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.

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.

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.

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.

Suppression of hypothalmic-pituitary-adrenal axis responses to stress in lactating women.

In the rat, lactation suppresses a variety of physiological responses to stress. We investigated whether stress-responsive neurohormonal systems are also restrained during breast feeding in humans. We chose treadmill exercise as a stressor because this stimulus produces an exercise intensity-dependent activation of the hypothalamic-pituitary-adrenal axis and the sympathomedullary system that is independent of differences in physical conditioning among subjects. Ten lactating and ten nonlactating women who were between 7 and 18 weeks postpartum performed 20 min of graded treadmill exercise. The final 5 min of exercise was set to elicit 90% of the maximal oxygen uptake of each subject. Plasma ACTH, cortisol, and glucose responses to exercise were significantly attenuated in lactating women (P < 0.001, P < 0.05, and P < 0.001, respectively). Basal norepinephrine levels were also reduced in lactating women (P < 0.05). These results indicate that stress-responsive neurohormonal systems are restrained in lactating women.

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.

Exercise-induced activation of the hypothalamic-pituitary-adrenal axis: marked differences in the sensitivity to glucocorticoid suppression.

Treadmill exercise activates the hypothalamic-pituitary-adrenal axis and evokes metabolic responses proportional to exercise intensity and duration. To determine whether glucocorticoid administration would alter humoral and metabolic regulation during exercise, we administered 4 mg dexamethasone (DEX) or placebo to 11 normal, moderately trained men (19-42 yr old) in a double blinded random fashion 4 h before high intensity intermittent treadmill running. Plasma levels of ACTH, cortisol, arginine vasopressin (AVP), lactate, and glucose were measured before, during, and after exercise. A wide range of ACTH responses were seen in the DEX-treated group and arbitrarily defined as two subsets of individuals according to their responses to dexamethasone: DEX nonsuppressors and DEX suppressors. Exercise-induced increases in heart rate and circulating concentrations of cortisol, AVP, lactate, and glucose were all significantly greater (P < 0.05) in nonsuppressors (n = 4) compared to suppressors (n = 7) after both placebo and DEX administration. Interestingly, heart rate, AVP, and lactate responses were unaltered by DEX alone in both groups. In summary, this study demonstrates that normal individuals exhibit differential neuroendocrine and metabolic responses to exercise and pituitary/adrenal suppression after pretreatment with DEX. These findings reflect marked individual differences in the stress response to exercise that may derive from or lead to differential glucocorticoid negative feedback sensitivity in humans.

High intensity exercise promotes escape of adrenocorticotropin and cortisol from suppression by dexamethasone: sexually dimorphic responses.

Exercise promotes escape of ACTH and cortisol from suppression by dexamethasone (DEX) in some healthy men and women. To determine whether stimulus strength, diurnal rhythmicity, or gender influences neuroendocrine escape during DEX suppression, we studied men (n = 5) and women (n = 5) during high intensity exercise tests after taking 4 mg DEX: two tests (one at 90% and one at 100% of maximal aerobic capacity) were conducted in the morning and two were performed in the afternoon on nonconsecutive days. Plasma ACTH and cortisol showed significantly greater increases with the 100% compared to the 90% intensity exercise (ACTH: 90%, 2 +/- 0.4; 100%, 3 +/- 0.5 pmol/L; cortisol: 90%, 53 +/- 5.3; 100% 93 +/- 23.6 nmol/L). Plasma cortisol responses were significantly higher in women than in men (P < 0.01). Plasma arginine vasopressin (AVP) exhibited significant intensity-dependent increases, with higher responses in women than men (P < 0.01). In conclusion, despite high dose glucocorticoid pretreatment, intense exercise can override the glucocorticoid negative feedback of hypothalamic-pituitary-adrenal activation in most normal men and women. This ability to override cortisol negative feedback inhibition may relate to the magnitude of the AVP response, the potency/specificity of the stressor to elicit a CRH/AVP response, and/or the sensitivity of the glucocorticoid negative feedback system at the time of the stress.

Vitamin and mineral status in physically active men: effects of a high-potency supplement.

