Role of nutrition in human performance in military populations.

The role of nutrition and performance is well established. Service members' physical and cognitive performance, sleep and mood are impacted by nutritional choices. Although many eating patterns have emerged, consensus among experts recommend a dietary pattern focused on predominantly whole plant-based foods. Adequate intakes of fruits, vegetables, whole grains, beans, legumes, nuts and seeds should be prioritised. Implementation of strategic and intentional fuelling strategies around times of activity maintain adequate energy stores, enhance recovery and protect against training injuries. Carbohydrates are prioritised before, during and after activity or a mission, although the type and amount will vary based on duration and intensity of activity. Protein is generally the focus after activity or a mission and may be included before activity depending on individual tolerance. There are no specific recommendations for fat consumption before, during and after exercise that will improve performance. That said, Service members generally tolerate low-fat meals/snacks prior to exercise, limit fat intake during exercise, may include fat as part of the post exercise meal/snack, and generally consume most fat during the maintenance and growth phase. Careful consideration and planning for food and fluid requirements should be made when Service members are exposed to heat, cold and/or altitude. Operational rations are formulated to meet the nutritional needs of all Service members across a variety of diverse climates, environments and altitudes. Service members may use dietary supplements to improve their performance and need to be aware of available resources to help them make informed decisions.

Risk factors for musculoskeletal-related occupational disability among US Army soldiers.

INTRODUCTION: Minimising temporary and permanent disability associated with musculoskeletal conditions (MSK-D) is critical to the mission of the US Army. Prior research has identified potentially actionable risk factors for overall military disability and its MSK-D subset, including elevated body mass index, tobacco use and physical fitness. However, prior work does not appear to have addressed the impact of these factors on MSK-D when controlling for a full range of factors that may affect health behaviours, including aptitude scores that may serve as a proxy for health literacy. Identifying risk factors for MSK-D when providing control for all such factors may inform efforts to improve military readiness. METHODS: We studied 494 757 enlisted Army soldiers from 2014 to 2017 using a combined medical and administrative database. Leveraging data from the Army's digital 'eProfile' system of duty restriction records, we defined MSK-D as the first restriction associated with musculoskeletal conditions and resulting in the inability to deploy or train. We used multivariable Cox proportional hazards regression to assess the associations between incident MSK-D and selected risk factors including aptitude scores, physical fitness test scores, body mass index and tobacco use. RESULTS: Among the subjects, 281 278 (45.14%) experienced MSK-D. In the MSK-D hazards model, the highest effect size was for failing the physical fitness test (adjusted HR=1.63, 95% CI 1.58 to 1.67, p<0.001) compared with scoring ≥290 points. CONCLUSIONS: The analysis revealed the strongest associations between physical fitness and MSK-D. Additional efforts are warranted to determine potential mechanisms for the observed associations between selected factors and MSK-D.

Comparing functional outcomes in minimally invasive versus open inguinal hernia repair using the army physical fitness test.

PURPOSE: The advantages of minimally invasive inguinal hernia repair (MIHR) over open hernia repair (OHR) continue to be debated. We compared MIHR to OHR by utilizing the Army Physical Fitness Test (APFT) as an outcome measure. METHODS: The APFT is a three-component test scored on a normalized 300 point scale taken semiannually by active-duty military. We identified 1119 patients who met inclusion criteria: 588 in the OHR group and 531 in the MIHR group. Changes in APFT scores, time on post-operative duty restrictions (military profile), and time interval to first post-operative APFT were compared using regression analysis. RESULTS: Postoperatively, no APFT score change difference was observed between the OHR or MIHR groups (- 7.3 ± 30 versus - 5.5 ± 27.7, p = 0.2989). Service members undergoing OHR and MIHR underwent their first post-operative APFT at equal mean timeframes (6.6 ± 5 months versus 6.7 ± 5.1, p = 0.74). No difference was observed for time in months spent on an official temporary duty restriction (military profile) for either OHR or MIHR (0.16 ± 0.16 versus 0.15 ± 0.17, p = 0.311). On adjusted regression analysis, higher pre-operative APFT scores and BMI ≥ 30 were independently associated with reduction in post-operative APFT scores. Higher-baseline APFT scores were independently associated with less time on a post-operative profile, whereas higher BMI (≥ 30) and lower rank were independently associated with longer post-operative profile duration. Higher-baseline APFT scores and lower rank were independently associated with shorter time intervals to the first post-operative APFT. CONCLUSION: Overall, no differences in post-operative APFT scores, military profile time, or time to first post-operative APFT were observed between minimally invasive or open hernioplasty in this military population.

