Herndon understands some clubs, tournaments or high school sports are following recommendations made by the American Association of Pediatrics (AAP) to wear masks while playing team sports. However, Herndon does not feel there are strong studies and sources cited to support these recommendations to find conclusive evidence that wearing a mask is safe during high intensity sports such as soccer. For players with asthma or other respiratory issues, it is of greater concern to wear masks during high intensity exercise. See below for excerpts from two publications informing our view from the World Health Organization and the International Journal of Environmental Research and Public Health.
Based on our findings,
According to the WHO article on Dec. 1, 2020:
Mask use during physical activity: Evidence
There are limited studies on the benefits and harms of wearing medical masks, respirators and non-medical masks while exercising. Several studies have demonstrated statistically significant deleterious effects on various cardiopulmonary physiologic parameters during mild to moderate exercise in healthy subjects and in those with underlying respiratory diseases (134-140). The most significant impacts have been consistently associated with the use of respirators and in persons with underlying obstructive airway pulmonary diseases such as asthma and chronic obstructive pulmonary disease (COPD), especially when the condition is moderate to severe (136). Facial microclimate changes with increased temperature, humidity and perceptions of dysp noea were also reported in some studies on the use of masks during exercise (134, 141). A recent review found negligeable evidence of negative effects of mask use during exercise but noted concern for individuals with severe cardiopulmonary disease (142).
WHO advises that people should not wear masks during vigorous intensity physical activity (143) because masks may reduce the ability to breathe comfortably. The most important preventive measure is to maintain physical distancing of at least 1 meter and ensure good ventilation when exercising.
The International Journal of Environmental Research and Public Health addresses the physiological effects of wearing a mask during exercise, and is helpful explaining it from a scientific point of view.
5. Special Considerations
Although moderate physical activity (walking on a treadmill at 2.5 miles/h) while wearing an N95 respirator did not appear to have any effect on ventilation , to date, there are not many studies that have examined higher intensities of exercise while wearing a mask. The World Health Organization does not currently recommend wearing a mask while exercising , and the CDC recognizes that it may be difficult to wear a mask during high intensity physical activities . Research examining military grade respirators suggest that there may be alterations to ventilation during high exercise intensities above 85% of maximum oxygen consumption . This finding was also supported by a recent study that examined the impact of wearing a surgical vs. N95 face mask on cardiopulmonary exercise capacity in 12 healthy males. It was reported that during an ergometer incremental exertion test (i.e., high intensity test to exhaustion), pulmonary function and ventilation were significantly reduced with the use of either mask. Cardiopulmonary exercise capacity was also reduced with mask wearing (lower peak blood lactate response), and participants also reported discomfort while wearing the mask, especially the N95 . It is important to note, however, that these studies examined very high intensity exercise, a level likely higher than an average workout for most individuals. Humidity , temperature , type of mask  and intensity of exercise  all appear to impact the effects of a mask during exercise, and should be taken into consideration if making a choice to wear a mask during exercise or not. To our knowledge, there are no studies that examine O2 saturation or the partial pressure of oxygen in response to exercise with a mask. At these high exercise intensities, we would expect that, while oxygen and carbon dioxide concentrations in the blood may remain relatively stable, there would be discomfort related to the temperature of the skin created by the mask and the breathing resistance caused by the mask. Exercisers may either need to persist through increased discomfort or lower their exercise intensity while wearing a mask if discomfort exists. Additionally, wearing loser cloth masks made with wicking materials that do not hold moisture should improve comfort during exercise.”