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NINDL, B. C., C. D. LEONE, W. THARION, R. F. JOHNSON, J. CASTELLANI, J. F. PATTON, and S. J. MONTAIN. Physical performance responses during 72 h of military operational stress. Med. Sci. Sports Exerc., Vol. 34, No. 11, pp. 1814–1822, 2002.To characterize the impact of prolonged work, underfeeding, and sleep deprivation (i.e., sustained operations; SUSOPS) on physical and occupational related performance during military operational stress.Ten male soldiers were tested on days 1 (D1), 3 (D3), and 4 (D4) of a control and an experimental week that included prolonged physical work (total daily energy expenditure ∼4500 kcal·d−1), underfeeding (∼1600 kcal·d−1), and sleep deprivation (∼2 h·d−1). Body composition was measured with dual-energy x-ray absorptiometry (DEXA). Ballistic power was assessed by 30 repetitive squat jumps and bench-press throws. Military-relevant occupational performance was evaluated with a 10-min box lift, obstacle course, grenade throw, rifle marksmanship, and a 25-min wall-build task.Fat-free mass (−2.3%) and fat mass (−7.3%) declined (P ≤ 0.05) during SUSOPS. Squat-jump mean power (−9%) and total work (−15%) declined (P ≤ 0.05) during SUSOPS. Bench-press power output, grenade throw, and marksmanship for pop-up targets were not affected. Obstacle course and box-lift performances were lower (P ≤ 0.05) on D3 but showed some recovery on D4. Wall building was ∼25% lower (P ≤ 0.05) during SUSOPS.Decrements in performance during SUSOPS are primarily restricted to tasks that recruit muscles that are over-utilized without adequate recovery. General military skill tasks and occupational physical performance tasks are fairly well maintained.