Table 1 Study characteristics of the included randomised controlled crossover studies

Roberge et al. 2014 [12]

n = 22 (women only)

age = 26.1, 4

height = 167.5, 5.9

weight = 67.5, 9.5

Sitting (20 min; rest)

FFP2/N95 respirator without valve (flat folded or premould randomised)

99.2, 0.7

(99.0, 0.7)

73.7, 14.8

(70.6, 12.8)

36.8, 3.1

(36.9, 3.0)

17.3, 3.2

(17.8, 3.8)

Chest wall temperature, aural temperature

Standing upright (20 min; rest)

99.1, 0.6

(98.7, 1.6)

78.6, 22.2

(76.9, 14.8)

35.1, 8.4

(37.4, 4.6)

17.2, 3.1

(17.3, 3.6)

Cycle ergometer (20 min; low intensity)

98.8, 0.7

(98.7, 1.2)

105.5, 15.9

(98.8, 18.2)

38.7, 3.1

(37.4, 3.3)

24.9, 6.1

(26.4, 4.2)

Li et al. 2021 [26]

n = 5 (women only)

age = 21.1, 0.5

height = 157.0, 3.8

weight = 49.1, 2.5

Cycle ergometer (Duration n.a.; graded until volitional exhaustion; vigorous intensity)

Surgical mask

162.6, 21.7

(162.6, 17.7)

43.2, 11.7

(51.8, 13.4)

23.0, 5.5

(26.9, 4.9)

195.6, 30.0

(197.6, 29.3)

Rating of perceived exertion (RPE)

n = 5 (men only)

age = 21.0, 1.6

height = 172.6 ± 4.5

weight = 59.4, 3.5

170.6, 11.3

(177.6, 10.5)

62.6, 15.4

(74.0, 13.4)

28.5, 4.9

(36.2, 3.8)

184.8, 26.8

(187.0, 28.15)

Kienbacher et al. 2021 [21]

n = 48 (8 women); age = 28 ± 8; weight = n.a

Basic life support (12 min; moderate intensity)

FFP2/N95 respirator without valve (Yao Wang Medical Protective Face Maskî, QingzhouYaowang Pharmaceuticals Co. Ltd., China);

96.0, 2.7

(97.0, 2.7)

110.0, 51.3

(105.0, 51.3)

Basic life support performance; blood pressure; RPE, end-tidal CO₂

FFP2/N95 respirator with valve (Meditrade Respima1 EECî, Meditrade1 GmbH, Germany)

97.0, 2.7

(97.0, 2.7)

108.0, 51.3

(105.0 51.3)

Fikenzer et al. 2020 [8]

n = 14 (men only); age = 38.1 ± 6.2; height = 183.0 ± 7.7; weight = 81.8 ± 8.4

Cycle ergometer semi recumbent (16.8 ± 2.8; graded until volitional exhaustion; vigorous intensity)

Surgical mask (SuavelÆ Protec Plus, Meditrade, Kiefersfelden, Germany);

183.0, 9.2

(187.0, 8.3)

39.3, 6.2

(40.9, 5.1)

114.0, 23.3

(131.0, 27.8)

37.9, 6.0

(39.7, 5.8)

269, 45

(277, 46)

269, 45

(277, 46)

Body plethysmography, spiroergometric and haemodynamic parameters, subjective complaints

FFP2/N95 respirator without valve (ShaoguanTaijie Protection Technology Co., Ltd., Gao Jie, China)

182.0, 11.2

(187.0, 8.3)

36.8, 5.9

(40.9, 5.1)

98.8, 18.6

(131.0, 27.8)

34.5, 5.3

(39.7, 5.8)

263, 42

(277, 46)

263, 42

(277, 46)

Kim et al. 2016 [22]

n = 12 (men only); age = 23.5 ± 1.6; height = 181 ± 6; weight = 81.8 ± 8.1

Treadmill walking (60 min; moderate intensity; 35 °C and 50% humidity)

FFP2/N95 respirator without valve (3 M model 1870 FFP2/N95 respirator FFR, 3 M, St Paul, MN)

97.8, 0.6

(97.9, 1.1)

105.9, 11.9

(106.2, 14.8)

41.3, 2.4

(40.9, 2.4)

28.4, 3.2

(28.1, 7.1)

Skin temperature, heat perception

Lässing et al. 2020 [25]l

n = 14 (men only); age = 25.7 ± 3.5; height = 183.8 ± 8.4; weight = 83.6 ± 8.4

Cycle ergometer (30 min, vigorous intensity)

Surgical mask (Suavel Protec Plus, Meditrade, Kiefersfelden, Germany)

95.3, 0.8

(95.2, 0.7)

160.1, 11.2

(154.4, 11.4)

32.1, 5.4

(34.0, 7.3)

77.1, 9.3

(82.4, 10.6)

33.1, 5.0

(34.5, 5.8)

2575, 310

(2685, 278)

Body plethysmography, spiroergometric and haemodynamic parameters

Sammito et al. 2021 [20]

n = 14 (3 women); age = 41 ± 12; height = 179 ± 11; weight = 80.7 ± 18.9

Sitting (5 min, rest)

FFP2/N95 respirator without valve (Gitemk FFP2 protective mask, Zhejiang Yinghua Technology, China)

97.4, 1.1

(96.7, 2.1)

76.0, 9.5

(76.9, 6.3)

None

Epstein et al. 2020 [24]

n = 16 (men only); age = 34 ± 4; height = 179 ± 7, weight = 76.3 ± 11.8

Cycle ergometer (16.3 ± 3.7; graded until volitional exhaustion; vigorous intensity)