Changes in nutritional status during supplementation with a high-potency multivitamin-mineral supplement were examined in 22 physically active men randomly assigned to take a supplement (n = 11) or placebo (n = 11) for approximately 12 wk. Four-day dietary intakes, blood concentrations, and urinary excretions of selected vitamins and minerals were measured before, during (approximately 6 and 12 wk), and after supplementation. No changes were observed in blood concentrations of vitamins A and C and measures of zinc, magnesium, and calcium status; the supplement provided less than 300% of the recommended dietary allowance (RDA) of these nutrients. In contrast, blood concentrations of thiamin, riboflavin, vitamins B-6 and B-12, pantothenate, and biotin increased significantly (P less than 0.05) by 6 wk to values that were maintained until the end of the supplementation. These vitamins were provided in amounts that ranged from 396% (biotin) to 6250% (vitamin B-6) of the RDA. Urinary excretions of these vitamins also increased during supplementation and both blood and urine values returned to presupplementation concentrations at approximately 13.5 wk postsupplementation.

Nutritional survey of the US Navy SEAL trainees.

The nutritional status of 267 male US Navy Sea, Air, and Land (SEAL) trainees was assessed to determine dietary patterns. Diet records, blood samples, 24-h urine collections, and physical characteristics were analyzed. Energy intake was 3886 +/- 73 kcal/d (SEM) with 15.7 +/- 0.2, 42.9 +/- 0.6, and 41.2 +/- 0.5% of the energy derived from protein, carbohydrate (CHO), and fat, respectively. Mean cholesterol intake (1008 +/- 35.7 mg/d [SEM]) exceeded the US Dietary Goal (less than or equal to 300 mg/d) and serum cholesterol concentration was 5.25 +/- 0.41 mmol/L (SEM). Over 38% of the trainees had cholesterol concentrations greater than 5.3 mmol/L, an indicator of high risk for cardiovascular disease. Mean sodium intake was 250 +/- 22 mmol/d. Over 86% of the trainees consumed greater than 144 mmol/d. Urinary Na excretion was high (146.7 +/- 6.7 mmol/d [SEM]) and correlated with Na intake (r = 0.365; p = 0.001). Potassium and selected vitamin intakes approximated the Military Recommended Dietary Allowances. Fat, cholesterol, and Na intakes were high relative to the dietary goals. Whether more dietary CHO would improve performance in endurance training remains to be determined.

Zinc status of highly trained women runners and untrained women.

Endurance training effects on zinc status were assessed by comparing 13 highly trained (HT) and 10 untrained (UT) women. Blood and 24-h urine samples before and after a 25-mg oral Zn load, and 3-d dietary records were evaluated. Mean daily Zn intakes did not differ and were below the Recommended Dietary Allowances for both groups. Fasting concentrations of plasma Zn, serum albumin, alpha 2-macroglobulin, and erythrocyte Zn content did not differ. However, HT women had significantly (p less than 0.05) higher urinary Zn excretion (HT: 6.7 +/- 0.8 and UT: 4.5 +/- 0.7 mumol/d) and reduced responses to the oral Zn than did UT in terms of maximal responses (HT: 11.0 +/- 1.6 and UT: 16.2 +/- 1.2 mumol/L) and areas under the curve (HT: 34.8 +/- 2.7 and UT: 43.6 +/- 2.7 mumol.L-1.4h-1). The greater urinary Zn excretion by HT women may reflect higher rates of skeletal muscle turnover. Whether their reduced responses to the Zn load reflect differences in plasma volume, entry or removal of plasma Zn, or absorption is unknown.

Biochemical indices of selected trace minerals in men: effect of stress.

Plasma zinc, iron, copper, and selenium and selected blood proteins were measured in 66 men before (BHW) and after (AHW) a 5-d period of sustained physical and psychological stress called Hell Week. Recovery blood samples were obtained from 26 men 7 d after Hell Week. Dietary intakes were determined BHW and during Hell Week; zinc, iron, copper, and selenium intakes during Hell Week averaged 23.6 +/- 3.4 mg/d, 35.4 +/- 3.9 mg/d, 3.0 +/- 0.5 mg/d, and 92.5 +/- 26.7 micrograms/d, respectively. C-reactive protein was detected in only five subjects BHW and in all subjects AHW. Zinc, iron, selenium, and albumin decreased by 33%, 44%, 12%, and 9%, respectively, whereas ferritin, ceruloplasmin, and creatine kinase concentrations increased AHW by 59%, 8%, and 266%, respectively. Haptoglobin concentrations increased 57% in 30 subjects but decreased 32% in 23 subjects AHW. The biochemical changes were transitory because protein (except ferritin) and mineral concentrations were similar to BHW values 7 d after Hell Week. Hell Week induced changes characteristic of an acute-phase response in physically active men.

