Impact of wearing a surgical and cloth mask during cycle exercise

2 We sought to determine the impact of wearing cloth or surgical masks on the cardiopulmonary 3 responses to moderate-intensity exercise. Twelve subjects (n=5 females) completed three, 8-min 4 cycling trials while breathing through a: non-rebreathing valve (laboratory control), cloth, or 5 surgical mask. Heart rate (HR), oxyhemoglobin saturation (SpO 2 ), breathing frequency (Fb), 6 mouth pressure, partial pressure of end-tidal carbon dioxide (P et CO 2 ) and oxygen (P et O 2 ), 7 dyspnea, were measured throughout exercise. A subset of n=6 subjects completed an additional 8 exercise bout without a mask (ecological control). There were no differences in Fb, HR or SpO 2 9 across conditions (all p >0.05). Compared to the laboratory control (0.9±0.7cmH 2 O[mean±SD]), 10 mouth pressure swings were greater with the surgical mask (4.7±0.9; p <0.0001), but similar with 11 the cloth mask (3.6±4.8cmH 2 O; p =0.66). Wearing a cloth mask decreased P et O 2 (-3.5±3.7mmHg) 12 and increased P et CO 2 (+2.0±1.3mmHg) relative to the ecological control (both p <0.05). There 13 were no differences in end-tidal gases between mask conditions and laboratory control (both 14 p >0.05). Dyspnea was similar between the control conditions and the surgical mask ( p >0.05) but 15 was greater with the cloth mask compared to laboratory (+0.9±1.2) and ecological (+1.5±1.3) 16 control conditions (both p <0.05). Wearing a mask during short-term moderate-intensity exercise 17 may increase dyspnea but has minimal impact on the cardiopulmonary response.


1
Despite these purported concerns, there is limited empirical data to support these claims.
2 In fact, recent evidence suggests that cloth or surgical masks have no impact on maximal 3 exercise capacity or oxygenation during vigorous exercise in healthy individuals (Shaw et al. 4 2020). A recent review corroborated this finding and concluded that the physiological effects of 5 wearing a mask were minimal and unlikely to impact the exercise response, independent of those 6 with severe cardiopulmonary disease (Hopkins et al. 2020). However, conclusions from the 18 airflow, due to the wind or via self-generated movement, may alter the impact of the mask on the 19 physiological response to exercise. 20 As such, the purpose of this study was to determine if wearing a cloth or surgical mask 21 impacts the cardiopulmonary response to exercise at an intensity that is commensurate with 22 moderate-to-vigorous physical activity under ecologically-relevant conditions. To test this, we 23 had healthy individuals exercise at 70% of their maximum heart rate while wearing either a cloth 24 mask, surgical mask, standard laboratory cardiopulmonary exercise testing mouthpiece 25 (laboratory control) or nothing (ecological control). The ecological control group wore a 26 modified mouthpiece (discussed below; see Figure 1) that allowed for subjects to exercise as 27 close to they normally would, while still measuring mouth pressures and gas concentrations. We 6 1 was followed by a 3-min resting baseline on the cycle ergometer while standard 2 cardiorespiratory variables were measured continuously. Next, subjects exercised under different 3 conditions (discussed below) in a randomized order. Each exercise condition consisted of a 2-4 min initiation phase to achieve steady state, followed by three minutes of exercise without a fan 5 and three minutes with a fan. Each bout of exercise was separated by at least eight minutes of 6 rest with the following exercise bout only starting once HR returned to within 20% of baseline The thermistor and sampling tubing were taped flush against the skin of the subjects to ensure 10 they did not interfere with the mask. To maintain the translatability of our findings to the general 11 population, we only performed techniques that would not alter how a mask is regularly worn.
12 Thus, for the two mask and ecological control condition, we did not measure parameters that

