Publications

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    Marc Taylor
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    ABSTRACT: Recent reports demonstrate neurotrophic properties of dehydroepiandrosterone sulfate (DHEAS) in men at rest, as well as profound neurotrophic responses to stress in both men and women. Little is known of neuroprotective–neurotrophic effects of DHEAS during stress exposure, either in men or women. This translational study was designed to examine neuroprotective–neurotrophic effects of DHEAS throughout intense stress exposure in healthy men and women. The study took place within a stressful 12-day military survival course. Utilizing a longitudinal cross-sectional repeated measures design, One hundred sixteen healthy active-duty military personnel (80% male) were studied before, during, and 24 h after the course. The dependent variable was the neurotrophin salivary nerve growth factor (sNGF). In terms of total hormone output, the effect of DHEAS on sNGF was mediated by testosterone. Unlike testosterone or cortisol, DHEAS reliably predicted sNGF at each time point, and change in DHEAS predicted change in sNGF across time points. Baseline DHEAS predicted total sNGF output across the stress trajectory. Consistent with preclinical as well as cross-sectional human research, this study demonstrates neuroprotective–neurotrophic effects of DHEAS in healthy men and women exposed to intense stress. Results are evaluated in relation to established criteria for causation.
    Steroids 06/2014; 87:54-58. · 2.80 Impact Factor
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    ABSTRACT: Common variants in serotonin and corticosteroid receptor genes influence human stress in laboratory settings. Little is known of their combined effects, especially in high stress environments. This study evaluated distinct and combined effects of polymorphisms in the serotonin transporter (5HTTLPRL/S), glucocorticoid receptor (Bcl1C/G), and mineralocorticoid (-2C/G) receptor genes on adrenocortical and cardiovascular responses to intense, realistic stress. One hundred forty four healthy, active-duty military men were studied before, during, and 24hours after a stressful 12-day survival course. Dependent variables were cortisol, heart rate (HR), systolic blood pressure (SBP), and diastolic blood pressure (DBP). 5HTTLPR SS carriers revealed higher overall cortisol concentrations than L carriers (p=.022). 5HTTLPR L carriers demonstrated higher stress-induced HR than non-carriers (SS) yet rebounded to a lower recovery value (p=.026), while Bcl1 G carriers showed higher mean stress-induced HR than non-carriers (CC) (p=.047). For DBP, 5HTTLPR S carriers showed higher overall values than non-carriers (LL) (p=.043), Bcl1 GG were higher than C carriers (p=.039), and -2C/G G carriers exceeded non-carriers (CC) (p=.028). A "high" composite genotype group revealed substantially higher overall cortisol concentrations than a "low" composite genotype group (p<.001), as was the case for DBP (p=.037). This study revealed a synergistic effect of common polymorphisms on the acute stress response in healthy men. Pending additional study, these findings may have implications for drug discovery, gene therapy, and stress inoculation strategies.
    Behavioural brain research 05/2014; · 3.22 Impact Factor
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    ABSTRACT: Ample evidence links stress to psychiatric and neurological disease. Although many studies examine stress hormone secretion and receptor activity, exciting new developments signify a shift in focus to neuromodulatory systems influencing neuronal development, survival, and neuroplasticity. The purpose of this study was to characterize salivary nerve growth factor (sNGF) responses to intense stress exposure in healthy military members undergoing survival training. A second purpose was to explore effects of age, sex, education, and body mass index (BMI). One hundred sixteen military members (80% male) were studied before, during, and 24 hours after a stressful mock-captivity exercise. sNGF was measured at all three time points. Reactivity, recovery, and residual elevation of sNGF were computed. General linear modeling with repeated measures evaluated effect of stress exposure, as well as the roles of age, sex, education, and BMI. sNGF increased 137% from baseline to intense stress. During recovery, sNGF remained elevated an average of 67% above baseline (i.e., residual elevation). Men showed greater sNGF reactivity than women quantified by larger absolute T1–T2Δ (+148.1 pg/mL vs. +64.9 pg/mL, p < 0.017). A noteworthy trend of higher sNGF concentrations in low BMI participants was observed (p = 0.058). No effects of age or education were shown. This study shows substantial reactivity and residual elevation of sNGF in response to intense stress exposure in healthy humans. Further research is needed to fully characterize this response, delineate correlates and mechanisms, and validate therapeutic applications.
