126 Exposure to simulated military operational stress decreases alertness in the morning but not the evening. (3rd May 2021) - LaGoy, Alice
Abstract: Introduction: Alertness, essential for optimal performance, may be modulated by acute stressors including: sleep loss, caloric restriction, cognitive load, and physical exertion. Prior sleep may attenuate sleep loss-related alertness decrements, thereby influencing performance and safety. We examined the effects of prior sleep and changes in alertness throughout the day and across days during a simulated military operational stress (SMOS) protocol. Methods: As part of a 5-day SMOS protocol, fifty-eight active-duty or recently-separated military personnel (45 men; 26±6 years) completed subjective (Profile of Mood States, Vigor subscale) and objective (3-minute Psychomotor Vigilance Task; PVT) alertness assessments each morning (~0900) and evening (~2200). PVT outcomes included median reaction time (RT) and lapses. Day 2 (D2) reflected baseline testing, in which participants received an 8-hour sleep opportunity (2300-0700) and 100% of their estimated caloric need. Day 4 (D4) reflected peak stress, after two nights of participants receiving two 2-hour sleep opportunities (0100-0300, 0500-0700) and 50% of their estimated caloric need. Mixed effects ANOVAs were used to assess the effects of day (D2, D4) and time (Morning, Evening) on alertness. D2 and D4 reflected alertness at baseline and peak stress, respectively. Separate ANOVAs were performed to assess the effects of prior sleep: the Pittsburgh Sleep Quality Index (PSQI) assessed at intake, baseline polysomnography-measured sleep efficiency (SE), and baseline frontal slow wave activity (SWA; 0.5-4Hz). All analyses controlled for age. Results: No significant interaction or main effects of day and time were found for Vigor or PVT lapses. Participants with higher PSQI scores reported lower Vigor (p=.01, η_p^2=.11). A significant interaction was found for PVT RT (p=.04, η_p^2=.07); morning RT was slower on D4 than D2, while evening RT did not differ across days. SE and SWA did not significantly influence alertness. Conclusion: SMOS led to objective alertness deficits in the morning but not evening. Subjective alertness did not change during SMOS but was influenced by prior sleep quality (PSQI). Thus, both circadian and prior sleep-related factors influence performance during operational stress. Fatigue mitigation strategies delivered before and during military operations may support performance and safety. Support (if any): Department of Defense Award #W81XWH-17-2-0070