Salivary C-reactive protein exhibits a diurnal pattern and relates to biobehavioral health in military men.

C-reactive protein is a systemic inflammatory biomarker that is positively associated with the development of disease. Salivary C-reactive protein (sCRP) has previously been reported to have a diurnal rhythm with higher levels upon awakening and lower levels thereafter. The aims of this study were to evaluate the stability of sCRP across two days, characterize the daily sCRP pattern, compute morning sCRP parameters, and evaluate associations with biobehavioral health in US Navy Explosive Ordnance Disposal (EOD) technicians. Seventy male EOD technicians (age = 34.9 ± 6.5 years) participated in this study, which included a tablet-based survey, measures of health and fitness, and saliva collection. In a free-living setting, participants self-collected saliva on 2 consecutive days at WAKE, WAKE+30, WAKE+60, 4p.m., and 9p.m., for a total of 10 samples. Parameters (e.g., area under the curve) were computed to characterize the morning sCRP magnitude and pattern. Pearson product-moment correlation analyses were used to assess the stability of sCRP samples and parameters across the study period and to examine associations with biobehavioral health. Average sCRP concentrations for the 2-day period were evaluated using an analysis of variance with repeated measures. The stabilities between corresponding time points on Days 1 and 2 were very high (rs = 0.87-.94, all ps ≤ 0.001). sCRP concentrations were highest at WAKE, decreased by 73.6 % at WAKE+30, and then plateaued for the rest of the day. Parameter stabilities were good to excellent (rs = 0.77-.98, all ps ≤ 0.001). We also observed associations between sCRP parameters, self-reported health behaviors, and objective measures of health and fitness. In this study of a military population, we characterized sCRP as diurnal with robust stability across 2 consecutive days, which demonstrates the feasibility of sCRP as a biomarker. These results have significant implications for study methodology and for using sCRP as a marker of dysfunction or disease.

Greater Fitness Is Associated With Improved Functional Movement Characteristics in Explosive Ordnance Disposal Technicians.

ABSTRACT: Hernández, LM, Coffin, SD, and Taylor, MK. Greater fitness is associated with improved functional movement characteristics in explosive ordnance disposal technicians. J Strength Cond Res 36(6): 1731-1737, 2022-Low fitness and poor functional movement (FM) have been linked to higher musculoskeletal injury risk. The FM Screen (FMS) and Y-Balance Test (YBT) are useful indicators of potential injury risk in military personnel. U.S. Navy Explosive Ordnance Disposal (EOD) technicians are the premier combat force for countering explosive hazards and must operate in austere environments. To safeguard health and mission success, it is critical to assess factors related to injury risk in this specialized military population. This study evaluated the relationship between fitness and FM characteristics in 64 male EOD technicians (mean age ± SD = 34.2 ± 7.0 years). Body fat percentage (BF%), maximum volume of oxygen uptake (V̇o2max), muscular strength, and FM (i.e., FMS, YBT) were assessed. Body fat percentage and V̇o2max were associated with FMS and YBT scores (all p < 0.05). A nonlinear model further revealed that the group with the lowest V̇o2max values had the bottommost FMS and YBT scores (all p < 0.01), but FM scores did not differ among those with a higher V̇o2max, implying a "threshold" effect. No correlations were observed with muscular strength. By characterizing the unique and shared contributions of BF% and V̇o2max, and exploring the nonlinear relationship between V̇o2max and FM, this study expands on accruing data that indicate individuals who are more physically fit have better FM and lower injury risk. Although muscular strength is a critical element of overall fitness, body composition and cardiorespiratory fitness may more strongly influence FM and injury risk.

The "yin and yang" of the adrenal and gonadal systems in elite military men.