    Psychoneuroendocrinology 01/2014; · 5.59 Impact Factor
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    Marc Taylor
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    ABSTRACT: We recently distinguished between spontaneous and deliberate dissociative states in military personnel exposed to stressful survival training, demonstrating not only that a substantial subset of participants (13%) deliberately dissociate under intense stress but also that most deliberate dissociators (76%) find it helpful (facilitative) to coping. In this brief report, we examine the relationship between spontaneous and deliberate subtypes of dissociation, and objective military performance in Special Forces and non–Special Forces personnel enrolled in survival school. Inverse relationships between dissociation and military performance were observed in both Special Forces and general soldier subgroups. Military performance did not differ between spontaneous and deliberate dissociators, nor did it differ between those who appraised dissociative states as facilitative versus debilitative to stress coping. This study evolves our understanding of factors influencing human performance in the high-stakes survival context.
    Military medicine 01/2014; 179. · 0.77 Impact Factor
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    Marc Taylor
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    ABSTRACT: Sleep disruption is an emergent military health issue, but remarkably little is known of its prevalence or comorbidities in the combat zone. This study was designed to quantify the prevalence and mental health correlates of sleep disruption among military personnel serving within a ground combat zone during Operation Enduring Freedom. This was a large, cross-sectional survey of active duty and reserve US Navy personnel (N=3,175). Self-reported sleep measures included total hours of sleep per day, total hours of sleep required to feel well-rested, difficulty falling asleep, and difficulty staying asleep. The survey also measured mental health symptoms, including posttraumatic stress symptoms, anxiety, and depression. Participants reported an average of 5.9 hours of sleep per day despite requiring on average 6.8 hours to feel well-rested. More than half (56%) were classified as sleep deficient, and 67% reported 6 or fewer hours of sleep per day. Adjusted for covariates, individuals endorsing sleep disruption were at substantially elevated risk of meeting criteria for posttraumatic stress disorder, generalized anxiety disorder, and major depressive disorder. This study documents the prevalence of sleep disruption in a very large and difficult-to-access sample of military members serving in a combat zone, and details robust associations with mental health.
    Military medicine 01/2014; · 0.77 Impact Factor
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    ABSTRACT: Abstract Evidence points to heightened physiological arousal in response to acute stress exposure as both a prospective indicator and core characteristic of posttraumatic stress disorder (PTSD). Since females may be at higher risk of 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 eighty-five military members (78% males) were studied before, during, and 24 hours 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 of 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. Additionally, 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.
    Stress (Amsterdam, Netherlands) 12/2013; · 3.21 Impact Factor
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    Marcus K Taylor, Gerald E Larson, Sonya B Norman
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    ABSTRACT: Anger and anger expression (ANGX) are concerns in the U.S. military population and have been linked to stress dysregulation, heart disease, and poor coping behaviors. We examined associations between depression, pain, and anger expression among military veterans. Subjects (N = 474) completed a depression scale, a measure of pain across the last 4 weeks, and an ANGX scale. A multiple regression model assessed the independent and additive relationships of depression and pain to ANGX. Almost 40% of subjects met the case definition for either major or minor depression. Subjects reported low-to-moderate levels of pain (mean = 6.3 of possible 20) and somewhat frequent episodes of ANGX. As expected, depression and pain were positively associated (r = 0.42, p < 0.001) and crossover effects of antidepressant and pain medication were shown. Specifically, frequency of antidepressant medication use was inversely associated with pain symptoms (r = -0.20, p < 0.001) and frequency of pain medication use was inversely linked to depressive symptoms (r = -0.21, p < 0.001). In a multiple regression model, depression (β = 0.58, p < 0.001) and pain (β = 0.21, p < 0.05) showed independent and additive relationships to ANGX (F = 41.5, p < 0.001, R(2)adj = 0.31). This study offers empirical support for depression-pain comorbidity and elucidates independent and additive contributions of depression and pain to ANGX.