Plasma pyridoxal and pyridoxal 5'-phosphate concentrations in response to ingestion of water or glucose polymer during a 2-h run.

The effects of ingesting a glucose polymer solution (GP) or water (W) on plasma pyridoxal 5'-phosphate (PLP) and pyridoxal (PL) concentrations were compared in six men (age: 30 +/- 2 y; VO2max: 57.4 +/- 3.2 mL.kg-1.min-1) under running (R) and control (C) conditions. Subjects ran for 2 h at 60-65% of VO2max for R and remained standing for C. For both R and C, 200 mL W or GP was ingested before (0-time) and every 30 min while running (30, 60, and 90 min). Plasma PLP decreased to 95% and 87% of 0-time at 180 min for WC and GPC and increased to 126% and 119% at 90 min and to 124% and 119% at 120 min for WR and GPR. By 60 min postrun, plasma PLP was 98% (WR) and 101% (GPR) of 0-time. There were no significant differences between W and GP conditions. Changes in PLP were not related to plasma volume or blood glucose, free fatty acids, lactate, alkaline phosphatase, aspartate aminotransferase, or alanine aminotransferase. No significant changes in plasma PL were noted. Exercise induces an increase in plasma PLP, perhaps due to transfer of B-6 vitamers from liver to skeletal muscle.

Magnesium, zinc, and copper status of US Navy SEAL trainees.

Magnesium, zinc, and copper status of 270 US Navy Sea, Air, and Land (SEAL) trainees was determined from dietary intakes and biochemical profiles. Although mean intakes exceeded the Recommended Dietary Allowances or the Estimated Safe and Adequate Intake range, intakes of 34%, 44%, and 37% of the trainees were below the recommendations for Mg, Zn, and Cu, respectively. Mean plasma concentrations were 0.85 +/- 0.004 mmol/L, 13.4 +/- 0.2 mumol/L, and 16.5 +/- 0.2 mumol/L for Mg, Zn, and Cu respectively. Mean 24-h urinary excretions were 5.7 +/- 0.2 mmol, 11.1 +/- 0.3 mumol, and 0.05 +/- 0.003 mumol, for Mg, Zn, and Cu, respectively. The data provided by the present study should be useful for comparing other physically active male populations.

Dietary patterns, gastrointestinal complaints, and nutrition knowledge of recreational triathletes.

Dietary habits, nutrition knowledge, and gastrointestinal complaints were evaluated in 21 female and 50 male triathletes; 30 completed hemoccult slides to determine the frequency of gastrointestinal bleeding. Triathletes trained 11 h/wk with weekly distances of 5.3, 116.5, and 40.9 km for swimming, biking, and running, respectively. Mean daily energy intake averaged 9058 and 11,591 kJ for women and men, respectively; 53.8% of the energy was from carbohydrates. Mean intakes of vitamins and most minerals exceeded the Recommended Dietary Allowances (RDAs), but many had intakes below RDAs for some nutrients; greater than 60% had low zinc and copper intakes. Because 39% took a daily multivitamin-mineral supplement, some had intakes 200-600% above the RDA. Although there were notable misconceptions about nutrition, nutrition knowledge was high. Upper-gastrointestinal complaints, reported by 50%, included bloating and abdominal gas; the incidence of positive hemoccult slides was 27%. The relation among performance, dietary patterns, nutrition knowledge, and gastrointestinal function remains to be established.

Nutritional survey of highly trained women runners.

