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 p p p p p p p 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.