Neuromuscular Performance and Hormonal Responses to Military Operational Stress in Men and Women

Abstract

Conkright, WR, Beckner, ME, Sinnott, AM, Eagle, SR, Martin, BJ, Lagoy, AD, Proessl, F, Lovalekar, M, Doyle, TLA, Agostinelli, P, Sekel, NM, Flanagan, SD, Germain, A, Connaboy, C, and Nindl, BC. Neuromuscular performance and hormonal responses to military operational stress in men and women. J Strength Cond Res 35(5): 1296–1305, 2021—Women have recently been integrated into ground close combat positions; however, there are limited data in women in these roles. We aimed to test the hypothesis that there would be no sex-specific neuromuscular responses, but hormonal signaling would be differentially impacted when exposed to simulated military operational stress (SMOS). Neuromuscular performance was assessed daily using a tactical mobility test (TMT) in 54 male and 15 female military members. Blood was drawn before/after TMT. Mood states were assessed each morning. Unloaded 300-m shuttle time increased 6% in both sexes and remained 7% higher after 1 day of recovery compared with baseline (p < 0.05 for both), whereas performance was maintained in other TMT events (p > 0.05). Growth hormone increased in men, but not women, before to after TMT (p < 0.001 vs. p = 0.086). Women experienced a greater decline in insulin-like growth factor-I across days compared with men ( = 0.778 vs. 0.209, respectively, p < 0.001). Brain-derived neurotrophic factor increased significantly in men only from before to after TMT on day 1 (men: +107% vs. women: +10%) but no difference on days 3 or 4. Cortisol increased 69% from before to after TMT when averaged by sex and day. Negative mood states (depression, tension, and anger) and altered hormonal concentrations were associated with poorer TMT performance. Acute SMOS differentially impacted circulating hormonal milieu in men and women, but no differences in physical performance responses. Unloaded 300-m shuttle was negatively impacted while other fitness domains were maintained. Relationships between performance and mood/endocrine signaling highlight the potential for self-report measures and biomarkers to serve as indicators of performance change.

Military tactical adaptive decision making during simulated military operational stress is influenced by personality, resilience, aerobic fitness, and neurocognitive function

“…Data presented herein are part of a larger study (U.S. Department of Defense award #W81XWH-17-2-0070; Beckner et al, 2021a ; Conkright et al, 2021a , b ). This prospective cohort study was designed to characterize the impact of 48 h of SMOS, involving sleep and caloric restriction and physical work, on military tactical adaptive decision making.…”

“…Warfare exposes military personnel to volatile, uncertain, complex, and ambiguous environments including sleep deprivation, caloric restriction, dehydration, prolonged bouts of physical exertion, and psychological burden ( Nindl et al, 2018 ; Vikmoen et al, 2020 ; Conkright et al, 2021a ). Laboratory-based studies designed to mimic combat or military field training through simulated military operational stress (SMOS) protocols have consistently demonstrated deleterious effects on warfighter’s physical, cognitive, and emotional performance/function ( Hoyt et al, 2006 ; Vikmoen et al, 2020 ; Beckner et al, 2021a ; Conkright et al, 2021a ).…”

“…Warfare exposes military personnel to volatile, uncertain, complex, and ambiguous environments including sleep deprivation, caloric restriction, dehydration, prolonged bouts of physical exertion, and psychological burden ( Nindl et al, 2018 ; Vikmoen et al, 2020 ; Conkright et al, 2021a ). Laboratory-based studies designed to mimic combat or military field training through simulated military operational stress (SMOS) protocols have consistently demonstrated deleterious effects on warfighter’s physical, cognitive, and emotional performance/function ( Hoyt et al, 2006 ; Vikmoen et al, 2020 ; Beckner et al, 2021a ; Conkright et al, 2021a ). In lieu of conducting cognitive research during live military scenarios due to operational security, and institutional human use review board-related constraints, surrogate efforts have been successful in mimicking operational stress in tightly controlled laboratory conditions and high-fidelity field and training exercises.…”

“…Select circulating biomarkers have been associated with performance and resilience in military personnel during operational stress ( Beckner et al, 2021a , b ; Conkright et al, 2021a ). Higher concentrations of neuropeptide-Y (NPY) have been associated with greater mental alertness and were reported to increase in special forces soldiers undergoing military survival training; of note, NPY increases were positively correlated with cortisol (CORT; Morgan et al, 2000 ).…”

Utility of extracellular vesicles as a potential biological indicator of physiological resilience during military operational stress

“…The simulated military operational stress protocol has been described in detail elsewhere (Beckner et al, 2021 ; Conkright et al, 2021 ). Briefly, the study protocol was completed over five consecutive days and nights in cohorts of up to four participants at a time.…”