Table 1.
Overview of the analyzed studies.
| Study, year | Study design | No. of participants and training statusa | Exercise protocol | Intervention | Time point of environmental exposure or intervention manipulation | Performance measurement (total time or mean power output (MPO) in watts) | PEDro Score |
|---|---|---|---|---|---|---|---|
| OXYGEN AVAILABILITY | |||||||
| Amann et al., 2006 | Crossover | 8 Well-trained male cyclists (63.3 ± 1.3 ml kg−1min−1) | 5 km cycling time-trial | Time-trial in normoxia (FiO2 = 0.21; CON.), hypoxia (FiO2 = 0.15; INTER), iso-oxia (FiO2 = 0.24–0.30; INTER) and hyperoxia (FiO2 = 1.00; INTER) | Exposure 3 min before trial, after a warm-up in normoxia | FiO2: 0.21 = 458 ± 7 s FiO2: 0.15 = 483 ± 8 s FiO2: 0.24–0.30 = 351 ± 7 s FiO2: 1.00 = 439 ± 7 s | 9 |
| Clark et al., 2007 | Crossover | 10 Well-trained male cyclists and triathletes (67.7 ± 1.3 ml kg−1min−1) | 5 min cycling time-trial | Time-trial in normoxia (FiO2 = 0.21; CON) and hypoxia (FiO2 = 0.19; 0.16; and 0.14 INTER) | Exposure before, during and after warm-up. Total of 40 min in hypoxia before trial | FiO2: 0.21 = 367 ± 42 MPO FiO2: 0.19 = 346 ± 41 MPO FiO2: 0.16 = 329 ± 38 MPO FiO2: 0.14 = 294 ± 37 MPO | 10 |
| Périard and Racinais, 2016 | Crossover | 12 Well-trained male cyclists | Cycling time-trial to complete 750 kJ | Time-trial in normoxia (FiO2 = 0.21; CON) and hypoxia (FiO2 = 0.15; INTER) | Exposure 5 min before trial, after a warm-up in normoxia | FiO2: 0.21 = 48.2 ± 5.7 min FiO2: 0.15 = 60.1 ± 6.5 min | 9 |
| Tucker et al., 2007 | Crossover | 11 Well-trained male cyclists (395 ± 33 PPO) | 20 km cycling time-trial | Time-trial in normoxia (FiO2 = 0.21; CON) and hyperoxia (FiO2 = 0.40; INTER) | Time point unknown, including oxygen inhaled in warm-up | FiO2: 0.21 = 28 ± 8 min FiO2: 0.40 = 27 ± 34 min | 9 |
| HEAT-STRESS | |||||||
| Abbiss et al., 2008 | Crossover | 10 Well-trained male cyclists (61.7 ± 5.0 ml kg−1min−1) | 16.1 km cycling time-trial | Time-trial in temperate (18.1°C, 58% RH; CON) and heat (32°C, 50% RH; INTER) | Exposure during warm-up (90 min fixed workload) and at rest. Total of 116.3 min in heat before trial | 18.1°C = 25.4 ± 1.6 min 32°C = 27.5 ± 1.9 min | 8 |
| Altareki et al., 2009 | Crossover | 9 Competitive male triathletes and cyclists (61.7 ± 8.6 ml kg−1min−1) | 4 km cycling time-trial | Time-trial in cool (13°C, 40%; CON) and heat (35°C, 60% RH; INTER) | Exposure before, during and after warm-up. Total of 21 min in heat before trial | 13°C = 382.8 ± 18.2 s 35°C = 390.1 ± 19.6 s | 8 |
| Castle et al., 2012 | Crossover | 7 Recreational male cyclists (58.8 ± 5.7 ml kg−1min−1) | 30 min cycling time-trial | Time-trial in temperate (22°C, 43% RH; CON) and heat (31°C, 64% RH; INTER) | Exposure during a 7 min warm-up in heat before trial | 22°C = 179.9 ± 50.9 MPO 31°C = 168.1 ± 54.1 MPO | 9 |
