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Schafer EA, Chapman CL, Castellani JW, Looney DP. Energy expenditure during physical work in cold environments: physiology and performance considerations for military service members. J Appl Physiol (1985) 2024; 137:995-1013. [PMID: 39205639 DOI: 10.1152/japplphysiol.00210.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2024] [Revised: 07/24/2024] [Accepted: 08/21/2024] [Indexed: 09/04/2024] Open
Abstract
Effective execution of military missions in cold environments requires highly trained, well-equipped, and operationally ready service members. Understanding the metabolic energetic demands of performing physical work in extreme cold conditions is critical for individual medical readiness of service members. In this narrative review, we describe 1) the extreme energy costs of performing militarily relevant physical work in cold environments, 2) key factors specific to cold environments that explain these additional energy costs, 3) additional environmental factors that modulate the metabolic burden, 4) medical readiness consequences associated with these circumstances, and 5) potential countermeasures to be developed to aid future military personnel. Key characteristics of the cold operational environment that cause excessive energy expenditure in military personnel include thermoregulatory mechanisms, winter apparel, inspiration of cold air, inclement weather, and activities specific to cold weather. The combination of cold temperatures with other environmental stressors, including altitude, wind, and wet environments, exacerbates the overall metabolic strain on military service members. The high energy cost of working in these environments increases the risk of undesirable consequences, including negative energy balance, dehydration, and subsequent decrements in physical and cognitive performance. Such consequences may be mitigated by the application of enhanced clothing and equipment design, wearable technologies for biomechanical assistance and localized heating, thermogenic pharmaceuticals, and cold habituation and training guidance. Altogether, the reduction in energy expenditure of modern military personnel during physical work in cold environments would promote desirable operational outcomes and optimize the health and performance of service members.
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Affiliation(s)
- Erica A Schafer
- Thermal and Mountain Medicine Division, United States Army Research Institute of Environmental Medicine (USARIEM), Natick, Massachusetts, United States
- Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee, United States
| | - Christopher L Chapman
- Thermal and Mountain Medicine Division, United States Army Research Institute of Environmental Medicine (USARIEM), Natick, Massachusetts, United States
- Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee, United States
| | - John W Castellani
- Thermal and Mountain Medicine Division, United States Army Research Institute of Environmental Medicine (USARIEM), Natick, Massachusetts, United States
| | - David P Looney
- Military Performance Division, United States Army Research Institute of Environmental Medicine (USARIEM), Natick, Massachusetts, United States
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Daniels M, Margolis LM, Rood JC, Lieberman HR, Pasiakos SM, Karl JP. Comparative analysis of circulating metabolomic profiles identifies shared metabolic alterations across distinct multistressor military training exercises. Physiol Genomics 2024; 56:457-468. [PMID: 38738316 PMCID: PMC11368567 DOI: 10.1152/physiolgenomics.00008.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2024] [Revised: 03/26/2024] [Accepted: 05/03/2024] [Indexed: 05/14/2024] Open
Abstract
Military training provides insight into metabolic responses under unique physiological demands that can be comprehensively characterized by global metabolomic profiling to identify potential strategies for improving performance. This study identified shared changes in metabolomic profiles across three distinct military training exercises, varying in magnitude and type of stress. Blood samples collected before and after three real or simulated military training exercises were analyzed using the same untargeted metabolomic profiling platform. Exercises included a 2-wk survival training course (ST, n = 36), a 4-day cross-country ski march arctic training (AT, n = 24), and a 28-day controlled diet- and exercise-induced energy deficit (CED, n = 26). Log2-fold changes of greater than ±1 in 191, 121, and 64 metabolites were identified in the ST, AT, and CED datasets, respectively. Most metabolite changes were within the lipid (57-63%) and amino acid metabolism (18-19%) pathways and changes in 87 were shared across studies. The largest and most consistent increases in shared metabolites were found in the acylcarnitine, fatty acid, ketone, and glutathione metabolism pathways, whereas the largest decreases were in the diacylglycerol and urea cycle metabolism pathways. Multiple shared metabolites were consistently correlated with biomarkers of inflammation, tissue damage, and anabolic hormones across studies. These three studies of real and simulated military training revealed overlapping alterations in metabolomic profiles despite differences in environment and the stressors involved. Consistent changes in metabolites related to lipid metabolism, ketogenesis, and oxidative stress suggest a potential common metabolomic signature associated with inflammation, tissue damage, and suppression of anabolic signaling that may characterize the unique physiological demands of military training.NEW & NOTEWORTHY The extent to which metabolomic responses are shared across diverse military training environments is unknown. Global metabolomic profiling across three distinct military training exercises identified shared metabolic responses with the largest changes observed for metabolites related to fatty acids, acylcarnitines, ketone metabolism, and oxidative stress. These changes also correlated with alterations in markers of tissue damage, inflammation, and anabolic signaling and comprise a potential common metabolomic signature underlying the unique physiological demands of military training.
