Heat tolerance classification criteria require population-specific thresholds for accurate assessment of acclimation state in adults. - Bowie JS; Szymanski MR; Struder JF; Filep EM; Morrissey-Basler MC; Brewer GJ; Thornton SN; Mahoney KJ; Sekiguchi Y; Kwon OS; Chon K; Casa DJ; et al. (Physiological reports, 2026)