Table 2.
A summary of the participants, exercise characteristics, environmental conditions and hydration strategies of the studies included in the heat exposure meta-analysis (in chronological order)
| Article | Sample size | Population | Exercise | Duration and intensity | Outcomes | Time point | Environmental condition | Core, rectal, oesophageal or tympanic temperature | Hydration strategy | BM change |
|---|---|---|---|---|---|---|---|---|---|---|
| Fink et al., 1975 [7] | 6 | Physically active males; 21–39 y | Cycling | 3*15 min @ 70–85% O2max | Glycogen use | Exercise-averaged | T: 9 °C & 55% RH; H: 41 °C & 15% RH | T: + 1.0 °C; H: + 1.8 °C | Fluid provided to maintain BM at pre-exercise level | T: − 0.2% BM; H: − 0.1% BM |
| Young et al., 1985 [8] | 13 | Healthy males; 22 y | Cycling | 30 min @ 70% O2max | RER, glycogen use | End of exercise (RER), exercise-averaged (glycogen use) | T: 21 °C & 30% RH; H: 49 °C & 20% RH | T: 38.0 ± 0.1 °C; H: 38.7 ± 0.1 °C* | Ad libitum | – |
| Dolny and Lemon, 1988 [44] | 8 | Males; 28 y | Cycling | 90 min @ 65% O2max | RER | Exercise-averaged | T: 20 °C & 53% RH; H: 30 °C & 59% RH | T: 38.0 ± 0.2 °C; H: 38.2 ± 0.1 °C* | Ad libitum | – |
| Barnett and Maughan, 1993 [45] | 5 | Fit males; 26 y | Cycling | 60 min @ 55% O2max | RER, CHOox | End of exercise | T: 22 °C & 67% RH; H: 35 °C & 60% RH | – | No fluid provided | T: − 0.8 ± 0.3 kg; H: − 1.3 ± 0.4 kg* |
| Snow et al., 1993 [46] | 7 | Active males; 24 y | Cycling | 40 min @ 70% O2peak | RER | Exercise-averaged | T: 20 °C & 20% RH; H: 40 °C & 20% RH | T: 38.1 ± 0.2 °C; H: 38.7 ± 0.1 °C* | No fluid provided | – |
| Nielsen and Kroug, 1994a [47] | 7 | Elite male runners; 27 y | Running | 60 min @ 75% O2max | RER | End of exercise | T: 18 °C & 50–60% RH; H: 32 °C & 50–60% RH | – | 400 mL of distilled water in both conditions | T: − 1.1% BM; H: − 2.2% BM |
| Nielsen and Kroug, 1994b [47] | 5 | Endurance trained males; 27 y | Cycling | 150 min @ 60% O2max | RER | End of exercise | T: 20 °C & 30–40% RH; H: 40 °C & 30–40% RH | – | 400 mL of distilled water in both conditions | T: − 0 to − 0.1% BM; H: − 2.5% BM |
| Febbraio et al., 1994a [6] | 13 | Endurance trained males; 21 y | Cycling | 40 min @ 70% O2max (measured in H condition) | RER, CHOox, glycogen use | End of exercise | T: 20 °C & 20% RH; H: 40 °C & 20% RH | T: 38.7 ± 0.1 °C; H: 39.7 ± 0.1 °C* | – | – |
| Febbraio et al., 1994b [5] | 12 | Endurance trained males; 22 y | Cycling | 40 min @ 70% O2max (measured in H condition) | RER, CHOox, glycogen use | End of exercise | T: 20 °C & 20% RH; H: 40 °C & 20% RH | T: 38.6 ± 0.1 °C; H: 39.6 ± 0.1 °C* | – | – |