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Affiliation(s)
- Michael Daniels
- Military Nutrition Division, United States Army Research Institute of Environmental Medicine, Natick, Massachusetts, United States
- Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee, United States
| | - Lee M Margolis
- Military Nutrition Division, United States Army Research Institute of Environmental Medicine, Natick, Massachusetts, United States
| | - Jennifer C Rood
- Pennington Biomedical Research Center, Baton Rouge, Louisiana, United States
| | - Harris R Lieberman
- Military Nutrition Division, United States Army Research Institute of Environmental Medicine, Natick, Massachusetts, United States
| | - Stefan M Pasiakos
- Military Nutrition Division, United States Army Research Institute of Environmental Medicine, Natick, Massachusetts, United States
- Office of Dietary Supplements, National Institutes of Health, Bethesda, Maryland, United States
| | - J Philip Karl
- Military Nutrition Division, United States Army Research Institute of Environmental Medicine, Natick, Massachusetts, United States
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Tourula E, Lenzini M, Rhodes A, Hetz SE, Pearson J. Facial fanning reduces heart rate but not tolerance to a simulated hemorrhagic challenge following exercise heat stress in young healthy humans. Am J Physiol Regul Integr Comp Physiol 2024; 326:R210-R219. [PMID: 38105763 DOI: 10.1152/ajpregu.00180.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Revised: 11/02/2023] [Accepted: 12/12/2023] [Indexed: 12/19/2023]
Abstract
We investigated whether reducing face skin temperature alters arterial blood pressure control and lower body negative pressure (LBNP) tolerance after exercise heat stress. Eight subjects (1 female; age, 27 ± 9 yr) exercised at ∼63% V̇o2max until core temperature had increased ∼1.5°C before undergoing LBNP to presyncope either with fanning to return face skin temperature to baseline (Δ-5°C, Fan trial) or without (No Fan trial). LBNP tolerance was quantified as cumulative stress index (CSI; mmHg·min). Before LBNP, whole body and face skin temperatures were elevated from baseline in both trials (38.0 ± 0.5°C and 36.3 ± 0.5°C, respectively, both P < 0.001). During LBNP, face skin temperature decreased in the Fan trial (30.9 ± 1.0°C) but was unchanged in the No Fan trial (36.1 ± 0.6°C, between trials P < 0.001). Mean arterial pressure was not different between trials (P = 0.237) and was similarly reduced at presyncope in both trials (from 82 ± 7 to 67 ± 8 mmHg, P < 0.001). During LBNP, heart rate was attenuated in the Fan trial at Mid LBNP (146 ± 16 vs. 158 ± 12 beats/min, P = 0.036) and at peak heart rate (158 ± 15 vs. 170 ± 15 beats/min; P < 0.001). LBNP tolerance was not different between trials (321 ± 248 vs. 328 ± 115 mmHg·min, P = 0.851). In exercise heat-stressed individuals, lowering face skin temperature to normothermic values suppressed heart rate thereby altering cardiovascular control during a simulated hemorrhagic challenge without reducing tolerance.