    Military medicine. 10/2013; 178(10):1065-1070.
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    Charles A. Morgan III, Marcus K. Taylor
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    ABSTRACT: 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 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 symptoms during stress. Fifty-six percent described dissociative experiences as spontaneous, 13.8% as deliberate, and 29.6% endorsed neither. In Special Forces soldiers only, those who endorsed facilitative dissociation exhibited higher total CADSS scores than those who endorsed debilitative dissociation. Seventy-two percent of spontaneous dissociators described the experience as debilitative to coping with stress; conversely, 77% of deliberate dissociators said their symptoms facilitated coping with stress. Individuals with prior trauma exposure tended to appraise dissociative symptoms 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.
    Journal of Traumatic Stress 01/2013; · 2.72 Impact Factor
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    Marcus K. Taylor
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    ABSTRACT: 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 (β = 0.40, p < 0.01), whereas DHEAS independently influenced NGF (β = 0.48, p < 0.01) and sAA (β = 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 medicine 01/2013; 78(1):100-106. · 0.77 Impact Factor
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    John Taverniers, Marcus K Taylor, Tom Smeets
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    ABSTRACT: 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.
    Stress (Amsterdam, Netherlands) 08/2012; · 3.21 Impact Factor
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    Rick LaCaille, Marcus K. Taylor
    Encyclopedia of Behavioral Medicine, 01/2012; Springer.
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    ABSTRACT: 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.
    Military medicine 12/2011; 176(12):1362-8. · 0.77 Impact Factor
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    ABSTRACT: 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 (β = 0.37, p < .001). When MH was added to the model, however, PH's influence was substantially attenuated and no longer significant (β = 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.
    Journal of Behavioral Medicine 11/2011; · 3.10 Impact Factor
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    ABSTRACT: 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.
    Stress (Amsterdam, Netherlands) 07/2011; 15(1):85-96. · 3.21 Impact Factor
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    ABSTRACT: A promising method to detect deception is the Guilty Knowledge Test (GKT) which assesses whether an individual possesses knowledge about a particular crime. Specifically, the GKT involves a series of questions with multiple answers where one answer is relevant to the crime and the others are not. In theory, if a "suspect" is guilty, s/he will recognize the crime-relevant item and display a physiological orienting response that is discernable from responses to irrelevant items. The most widely studied physiological endpoint in conjunction with the GKT is the galvanic skin response (GSR) which reflects activity of the eccrine sweat gland and represents sympathetic modulation of the autonomic nervous system. Little is known regarding the validity of alternate physiological endpoints or if combined endpoints enhance detection accuracy over GSR alone. In this study we compared different physiological approaches to detect deception with the GKT. Secondarily, we explored sociobehavioral moderators of deception, including values, ethnic identity and resilience. Forty-two military men (age 23.9 +/- 0.4 years) participated in a mock-crime and then completed a 10-question GKT. Endpoints included GSR, heart rate (HR; reflecting vagal modulation), and finger pulse line length (FPLL; a blood pressure waveform calculation reflecting combined sympathetic-parasympathetic modulation). Separate one-way repeated measures ANOVA with five levels compared mean physiological responses to each question. A common scoring procedure (Lykken, 1959) was applied to classify subjects as guilty or innocent for each physiological endpoint. ROC curves were then constructed to assess the diagnostic value of each endpoint and to determine whether combined measures detected guilt more effectively than GSR alone.
