Short-term hot water immersion results in substantial thermal strain and partial heat acclimation; comparisons with heat-exercise exposures

• Published in: Journal of thermal biology 2021-04, Vol.97, p.102898-102898, Article 102898
• Main Authors: Greenfield, Andrew M., Pereira, Felipe Gorini, Boyer, William R., Apkarian, Marc R., Kuennen, Matthew R., Gillum, Trevor L.
• Format: Article
• Language: English
• Subjects: Acclimation; Heart rate; Heat; Heat illness; Heat stress; Hyperthermia; Immersion; Passive; Physical training; Temperature; Thermoregulation
• ISSN: 0306-4565; 1879-0992
• DOI: 10.1016/j.jtherbio.2021.102898

To examine the effectiveness of hot water immersion (HWI) as a heat acclimation strategy in comparison to time and temperature matched, exercise-heat acclimation (EHA). 8 males performed heat stress tests (HST) (45 min of cycling at 50% of VO2max in 40 °C, 40% RH) before and after heat acclimation sessions. Acclimation sessions were either three consecutive bouts of HWI (40 min of submersion at 40 °C) or EHA (40 min of cycling at 50% VO2max in 40 °C, 40% RH). Average change in tympanic temperature (TTympanic) was significantly higher following HWI (2.1 °C ± 0.4) compared to EHA (1.5 °C ± 0.4) (P  0.05). HWI induced significantly greater thermal strain compared to EHA at equivalent temperatures during time-matched exposures. However, the greater degree of thermal strain did not result in between intervention differences for cardiovascular, thermoregulatory, or perceptual variables. Findings suggest three HWI sessions may be a potential means to lower HR, TCore, and perceptual strain during exercise in the heat. •Hot water immersion at 40 °C induces greater thermal strain as compared to heat-exercise exposures at 40 °C and 50% VO2Max.•Hot water immersion attenuates rate of perceived exertion and thermal sensation.•Passive acclimation eliminates barriers to accessibility and unwanted physical exertion.