Table 1.

Characteristics of included studies ¹⁴ , ¹⁵ , ¹⁶ , ¹⁷ , ¹⁸ , ¹⁹ including four studies prompted by the COVID‐19 pandemic ²⁰ , ²¹ , ²² , ²³

Study	Study design	Population, recruiting	Exposure duration	Control group	Mask or respirator	Outcomes measured	Findings
Goh et al Singapore Published 2019 14	Randomised, crossover study	106 children (7–14 years)	Five minutes rest and five minutes walking	Yes, crossover design	N95	ETCO2, FICO2, SpO2, HR, RR, comfort	No differences in RR, HR, SpO2. Marginal increase in ETCO2 and FICO2. 7% reported discomfort.
Smart et al UK Published 2020 15	Randomised, crossover study	24 children (8–11 years)	Three minutes walking and three minutes running	No	N95	Comfort, breathability, hotness, fit	Main complaint hotness. One‐third had a negative subjective perception of breathing.
Samannan et al USA Published 2020 20	Clinical observation	15 adults from medical house staff and 15 COPD patients	30 minutes rest and six minutes walking	No	Surgical	ETCO2, SpO2, HR, RR; COPD patients: pCO2 and pO2	No differences in RR, HR, SpO2 and ETCO2. Decrease in oxygenation after walking in COPD patients.
Roberge et al USA Published 2012 16	Nonrandomised, crossover study	20 adults from public	one hour walking	Yes, crossover design	Surgical	PtcCO2, SpO2, HR, RR, temperature, comfort	Mild increases of HR, RR and PtcCO2 without clinical significance.
Butz Germany Published 2005 17	Randomised crossover study	15 adults from medical staff	30 minutes rest	Yes, crossover design	Surgical	PtcCO2, SpO2, HR, RR, CO2 concentration under mask, comfort	Significant increase in PtcCO2. No change in SpO2, HR and RR. CO2 accumulation under mask.
Beder et al Turkey Published 2008 18	Clinical observation	53 surgeons	Operations between one and four hours	No	Surgical	SpO2, HR	Decrease in SpO2. Slight increase in HR compared with preoperative values.
Dattel et al USA Published 2020 21	Clinical observation	32 pilots from Aeronautical University	90 minutes flight simulator (altitude of 5,000 feet)	No	Surgical, cloth	ETCO2 and, SpO2, HR, RR	No significant changes or differences between mask types. ETCO2and SpO2 within acceptable range.
Person et al France Published 2018 19	Randomised, cross over study	44 adults from public	Six minutes walking	Yes, crossover design	Surgical	Distance, HR, SpO2, dyspnea	No differences in distance, HR or SpO2. Significantly more dyspnea.
Fikenzer et al Germany Published 2020 22	Randomised, cross over study	12 adults from medical staff	Ergo‐spirometry (incremental exertion test)	Yes, crossover design	Surgical, N95	HR, RR, pCO2, pO2, VE, VT, Pmax, VO2max/kg	No significant changes with surgical masks. Pulmonary parameters and maximum power decreased significantly with N95 respirators.
Epstein et al Israel Published 2020 23	Randomised, cross over study	16 adults, from public	Cycle ergometry (incremental exertion test)	Yes, crossover design	Surgical, N95	ETCO2, SpO2, HR, RR, time to exhaustion	Significant increase in ETCO2 with N95 respirators. No significant changes in SpO2, HR, RR and time to exhaustion.

COPD, chronic obstructive pulmonary disease; ETCO₂, end‐tidal carbon dioxide; FICO₂, fractional concentration of inspired carbon dioxide; P_tcCO₂, transcutaneous carbon dioxide; RR, respiratory rate; SpO₂ = oxygen saturation; HR, heart rate; P, power; VO₂, oxygen uptake; VE, minute ventilation; VT, tidal volume; pCO₂, partial pressure of carbon dioxide; pO₂, partial pressure of oxygen; VO₂max/kg, maximal oxygen consumption per kilogram bodyweight.