AbstractThis study aimed to determine if trunk posture during walking is related to increases in rectal temperature (Tre). 24 males treadmill walked in one of four conditions (1): 30 min at 3.0 mph and 0% grade, 20C and 50% relative humidity (RH), wearing healthcare worker (HCW) PPE; (2): 30 min at 3.0 mph and 0% grade, 27.5C and 60% RH, HCW PPE; (3): 30 min at 3.0 mph and 0% grade, 32.5C and 70% RH, HCW PPE; and (4): 40 min at 40% VO2max, 30C and 70% RH, wearing firefighter PPE. Trunk posture (Zephyr BioHarness 3) and Tre were measured continuously. Tre was positively related to trunk posture, controlling for covariates (B=3.49, p<.001). BMI and age moderated this relationship (Tre age, B = 0.76, p<.001; Tre*BMI, B=1.85, p<.001). Trunk posture measurement may be useful in monitoring fall potential and magnitude of heat stress of workers in hot environments.Practitioner Summary: Occupational hyperthermia increases worker risk for heat illness and injury but is difficult to monitor in the field. This investigation shows that trunk posture is independently and positively related to core temperature. Non-invasive measurement or visual inspection of trunk posture could provide novel insight on individual heat strain level.