Effects of Face Mask Use on Objective and Subjective Measures of Thermoregulation During Exercise in the Heat

BACKGROUND

While increased face mask use has helped reduce COVID-19 transmission, there have been concerns about its influence on thermoregulation during exercise in the heat, but consistent, evidence-based recommendations are lacking.

HYPOTHESIS

No physiological differences would exist during low-to-moderate exercise intensity in the heat between trials with and without face masks, but perceptual sensations could vary.

STUDY DESIGN

Crossover study.

LEVEL OF EVIDENCE

Level 2.

METHODS

Twelve physically active participants (8 male, 4 female; age = 24 ± 3 years) completed 4 face mask trials and 1 control trial (no mask) in the heat (32.3°C ± 0.04°C; 54.4% ± 0.7% relative humidity [RH]). The protocol was 60 minutes of walking and jogging between 35% and 60% of relative VO2max. Rectal temperature (Trec), heart rate (HR), temperature and humidity inside and outside of the face mask (Tmicro_in, Tmicro_out, RHmicro_in, RHmicro_out) and perceptual variables (rating of perceived exertion (RPE), thermal sensation, thirst sensation, fatigue level, and overall breathing discomfort) were monitored throughout all trials.

RESULTS

Mean Trec and HR increased at 30- and 60-minute time points compared with 0-minute time points, but no difference existed between face mask trials and control trials (P > 0.05). Mean Tmicro_in, RHmicro_in, and humidity difference inside and outside of the face mask (ΔRHmicro) were significantly different between face mask trials (P < 0.05). There was no significant difference in perceptual variables between face mask trials and control trials (P > 0.05), except overall breathing discomfort (P < 0.01). Higher RHmicro_in, RPE, and thermal sensation significantly predicted higher overall breathing discomfort (r2 = 0.418; P < 0.01).

CONCLUSION

Face mask use during 60 minutes of low-to-moderate exercise intensity in the heat did not significantly affect Trec or HR. Although face mask use may affect overall breathing discomfort due to the changes in the face mask microenvironment, face mask use itself did not cause an increase in whole body thermal stress.

CLINICAL RELEVANCE

Face mask use is feasible and safe during exercise in the heat, at low-to-moderate exercise intensities, for physically active, healthy individuals.

Air Hunger: A Primal Sensation and a Primary Element of Dyspnea

The sensation that develops as a long breath hold continues is what this article is about. We term this sensation of an urge to breathe "air hunger." Air hunger, a primal sensation, alerts us to a failure to meet an urgent homeostatic need maintaining gas exchange. Anxiety, frustration, and fear evoked by air hunger motivate behavioral actions to address the failure. The unpleasantness and emotional consequences of air hunger make it the most debilitating component of clinical dyspnea, a symptom associated with respiratory, cardiovascular, and metabolic diseases. In most clinical populations studied, air hunger is the predominant form of dyspnea (colloquially, shortness of breath). Most experimental subjects can reliably quantify air hunger using rating scales, that is, there is a consistent relationship between stimulus and rating. Stimuli that increase air hunger include hypercapnia, hypoxia, exercise, and acidosis; tidal expansion of the lungs reduces air hunger. Thus, the defining experimental paradigm to evoke air hunger is to elevate the drive to breathe while mechanically restricting ventilation. Functional brain imaging studies have shown that air hunger activates the insular cortex (an integration center for perceptions related to homeostasis, including pain, food hunger, and thirst), as well as limbic structures involved with anxiety and fear. Although much has been learned about air hunger in the past few decades, much remains to be discovered, such as an accepted method to quantify air hunger in nonhuman animals, fundamental questions about neural mechanisms, and adequate and safe methods to mitigate air hunger in clinical situations. © 2021 American Physiological Society. Compr Physiol 11:1449-1483, 2021.