With the Ironman World Championship in Kona this Saturday, this Research Roundup is a heat and humidity special for triathletes and other endurance athletes, built around four big topics instead of four single studies. How much heat and humidity each slow you down when you separate the two, what the largest reviews say about heat acclimation and whether sauna and hot baths work as well as active methods, how fast heat adaptations arrive and how fast they fade, and which in-race cooling strategies work, while also being practically feasible.