| Young et al., 1995 [39] | 18 | Healthy males; 2 groups of 9; 20 y | Cycling | 60 min @ 60% O2max | Glycogen use | Post exercise | T: 20 °C; H: 35 °C (water immersion) |
Group 1 T: 37.4 ± 0.2 °C; H: 38.3 ± 0.1 °C Group 2 T: 37.9 ± 0.3 °C; H: 38.5 ± 0.1 °C |
– | – |
| Hargreaves et al., 1996 [10] | 6 | Endurance trained males; 20 y | Cycling | 40 min @ 65% V̇O2peak | RER, CHOox | End of exercise | T: 20 °C & 50% RH; H: 40 °C & 50% RH | T: 38.2 ± 0.2 °C; H: 39.1 ± 0.2 °C* | – | T: − 0.7 ± 0.1 kg; H: − 1.2 ± 0.1 kg* |
| Galloway and Maughan, 1997 [48] | 8 | Healthy males; 25 y | Cycling | 60 min @ 70% O2max | RER, CHOox | End of exercise | T: 21 °C & 70% RH; H: 31 °C & 70% RH | T: 39.3 °C; H: 39.6 °C* | No fluid provided | – |
| Cheuvront and Haymes, 2001 [33] | 8 | Female marathon runners; 37 y | Running | 30 km @ best marathon race pace | RER, CHOox | End of exercise | T: 20 °C & 54% RH; H: 30 °C & 55% RH | T: 38.4 ± 0.1 °C; H: 39.2 ± 0.2 °C | Ad libitum | T: − 2.4 ± 0.6 kg; H: − 3.2 ± 0.8 kg* |
| Marino et al., 2001 [49] | 9 | Highly trained endurance male runners; 25 y | Running | 30 min @ 70% of peak treadmill running speed | RER | End of exercise | T: 15 °C & 60% RH; H: 35 °C & 60% RH | T: 38.6 ± 0.1 °C; H: 38.5 ± 0.2 °C* | – | – |
| Nybo and Nielsen, 2001 [11] | 8 | Endurance trained males; 23 y | Cycling | 60 min @ 57% O2max | RER, CHOox | Exhaustion (30–50 min) | T: 18 °C & 40% RH; H: 40 °C & 20% RH | T: 37.8 ± 0.1 °C; H: 40.0 ± 0.1 °C* | T: 0.3 ± 0.1 L; H: 0.8 ± 0.1 L of pre-warmed water | T: − 0.7 ± 0.1% BM; H: − 0.7 ± 0.2% BM |
| Jentjens et al., 2002 [50] | 9 | Trained males; 24 y | Cycling | 90 min @ 55% O2max | RER, CHOox, glycogen use | Average 60–90 min | T: 16 °C & 60% RH; H: 35 °C & 27% RH | T: 38.3 ± 0.1 °C; H: 38.9 ± 0.2 °C* | Fluid provided every 15 min: 3 mL/kg BM | T: − 1.3 ± 0.1 kg; H: − 3.0 ± 0.2 kg* |
| Yamashita et al., 2005 [51] | 6 | Healthy males; 19 y | Cycling | 120 min @ 60% O2max | RER | End of exercise | T: 20 °C & 60% RH; H: 30 °C & 60% RH | T: 38.3 ± 0.3 °C; H: 38.9 ± 0.7 °C | – | T: − 1.2 ± 0.2 kg; H: − 2.0 ± 0.9 kg |
| Hayashi et al., 2006 [12] | 13 | Healthy males; 25 y | Cycling | 60 min @ 50% O2peak | RER, CHOox | End of exercise | T: 10 °C; H: 35 °C; H + : 45 °C (perfused suit) | T: 37.3 °C; H: 38.6 °C; H + : 39.2 °C* | No fluid provided | – |
| Hettinga et al., 2007 [52] | 10 | Well trained males; 24 y | Cycling | 20 min @ 60% of power output @ O2max | RER | Exercise-averaged | T: 16 °C & 20% RH; H: 36 °C & 3% RH | T: 37.0 ± 0.1 °C; H: 37.4 ± 0.6 °C* | – | – |
| Shorten et al., 2009 [53] | 11 | Active males; 21 y | Running | 40 min @ 70% O2peak | RER, CHOox | End of exercise | T: 25 °C & 30% RH; H: 36 °C & 30% RH | T: 36.1 ± 0.3 °C; H: 38.9 ± 0.3 °C* | – | T: − 0.7 ± 0.2 kg; H: − 0.7 ± 0.4 kg |