Mean daily intakes from 3-day dietary records for calories, energy-providing nutrients, and selected minerals were calculated for 51 highly trained women runners. Selected blood constituents relating to mineral status were also measured. Intakes of calcium, magnesium, iron, and copper were above the amounts recommended by the National Research Council whereas zinc intake was below the recommended dietary allowances (RDA). Caloric intakes, although above the RDA for sedentary women, appeared low for women running 10 miles/day. Concentrations of serum ferritin and plasma zinc were indicative of marginal iron and zinc status in many of the women. Whether the nutrient content of the diets consumed by these women is adequate relative to energy output or whether training lowers nutrient requirements by enhancing metabolic efficiency will require further investigation.

Dark adaptation in hyperprolactinemic women.

In a study to test the hypothesis that hyperprolactinemia is caused by subclinical zinc deficiency, dark-adaptation curves of seven women with primary hyperprolactinemia and seven normal women were measured to assess tissue zinc status. Although plasma zinc levels, final dark-adapted thresholds, and the time courses of rod dark-adaptation did not differ significantly between patients and normal subjects, the median cone plateau of the hyperprolactinemic patients was significantly higher (0.66 log units) than that of normal subjects. It appears unlikely that derangements of vitamin A metabolism, for which zinc is a cofactor, explains this unanticipated and subtle abnormality in dark adaptation of the hyperprolactinemic women.

Alterations in magnesium and zinc metabolism in thyroid disease.

Magnesium (Mg) and zinc (Zn) status was assessed in subjects to evaluate the effects of thyroid diseases on Mg and Zn metabolism. Plasma and red blood cell (RBC) concentration and peripheral blood mononuclear cell (MNC) content of Mg and Zn, and 24-hour urinary excretion of Mg, Zn, creatinine (Cr), calcium (Ca), sodium (Na), and potassium (K) were measured in 11 thyrotoxic, 29 hypothyroid, and 25 euthyroid control subjects. Serum albumin, alpha 2-macroglobulin, and the binding of Zn to albumin were also determined. Plasma and RBC Mg concentrations were low in half of the hyperthyroid subjects, but mean values were not significantly different from controls. Urinary excretion and clearance of Mg were lower in hypothyroid subjects, but differences were removed when expressed relative to Cr excretion and clearance. Similar patterns were noted for urinary Ca, Na, and K, suggesting that their reduced excretion reflects alterations in renal hemodynamics. Plasma Zn was lower in hypothyroid subjects and correlated with serum albumin; MNC Zn and urinary Zn were also low. Plasma Zn concentration was normal and serum albumin significantly lower in the hyperthyroid group than in the control group. Further, RBC Zn content was significantly lower in hyperthyroid subjects, and inversely related to plasma thyroxine concentration. The hyperthyroid group also excreted significantly greater amounts of Zn than controls, indicative of a catabolic process. This increased urinary loss may reflect a shift in the distribution of plasma Zn between ultrafilterable and Zn-albumin complexes. In summary, this study provides evidence for marked alterations in Zn homeostasis in persons with thyroid disease. Whether the observations indicate deficiency states and have clinical implications will require further investigation.

Hormonal and metabolic responses of untrained, moderately trained, and highly trained men to three exercise intensities.

Untrained, moderately trained (runners, 15 to 25 mi/wk), and highly trained (runners, greater than 45 mi/wk) men participated in graded treadmill exercise at 50%, 70%, and 90% of their maximal oxygen consumption to quantify the relation between intensity of exercise and sympathetic nervous system and metabolic responses. Sympathetic system activation was noted at all intensities tested and was proportional to the relative exercise intensity. The magnitudes of the norepinephrine (NE) and epinephrine (E) responses were similar in all three groups of men at each relative exercise intensity and correlated with the magnitudes of change in levels of circulating plasma adrenocorticotropin hormone, cortisol, lactate (La), phosphate (Pi), and glucose (GI). The magnitudes of change in concentrations of La, Pi, and GI were also similar for the three groups at each relative exercise intensity. In contrast, a lower degree of sympathetic system activation in response to a given absolute workload was noted in the moderately and highly trained men as compared to that of the untrained men. Sympathetic and metabolic responses to exercise are similar under conditions of comparable relative exercise intensities, regardless of conditioning level. The sympathetic-adrenal medullary system is more sensitive to exercise than the hypothalamic-pituitary-adrenal axis. For a given absolute workload, the degree of activation significantly lower in trained individuals.