We recently established daily, free-living profiles of the adrenal hormone cortisol, the (primarily adrenal) anabolic precursor dehydroepiandrosterone (DHEA) and the (primarily gonadal) anabolic hormone testosterone in elite military men. A prevailing view is that adrenal and gonadal systems reciprocally modulate each other; however, recent paradigm shifts prompted the characterization of these systems as parallel, cooperative processes (i.e. the "positive coupling" hypothesis). In this study, we tested the positive coupling hypothesis in 57 elite military men by evaluating associations between adrenal and gonadal biomarkers across the day. Salivary DHEA was moderately and positively coupled with salivary cortisol, as was salivary testosterone. Anabolic processes (i.e. salivary DHEA and testosterone) were also positively and reliably coupled across the day. In multivariate models, salivary DHEA and cortisol combined to account for substantial variance in salivary testosterone concentrations across the day, but this was driven almost exclusively by DHEA. This may reflect choreographed adrenal release of DHEA with testicular and/or adrenal release of testosterone, systemic conversion of DHEA to testosterone, or both. DHEA and testosterone modestly and less robustly predicted cortisol concentrations; this was confined to the morning, and testosterone was the primary predictor. Altogether, top-down co-activation of adrenal and gonadal hormone secretion may complement bottom-up counter-regulatory functions to foster anabolic balance and neuronal survival; hence, the "yin and yang" of adrenal and gonadal systems. This may be an adaptive process that is amplified by stress, competition, and/or dominance hierarchy.

Sex differences in cardiovascular and subjective stress reactions: prospective evidence in a realistic military setting.

Evidence points to heightened physiological arousal in response to acute stress exposure as both a prospective indicator and a core characteristic of posttraumatic stress disorder (PTSD). Because females may be at higher risk for PTSD development, it is important to evaluate sex differences in acute stress reactions. This study characterized sex differences in cardiovascular and subjective stress reactions among military survival trainees. One hundred and eighty-five military members (78% males) were studied before, during, and 24 h after stressful mock captivity. Cardiovascular (heart rate [HR], systolic blood pressure [SBP], diastolic blood pressure [DBP]) and dissociative states were measured at all three time points. Psychological impact of mock captivity was assessed during recovery. General linear modeling with repeated measures evaluated sex differences for each cardiovascular endpoint, and causal steps modeling was used to explore interrelationships among sex, cardiovascular reactions and psychological impact of mock captivity. Although females had lower SBP than males at all three time points, the difference was most pronounced at baseline and during stress. Accordingly, females showed greater residual elevation in SBP during recovery. Females had lower DBP at all three time points. In addition, females reported greater psychological impact of mock captivity than males. Exploratory causal steps modeling suggested that stress-induced HR may partially mediate the effect of sex on psychological impact of mock captivity. In conclusion, this study demonstrated sex-specific cardiovascular stress reactions in military personnel, along with greater psychological impact of stress exposure in females. This research may elucidate sex differences in PTSD development.

Delayed memory effects after intense stress in Special Forces candidates: exploring path processes between cortisol secretion and memory recall.

The aim of this paper is twofold. First, it explores delayed effects of high endogenously evoked cortisol concentrations on visuo-spatial declarative memory. Subsequently, it applies multiple mediation (MM) analyses to reveal path processes between stress and cognitive performance in a sample of 24 male Special Forces (SF) candidates (mean age = 27.0 years, SD = 4.1). The SF candidates were randomly assigned to a control (n = 12) or an intense stress group (n = 12), and cortisol secretion for the intense stress condition was triggered by a brusque 60 min prisoner of war exercise. Stress exposure provoked robust increases in cortisol concentrations and a significant decline in immediate recall performance, measured with the Rey-Osterrieth Complex Figure (ROCF). The relative retrieval differences in regard to the ROCF persisted even after a recovery period of 24 h, as both groups showed similar levels of memory decline over 24 h. Next, the study applied a MM design that involved distribution-independent asymptotic and resampling strategies to extend traditional bivariate analyses. MM results showed that ROCF performance was mediated by increases in cortisol concentrations. Considering the studied variables, the current analysis was the first to provide statistical support for the generally accepted thesis that cortisol secretion in itself, rather than subjective strain or the experimental treatment, affects cognitive performance. The revelation of such path processes is important because it establishes process identification and may refine existing paradigms.

Spontaneous and deliberate dissociative states in military personnel: are such states helpful?

