Distinguishing Acute And Mounting Stress Responses Among Active Duty Military

Abstract

PURPOSE: To characterize acute vs. mounting cognitive and physical stress responses within a tactical timeline. Biomarkers of stress were extracted from saliva samples taken during a Live-Fire “Stress Shoot” (LFSS), eliciting acute stress. The LFSS was completed prior to (Pre) and following (Post) a 3-day intensive combat training exercise, eliciting mounting stress. METHODS: 46 active duty Soldiers (24.47 ± 4.13 years old, 4 women) completed the 3-day mission and 2 runs of the LFSS. The LFSS involved a marksmanship course with complex rules of engagement (high cognitive load) and physically taxing activities (shuttle run test, kettlebell presses). Salivary biomarkers were collected before (Baseline) and after the LFSS at 4-time points: at LFSS offset (T0) and in 20-minute intervals thereafter (T20, T40, T60). Biomarkers included cortisol to capture cognitive stress and lactate to capture physical stress. The main effects of Sample Time (T0 vs T20 vs. T40 vs T60) and of Mission Phase (Pre vs. Post) were analyzed with non-parametric repeated measures analyses (Friedman Test) with Bonferroni-corrected posthoc pairwise comparisons. RESULTS: Cortisol peaked at T20 (Pre DC=3.39, p<0.001; Post DC=4.47, p<0.001), while lactate peaked at T0 (Pre DC=7.54, p<0.001; Post DC=2.72, p=0.007). There was also a main effect of Mission Phase for cortisol at T20 (DC=2.12, p=0.36) and for lactate at T0 (DC=2.72, p=0.007). Both biomarkers showed decreased concentrations after the 3-day mission (Cortisol at T20: Pre = 4.30ng/mL, Post = 3.47ng/mL; Lactate at T0: Pre = 193745ng/mL, Post = 114346ng/mL). CONCLUSION: The present results reveal heightened acute stress responses through peaks in salivary cortisol and lactate following an acute tactical stressor (LFSS). Together, this suggests that the primary stress responses experienced by active-duty Soldiers are due to acute stress, rather than mounting stress. [1927 of 2000 characters]