Determine how matched duration but varied exposure scheduling impacts heat acclimation in male and female adults. Thirty males and thirty females walked daily (7 days, 38°C, 60% RH, 6.1 METs) in one of four groups (sustained males/females SM/SF, periodic males/females PM/PF). SM/SF performed 90-min exposures; PM/PF completed three 30-min exposures 3 h apart. Females had similar ovarian-hormone fluctuation. Acclimation markers were assessed within the first 30-min exposure on days 1, 4, and 7. SM/SF rectal temperature decreased from day 1 to days 4 and 7 (37.5 ± 0.3°C, 37.3 ± 0.3°C, 37.2 ± 0.3°C, p 0.05). SM/SF 3-site surface temperature decreased from day 1 to days 4 and 7 (37.1 ± 0.5°C, 36.9 ± 0.4°C, 36.8 ± 0.4°C, p < 0.001) but was unchanged from day 4 to 7 (p = 0.090). PM/PF 3-site surface temperature was unchanged from day 1 (37.0 ± 0.4°C) to days 4 (37.0 ± 0.4°C, p = 0.726) and 7 (36.9 ± 0.4°C, p = 0.109) but decreased from day 4 to 7 (p = 0.013). Females had higher rectal (p < 0.001) and 3-site surface (p = 0.036) temperatures than males throughout acclimation. Thrice-daily exposures are not as effective at inducing heat adaptations compared to once-daily exposures. Sex differences persisted throughout acclimation without altering adaptations.
Rosales et al. (Sun,) studied this question.