    12/2010;
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    ABSTRACT: Risk is an inherent component of military operations. A 31-item Military Operational Risk Taking Scale (MORTS) was developed to identify military personnel with the tendency to engage in or avoid operationally nonessential risks which are maladaptive to the mission. Three hundred and thirty-three active duty Marine Corps personnel completed the MORTS along with 2 measures of non-military-specific risk taking: Domain-Specific Risk-Attitude Scale (DOSPERT) and Evaluation of Risk Scale (EVAR) as well as the State-Trait Anxiety Inventory (STAI). The MORTS had excellent internal reliability and convergent validity with risk taking scales of other domains. The responses to the 31 items of the MORTS were subjected to a Principal Component Analysis (PCA) with a Varimax rotation. Preliminary findings demonstrate that the MORTS may identify individuals who are likely to participate in essential/adaptive versus nonessential/maladaptive operational risk.
    Military Psychology 04/2010; 22(2):128-142. · 0.72 Impact Factor
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    ABSTRACT: 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. 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. 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. 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.
    Aviation Space and Environmental Medicine 11/2009; 80(11):962-7. · 0.78 Impact Factor
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    ABSTRACT: A motion system collected 120-Hz data from 14 baseball adult hitters using normal and choke-up bat grips. Six swings were digitized for each hitter, and temporal and kinematic parameters were calculated. Compared with a normal grip, the choke-up grip resulted in 1) less time during stride phase and swing; 2) the upper torso more opened at lead foot contact; 3) the pelvis more closed and less bat linear velocity at bat-ball contact; 4) less range of motion of the upper torso and pelvis during swing; 5) greater elbow flexion at lead foot contact; and 6) greater peak right elbow extension angular velocity. The decreased time during the stride phase when using a choke-up grip implies that hitters quicken their stride when they choke up. Less swing time duration and less upper torso and pelvis rotation range of motion using the choke-up grip supports the belief of many coaches and players that using a choke-up grip results in a "quicker" swing. However, the belief that using a choke-up grip leads to a faster moving bat was not supported by the results of this study.
    Journal of applied biomechanics 08/2009; 25(3):203-9. · 1.26 Impact Factor
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    ABSTRACT: We propose that learning proper hitting kinematics should be encouraged at a young age during youth baseball because this may help reinforce proper hitting kinematics as a player progresses to higher levels of baseball in their adult years. To enhance our understanding between youth and adult baseball hitting, kinematic and temporal analyses of baseball hitting were evaluated with a high-speed motion analysis system between 12 skilled youth and 12 skilled adult baseball players. There were only a small number of temporal differences between youth and adult hitters, with adult hitters taking significantly greater time than youth hitters during the stride phase and during the swing. Compared with youth hitters, adult hitters a) had significantly greater (p < .01) lead knee flexion when the hands started to move forward; b) flexed the lead knee over a greater range of motion during the transition phase (31 degrees versus 13 degrees); c) extended the lead knee over a greater range of motion during the bat acceleration phase (59 degrees versus 32 degrees); d) maintained a more open pelvis position at lead foot off ground; and e) maintained a more open upper torso position when the hands started to move forward and a more closed upper torso position at bat-ball contact. Moreover, adult hitters had greater peak upper torso angular velocity (857 degrees/s versus 717 degrees/s), peak left elbow extension angular velocity (752 degrees/s versus 598 degrees/s), peak left knee extension angular velocity (386 degrees/s versus 303 degrees/s), and bat linear velocity at bat-ball contact (30 m/s versus 25 m/s). The numerous differences in kinematic and temporal parameters between youth and adult hitters suggest that hitting mechanics are different between these two groups.
    Journal of applied biomechanics 08/2009; 25(3):210-8. · 1.26 Impact Factor
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    ABSTRACT: 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.
    Journal of Traumatic Stress 07/2009; 22(3):212-7. · 2.72 Impact Factor

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