A comparison between heat and temperate-cool environment regarding changes in core temperature with regular exercise: A meta-analysis of randomized controlled trials

Abstract

Purpose: Previous several meta-analyses reported that regular exercise decreased core temperature. However, those meta-analyses included non-randomized controlled trials and did not consider a difference in environment. This meta-analysis aimed to limit studies to randomized controlled trials (RCTs) and evaluate the differences in effects of regular exercise under heat and cool environment on core temperature. Methods: Inclusion criteria were RCTs involving healthy adults, performing exercise in heat index (HI; according to National Weather Service) ≥27°C as the heat environment group (HEAT) and in HI <27°C as the temperate-cool environment group (NORMAL), performing same exercise protocol on both groups, and reporting core temperature at rest or the end of exercise tests. In statistical analyses, the mean differences ([mean value at postintervention in the HEAT – mean value at baseline in the HEAT] – [mean value at postintervention in the NORMAL – mean value at baseline in the NORMAL]) in core temperature were converted into the Hedges’ g values; these values were pooled, and heterogeneity (i.e., a difference among RCTs) was assessed using a Q value. Results: RCTs evaluating core temperature at rest and the end of exercise tests were 5 studies (100 subjects; mean age, 22 to 28 years) and 7 studies (128 subjects; age, 21 to 28 years), respectively. The duration of intervention ranged from 3 to 12 days. Results of the meta-analyses indicated that the pooled g value in core temperature at rest did not decrease significantly (-0.08 [95% confidence interval: -0.18 to 0.03]), and significant heterogeneity was not contained (Q=8.9; P=0.11); in addition, that the pooled g value in core temperature at the end of exercise tests decreased significantly (-0.63 [95% confidence interval: -1.24 to -0.02]), but significant heterogeneity was contained (Q=18.0; P<0.01). Conclusions: The present study is a finding with few RCTs but indicates that regular exercise under heat environment decreases core temperature at the end of exercise than that under normal environment. However, since the results of the meta-analysis contained heterogeneity, the effect may also depend on other factors. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.