Narrative approach in understanding the drivers for resilience of military combat medics.

INTRODUCTION: Qualitative insights may demonstrate how combat medics (CM) deal with stressors and identify how resilience can potentially develop. Yet, qualitative research is scant in comparison to the many quantitative studies of health outcomes associated with military service. METHOD: Semistructured qualitative interviews were used to collect personal narratives of US Army CMs who had previously served in Iraq or Afghanistan. RESULTS: Thematic analysis revealed three key driving forces for how resilience develops in the context of combat and war. The first was patriotism, which captures loyalty and full commitment to the military and its missions. The second was commitment to their family, reflecting the balance of responsibility to family of origin with the obligation one feels towards their military family. The last driving force was faith, or the drive to reach towards the transcendent to provide a moral compass and develop empathy in the face of difficult situations. CONCLUSIONS: An individual's commitment to country, military family and faith strengthens their resilience, and this can be used to inform future research efforts as well as current clinical practice.

Plasma HSP70 levels correlate with health risk factors and insulin resistance in African American subjects.

The family of heat shock proteins works at the cellular level to protect cells against many chronically and acutely induced stressful conditions. The induction of certain family members, such as HSP70 and HSP90 via a heat shock factor 1 activated pathway, may have broad therapeutic benefits in the treatment of various types of tissue trauma and metabolic diseases. HSPs with their ability to improve cytoprotective functions and enhance tissue regeneration, offer a new potential in treating conditions such as diabetes and obesity. We hypothesized that the plasma levels of HSP70 and/or HSP90 would be significantly lower in obese than non-obese African American men and women. The objective of the study was to provide an analysis of plasma HSP70 and HSP90 concentrations of African American subjects grouped according to widely accepted health risk indices and insulin resistance. Comparisons of HSP70 and HSP90 concentrations by BMI, percent body fat, waist circumference, insulin resistance, plasma cortisol levels and gender were conducted. HSP70 concentration inversely correlated with BMI, percentage body fat, waist circumference, and insulin resistance. No significant correlation was observed for HSP90 concentration with the aforementioned indices. Our results show that high risk health conditions, such as obesity and type-2 diabetes, may be associated with compromised expression of specific heat shock proteins such as HSP70.

Glucocorticoid receptor density correlates with health risk factors and insulin resistance in Caucasian and African American subjects.

Activation of the hypothalamic-pituitary-adrenal axis leads to secretion of cortisol, which binds to peripheral glucocorticoid receptor and mediates a complex series of metabolic and immune effects. Cortisol also binds to receptors in the hypothalamus and pituitary, and inhibits further secretion of adrenocorticotropic hormone thus preventing an excessive response. Excess glucocorticoid effect is seen in Cushings disease, adrenal adenomas/carcinomas and in glucocorticoid resistance. Within such pathology there are health consequences of excessive glucocorticoid action, including obesity, hypertension, and glucose intolerance or diabetes. We hypothesized that increased glucocorticoid receptor in peripheral tissue might mediate an excess glucocorticoid effect in the absence of increased cortisol secretion. The objective of the study was to investigate the relationship between glucocorticoid receptor density in leukocytes and health risk indices relevant to obesity and diabetes in a sample of Caucasian and African American subjects. Comparison of glucocorticoid receptor concentration with subject body mass index, percentage body fat, waist circumference, insulin resistance, plasma cortisol levels, gender, and lipid profiles were conducted. Increased glucocorticoid receptor density significantly correlated with body mass index, percentage body fat, waist circumference, and insulin resistance. No significant correlation was observed for glucocorticoid receptor density with lipid profiles. Furthermore, no significant differences were observed in glucocorticoid receptor density between Caucasian and African American subjects or male and female participants. Our results show that high risk health conditions, such as obesity and type-2 diabetes, may be associated with a form of hypothalamic-pituitary-adrenal axis dysfunction, characterized by localized leukocyte glucocorticoid receptor over-expression.