This study explored distinctions between spontaneous and deliberate dissociative states in 335 military personnel exposed to stressful survival training. Participants completed the Clinician-Administered Dissociative States Scale (CADSS) after a stressful mock-captivity event. They were also asked to indicate whether the dissociative experiences just happened (i.e., spontaneous), or whether they chose to have them happen (i.e., deliberate); and whether they appraised the dissociative experience as helpful (i.e., facilitative) or hurtful (i.e., debilitative) to their ability to cope with the stressful event. A majority (95.4%) endorsed dissociative states during stress. More than half (57.4%) described dissociative experiences as spontaneous, 13.0% as deliberate, and 29.5% endorsed neither. In Special Forces soldiers only, those who endorsed facilitative dissociation exhibited higher total CADSS scores than those who endorsed debilitative dissociation. Seventy-three percent of spontaneous dissociators described the experience as debilitative to coping with stress; conversely, 76% of deliberate dissociators said these experiences facilitated coping with stress. Individuals with prior trauma exposure tended to appraise dissociative states as more debilitative to coping. This research may enhance the fidelity of studies of dissociation constructs and may offer pivot points for prevention and treatment of stress-related disorders.

Relationships of hardiness to physical and mental health status in military men: a test of mediated effects.

Evidence links the personality trait hardiness to both mental (MH) and physical health (PH) status, but few unifying models delineate interrelationships of these variables. The first purpose of this study was to examine the association of hardiness to MH and PH in military men. Second, we tested the hypothesis that MH would mediate the association of hardiness with PH. Identical measures were collected in two separate, demographically-similar samples (n = 65 and n = 55). All subjects completed a background questionnaire, the Dispositional Resilience Scale-15 and the Short Form 36 Medical Outcomes Survey. Associations between hardiness, PH and MH were examined using regression-based mediation analyses followed by the Sobel test of indirect effects. In the total sample, hardiness predicted PH in an initial regression model (ß = 0.37, p < .001). When MH was added to the model, however, PH's influence was substantially attenuated and no longer significant (ß = 0.06, p > .05). A Sobel test of significance confirmed a mediated effect (p < .001). Similar patterns were observed in each individual sample. Hardiness is associated with PH in military men, and this relationship is mediated by MH.

Dehydroepiandrosterone and dehydroepiandrosterone sulfate: anabolic, neuroprotective, and neuroexcitatory properties in military men.

Evidence links dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS) to crucial military health issues, including operational stress, resilience, and traumatic brain injury. This study evaluated the anabolic, neuroprotective, and neuroexcitatory properties of DHEA(S) in healthy military men. A salivary sample was obtained from 42 men and assayed for DHEA(S), testosterone, nerve growth factor (NGF; which supports nerve cell proliferation), and salivary alpha amylase (sAA; a proxy of sympathetic nervous system function). Separate regression analyses were conducted with DHEA and DHEAS as independent variables, and testosterone, NGF, and sAA as dependent variables, respectively. The models explained 23.4% of variance in testosterone (p < 0.01), 17.2% of variance in NGF (p < 0.01), and 7.4% of variance in sAA (p = 0.09). Standardized beta coefficients revealed that DHEA independently influenced testosterone (beta = 0.40, p < 0.01), whereas DHEAS independently influenced NGF (beta = 0.48, p < 0.01) and sAA (beta = 0.36, p < 0.05). DHEA demonstrated anabolic properties, whereas DHEAS demonstrated neuroprotective and neuroexcitatory properties in military men. This area of study has broad implications for stress inoculation, traumatic brain injury rehabilitation, and regenerative medicine in military personnel.

Military Exposures Predict Mental Health Symptoms in Explosives Personnel but Not Always as Expected.

