Severe decrements in cognition function and mood induced by sleep loss, heat, dehydration, and undernutrition during simulated combat.
BACKGROUND
Military exercises generate high levels of stress to simulate combat, providing a unique opportunity to examine cognitive and physiologic responses of normal humans to acute stress.


METHODS
Cognitive and physiologic markers of stress were evaluated before, during, and after an intense training exercise conducted for 53 hours in the heat. Cognitive performance, mood, physical activity, sleep, body composition, hydration, and saliva cortisol, testosterone, and melatonin were assessed. Volunteers were 31 male U.S. Army officers from an elite unit, aged 31.6 +/- .4 years.


RESULTS
Wrist activity monitors documented that soldiers slept only 3.0 +/- .3 hours during the exercise and were active throughout. Volunteers lost 4.1 +/- .2 kg (p < .001) of weight, predominately water (3.1 +/- .3 L) (p < .001). Substantial degradation in cognitive function, assessed with computerized tests, occurred. Vigilance, reaction time, attention, memory, and reasoning were impaired (p < .001). Mood, including vigor (p < .001), fatigue (p < .001), confusion (p < .001), depression (p < .001), and tension (p < .002), assessed by questionnaire, deteriorated. The highest cortisol and testosterone levels were observed before the exercise.


CONCLUSIONS
This study quantifies the overwhelmingly adverse impact of multiple stressors on cognitive performance, mood, and physiologic parameters, during a continuous but brief military exercise conducted by highly motivated, well-trained officers.
Lieberman
Harris R
HR
Military Nutrition Division, U.S. Army Research Institute of Environmental Medicine, Natick, MA, USA. harris.lieberman@na.amedd.army.mil
Bathalon
Gaston P
GP
Falco
Christina M
CM
Kramer
F Matthew
FM
Morgan
Charles A
CA
Niro
Philip
P
D000328:Adult; D000704:Analysis of Variance; D001143:Arousal / Q000502:physiology; D001288:Attention; D002755:Choice Behavior / Q000502:physiology; D003072:Cognition Disorders / Q000209:etiology*; D003198:Computer Simulation; D003681:Dehydration / Q000150:complications*; D015444:Exercise; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism; D008297:Male; D044342:Malnutrition / Q000150:complications*; D008889:Military Personnel; D019964:Mood Disorders / Q000209:etiology*; D009483:Neuropsychological Tests; D011597:Psychomotor Performance / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D012463:Saliva; D012892:Sleep Deprivation / Q000150:complications*; D011795:Surveys and Questionnaires; D013997:Time Factors; D014940:Work Schedule Tolerance
D006854:Hydrocortisone