African Americans and Caucasian Americans: differences in glucocorticoid-induced insulin resistance.

African Americans are more insulin resistant than Caucasian Americans and this discrepancy cannot be explained by measures of body weight or body composition. The aim of the study was to compare the sensitivity of African Americans and Caucasian Americans to glucocorticoids by measuring glucose and insulin responses to a meal challenge under conditions of placebo and glucocorticoid. A total of 160 healthy or overweight/obese African American and Caucasian American participants completed exercise testing and a liquid meal challenge during separate laboratory visits. Participants were evaluated following treatments with placebo and dexamethasone (4 mg). Main outcome measures were correlation between body composition measures (body mass index, percent body fat, waist circumference) and insulin responses; insulin and glucose responses after a liquid meal challenge; and calculated HOMA. After dexamethasone treatment African Americans were significantly more hyperinsulinemic after a meal as indicated by higher peak insulin (p=0.02) and postprandial insulin areas under the curve (p=0.006) than Caucasians. Additionally, African Americans were more insulin resistant than Caucasian Americans under both placebo and dexamethasone as determined by fasting insulin and HOMA (p=0.05). Waist circumference correlated with post-dexamethasone insulin AUC and HOMA in Caucasian Americans (p<0.05), but none of the body composition measures were predictive of IR for African Americans. African Americans are more sensitive to glucocorticoids (dexamethasone) than Caucasian Americans, as indicated by significantly greater peak insulin and postprandial insulin areas under the curve. The glucocorticoid receptor and its potential interactions with stress may contribute to this ethnic disparity.

Effect of creatine on performance of militarily relevant tasks and soldier health.

PURPOSE: Determine the short-term effects of creatine supplementation on performance of military tasks, thermoregulation, and health risks. METHODS: Male military personnel were randomly assigned to a creatine (CR; N = 8) or a placebo (CON; N = 8) supplementation group. Testing was conducted at baseline, after a 6-day load phase (20 g/d), and after 4 weeks of taking 6 g/d. Measurements included body composition, liver/kidney function tests, core body temperatures during a 10-mile march and 5-mile run, and performance on physical tasks. RESULTS: Serum and urine creatine increased significantly in the CR group. Body mass and number of pull-ups performed increased significantly in the CR group but not the CON group by week 4. No significant differences between the CR and CON groups were found for other performance measures, body composition, core body temperature, or other biochemical measures. CONCLUSION: Creatine supplementation increased body mass and pull-up performance but did not cause acute health problems. Creatine did not increase core temperature compared with placebo under the environmental conditions of the study, and it is unlikely that creatine will enhance the overall readiness or performance of soldiers.

Uptake and killing of Listeria monocytogenes by normal human peripheral blood granulocytes and monocytes as measured by flow cytometry and cell sorting.