OBJECTIVE: The aim of this study was to determine the unique and combined associations of various military stress exposures with positive and negative mental health symptoms in active duty service members. MATERIALS AND METHODS: We investigated 87 male U.S. Navy Explosive Ordnance Disposal (EOD) technicians (age M ± SE, range 33.7 ± 0.6, 22-47 years). Those who endorsed a positive traumatic brain injury diagnosis were excluded to eliminate the confounding effects on mental health symptoms. Using a survey platform on a computer tablet, EOD technicians self-reported combat exposure, deployment frequency (total number of deployments), blast exposure (vehicle crash/blast or 50-m blast involvement), depression, anxiety, posttraumatic stress, perceived stress, and life satisfaction during an in-person laboratory session. RESULTS: When controlling for other military stressors, EOD technicians with previous involvement in a vehicle crash/blast endorsed worse mental health than their nonexposed counterparts. The interactions of vehicle crash/blast with deployment frequency and combat exposure had moderate effect sizes, and combat and deployment exposures demonstrated protective, rather than catalytic, effects on negative mental health scores. CONCLUSIONS: Military stressors may adversely influence self-reported symptoms of negative mental health, but deployment experience and combat exposure may confer stress inoculation.

Effects of dehydroepiandrosterone supplementation during stressful military training: a randomized, controlled, double-blind field study.

Dehydroepiandrosterone (DHEA) and DHEA sulfate (DHEAS) are anabolic prehormones involved in the synthesis of testosterone. Both have been shown to exert neuroprotective effects during stress. In this randomized, controlled, double-blind field study, we examined the effects of a 12-day DHEA regimen on stress indices in military men undergoing survival training. Forty-eight men were randomized to either a DHEA treatment group or placebo control group. The treatment group received 50 mg of oral DHEA supplementation daily for 5 days during classroom training followed by 7 days of 75 mg during stressful field operations. Control subjects received identical placebo pills. Salivary assays (DHEA[S], testosterone, and cortisol) were conducted at four time points: distal pre-stress (T1), proximal pre-stress (T2), mock-captivity stress (T3), and 24 h recovery (T4). Subjective distress was also assessed at T1, T3, and T4. As expected, DHEA treatment resulted in higher salivary concentrations of DHEA and DHEAS during daily living, mock-captivity stress, and recovery. Similar patterns were observed for salivary markers of anabolic balance: DHEA/cortisol, DHEAS/cortisol, and testosterone/cortisol concentration ratios. Despite notable time effects, no group differences emerged for subjective distress. A brief, low dose DHEA regimen yielded large increases in salivary DHEA(S) concentrations and enhanced anabolic balance throughout sustained military stress. These physiological changes did not extrapolate to subjective distress.

Science of interdisciplinary salivary bioscience: history and future directions.

Salivary bioscience is noteworthy in its history, as well as in the breadth and scope of its impact. The minimally invasive nature of sampling oral fluid allows for evaluation of individual and intra-individual change in biological processes in ways and settings not possible with traditional biospecimens. The range of measurements is expansive (e.g., DNA, hormones, cytokines, antibodies) and modern technologies enable simultaneous multisystem assessment from a singlet specimen. Used in combination with modern multivariate analytical models, the capacity to repeatedly assess multisystem and level measurements collected from the same individual over time enable operationalization, testing and refinement of complex biobehavioral models. This review describes the emerging narrative of salivary bioscience, and aims to inform and reveal opportunity for innovation and discovery.

Oral fluid collected from humans and animals that can be used in medical and research settings has a rich history of development and represents the growing field of salivary bioscience. This is in part due to the ease of oral fluid collection (for example, no blood draw necessary), which allows researchers and clinicians the opportunity to evaluate how individuals differ in biological processes both over time and how they compare to other individuals (the same can be said for animals), while using a minute amount of liquid to do so. The ease of collection and modern technology allows these samples to be collected at multiple time points and in places where this was not possible previously, like in the home. Modern technology has made it possible to use a small amount of oral fluid to assess many different biological measurements, including ones associated with hormones, infection and stress. This review provides more information about the history, innovations, and future potential of oral fluid in research and medicine.

Combat and blast exposure blunt sympathetic response to acute exercise stress in specialised military men.

Electrodermal activity (EDA)-a measure of electrical skin conductance reflecting (exclusive) sympathetic control of the eccrine sweat gland-holds promise as an indicator of central sympathetic activation. The aim of this study was to determine whether combat and blast exposure modulate the EDA response to acute exercise stress in specialised military men. Fifty-one men (age M = 36.1, SD = 6.5) participated in this study as part of the Explosive Ordnance Disposal Operational Health Surveillance System. The EDA complex (i.e., tonic + phasic conductance) was continuously measured throughout a maximal effort, graded exercise test. As expected, exercise stress resulted in measurable, stepwise increases in EDA before tapering at higher exercise intensities. Individuals with more substantial combat exposure and those with blast exposure demonstrated blunted EDA patterns in comparison to their low/nonexposed counterparts. This blunted pattern might imply sub-optimal sympathetic nervous system function in the exposed cohorts and enhances our knowledge of factors influencing resilience in these men.

