Tyler et al. 2016, Heat adaptation and exercise performance meta-analysis

Meta-analysis of 96 articles. Heat acclimation reliably lowers resting and exercising core temperature, lowers exercising heart rate (~11-12 bpm), raises sweat rate and brings sweating on earlier, and has been associated with plasma volume expansion (though the magnitude is inconsistent across analyses, and a later RCT meta-analysis found no statistically significant change), with a moderate-to-large performance benefit when the test is in the heat that grows with longer regimens. The anchor for what heat acclimation robustly does; it does not establish a cool-condition performance transfer. Strong.