Cellular components of innate immunity (NK cells, monocytes and granulocytes) play an important role in early resistance to Listeria monocytogenes in the mouse model. Minimally invasive methods of measuring the bacteriocidal capacity of these cells may be useful as a biomarker of susceptibility in humans. A technique was developed whereby the uptake and survival of L. monocytogenes could be measured in human granulocytes and monocytes using small volumes of peripheral blood. This method used flow cytometry to detect the presence of PKH-2-labeled bacteria within these cells. Survival of bacteria was determined by sorting of infected cells based on a combination of fluorescence and light scattering properties. Considerable variation in bacterial recovery was seen between normal volunteers. There was consistently greater survival of a fully virulent strain of L. monocytogenes within monocytes and granulocytes compared with an isogenic strain lacking the hemolysin, listeriolysin O, when measured at baseline. There was no evidence of longer-term bacterial survival or growth at 2 or 24 h. This technique may be useful for assessment of both host resistance and pathogen virulence.

Cyclical mastalgia: prevalence and associated health and behavioral factors.

Perimenstrual breast pain (cyclical mastalgia) is a common problem that can be sufficiently severe to interfere with usual activities, and has been associated with elevated mammography usage in young women. This study was undertaken to replicate clinic-based research on cyclical mastalgia, and to examine the association between this disorder and health-related behaviors and perceived stress. Using random digit dialing throughout Virginia, 874 women aged 18-44 were interviewed. Sixty-eight per cent of women experienced cyclical breast symptoms; 22% experienced moderate to extreme discomfort (classified as cyclical mastalgia). Hormonal contraceptive usage was associated with significantly less mastalgia and premenstrual syndrome (PMS). Smoking, caffeine consumption and perceived stress were associated with mastalgia (odds ratios = 1.52, 1.53 and 1.7, respectively). Young women (under 35 years) with mastalgia were more likely to have had a mammogram (20.2%) than those without mastalgia (9.9%). Most women with this disorder (77.5%) did not have PMS. The prevalence of cyclical mastalgia and its association with mammography replicate clinic-based findings. Associations with smoking and stress had not previously been reported. Prospective research is needed to determine the biopsychosocial factors contributing to this disorder.

Increased vasopressin and adrenocorticotropin responses to stress in the midluteal phase of the menstrual cycle.

Accumulating evidence indicates that gonadal steroids modulate functioning of the hypothalamic-pituitary-adrenal (HPA) axis, which has been closely linked to the pathophysiology of anxiety and depression. However, the effect of the natural menstrual cycle on HPA axis responsivity to stress has not been clearly described. In nine healthy women, metabolic and hormonal responses to treadmill exercise stress during the early follicular phase of the menstrual cycle, when gonadal steroid levels are low, were compared with responses in the midluteal phase of the cycle, when both progesterone and estrogen levels are relatively high. Exercise intensity was gradually increased over 20 min to reach 90% of each subject's maximal oxygen consumption during the final 5 min of exercise. Basal plasma lactate, glucose, ACTH, vasopressin, oxytocin, and cortisol levels were similar in the two cycle phases. However, in response to exercise stress, women in the midluteal phase had enhanced ACTH (P < 0.0001), vasopressin (P < 0.01), and glucose (P < 0.001) secretion. These findings suggest that relatively low levels of gonadal steroids during the early follicular phase of the menstrual cycle provide protection from the impact of stress on the HPA axis.

Femoral neck stress fractures and metabolic bone disease.

OBJECTIVE: To determine whether metabolic bone disease plays a role in the cause of femoral neck stress fractures. STUDY DESIGN: Twenty-three patients with femoral neck stress fractures were enrolled prospectively in the study. Examination included computed tomography bone densitometry, trace mineral analysis, and histomorphometric analysis of the iliac crest in thirteen patients who underwent surgical treatment of their stress fractures. A control group of fifteen patients undergoing iliac crest bone grafting for scaphoid nonunions underwent similar examinations. SETTING: Tertiary military medical center. RESULTS: Patients with femoral neck stress fractures had lower bone mineral density than did control patients (p = 0.010), but no trace mineral deficiencies or consistent histomorphometric differences were noted. CONCLUSIONS: Bone mineral density is decreased in patients with femoral neck stress fractures. Despite observations of decreased bone mineral density in the stress fracture group, osteoporosis, as determined by histomorphometry, is not a consistent finding.

