Mikkelsen et al. 2019, Prolonged heat acclimation and aerobic performance

Randomised controlled trial, 21 trained cyclists, 5.5 weeks. In cool conditions (14°C), 15 km time-trial power rose ~6% in the heat group and ~5.5% in the matched control, with no group difference; VO2max unchanged in both; plasma volume rose in both. The cool-condition gain was the training effect, not the heat. The longest-duration heat-acclimation RCT with a matched control, and the strongest single rebuttal of the cool-condition transfer claim. Strong.