It was my understanding that training in the heat not only helps with performance in the heat (duh), but also performance in the cool. So there’s simple guidance: train hot whenever you can.

That might not actually be the case (thanks 182lb Pure Climber for the link), with the study below indicating that there’s no performance benefit to be had from training hot for cool weather events. The sample isn’t massive (only 24 individuals), or diverse (tall males > 6′, 29-47 years old, 72.4-88.4kg), but they were all well-trained beforehand (VO2Max pivoting around 58 + at least three years of cycling). So very interesting if you, like the 182lb Pure Climber and myself, fall close to this cohort.

Of course it is possible that a larger, more diverse sample could provide greater insight, or potentially conflicting results. But, for me at least, I’m going to make sure I have all the fans on the next time I hit the Zwift.

Acclimation for HEAT was verified by lower sweat sodium [Na⁺], reduced steady-state heart rate and improved submaximal exercise endurance in the heat. However, when tested in cool conditions both peak power output and VO_2max remained unchanged for HEAT (pre 60.0 ± 1.5 vs. 59.8 ± 1.3 mL O₂/min/kg). TT performance tested in 14°C was improved for HEAT and average power output increased from 298 ± 6 to 315 ± 6 W (P < 0.05), but a similar improvement was observed for CON (from 294 ± 11 to 311 ± 10 W). Based on the present findings, we conclude that training in the heat was not superior compared to normal (control) training for improving aerobic power or TT performance in cool conditions.

NIH