| Peiffer and Abbiss, 2011 | Crossover | 9 Trained male cyclists (60.5 ± 4.5 ml kg−1min−1) | 40 km cycling time-trial | Time-trial in temperate (22°C, 40% RH; CON), cool (17°C, 40% RH; INTER), warm (27°C 40% RH; INTER), and hot (32°C, 40% RH; INTER) | Time point unknown, including temperature in warm-up | 17°C = 58.8 ± 2.0 min 22°C = 59.0 ± 2.3 min 27°C = 59.1 ± 2.3 min 32°C = 60.7 ± 2.9 min | 8 |
| Périard et al., 2011 | Crossover | 8 Well-trained male cyclists (66.4 ± 5.3 ml kg−1min−1) | 40 km cycling time-trial | Time-trial in temperate (20°C, 40%: CON) and heat (35°C, 60% RH; INTER) | Exposure 5 min before trial, after a warm-up in temperate | 20°C = 59.8 ± 2.6 min 35°C = 64.3 ± 2.8 min | 8 |
| Périard and Racinais, 2015 | Crossover | 11 Well-trained cyclists, 10 males and 1 female (60.2 ± 6.3 ml kg−1min−1) | Cycling time-trial to 750 kJ complete | Time-trial in temperate (20°C, 40%; CON) and heat (35°C, 60% RH; INTER) | Exposure 5 min before trial, after a warm-up in temperate | 20°C = 48.8 ± 12.7 min 35°C = 55.8 ± 14.4 min | 8 |
| Périard and Racinais, 2016 | Crossover | 12 Well-trained male cyclists | Cycling time-trial to 750 kJ complete | Time-trial in temperate (18°C, 40%; CON) and heat (35°C, 60% RH; INTER) | Exposure 5 min before trial, after a warm-up in temperate | 18°C = 48.2 ± 5.7 min 35°C = 55.4 ± 5.0 min | 8 |
| Schmit et al., 2016 | Parallel group | 34 Well-trained triathletes, gender unknown. Temperate (n = 22; 63.3 ± 2.1 ml kg−1min−1), Heat (n = 12; 62.2 ± 3.6) | 20 km cycling time-trial | Time-trial in temperate (21°C, 50%; CON) acute heat exposure (35°C, 50% RH at 0; INTER and 11 ± 4 days; INTER) | Exposure 15 min before trial during a warm-up, the second heat trail took place 11 ± 4 days after trial 1 with no acclimatization | 0 days 21°C = 32.2 ± 2.0 min 35°C = 33.2 ± 1.58 min 11 ± 4 days after first trial 21°C = 31.5 ± 1.4 min 35°C = 32.4 ± 1.2 min | 7 |
| Tatterson et al., 2000 | Crossover | 11 National male road cyclists (66.7 ± 13.6) | 30 min cycling time-trial | Time-trial in temperate (23°C, 60% RH; CON) and heat (32°C, 60% RH; INTER) | Time point unknown, including temperature in warm-up | 23°C = 345 ± 9 MPO 32°C = 323 ± 8 MPO | 8 |
| Tucker et al., 2004 | Crossover | 10 Recreational male cyclists (376 ± 47 PPO) | 20 km cycling time-trial | Time-trial in cool (15°C, 60% RH; CON) and heat (35°C, 60% RH; INTER) | Time point unknown, including temperature in warm-up | 15°C = 28.8 ± 1.8 min 35°C = 29.6 ± 1.9 min | 8 |
| VanHaitsma et al., 2016 | Crossover | 20 Trained male cyclists (54.8 ± 5.9) | 40 km cycling time-trial | Time-trial in temperate (21°C, 20% RH; CON) and heat (35°C, 25% RH; INTER) | Time point unknown, including temperature in warm-up | 21°C = 75.2 ± 6.6 min 35°C = 79.0 ± 7.2 min | 8 |
| PRE-COOLING STRATEGIES | |||||||
| Barwood et al., 2012 | Crossover | 11 Trained male cyclists | 40 km cycling time-trial | Time-trial in heat (32°C, 53% RH) with use of no spray (CON), menthol spray (INTER) and placebo cooling spray (INTER) | 10 min warm-up in heat, existed chamber (5 min rest in ~22°C), re-entered and sprayed with solution. Total of ~23 min in heat | CON = 71.58 ± 62 min Placebo = 70.94 ± 6.1 min Menthol = 71.04 ± 5.5 min | 9 |