Individual reactivity and physiology of the stress response.

The biological response to stress involves the activation of two main neuroendocrine components, the hypothalamic-pituitary-adrenal axis and the sympathoadrenal medullary systems. Looking at the responses to stressors in a laboratory setting, e.g., cortisol production after exercising on a treadmill, is a valid and controlled way to study how people react to psychological and physical stressors. A common finding in such studies is that individuals respond bimodally to stress. More recently, researchers have been interested in the possible reasons why healthy individuals exhibit differential reactivity to stressors. The literature on the neuroendocrine responses to stress, with a particular focus on investigations of individual reactivity to psychological and physical stressors, is reviewed.

Endocrine response to high-intensity exercise: dose-dependent effects of dexamethasone.

We recently reported that in 30-50% of healthy men and women the release of ACTH and cortisol stimulated by exercise is not suppressed by prior administration of a 4-mg dose of dexamethasone (DEX). We now explore other potential differences between these subjects and those whose exercise response was suppressed by examining the effect of a smaller, 1-mg, dose of DEX on exercise-stimulated ACTH and cortisol. Men (n = 15) and women (n = 9) were studied during three high intensity exercise tests: one after taking placebo, one after taking 1 mg DEX, and one after taking 4 mg DEX. Before participation, subjects underwent a test for classification as either a high (HR; n = 10) or low (LR; n = 14) reactor and a maximal exercise test to assess maximal aerobic capacity. Distinct dose-related reductions in plasma concentrations of ACTH, cortisol, and dehydroepiandrosterone (DHEA) were noted for HR under the treatment conditions, whereas both doses of DEX blocked ACTH, cortisol, and DHEA release in LR. Furthermore, basal plasma cortisol, DHEA, and DHEA sulfate were significantly higher in HR compared to LR. Thus, there are inherent basal and stress-reactive differences in HR and LR, and these differences may be useful in constructing a model for the mechanisms and physiological regulation of hypothalamic-pituitary-adrenal axis activation. The question of whether these differences in reactivity of the ACTH-cortisol axis between the HR and LR groups have implications for individual short term function or long term health remains to be answered.

Expression of lymphocyte subsets after exercise and dexamethasone in high and low stress responders.

PURPOSE: Recent work indicates that among the normal population, persons can be classified as low (LR) or high (HR) stress responders based on hypothalamic-pituitary-adrenal (HPA) axis responses to high-intensity exercise. We studied whether differential activation of the HPA axis affected cytokine production and expression of selected lymphocyte subsets in HR and LR in response to high-intensity exercise after placebo and dexamethasone (DEX; 4 mg). METHODS: Healthy HR (N = 12) and LR (N = 10) underwent two exercise tests at 90% of VO2max, 8 h after placebo or DEX. Expression of lymphocyte surface markers (CD3+, CD4+, CD8+, CD56+), adhesion molecule markers (intercellular adhesion molecule-1/ICAM-1: CD54+ and L-selectin: CD62L+), and concentrations of plasma interleukin 6 (IL-6) were examined before and after exercise. RESULTS: Baseline percentages of CD8+ and CD56+ cells were significantly higher, and concentrations of IL-6 and percentages of CD4+ cells were significantly lower in HR as compared with LR. The percentage of CD54+ and CD62L+ cells was not significantly different in HR and LR. DEX significantly reduced the percentage of CD3+ and CD4+ and increased the percentage of CD8+ and CD56+ subsets; the percent of cells expressing CD54+ increased, whereas CD62L+ decreased. Exercise-induced changes in the percentage of lymphocyte subsets were similar to those induced by DEX. CONCLUSION: In summary, HR and LR have different baseline patterns of IL-6 and lymphocyte subsets, which may reflect differential sensitivity to endogenous glucocorticoids. However, exogenous glucocorticoids induced similar patterns of lymphocyte expression in HR and LR.