Effect of psychological skills training during military survival school: a randomized, controlled field study.

In this randomized, controlled field study, we examined the effects of a brief psychological skills training (PST) intervention on stress responses during military survival school. A second purpose was to build upon prior research in this unique environment by extending the follow-up window to 3 months. Baseline subjective distress (dissociative) symptoms were measured in 65 male military subjects, who were then randomized either to PST or a control group that received no training beyond the normal survival school curriculum. PST received training in arousal control, mental imagery, goal setting, and positive self-talk in two separate 40-minute sessions before stressful field exercises. Stress symptoms were then assessed during a mock-captivity phase of training, as well as 24 hours, 1 month, and 3 months after completion of training. Repeated-measures analyses of variance with follow-up paired t tests examined differences between groups and across time. Survival training precipitated remarkable increases in subjective distress, but few substantive group differences emerged. This study extends prior work quantifying the human stress response to intense military training.

Toward a "Dashboard" Indicator of Retention in U.S. Navy Personnel.

INTRODUCTION: Retention is a top priority for the U.S. Navy. However, our understanding of factors influencing retention of Navy personnel is limited. Current research implies that poor mental health, low appraisals of unit cohesion, low leadership satisfaction, and low social support may adversely affect retention. There is a need to understand how these and other factors influence retention in U.S. Navy personnel. We evaluated a broad range of factors influencing job satisfaction and career intentions (proxies of retention) in a large sample of Navy service members. MATERIALS AND METHODS: Seven hundred and ninety-eight U.S. Navy men and women participated in this study as part of the Naval Unit Behavioral Health Needs Survey (NHRC.2014.0006). Independent variables included personal and unit morale, unit cohesion, affective organizational commitment, social support, behavioral health, sleep, leadership satisfaction, and perceived stress. Dependent variables include job satisfaction and career intentions. Separate multivariate regression models examined the unique and combined associations of independent and demographic variables with each dependent variable, respectively. RESULTS: Regression models accounted for 48% of variance in job satisfaction and 55% of variance in career intentions, respectively. The most robust predictors of job satisfaction were affective organizational commitment (i.e., one's emotional attachment to, identification with, and involvement in an organization), depressive symptoms, unit cohesion, and perceived stress; primary predictors of career intentions included affective organizational commitment, years of military service, marital status, and race/ethnicity. CONCLUSION: In this study, we identified diverse predictors of job satisfaction and career intentions of Navy men and women, with overall models accounting for substantial variance in both outcomes. This study informs evidence-based policies, programs, practices, and processes designed to influence job satisfaction, career intentions, and retention in U.S. Navy service members. These study findings also inform the development of a dashboard indicator of retention of U.S. Navy men and women.

Post-awakening Cortisol in Explosive Ordnance Disposal Technicians: A Replication Study in a Novel Population.