| Byrne et al., 2011 | Crossover | 7 Recreational male cyclists | 30 min cycling time-trial | Time-trial in the heat (32°C, 60% RH) ingesting 900mL of hot (37°C; CON) or cold fluid (2°C; INTER) 10 min before trial | After fluid ingestion, 5 min at rest in heat, temperature of warm-up unknown | 37°C fluid = 261 ± 22 MPO 2°C fluid = 275 ± 27 MPO | 8 |
| Duffield et al., 2010 | Crossover | 8 Moderate to well-trained male cyclists (lactate threshold 221 ± 42 W) | 40 min cycling time-trial | Time-trial in the heat (33°C, 50% RH) with (INTER) and without (CON) lower body cold water immersion (CWI) at 14°C before trial | 20 min of CWI, 5 min warm-up in heat. Time between CWI and warm up ~8–10 min, ≤ 5 min from warm-up and trial start | CON = 178 ± 26 MPO 14°C CWI = 198 ± 25 MPO | 8 |
| Gonzales et al., 2014 | Crossover | 10 trained male cyclists (59.1 ± 7.0 ml kg−1min−1) | 20 min cycling time-trial | Time-trial in the heat (30°C, 79% RH) with (INTER) and without (CON) a cooling vest worn and refrigerated headband | 18 min warm-up with cooling vest and headband in heat. Rested in heat for 10 min (no vest) before trial. Total of 28 min in heat | CON = 222 ± 47 MPO Cooling vest = 239 ± 45 MPO | 8 |
| FEEDBACK MANIPULATIONS | |||||||
| Albertus et al., 2005 | Crossover | 15 Competitive male cyclists (397 ± 58 PPO) | 20 km cycling time-trial | Time-trial with correct fb (CON) and positive deception (Pos-fb; INTER) | Informed traveled 25-m further than they had every km | CON = 28.4 ± 1.6 min Pos-fb = 28.6 ± 1.5 min | 8 |
| Castle et al., 2012 | Crossover | 7 Recreational male cyclists (58.8 ± 5.7 ml kg−1min−1) | 30 min cycling time-trial | Time-trial in the heat without deception (31°C, 64% RH; CON) and with deception (told the temperature was 26°C, 60% RH, reality: 32°C, 65% RH; Pos-fb; INTER) | From the onset of the trial and displayed incorrectly during trial on a computer screen | CON = 179.9 ± 50.9 MPO Pos-fb = 184.4 ± 60.4 MPO | 9 |
| Jones et al., 2016b | Parallel group | 20 Trained male cyclists, CON (n = 10; 57.6 ± 6.7 ml kg−1min−1), Deception (n = 10; 58.7 ± 6.6 ml kg−1min−1) | 16.1 km cycling time-trial | Time-trial with accurate ride-alone fb (CON), against a pacer representing MPO of CON (Neutr-fb; INTER), unaware of MPO of pacer 102% above baseline (Neg-fb; INTER) and a subsequent ride-alone trial (not informed of deception in previous trial and not included in meta-analysis) | From the onset of the trial | Control Group: CON = 27:10 ± 2:08 min Neutr-fb = 26:47 ± 1:55 min Inform-fb = 26:55 ± 1:58 min Deception Group: CON = 27:00 ± 1:31 min Pos-fb = 26:41 ± 1:13 min Inform-fb = 26:56 ± 1:38 min | 9 |
