Eighty-four hours of sustained operations alter thermoregulation during cold exposure.
PURPOSE; This study examined the effects of short-term (3.5 d) sustained military operations (SUSOPS) on thermoregulatory responses to cold stress.


METHODS
Ten men (22.8 +/- 1.4 yr) were assessed during a cold-air test (CAT) after a control week (control) and again after an 84-h SUSOPS (sleep = 2 h.d (-1), energy intake = approximately 1650 kcal.d(-1), and energy expenditure = approximately 4500 kcal.d(-1). CAT consisted of a resting subject (seminude) being exposed to an ambient temperature ramp from 25 degrees C to 10 degrees C during the initial 30 min of CAT, with the ambient temperature then remaining at 10 degrees C for an additional 150 min.


RESULTS
SUSOPS decreased (P< 0.05) body weight, % body fat, and fat-free mass by 3.9 kg, 1.6%, and 1.8 kg, respectively. During CAT, rectal temperature decreased to a greater extent (P< 0.05) after SUSOPS (0.52 +/- 0.09 degrees C) versus control (0.45 +/- 0.12 degrees C). Metabolic heat production was lower (P< 0.05) after SUSOPS at min 30 (55.4 +/- 3.3 W.m (-2)) versus control (66.9 +/- 4.4 W.m(-2)). Examination of the mean body temperature-metabolic heat production relationship indicated that the threshold for shivering was lower (P< 0.05) after SUSOPS (34.8 +/- 0.2 degrees C) versus control (35.8 +/- 0.2 degrees C). Mean weighted skin temperatures ( degrees C) were lower during the initial 1.5 h of CAT in SUSOPS versus control. Heat debt was similar between trials.


CONCLUSIONS
These results indicate that sustained (84-h) military operations leads to greater declines in core temperature, due to either a lag in the initial shivering response or heat redistribution secondary to an insulative acclimation.
Castellani
John W
JW
US Army Research Institute of Environmental Medicine. Natick, MA 01760-5007, USA. john.castellani@na.amedd.army.mil
Stulz
Dean A
DA
Degroot
David W
DW
Blanchard
Laurie A
LA
Cadarette
Bruce S
BS
Nindl
Bradley C
BC
Montain
Scott J
SJ
D000328:Adult; D001823:Body Composition; D001833:Body Temperature Regulation / Q000502:physiology; D003080:Cold Temperature; D002149:Energy Intake; D006801:Humans; D008297:Male; D008889:Military Personnel; D012768:Shivering / Q000502:physiology; D012881:Skin Temperature; D012892:Sleep Deprivation / Q000503:physiopathology; D013997:Time Factors; D014481:United States