INTRODUCTION: Amassing evidence suggests that post-awakening salivary cortisol rhythms (changes in cortisol throughout the day) may indicate health status. We previously established summary parameters for salivary cortisol in U.S. Navy Sea, Air, and Land and reported excellent parameter stability across 2 days of repeated sampling. To confirm the generalizability of our original findings to other military populations, we replicated the procedures of our prior report in another specialized military group. The purpose of this study was to (1) establish summary parameters of daily salivary cortisol rhythms, (2) evaluate summary parameter stability, and (3) assess the impact of sampling compliance in U.S. Navy Explosive Ordnance Disposal (EOD) technicians. MATERIALS AND METHODS: Seventy active duty, male Explosive Ordnance Disposal technicians (mean ± SD age; 34.9 ± 6.5 years) self-collected saliva samples in a nondeployed setting on two consecutive weekdays at WAKE, WAKE + 30 min, WAKE + 60 min, 4 p.m., and 9 p.m. For salivary cortisol, we computed summary parameters, i.e., measures of magnitude and measures of pattern, and then evaluated their stabilities via correlational analyses and Cronbach's alpha (α). Compliance was objectively and subjectively evaluated using actigraphy and self-reported data, respectively. This research was conducted under a Naval Health Research Center Institutional Review Board approved study (NHRC.2015.0013). RESULTS: Average salivary cortisol concentrations increased at WAKE + 30 (mean ± SE reactivity; 48.9 + 6.8%) from WAKE, followed by a swift recovery at WAKE + 60. Approximately 10.9% of the group were classified as negative-responders (i.e., < 0% change from WAKE to WAKE + 30). The measures of magnitude demonstrated fair stability across two days (r value range: 0.37-0.45, ps < 0.01; α range: 0.54-0.62). Fifty-five percent of the sample was classified as compliant (defined as <15 min deviation from target sampling times) across both days. Compliance decreased to 31% when compliance criteria were refined to <5 min deviation; however, controlling for compliance did not overwhelmingly influence the more stable summary parameters of magnitude. CONCLUSIONS: These findings demonstrate a thorough replication, with some additional refinement, of our prior study, implying generalizability across diverse military populations. Study limitations include unsupervised saliva collection in a free-living setting, which is counterbalanced by ecological validity. The noninvasive salivary sampling protocol used in this study yields stable estimations of daily cortisol rhythms in specialized military men and is recommended as an operational health surveillance tool by which to monitor chronically stressed military members.

Trauma Exposure and Functional Movement Characteristics of Male Tactical Athletes.

CONTEXT: Tactical athletes commonly experience high levels of physical stress, which may increase their risk of musculoskeletal injury. It is critical to understand psychological predictors of functional movement (FM), which may help prevent musculoskeletal injury in this population. OBJECTIVE: To determine the associations of combat and trauma exposure with FM characteristics of male tactical athletes. Secondary objectives were to explore confounding influences of age and physical injury history as well as the mediating role of bodily pain. DESIGN: Cross-sectional study. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: Eighty-two healthy, male, active-duty US Navy Explosive Ordnance Disposal personnel (age = 34.0 ± 6.7 years). MAIN OUTCOME MEASURE(S): Participants completed measures of combat exposure, trauma exposure, physical injury history, and bodily pain. We assessed FM characteristics (ie, Functional Movement Screen [FMS], Y-Balance Test), from which we derived a composite functional status (CFS) measure. Hypotheses were tested using correlational and multiple regression (causal-steps) models. RESULTS: In unadjusted models, trauma exposure was inversely associated with the FMS (P = .005) and CFS (P = .009) scores. In adjusted models, these relationships were robust to the confounding influences of age and physical injury history. Trauma exposure and bodily pain were substantive, independent predictors of FMS and CFS in causal-steps models (all P values < .05), implying additive rather than mediated effects (R2adj = 0.18-0.20). Combat exposure did not predict FM characteristics. CONCLUSIONS: To our knowledge, this is the first evidence of the influence of trauma exposure on the FM characteristics of male tactical athletes, independent of age, physical injury, and bodily pain. This program of research may help to advance the prevention and treatment of musculoskeletal injuries in the tactical environment.

Behavioral predictors of acute stress symptoms during intense military training.

A better understanding of factors influencing human responses to acute stress is needed to enhance prevention and treatment of stress-related disorders. In the current study, the authors examined predictors of acute stress symptoms during intense military training in 35 men. In univariate and multivariate models, perceived stress, passive coping, and emotion-focused coping during daily living predicted acute stress symptoms in response to realistic survival training, whereas active coping and problem-focused coping did not. Baseline stress levels and coping styles, both of which may be modifiable, appear to play a fundamental role in the human response to acute uncontrollable stress. Additional research is needed to better elucidate the relative and interactive contributions of behavioral predictors of acute stress.

Anger expression and stress responses in military men.