| Jones et al., 2016a | Parallel group | 17 Trained male cyclists, CON (n = 9; 54.1 ± 5.9 ml kg−1min−1), Deception (n = 8; 53.3 ± 4.4 ml kg−1min−1) | 16.1 km cycling time-trial | Time-trial with accurate ride-alone fb (CON), against a pacer representing MPO of CON (Neutr-fb; INTER), unaware or aware that MPO of pacer was increased 102% above (Neg-fb; INTER) and a subsequent ride-alone trial after being informed of the nature of a previous trial (Inform-fb; INTER) | From the onset of the trial | Control Group: CON = 26:31 ± 1:44 min Neutr-fb = 26:15 ± 1:31 min Inform-fb = 26:40 ± 1:30 min Deception Group: CON = 26:40 ± 0:52 min Pos-fb = 26:22 ± 0:44 min Inform-fb = 26:34 ± 0:54 min | 9 |
| Shei et al., 2016 | Crossover | 14 Competitive male cyclists (61.6 ± 0.6 ml kg−1min−1) | 4 km cycling time-trial | Time-trial with correct fb ride-alone (CON), unaware of MPO of pacer 102% above baseline (Neg-fb; INTER) and a subsequent trial after deception was revealed with known pacer at 102% (Inform-fb; INTER) | From the onset of the trial | CON = 366.4 ± 3.6 MPO Neg-fb = 358.6 ± 2.7 MPO Inform-fb = 358.1 ± 2.8 MPO | 8 |
| Smits et al., 2016 | Parallel group | 20 Trained male cyclists and triathletes, CON (n = 10;53.7 ± 7.1 ml kg−1min−1) and No-fb (n = 10; 59.0 ± 7.7 ml kg−1min−1) | 20 km cycling time-trial | Time-trial with distance only fb (CON) and no fb (No-fb; INTER) | From the onset of the trial, cyclists stopped at completed distance | CON = 28.7 ± 3.7 min No-fb = 31.0 ± 2.8 min | 8 |
| Swart et al., 2009 | Crossover | 12 Competitive cyclists (56.6 ± 6.6 ml kg−1min−1) | 40 km cycling time-trial | Time-trial with distance only fb (CON) and no fb (No-fb; INTER) | From the onset of the trial, at final km, cyclists were then informed they had 1-km to complete | CON = 265.5 ± 36.4 MPO No-fb = 256.6 ± 36.6 MPO | 8 |
| Waldron et al., 2015 | Crossover | 9 Well-trained male cyclists (60.5 ± 3.3 ml kg−1min−1) | 4 km cycling time-trial | Time-trial with correct ascending fb (CON) and increased ascending fb by 102% compared to CON (Pos-fb; INTER) | An ascending distance clock was continuously displayed and visible to participants | CON = 354 ± 39 s Pos-fb = 372 ± 36 s | 9 |
| Williams et al., 2012 | Parallel group | 22 Non-competitive and untrained males in cycling, CON (n = 11) and No-fb (n = 11) groups (50 ± 9 ml kg−1min−1) | 4 km cycling time-trial | Time-trial with distance only fb (CON) and no fb (No-fb; INTER) | From the onset of the trial, cyclists stopped at completed distance | Group 1 CON = 198 ± 39 MPO No-fb = 179 ± 47 MPO Group 2 CON = 181 ± 37 MPO No-fb = 171 ± 53 MPO | 9 |
a
Data for VO2max in mL/kg/min and peak power output in watts are presented in mean ± standard deviations. PPO, peak power output; FiO2, fraction of inspired oxygen; RH, relative humidity; CON, control trial; INTER, intervention trial; fb, feedback; Pos-fb, positive deceptive feedback; Neg-fb, negative deceptive feedback; Neutr-fb, neutral feedback; No-fb, no; Inform-fb, informed of the nature of a previous trial.