26
Steady state exercise variables during the ecological control are presented in Figure 3.
27 Similar to the laboratory control, heart rate, SpO 2 , breathing frequency and relative respiration 12 1 respectively. Additionally, mean differences in P et CO 2 with the fan on were -1±2 mmHg for the 2 laboratory control, -1±1 mmHg X with the surgical mask and -1±1 mmHg with the cloth mask.  26 relative to the laboratory control condition. Yet in both mask conditions, no differences in HR, 27 SpO 2 , breathing frequency and relative respiration depth were observed relative to the laboratory 1 or ecological control, suggesting differences in respiratory gas pressures were inconsequential 2 during exercise. Third, wearing a cloth or surgical mask increased face temperatures, but 3 dyspnea was only significantly higher when wearing a cloth mask relative to both ecological and 4 laboratory controls. In agreement with conclusions from the Hopkins and colleagues review 5 (2020), we interpret our findings to indicate that wearing a surgical or cloth mask during a 6 relatively short bout of moderate-to-vigorous exercise has no impact on the physiological 7 response. While inspired and end-tidal gas pressures were statistically different with the masks,  (Figures 2 and 5), it is reasonable to assume that wearing a mask increased external 18 dead space by no more than ~100-150 mL (Hopkins et al. 2020). Such an increase in dead space 19 resulted in small but significant alteration in inspired gas fractions but had minimal (if any) 20 physiological effects. When the fan was used (simulating outdoor exercise), any differences in 21 P I O 2 or P I CO 2 between conditions were eliminated. Presumably, the added 'wind speed' would 22 'flush' the masks of any exhaled gases and eliminated any difference. 23 24 Expired gas pressures. We found P et CO 2 and P et O 2 was not different between the laboratory 25 control and mask conditions (Figure 5).  (Figure 6). This difference in end-tidal gas pressures is due to the 15 increased external dead space with a cloth mask. Compared to the ecological control, the 16 differences in surgical and cloth mask end-tidal gases were due to the different mask properties. 17 The cloth masks used in the present study, which were brought by participants, fit well to their  25 Perspectives on gas pressure changes. Although there were statistically significant changes in 26 gas concentrations between the masks, it is important to discuss the physiological context. The 27 differences in P I O 2 and P I CO 2 ranged from 1 to 4 mmHg, respectively (Figures 5 and 6). At sea 1 level ( barometric pressure = 760mmHg), these changes amount to a 0.5% reduction in the 2 inspired fraction of oxygen , and a 0.1% increase in the inspired fraction of carbon dioxide .
3 Physiologically, this drop in inspired oxygen is insignificant as it does not reach levels that elicit 4 a ventilatory response (Weil et al. 1970; Teppema and Dahan 2010). Furthermore, a 4 mmHg 5 reduction in P I O 2 regularly occurs due to variations in weather or minor changes in elevation. For 6 example, barometric pressure can vary by ~30 mmHg at a fixed elevation due to normal weather 7 variations and this would alter P I O 2 by ~6 mmHg (Crippen 1993). Similarly, going from sea 8 level (e.g., Vancouver, BC) to approximately 300 m above sea level (e.g., Waterloo, ON) will 9 translate to a ~4 mmHg decrease in P I O 2 . A drop in barometric pressure of at least 50 mmHg 10 (corresponding to a ~10 mmHg decrease in P I O 2 ) is required for decreasing VȮ 2max and can 11 significantly reduce SpO 2 in aerobically trained individuals (Gore et al. 1996). In the present 12 study, subjects were not aerobically trained and the drop in P I O 2 was smaller while wearing a 13 surgical or cloth mask. Thus, it is not surprising that we did not observe a change in SpO 2 or 14 breathing pattern during exercise (Figures 2 and 3) 15 In contrast, relatively small changes in P I CO 2 can impact ventilation. For example, 16 breathing air with inspired CO 2 fraction of 1% (~8 mmHg) will increase arterial carbon dioxide 17 by 1 mmHg, which increases ventilation at rest (Ellingsen et al. 1987). However, we saw an 18 increase in the inspired fraction of CO 2 of ~1 mmHg, thus it is unsurprising that ventilation did 19 not change across the conditions. Finally, performing locomotor likely exercise outdoors 20 diminishes any effect that wearing a mask has on gas concentrations due to enhanced airflow. 21 Altogether, our results suggest that the small differences in respired gases that occur while 22 wearing a mask are inconsequential to an individual's exercise performance or capacity.