HA regimens lasting <14 days induce many beneficial physiological and perceptual adaptations to high ambient temperatures, and improve subsequent exercise performance and capacity in the heat; however, the extent of the adaptations is greatest when HA regimens lasting longer than 14 days are adopted. Large methodological differences in the HA literature mean that there is still uncertainty regarding the magnitude and time course of potential adaptation for a number of physiological and perceptual variables.

Exercise is impaired in hot, compared with moderate, conditions. The development of hyperthermia is strongly linked to the impairment and as a result various strategies have been investigated to combat this condition. This meta-analysis focused on the most popular strategy: cooling. Precooling has received the most attention but recently cooling applied during the bout of exercise has been investigated and both were reviewed. We conducted a literature search and retrieved 28 articles which investigated the effect of cooling administered either prior to (n=23) or during (n=5) an exercise test in hot (wet bulb globe temperature >26°C) conditions. Mean and weighted effect size (Cohen's d) were calculated. Overall, precooling has a moderate (d=0.73) effect on subsequent performance but the magnitude of the effect is dependent on the nature of the test. Sprint performance is impaired (d=−0.26) but intermittent performance and prolonged exercise are both improved following cooling (d=0.47 and d=1.91, respectively). Cooling during exercise has a positive effect on performance and capacity (d=0.76). Improvements were observed in studies with and without cooling-induced physiological alterations, and the literature supports the suggestion of a dose–response relationship among cooling, thermal strain and improvements in performance and capacity. In summary, precooling can improve subsequent intermittent and prolonged exercise performance and capacity in a hot environment but sprint performance is impaired. Cooling during exercise also has a positive effect on exercise performance and capacity in a hot environment.

Context: Cooling the neck region can improve the ability to exercise in a hot environment. It might improve performance by dampening the perceived level of thermal strain, allowing individuals to override inhibitory signals.Objective: To investigate whether the enhanced ability to exercise in a hot environment observed when cooling the neck region occurs because of dampening the perceived level of thermal strain experienced and the subsequent overriding of inhibitory signals.Design: Crossover study. Setting: Walk-in environmental chamber.Patients or Other Participants: Eight endurance-trained, nonacclimated men (age 5 26 6 2 years, height 5 1.79 6 0.04 m, mass 5 77.0 6 6.2 kg, maximal oxygen uptake [V O 2max ] 5 56.2 6 9.2 mL?kg 21 ?min 21 ) participated.Intervention(s): Participants completed 4 running tests at approximately 70% V O 2max to volitional exhaustion: 2 familiarization trials followed by 2 experimental trials (cooling collar [CC] and no collar [NC]). Trials were separated by 7 days. Familiarization and NC trials were performed without a collar and used to assess the test variability.Main Outcome Measure(s): Time to volitional exhaustion, heart rate, rectal temperature, neck skin temperature, rating of perceived exertion, thermal sensation, and feeling scale (pleasure/displeasure) were measured.Results: Time to volitional exhaustion was increased by 13.5% 6 3.8% (CC 5 43.15 6 12.82 minutes, NC 5 38.20 6 11.70 minutes; t 7 5 9.923, P , .001) with the CC, which reduced mean neck skin temperature throughout the test (P , .001). Participants terminated exercise at identical levels of perceived exertion, thermal sensation, and feeling scale, but the CC enabled participants to tolerate higher rectal temperatures (CC 5 39.616C 6 0.456C, NC 5 39.186C 6 0.76C; t 7 5 23.217, P 5 .02) and heart rates (CC 5 181 6 6 beats/min, NC 5 178 6 9 beats/min; t 7 5 22.664, P 5 .03) at the point of termination.Conclusions: Cooling the neck increased the time taken to reach volitional exhaustion by dampening the perceived levels of thermal strain.Key Words: hyperthermia, thermoregulation, treadmill, exhaustion, fatigue Key Points N Cooling the neck region dampened the perceived level of thermal strain, enabling participants to increase the time to reach volitional exhaustion. N Dampening of the perceived level of thermal strain delayed the point of voluntary termination of exercise. N When their neck regions were cooled, participants tolerated higher rectal temperatures and heart rates before they voluntarily terminated exercise than when their neck regions were not cooled.

The aim of this two-part experiment was to investigate the effect of cooling the neck on time-trial performance in hot conditions (~30°C; 50% RH). In Study A, nine participants completed a 75-min submaximal (~60% V(O₂(max)) pre-load phase followed by a 15-min self-paced time-trial (TT) on three occasions: one with a cooling collar (CC(90)), one without a collar (NC(90)) and one with the collar uncooled (C(90)). In Study B, eight participants completed a 15-min TT twice: once with (CC(15)) and once without (NC(15)) a cooling collar. Time-trial performance was significantly improved in Study A in CC(90) (3,030 ± 485 m) compared to C(90) (2,741 ± 537 m; P = 0.008) and NC(90) (2,884 ± 571 m; P = 0.041). Fifteen-minute TT performance was unaffected by the collar in Study B (CC(15) = 3,239 ± 267 m; NC(15) = 3,180 ± 271 m; P = 0.351). The collar had no effect on rectal temperature, heart rate or RPE. There was no effect of cooling the neck on S100β, cortisol, prolactin, adrenaline, noradrenaline or dopamine concentrations in Study A. Cooling the neck via a cooling collar can improve exercise performance in a hot environment but it appears that there may be a thermal strain threshold which must be breached to gain a performance benefit from the collar.

Cooling the surface of the neck improves time trial performance in a hot environment without altering physiological or neuroendocrinological responses. Maintenance of a lower neck temperature via the replacement of a CC has no additional benefit to an acute cooling intervention.