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Affiliation(s)
- Erica Tourula
- William J. Hybl Sports Medicine and Performance Center, Department of Human Physiology and Nutrition, University of Colorado Colorado Springs, Colorado, United States
- Department of Kinesiology, H. H. Morris Human Performance Laboratories, School of Public Health, Indiana University, Bloomington, Indiana, United States
| | - Miramani Lenzini
- William J. Hybl Sports Medicine and Performance Center, Department of Human Physiology and Nutrition, University of Colorado Colorado Springs, Colorado, United States
| | - Addison Rhodes
- William J. Hybl Sports Medicine and Performance Center, Department of Human Physiology and Nutrition, University of Colorado Colorado Springs, Colorado, United States
| | - Sarah E Hetz
- William J. Hybl Sports Medicine and Performance Center, Department of Human Physiology and Nutrition, University of Colorado Colorado Springs, Colorado, United States
| | - James Pearson
- William J. Hybl Sports Medicine and Performance Center, Department of Human Physiology and Nutrition, University of Colorado Colorado Springs, Colorado, United States
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Margolis LM, Pasiakos SM. Performance nutrition for cold-weather military operations. Int J Circumpolar Health 2023; 82:2192392. [PMID: 36934427 PMCID: PMC10026745 DOI: 10.1080/22423982.2023.2192392] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/20/2023] Open
Abstract
.High daily energy expenditure without compensatory increases in energy intake results in severe energy deficits during cold-weather military operations. The severity of energy deficits has been proportionally linked to declines in body mass, negative protein balance, suppression of androgen hormones, increases in systemic inflammation and degraded physical performance. Food availability does not appear to be the predominant factor causing energy deficits; providing additional rations or supplement snack bars does not reduce the severity of the energy deficits. Nutrition interventions that allow greater energy intake could be effective for reducing energy deficits during cold-weather military operations. One potential intervention is to increase energy density (i.e. energy per unit mass of food) by increasing dietary fat. Our laboratory recently reported that self-selected higher energy intakes and reductions in energy deficits were primarily driven by fat intake (r = 0.891, r2 = 0.475), which, of the three macronutrients. Further, soldiers who ate more fat lost less body mass, had lower inflammation, and maintained net protein balance compared to those who ate less fat. These data suggest that consuming high-fat energy-dense foods may be a viable nutritional intervention that mitigates the negative physiological effects of energy deficit and sustains physical performance during cold-weather military operations.
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Affiliation(s)
- Lee M Margolis
- Military Nutrition Division, U.S. Army Research Institute of Environmental Medicine, Natick, MA, USA
| | - Stefan M Pasiakos
- Military Performance Division, U.S. Army Research Institute of Environmental Medicine, Natick, MA, USA
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Lavergne FV, Laroche-Nantel R, Prud'Homme D, Giroux I. Facteurs influençant l’apport alimentaire en rations des soldats canadiens dans l’Arctique : un sondage national. CAN J DIET PRACT RES 2023; 84:54-57. [PMID: 36004738 DOI: 10.3148/cjdpr-2022-021] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Purpose: To document Canadian Armed Forces (CAF) soldiers' perceptions of factors influencing their dietary intake of combat rations during Arctic field training.Methods: A bilingual digital questionnaire was sent nationally to soldiers who trained in the Arctic between 2015 and 2018. It consisted of 6 open-ended and 33 closed-ended questions on factors influencing ration intake and acceptability.Results: Of the 54 completed questionnaires (response rate: 31%), 6 were incomplete and were excluded. The final sample consisted of 48 military personnel from nine provinces with an average of 12.1 ± 6.8 years of CAF experience. Factors with the greatest negative impact on dietary intake were food temperature, eating on the move, exercise and activity schedules, and equipment needed for preparation and eating. Participants reported consuming between 61% and 71% of their rations. They noted that a considerable amount of time was required to prepare the rations since they were frozen. Sixty-five percent of soldiers reported weight loss while training in the Arctic.Conclusions: Multiple factors influenced soldiers' dietary intake and practices. These results will guide future research and assist in decision-making regarding possible changes to Arctic rations.