| Fernandez-Elias et al., 2015 [18] | 7 | Endurance trained males; 25 y | Cycling | 40 min @ 75% O2max | CHOox, glycogen use | Exercise-averaged | T: 25 °C & 28% RH; H: 36 °C & 25% RH | T: 38.5 ± 0.4 °C; H: 39.2 ± 0.4 °C* | – | T: − 2.7 ± 0.3% BM; H: − 3.0 ± 0.2% BM |
| O'Hearn et al., 2016 [54] | 8 | Healthy males; 25 y | Running | 30 min @ 50% O2max | CHOox | End of exercise | T: 23 °C & 35% RH; H: 42 °C & 24% RH | T: 37.6 °C; H: 39.0 °C* | – | T: − 0.8% BM; H: − 1% BM* |
| Collins et al., 2017 [55] | 12 | Recreationally trained males; 25 y | Cycling | 60 min @ 60% Wmax | CHOox | Exercise-averaged | T: 20 °C & 60% RH; H: 33 °C & 60% RH | T: 37.9 ± 0.3 °C; H: 38 ± 0.3 °C* | 500 mL in both conditions | – |
| Hoffman et al., 2018 [35] | 10 | Endurance trained (4 females/6 males); 31 y | Running | 120 min @ 60% O2max | CHOox | End of exercise | T: 22 °C & 44% RH; H: 30 °C & 35% RH; H + : 35 °C & 26% RH | T: 38.4 ± 0.4 °C; H: 38.8 ± 0.6 °C; H + : 39.6 ± 0.7 °C* | Ad libitum | T: − 1.7 ± 0.7% BM; H: − 1.9 ± 0.7% BM; H + : − 1.7 ± 0.7% BM |
| Maunder et al., 2020 [56] | 20 | Endurance trained males; 37 y | Cycling | 20 min @ VT1 (measured in H condition) | CHOox | End of exercise | T: 18 °C & 60% RH; H: 35 °C & 60% RH | Higher in H* | Ad libitum | – |
| Foster et al., 2023 [37] | 10 | Trained participants (1 female/9 males); 30 y | Cycling | 60 min @ 6 W/kg | RER, CHOox | End of exercise | T: 25 °C & 23% RH; H: 40 °C & 22% RH | T: 37.9 ± 0.3 °C; H: 38.0 ± 0.3 °C | Ad libitum | – |
| Schoerberlein et al., 2023 [36] | 9 | Healthy participants (4 females/5 males); 27 y | Cycling | 30 min @ 35% (15 min) & 52% (15 min) O2max | RER, CHOox | End of exercise | T: 22 °C & 35% RH; H: 39 °C & 38% RH | T: 37.7 ± 0.3 °C; H: 38.1 ± 0.3 °C* | – | T: − 0.5 ± 0.1% BM; H: − 1.6 ± 0.3% BM* |
| Mora-Rodriguez et al., 2024 [38] | 9 | Healthy participants (1 females/8 males); 31 y | Cycling | 50 min @ 58% O2max | RER, CHOox, Glycogen use | Exercise-averaged | T: 21 °C; H: 33 °C | T: 36.6 ± 0.6 °C; H: 37.2 ± 0.3 °C* | – | T: − 0.4 ± 0.1 kg; H: − 0.6 ± 0.2 kg* |
| Rosbrook et al., 2024 [57] | 10 | Healthy males; 25 y | Walking | 90 min @ 1.56 m/s with incline to elicit VT1 | RER, CHOox | End of exercise | T: 20 °C & 40% RH; H: 37 °C & 20% RH | T: 38.3 ± 0.2 °C; H: 39.3 ± 0.2 °C* | – | T: − 0.9 ± 0.6% BM; H: − 1.7 ± 0.6% BM* |
BM body mass, CHOox carbohydrate oxidation, H hot, H+ Second hot condition, RER respiratory exchange ratio, RH relative humidity, T temperate, O2max maximal oxygen consumption, O2peak peak oxygen consumption, VT ventilatory threshold, Wmax maximum workload, y years
*Significant difference was reported between environmental conditions