Wet clothing is less insulative than dry clothing and consequently increases heat loss in cold air. Tactical necessity can render removal of wet clothing impossible and/or require Warfighters to remain static to avoid detection, limiting heat production and posing a threat of hypothermia (core temperature <35 °C). This study aimed to characterize body temperatures and evaluate hypothermia risk while statically exposed to 5 °C air wearing three wet military uniforms. Further, low-speed loaded walking was evaluated as a strategy to raise end-static temperatures. Twelve adults (11 M, 1 F) randomly completed three wet-cold trials wearing either the Improved Hot Weather Combat Uniform (IHWCU), Army Combat Uniform (ACU), or ACU with silk-weight base layer (ACU+). Each trial involved 180 min of cold air (5.3 ± 0.3 °C, 0.8 m·s-1) exposure after a clothed 2 min head-out immersion (34.0 ± 0.2 °C). Volunteers were static for 60 min followed by 120 min of walking with a rucksack. Rectal temperature (Tre) area under the curve did not differ among the three wet uniforms when static (p = 0.431) with Tre increasing, rather than decreasing, across the 60 min (IHWCU: +0.26 ± 0.19 °C, ACU: +0.37 ± 0.21 °C, ACU+: +0.36 ± 0.20 °C). Hypothermia risk with 60 min static wet-cold exposure therefore appears minimal, regardless of the military uniform worn, in an otherwise low stress cohort. End-static finger temperatures (IHWCU: 9.48 ± 2.30 °C, ACU: 9.99 ± 1.82 °C, ACU+: 9.27 ± 1.66 °C, p > 0.999) were reduced by ∼20-23 °C posing a considerable dexterity concern. Heat production of ∼210 W·m2 appeared sufficient to begin to reverse negative cumulative heat storage and initiate slight elevations of rectal and peripheral temperatures, although finger temperatures increased <2 °C after 120 min. ClinicalTrials.gov ID: NCT05409937.
Keywords: core temperature; heat loss; skin temperature; thermoregulation.