Tyrosine improves working memory in a multitasking environment.

Previous studies indicate that tyrosine may prove useful in promoting improved performance in situations in which performance is compromised by stress. To extend the generality of previous tyrosine findings, the present study examined the effects of tyrosine ingestion on performance during both a Multiple Task and a Simple Task battery. The multiple task battery was designed to measure working memory, arithmetic skills, and visual and auditory monitoring simultaneously, whereas the simple task battery measured only working memory and visual monitoring. Ten men and 10 women subjects underwent these batteries 1 h after ingesting 150 mg/kg of l-tyrosine or placebo. Administration of tyrosine significantly enhanced accuracy and decreased frequency of list retrieval on the working memory task during the multiple task battery compared with placebo. However, tyrosine induced no significant changes in performance on the arithmetic, visual, or auditory tasks during the Multiple Task, or modified any performance measures during the Simple Task battery. Blood levels of ACTH and cortisol were not, but heart rate and blood pressure were significantly increased during the performance tasks. The present results indicate that tyrosine may sustain working memory when competing requirements to perform other tasks simultaneously degrade performance, and that supplemental tyrosine may be appropriate for maintaining performance when mild to severe decrements are anticipated.

Energy metabolism increases and regional body fat decreases while regional muscle mass is spared in humans climbing Mt. Everest.

The objectives of the study were to determine regional changes in body composition, energy expenditure by means of doubly labeled water, and net energy balance during exposure to high and extreme altitudes (5,300-8,848 m). This study focuses on a subset of subjects who consumed the doubly labeled water (three base camp personnel and seven climbers). Regional body composition was determined by measuring skinfold thicknesses and circumferences at 10 different sites on the body. Energy expenditure was measured by doubly labeled water excretion. Discrepancies between actual energy expenditure and data obtained from diet records and body weight changes suggested a chronic underreporting of dietary energy intake, especially by those subjects who reached the highest altitudes. This underreporting may be due in part to diminished cognition or to a preferential focus on survival, rather than on filling out diet records accurately. Mean adjusted dietary intakes were 10.50 +/- 0. 65 MJ/d (2510 +/- 155 kcal/d) for those who remained at base camp, and 20.63 +/- 6.56 MJ/d (4931 +/- 1568 kcal/d) for those who climbed above base camp. Energy expenditure averaged 2.5-3.0 times sea level resting energy expenditure. Differential changes in regional body composition suggested a preferential loss of fat mass and a relative sparing of muscle mass, despite insufficient energy intake to maintain body weight.

Differential hypothalamic-pituitary-adrenal axis reactivity to psychological and physical stress.

Healthy men exhibit a differential hypothalamic-pituitary-adrenal axis (HPA) response to exercise stress and fall into two groups: high responders (HR) and low responders (LR). The present study examined whether HR to physical stress also exhibit higher HPA reactivity to psychological stress than LR. We examined 14 HR and 13 LR classified based on their ACTH responses to high intensity exercise after pretreatment with dexamethasone. Both groups were of similar age, height, weight, and fitness level. Trait anxiety scores on the Spielberger Trait Anxiety Scale were not different. Subjects underwent a psychological stress test consisting of an interview and mental arithmetic. This test raised heart rate, blood pressure, and plasma ACTH and cortisol levels in both HR and LR. HR tended to have higher heart rates and blood pressures in anticipation of the psychological stress test than LR. ACTH responses of HR were higher, although not significantly, throughout the psychological stress test than LR. HR had a significantly (P < 0.05) greater net integrated cortisol response to the psychological stress than LR. This suggests that the adrenal cortexes of the HR are hypertropic and/or hypersensitive to ACTH. We conclude that men who are highly responsive to exercise stress are also highly responsive to psychological stress.