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Affiliation(s)
- Florence V Lavergne
- École interdisciplinaire des sciences de la santé, Faculté des sciences de la santé, Université d'Ottawa, ON
| | - Raphaëlle Laroche-Nantel
- École interdisciplinaire des sciences de la santé, Faculté des sciences de la santé, Université d'Ottawa, ON
| | | | - Isabelle Giroux
- École des sciences de la nutrition, Faculté des sciences de la santé, Université d'Ottawa, ON
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Kelly KR, Arrington LJ, Bernards JR, Jensen AE. Prolonged Extreme Cold Water Diving and the Acute Stress Response During Military Dive Training. Front Physiol 2022; 13:842612. [PMID: 35874531 PMCID: PMC9304957 DOI: 10.3389/fphys.2022.842612] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Accepted: 06/14/2022] [Indexed: 11/13/2022] Open
Abstract
Introduction: Cold water exposure poses a unique physiological challenge to the human body. Normally, water submersion increases activation of parasympathetic tone to induce bradycardia in order to compensate for hemodynamic shifts and reduce oxygen consumption by peripheral tissues. However, elevated stress, such as that which may occur due to prolonged cold exposure, may shift the sympatho-vagal balance towards sympathetic activation which may potentially negate the dive reflex and impact thermoregulation. Objective: To quantify the acute stress response during prolonged extreme cold water diving and to determine the influence of acute stress on thermoregulation. Materials and Methods: Twenty-one (n = 21) subjects tasked with cold water dive training participated. Divers donned standard diving equipment and fully submerged to a depth of ≈20 feet, in a pool chilled to 4°C, for a 9-h training exercise. Pre- and post-training measures included: core and skin temperature; salivary alpha amylase (AA), cortisol (CORT), osteocalcin (OCN), testosterone (TEST) and dehydroepiandosterone (DHEA); body weight; blood glucose, lactate, and ketones. Results: Core, skin, and extremity temperature decreased (p < 0.001) over the 9-h dive; however, core temperature was maintained above the clinical threshold for hypothermia and was not correlated to body size (p = 0.595). There was a significant increase in AA (p < 0.001) and OCN (p = 0.021) and a significant decrease in TEST (p = 0.003) over the duration of the dive. An indirect correlation between changes in cortisol concentrations and changes in foot temperature (ρ = -0.5,p = 0.042) were observed. There was a significant positive correlation between baseline OCN and change in hand temperature (ρ = 0.66, p = 0.044) and significant indirect correlation between changes in OCN concentrations and changes in hand temperature (ρ = -0.59, p = 0.043). Conclusion: These data suggest that long-duration, cold water diving initiates a stress response—as measurable by salivary stress biomarkers—and that peripheral skin temperature decreases over the course of these dives. Cumulatively, these data suggest that there is a relationship between the acute stress response and peripheral thermoregulation.
