased dyspnea (a feeling of respiratory discomfort), but it did not reduce the distance patients could reach during the test.

As part of his master’s degree at UQAM, Charbonneau-Rousseau (2018) showed that wearing a respiratory protection mask (common in the construction sector) during exercise (intensity corresponding to 30–80% of the heart -rate reserve) is accompanied by an increase in the respiratory rate, end-expiratory pressure and perception of effort. He attributes these effects to the micro-environment created by the mask, which affects the temperature and the concentrations of O2 and CO2 in the air. However, his research did not reveal any significant effect of the protective mask on heart rate, internal temperature, brain oxygenation and reaction time.

Warning! The context of the studies by Person et al. and Charbonneau-Rousseau does not reflect the training intensity of high-level athletes and therefore does not meet sporting standards. It is therefore possible that the conclusions would not be the same.

A review of the fundamental knowledge on respiration physiology shows that the relationship between the percentage of O2 in the air reaching the pulmonary alveoli (where gas exchange with the blood occurs) and arterial O2 saturation is not linear: a significant reduction in O2 concentration in alveolar air causes only a small decrease in hemoglobin O2 saturation.

During exercise, the need for O2 obviously increases, resulting in an increase in the depth and frequency of inspiration-expiration cycles. If there is an obstruction at the air intake, as when wearing a mask, the sympathetic nervous system becomes even more active: more air is inhaled and the heart rate increases to ensure that sufficient O2 is delivered to the cells that need it, especially in active muscles.

You might think that wearing a mask increases the respiratory dead space (volume of non-alveolar air, which therefore does not allow gas exchange with the blood) and therefore reduces performance. In the study by Jensen et al. (2011), although the dead space increased by wearing the face mask did cause early dyspnea, the neuromuscular and neuroventilatory coupling of the respiratory system remained relatively unaffected during exercise, thereby preserving exercise ability.

Although the number of studies on the physiological stresses associated with wearing an antiviral mask during exercise is not very high, the studies generally point to the following conclusions during submaximal exercise:
• The perception of exercise is accentuated.
• Discomfort is a result of resistance during inspiration and expiration, but more so from heat and moisture, sweat accumulation and mechanical pressure on the face.
• Increased respiratory (to counter the effects of air intake resistance) and cardiac rates are generally well tolerated in healthy people.
• Despite these physiological adjustments, physical performance is generally affected very slightly or not at all.
• Subjects tend to adapt to wearing a mask after 30–60 minutes.

To conclude on submaximal efforts, here is a quote from British professor Deborah Baines, trustee of The Physiological Society: “So, does a face mask restrict flow of air into the lungs? The bottom line is, if used correctly, it does not. If airflow is restricted, fewer millilitres of O2 get to the alveoli, and less CO2 is exhaled. While this reduces the percentage of O2 in our lungs, and increases CO2, the body senses these changes in the lungs and stimulates breathing. This means that you will take more breaths and blood oxygenation/saturation will be maintained. In other words, paper face masks and fabric face coverings do not affect blood O2 saturation, so please spread the word and counter misinformation you see on the Internet or hear in conversation.” »

In short, for healthy subjects (i.e. with normal physiological and cardiopulmonary functions), the body compensates for the mechanical restriction caused by the mask to produce the desired work, if the intensity of exercise is submaximal.

In regard to maximum-intensity activities, the story could be different. The body adapts to the airflow being limited when wearing the face mask mainly through compensatory stimulation of certain elements (e.g. respiratory rate). However, during prolonged or repeated maximal-exertion activities, these elements are at their maximum (or almost), which could limit the possible compensatory effects. This is discussed in another Savoir-Sport sheet (S895: http://www.insquebec.org/formation/savoir-sport/?requestedFiche=S895).. It points out that in the case of maximal-intensity aerobic activities (close to VO2max), the subject will not be able to employ physiological compensation methods, resulting in a reduction in the capacity for intense exercise and therefore performance. It is not known whether this type of limitation presents health risks.