Practical Cooling Strategies During Continuous Exercise in Hot Environments: A Systematic Review and Meta-Analysis

Abstract

BackgroundPerforming exercise in thermally stressful environments impairs exercise capacity and performance. Cooling during exercise has the potential to attenuate detrimental increases in body temperature and improve exercise capacity and performance.ObjectiveThe objective of this review was to assess the effectiveness of practical cooling strategies applied during continuous exercise in hot environments on body temperature, heart rate, whole body sweat production, rating of perceived exertion (RPE), thermal perception and exercise performance.MethodsElectronic database searches of MEDLINE, SPORTDiscus, Scopus and Physiotherapy Evidence Database (PEDro) were conducted using medical subject headings, indexing terms and keywords. Studies were eligible if participants were defined as ‘healthy’, the exercise task was conducted in an environment ≥25 °C, it used a cooling strategy that would be practical for athletes to use during competition, cooling was applied during a self-paced or fixed-intensity trial, participants exercised continuously, and the study was a randomised controlled trial with the comparator either a thermoneutral equivalent or no cooling. Data for experimental and comparator groups were meta-analysed and expressed as a standardised mean difference and 95 % confidence interval.ResultsFourteen studies including 135 participants met the eligibility criteria. Confidence intervals for meta-analysed data included beneficial and detrimental effects for cooling during exercise on core temperature, mean skin temperature, heart rate and sweat production during fixed-intensity exercise. Cooling benefited RPE and thermal perception during fixed-intensity exercise and improved self-paced exercise performance.ConclusionCooling during fixed-intensity exercise, particularly before a self-paced exercise trial, improves endurance performance in hot environments by benefiting RPE and thermal perception, but does not appear to attenuate increases in body temperature.

Per-Cooling (Using Cooling Systems during Physical Exercise) Enhances Physical and Cognitive Performances in Hot Environments. A Narrative Review

“…Other studies confirmed this finding by using various cooling interventions during exercise, such as fanning [128,211], the application of an ice vest [123,212] and the ingestion of cold fluid [195,213]. Conversely, Ruddock's meta-analysis [129] showed no beneficial effects on heart rate, confirming improved endurance performance. Although the greatest improvement in performance was observed when both the core temperature and the heart rate were reduced by cooling [123], a possible improvement was also observed in the absence of a reduction in heart rate or core temperature [116][117][118]132].…”

“…Several reviews and meta-analyses have recently been published on the benefits of per-cooling [27,107,129]. However, no clear conclusion has been drawn regarding the effects of per-cooling on different types (i.e., 'aerobic', 'anaerobic' and cognitive) of performance.…”

“…The efficacy of the cooling method depends on the site at which cooling is applied and may be linked to tissue perfusion (e.g., the limited effects of cold water and slurry ingestion are due to the reduced splanchnic blood flow during exercise in the heat [155]). Hence, continuous cooling over an area with high tissue perfusion seems to be an ideal method for attenuating increases in body temperature [129].…”

“…Noticeably, per-cooling seems to improve perceptual measures such as thermal perception and the rating of perceived exertion (RPE), thereby inducing better self-selected intensities during time trials [129].…”

Alleviating Heat Strain During Exercise: Hand Cooling and Thermoregulation

“…Cooling is used as an acute strategy that has less physical and logistical demands than heat acclimation. It can be applied before exercise, at intervals or continuously during exercise and generally has favourable effects on exercise capability in hot environments [6][7][8][9]. Cooling strategies used during exercise, when the effects of heat strain are most pronounced, can be effective but there are few strategies that might be practically useful during continuous exercise in the heat.…”