THE IMPACT OF HEAT EXPOSURE SCHEDULE AND SEX ON HEAT ACCLIMATION

Author

Alejandro Manuel Rosales, University of Montana, Missoula

Year of Award

2025

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Integrative Physiology and Rehabilitation Sciences

Department or School/College

School of Integrative Physiology and Athletic Training

Committee Chair

Dustin R. Slivka

Commitee Members

Brent C. Ruby, John C. Quindry, Charles L. Dumke, Richard W. Willy

Keywords

Acclimatization, Blood Flow, Environmental Exercise Physiology, Skin Conductivity, Thermal Tolerance, Thermoregulation

Abstract

PURPOSE: Determine if matched duration, but schedule varied heat exposures impact heat acclimation while also examining sex-differences.

METHODS: Over 7 days, males (n=30, 178.5±8.4 cm, 82.0±13.4 kg) and females (n=30,167.4±5.6 cm, 63.1±9.1 kg) walked (1.6 m·s-1, 5% grade) daily in the heat (38°C, 60%RH) in one of four 90-minute exposure groups (Sustained Males/Females, Periodic Males/Females). Sustained groups were exposed continuously. Periodic groups completed three 30-minute exposures 3 hours apart. Heat acclimation was assessed on Days 1, 4, and 7 during the initial 30-minute exposure. Telemetry pill ingestion coincided with measurement days.

RESULTS: Sustained group rectal temperature decreased from Day 1 to Days 4 and 7 (37.5±0.3, 37.3±0.3, 37.2±0.3°C, p<0.001) and further decreased from Day 4 to 7 (p=0.011). Periodic group rectal temperature did not change on Days 1, 4, and 7 (37.4±0.3, 37.4±0.3, 37.3±0.3°C, p>0.05). Sustained group surface temperature decreased from Day 1 on Days 4 and 7 (37.1±0.5, 36.9±0.4, 36.8±0.4°C, p<0.001) but did not decrease from Day 4 to 7 (p=0.09). Periodic group surface temperature did not change until Day 4 and 7 were compared (37.0±0.4, 37.0±0.4, 36.9±0.4°C, p=0.013). Peak core temperature measured via telemetry pill indicated that Sustained groups (38.6±0.5°C) were higher overall than the Periodic groups (38.2±0.3°C, p<0.001). Higher rectal and surface temperatures in females than males occurred regardless of acclimation (p<0.05). Although, telemetry derived peak core temperature was similar across sex (p=0.85).

CONCLUSIONS: In 7-days, one daily 90-minute exposure is more effective than three daily 30-minute exposures. Sex-differences are present prior to and throughout heat acclimation.

Recommended Citation

Rosales, Alejandro Manuel, "THE IMPACT OF HEAT EXPOSURE SCHEDULE AND SEX ON HEAT ACCLIMATION" (2025). Graduate Student Theses, Dissertations, & Professional Papers. 12440.
https://scholarworks.umt.edu/etd/12440