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Affiliation(s)
- Karen R. Kelly
- Applied Translational Exercise and Metabolic Physiology Team, Warfighter Performance, Naval Health Research Center, San Diego, CA, United States
- *Correspondence: Karen R. Kelly,
| | - Laura J. Arrington
- Applied Translational Exercise and Metabolic Physiology Team, Warfighter Performance, Naval Health Research Center, San Diego, CA, United States
- Leidos, Inc., San Diego, CA, United States
| | - Jake R. Bernards
- Applied Translational Exercise and Metabolic Physiology Team, Warfighter Performance, Naval Health Research Center, San Diego, CA, United States
- Leidos, Inc., San Diego, CA, United States
| | - Andrew E. Jensen
- Applied Translational Exercise and Metabolic Physiology Team, Warfighter Performance, Naval Health Research Center, San Diego, CA, United States
- Leidos, Inc., San Diego, CA, United States
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Daigle K, Subach R, Valliant M. Academy of Nutrition and Dietetics: Revised 2021 Standards of Practice and Standards of Professional Performance for Registered Dietitian Nutritionists (Competent, Proficient, and Expert) in Sports and Human Performance Nutrition. J Acad Nutr Diet 2021; 121:1813-1830.e55. [PMID: 34183294 DOI: 10.1016/j.jand.2021.04.018] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Accepted: 04/19/2021] [Indexed: 11/25/2022]
Abstract
Nutrition in sports and human performance incorporates knowledge of the intersection of human physiology and nutrition. Registered dietitian nutritionist (RDN) practitioners in sports and human performance focus on nutrition care that is specific to the individual and their sport/occupational requirements. The Dietitians in Sports, Cardiovascular and Wellness Dietetic Practice Group, along with the Academy of Nutrition and Dietetics Quality Management Committee, have updated the Standards of Practice (SOP) and Standards of Professional Performance (SOPP) for RDNs working in sports and human performance. The SOP and SOPP for RDNs in Sports and Human Performance Nutrition provide indicators that describe three levels of practice: competent, proficient, and expert. The SOP uses the Nutrition Care Process and clinical workflow elements for delivering care to athletic/professional populations. The SOPP describes the following six domains that focus on professional performance: Quality in Practice, Competence and Accountability, Provision of Services, Application of Research, Communication and Application of Knowledge, and Utilization and Management of Resources. Specific indicators outlined in the SOP and SOPP depict how these standards apply to practice. The SOP and SOPP are complementary resources for RDNs and are intended to be used as a self-evaluation tool for assuring competent practice in sports and human performance and for determining potential education and training needs for advancement to a higher practice level in a variety of settings.
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Negative energy balance during military training: The role of contextual limitations. Appetite 2021; 164:105263. [PMID: 33862189 DOI: 10.1016/j.appet.2021.105263] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Revised: 02/09/2021] [Accepted: 04/09/2021] [Indexed: 12/25/2022]
Abstract
During multiday training exercises, soldiers almost systematically face a moderate-to-large energy deficit, affecting their body mass and composition and potentially their physical and cognitive performance. Such energy deficits are explained by their inability to increase their energy intake during these highly demanding periods. With the exception of certain scenarios in which rations are voluntarily undersized to maximize the constraints, the energy content of the rations are often sufficient to maintain a neutral energy balance, suggesting that other limitations are responsible for such voluntary and/or spontaneous underconsumption. In this review, the overall aim was to present an overview of the impact of military training on energy balance, a context that stands out by its summation of specific limitations that interfere with energy intake. We first explore the impact of military training on the various components of energy balance (intake and expenditure) and body mass loss. Then, the role of the dimensioning of the rations (total energy content above or below energy expenditure) on energy deficits are addressed. Finally, the potential limitations inherent to military training (training characteristics, food characteristics, timing and context of eating, and the soldiers' attitude) are discussed to identify potential strategies to spontaneously increase energy intake and thus limit the energy deficit.
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Pasiakos SM. Nutritional Requirements for Sustaining Health and Performance During Exposure to Extreme Environments. Annu Rev Nutr 2020; 40:221-245. [PMID: 32530730 DOI: 10.1146/annurev-nutr-011720-122637] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Dietary guidelines are formulated to meet minimum nutrient requirements, which prevent deficiencies and maintain health, growth, development, and function. These guidelines can be inadequate and contribute to disrupted homeostasis, lean body mass loss, and deteriorated performance in individuals who are working long, arduous hours with limited access to food in environmentally challenging locations. Environmental extremes can elicit physiological adjustments that alone alter nutrition requirements by upregulating energy expenditure, altering substrate metabolism, and accelerating body water and muscle protein loss. The mechanisms by which the environment, including high-altitude, heat, and cold exposure, alters nutrition requirements have been studied extensively. This contemporary review discusses physiological adjustments to environmental extremes, particularly when those adjustments alter dietary requirements.
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Affiliation(s)
- Stefan M Pasiakos
- Military Nutrition Division, US Army Research Institute of Environmental Medicine, Natick, Massachusetts 01760, USA;
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