INTRODUCTION: A better understanding of individual differences in the human stress response may enhance prevention and treatment of operational stress reactions. In this study, we examined the relationships of anger experience and expression to stress indices during daily living and in response to military survival training in 45 men. METHODS: Prior to participation in survival training, subjects completed self-report measures of perceived stress and anger. The revised Impact of Event Scale was then administered 24 h after the conclusion of training. RESULTS: As expected, outward anger expression was positively associated with perceived stress during free living (P < 0.0125). Outward anger expression, inward anger expression, and angry temperament then combined to account for 25% of the variance in psychological impact of a stressful mock-captivity challenge. CONCLUSION: Anger characteristics are associated with human stress endpoints, both during daily living and in response to an ecologically valid stressor. These findings may assist in the prevention and treatment of operational stress reactions.

Genetic, Physiologic, and Behavioral Predictors of Cardiorespiratory Fitness in Specialized Military Men.

INTRODUCTION: Cardiorespiratory fitness (CRF) is a crucial performance requirement of specialized military occupations. Age and physical activity are established predictors of CRF, but it is not clear how these predictors combine with each other and/or with genetic predisposition. The goal of this study was to derive inclusive explanatory models of CRF in US Navy Explosive Ordnance Disposal (EOD) operators, synthesizing conventional (e.g., age, body composition, and physical activity) and novel influences (e.g., genetic variance). MATERIALS AND METHODS: In this cross-sectional study, 40 male, active duty EOD operators completed a graded exercise test to assess maximal oxygen consumption and ventilatory threshold (VT) using the Bruce protocol. Aerobic performance was further quantified via time of test termination and time at which VT was achieved. Body composition was determined via dual x-ray absorptiometry, and physical activity was assessed by self-report. Genetic variants underlying human stress systems (5HTTLPR, BclI, -2 C/G, and COMT) were assayed. Descriptive analyses were conducted to summarize subject characteristics. Hypotheses were tested with linear regression models. Specifically, separate univariate regression models first determined associations between each of the independent and dependent variables. This protocol was approved by the Naval Health Research Center Institutional Review Board (NHRC.2015.0013). RESULTS: In univariate regression models, age, body composition, physical activity, and 5HTTLPR consistently predicted CRF and/or aerobic performance (R2 range 0.07-0.55). Multivariate regression models routinely outperformed the univariate models, explaining 36-62% of variance. CONCLUSION: This study signifies a shift toward inclusive explanatory models of CRF and aerobic performance, accounting for combined roles of genetic, physiologic, and behavioral influences. Although we were able to quantify combined effects, we were unable to evaluate interaction effects (e.g., gene-gene, gene-behavior) due to limited statistical power. Other limitations are that this specialized military population may not readily generalize to broader populations, and the current sample was all male. Considering these limitations, we aim to replicate this study in various populations, both male and female. Despite its limitations, this study reflects a shift toward more comprehensive predictive models of CRF, explaining the unique and shared contributions of genetic predisposition, physiology, and behavior. These findings have implications for assessment, selection, and training of specialized military members, and may also impact mission success and survivability. Future studies are needed to better characterize additive, interactive, and mediated effects.

Psychological Strategies During Military Training Are Linked to Resilience in US Navy Explosive Ordnance Disposal Operators.

PURPOSE: We describe the psychological strategies (PS) used by a specialized military population, US Navy explosive ordnance disposal (EOD), during training and military operations. We also aim to establish the relationship between PS and resilience. METHODS: The Test of Performance Strategies was adapted to the military environment and subsequently was administered to 58 EOD Operators in conjunction with the 10-item Connor- Davidson Resilience Scale. Differences between high- and low-resilience Operators for PS were evaluated with discriminant models. RESULTS: The PS of EOD Operators were comparable to those of Olympic athletes described in our prior study. The most frequently used strategies during training and military operations were goal setting and emotional control. Discriminant analysis indicated an overall difference between high- and low-resilience Operators with respect to the six training subscales (ρ < .05), with goal setting, emotional control, and attentional control contributing most to the discriminant function. CONCLUSION: EOD Operators' use of PS was comparable to that of elite athletes. We provide evidence that more-resilient EOD Operators differ from their less resilient counterparts in the strategies they use. These findings have implications for mental preparation strategies used during military training and operations.