The effect of post-exercise heat exposure (passive heat acclimation) on endurance exercise performance
a systematic review and meta-analysis.
DOI:
https://doi.org/10.51224/SRXIV.382Keywords:
Heat acclimation, Heat exposure, Hot water immersion, Sauna, Steam bath, Exercise, Exercise performance, Endurance Performance, Athlete, SportAbstract
Background“Active” heat acclimation (exercise-in-the-heat) can improve exercise performance in the heat. An alternative strategy is “passive” heat acclimation using post-exercise heat exposure, but its efficacy is unclear.
Objectives
To synthesise a systematic review and meta-analysis that answers the question: Does post-exercise heat exposure improve endurance exercise performance?
Methods
MEDLINE, CENTRAL, ClinicalTrials.gov, WHO ICTRP, and EU CTR were searched from inception to February 2024 to identity studies meeting the following inclusion criteria: (i) healthy male or female healthy adults; (ii) an exercise training intervention with post-exercise heat exposure (treatment group); (iii) a non-heat exposure control group completing the same training; and (iv) outcomes measuring the primary outcome (endurance exercise performance in the heat) or any of the secondary outcomes (performance in cool conditions, VO2max, lactate threshold, economy, heart rate, RPE, core temperature, sweat rate, and/or thermal sensations during exercise. Study quality was assessed using the Cochrane Risk of Bias 2 tool. To determine the effect of post-exercise heat exposure, between-group ratio of means or standardized mean differences (SMD) were calculated for each outcome and weighted by the inverse of their variance to calculate an overall effect estimate (ratio of mean or Hedges’ g) in a random effects meta-analysis, with 95% confidence intervals (CI) and prediction intervals (PI). The quality of evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) tool.
Results
Ten studies (k=10) including 199 participants (156 males and 43 females, aged 20–32 years) met the inclusion criteria. Interventions lasted 5–21 days with 40–105 minutes/day of exercise and 14–40 minutes/session of post-exercise heat exposure (sauna or hot water immersion). The effect of post-exercise heat exposure on the primary outcome — performance in hot conditions — was trivial with poor precision (ratio of means = 1.04, 95%CI 0.94 to 1.15, P=0.46; k=4, n=60) and had low predictive certainty (95%PI 0.81 to 1.33). There was also a trivial effect on performance in cool conditions and speed at lactate threshold, and a small effect on VO2max, along with a trivial effect on RPE, small effects on heart rate, core temperature, and sweat rate, and a moderate effect on thermal sensations. However, the certainty of evidence was graded as low to very low across all outcomes due to small sample sizes, high risk of bias, risk of publication bias, imprecision in the effect estimates, and low statistical power.
Conclusions
Given the predominance of low to very low certainty of evidence, the effect of post-exercise heat exposure as a method of heat acclimation to improve endurance exercise performance is uncertain. Further high-quality trials are needed to make conclusions concerning its efficacy.
Metrics
References
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