FFP2/N95 respirator without valve (Duckbill style fluid shield 2 FFP2/N95 respirator particulate filter respirator, Halyard)

97.6, 1.3

(98.1, 1.1)

168.8, 12.8

(170.5, 11.7)

36.6, 5.4

(36.7, 7.5)

154, 30

(157, 31)

Rating of perceived exertion (Borg), blood pressure

Surgical mask (Kimberly-Clark)

97.7, 1.6

(98.1, 1.1)

165.8, 16.0

(170.5, 11.7)

36.2, 7.0

(36.7, 7.5)

153, 31

(157, 31)

Mapelli et al. 2021 [27]

n = 12 (6 women); age = 40.8 ± 12.4

Cycle ergometer (duration n.a.; graded until volitional exhaustion; vigorous intensity)

FFP2/N95 respirator without valve (KFFP2/N95 respirator particulate respirator, BYD care, China)

95.1, 3.1

(97.3, 1.2)

167.0, 16.1

(170.0, 14.0)

37.1, 4.5

(41.5, 8.0)

71.6, 21.2

(92.3, 26.0)

28.2, 8.8

(31.0, 6.7)

2268, 794

(2578, 763)

184, 54

(194, 57)

Spiroergometric data

Surgical mask (disposable medical mask, Aiminde, China)

96.5, 1.2

(97.3, 1.2)

168.0, 16.0

(170.0, 14.0)

37.7, 5.5

(41.5, 8.0)

76.2, 21.6

(92.3, 26.0)

27.5, 6.9

(31.0, 6.7)

2217, 691

(2578, 763)

187, 54

(194, 57)

Bertoli et al. 2021 [19]

n = 10 (7 women); age = 43 ± 10; height = 161 ± 5; weight = 65.7 ± 17.2

Lying down (no mask = 11.4 ± 2.7 min, mask 11.9 ± 2.2 min; rest)

FFP2/N95 respirator without valve (manufacturer details n.a.)

3.0, 0.6

(2.9, 0.5)

182, 37

(179, 34)

Energy expenditure

Person et al. 2018 [23]

n = 44 (26 women); age = 21.6 ± 2.8; height = 172.1 ± 8.3; 66.0 ± 11.4

Walking (6 min; moderate intensity)

surgical mask (manufacturer details n.a

98.3, 1.1

(98.3, 1.0)

134.6, 22.9

(138.7, 23.6)

Kim et al. 2015 [11]

n = 16 (women only); age = 24.8 ± 3.5; height = 167.9 ± 6.3; weight = 66.0 ± 8.6

Standing upright (20 min, rest)

FFP2/N95 respirator without valve (3 M 9210 flat-fold model (3 M, St. Paul, MN) or a Moldex cup-shaped model in either medium/large size (Moldex2200) or small size (Moldex 2201) (Moldex, Culver City, CA))

99.1, 0.5

(98.5, 1.8)

78.9, 15.5

(78.1, 15.6)

37.4, 3.5

(38.1, 5.1)

Rating of perceived exertion, blood pressure

Cycle ergometer semirecumbent (20 min, low intensity)

98.7, 0.6

(98.5, 1.3)

101.9, 15.0

(97.1, 19.3)

39.3, 3.2

(38.1, 3.4)

Sitting (20 min, rest)

99.1, 0.6

(98.9, 0.7)

73.5, 10.6

(67.8, 12.5)

37.4, 3.0

(37.3, 3.3)

Shaw et al. 2020 [28]

n = 14 (7 women); age = 28.2 ± 8.7; height = 180 ± 5; weight = 86 ± 12

Cycle ergometer (10.3 ± 2.35 min; graded until volitional exhaustion; vigorous intensity)

Surgical mask CRC-Elm 5, Hawketree Solutions, Ottawa, ON, Canada

96.0, 3,0

(96.0, 4.0)

179.0, 19.0

(179.0, 16.0)

241, 57

(234, 56)

Continuous-wave near-infrared spectroscopy (vastus lateralis right); rating of perceived exertion

Roberge et al. 2010 [30]

n = 10 (7 women); age = 25.1 ± 7.2; height = 169 ± 12; weight = 76 ± 24

Treadmill walking (60 min, low intensity)

FFP2/N95 respirator without valve (cup shaped, manufacturer details n.a.);

98.1, 0.9

(98.5, 0.8)

98.1, 8.5

(92.3, 8.2)

39.7, 6.0

(40.7, 3.5)

25.2, 4.0

(27.7, 7.1)

23.4, 6.7

(20.9, 8.2)

Mask dead space gases, subjective complaints

FFP2/N95 respirator with exhalation valve (cup shaped, manufacturer details n.a.)

98.4, 1.0

(98.5, 0.8)

95.1, 9.7

(92.3, 8.2)

41.5, 4.9

(40.7, 3.5)

25.2, 6.1

(27.7, 7.1)

21.2, 4.5

(20.9, 8.2)

Treadmill walking (60 min, moderate intensity)

FFP2/N95 respirator without valve

98.4, 0.7

(98.5, 0.8)

106.4, 9.2

(101.3, 11.8)

42.0, 5.6

(40.8, 3.2)

26.6, 6.8

(27.7, 8.6)

24.4, 6.0

(23.0, 6.5)

FFP2/N95 respirator with exhalation valve

98.2, 1.0

(98.5, 0.8)

106.4, 9.3

(101.3, 11.8)

42.6, 6.2

(40.8, 3.2)

25.5, 5.7

(27.7, 8.6)

23.0, 5.9

(23.0, 6.5)