["The Journal of Physiology, Volume 604, Issue 7, Page 2757-2777, 1 April 2026. ", "\nAbstract figure legend Adaptive responses to hot‐dry and warm‐humid heat acclimation.\n\n\n\n\nAbstract\nThis study compared adaptive responses and cross‐acclimation between dry and humid heat acclimation (HA). In a cross‐over design, trained males completed a heat stress test in hot‐dry (Dry‐HST: 42°C, 25% relative humidity [RH]) and warm‐humid (Humid‐HST: 33°C, 80% RH) conditions before and after 8 days of controlled heart rate (HR) HA in hot‐dry (Dry‐HA, n = 10) and warm‐humid (Humid‐HA, n = 12) environments (wet‐bulb globe temperature: ∼31°C). Bayesian multi‐level models were used to determine posterior means and 90% credible intervals. Mean power output increased similarly during Dry‐HA and Humid‐HA but was higher throughout Dry‐HA (13 W [6, 20]). Sweat rate increased during both regimens but was higher throughout Dry‐HA (100 mL·h−1 [20, 180]). Plasma volume expanded with Dry‐HA (201 mL [71, 324]) and Humid‐HA (113 mL [−5, 232]), as did haemoglobin mass (24 g [2, 46] and 26 g [6, 47]). During the Dry‐HST, end‐exercise rectal temperature changed by −0.2°C (−0.3, −0.1; Dry‐HA) and −0.3°C (−0.4, −0.2; Humid‐HA), and during the Humid‐HST by −0.3°C (−0.4, −0.2; Dry‐HA) and −0.1°C (−0.2, 0.0; Humid‐HA). HR changed by −2 beats·min−1 (−5, −1; Dry‐HA) and −5 beats·min−1 (−9, −2; Humid‐HA) during the Dry‐HST, and by −6 beats·min−1 (−9, −4; Dry‐HA) and −1 beats·min−1 (−4, −2; Humid‐HA) during the Humid‐HST. Our data indicate that Dry‐HA and Humid‐HA induced similar adaptations, despite work rate and sweat rate being higher during Dry‐HA. Cross‐acclimation benefits were also similar between interventions. The adaptive stimulus to heat stress, whether dry or humid, appears more impactful on the exercise‐HA phenotype than the specificity of the environment.\n\n\n\n\n\n\n\n\n\nKey points\n\nThe adaptive response to dry and humid heat remains poorly understood, as are the cross‐acclimation benefits between these environments.\nA cross‐over design approach was used to compare the adaptive response to hot‐dry and warm‐humid heat acclimation (HA), and the cross‐acclimation provided by each environment.\nThe negligible physiological differences observed between dry and humid HA regimens suggest that the specificity of the environmental characteristics was overshadowed by the overall adaptive stimulus (controlled heart rate [HR] HA).\nThe greater work rate sustained for a similar HR, rectal temperature, rating of perceived exertion and thermal comfort during dry compared to humid HA highlights that drier conditions may better preserve physical training quality.\nAthletes, soldiers and workers may use dry heat to optimise preparation for competition and work in both dry and humid heat, with the possibility of habituating to humid heat in the final few acclimation sessions if such conditions are anticipated.\n\n\n"]