Search

The Food and Drug Administration's (FDA) obesity drug guidance is set on the basis of body mass index (BMI), with thresholds of either BMI ≥30 or BMI ≥27 kg/m² with weight-related comorbidities. While BMI is associated with obesityrelated health outcomes, there are known limitations to use as a direct measure of body fat or metabolic health, and the American Medical Association has highlighted limitations of BMI in assessing individual obesity risks. BMI thresholds impose a barrier to treatment. In a sample from the NHANES dataset (n=6,646 men and women), 36% of individuals with metabolic syndrome (MetS) may not be eligible for obesity pharmacotherapy. This analysis provides quantifiable justification for refinement of the BMI treatment criteria with a more holistic assessment of individual obesity-related disease risk. [ABSTRACT FROM AUTHOR]

Few US Marines earn perfect 300 scores on both their Physical Fitness Test (PFT) and Combat Fitness Test (CFT). The number 300 invokes the legendary 300 Spartans that fought at the Battle of Thermopylae, which inspired high physical fitness capabilities for elite ground forces ever since. Purpose: Determine distinguishing characteristics of the "300 Marines" (perfect PFT and CFT scores) that may provide insights into the physical and physiological requirements associated with this capability. These tests have been refined over time to reflect physical capabilities associated with Marine Corps basic rifleman performance. Materials and methods: Data were analyzed from US Marines, including 497 women (age, 29 ± 7 years; height 1.63 ± 0.07 m; body mass, 67.4 ± 8.4 kg) and 1,224 men (30 ± 8 years; 1.77 ± 0.07 m; 86.1 ± 11.1 kg). Marines were grouped by whether they earned perfect 300 scores on both the PFT and CFT (300 Marines) or not. We analyzed group differences in individual fitness test events and body composition (dual-energy x-ray absorptiometry). Results: Only 2.5% (n = 43) of this sample earned perfect PFT and CFT scores (n = 21 women; n = 22 men). Compared to sex-matched peers, 300 Marines performed more pull-ups, with faster three-mile run, maneuver-under-fire, and movement-to-contact times (each p < 0.001); 300 Marines of both sexes had lower fat mass, body mass index, and percent body fat (each p < 0.001). The lower percent body fat was explained by greater lean mass (p = 0.041) but similar body mass (p = 0.085) in women, whereas men had similar lean mass (p = 0.618), but lower total body mass (p = 0.025). Conclusion: Marines earning perfect PFT and CFT scores are most distinguished from their peers by their maneuverability, suggesting speed and agility capabilities. While both sexes had considerably lower percent body fat than their peers, 300 Marine women were relatively more muscular while men were lighter. [ABSTRACT FROM AUTHOR]

Objective: Determine if relative body fat (%BF) remains a biological norm in physically active, non‐obese American men and women and determine reference values for other components of body composition. Methods: Participants (n = 174 men, 70 women) were physically fit U.S. Marine 2nd Lieutenants, in their third decade of physical maturity (age 21–30). Body composition was assessed by dual‐energy x‐ray absorptiometry (DXA) and bioelectrical impedance analysis (BIA); and body images were obtained by 3D body scans. Results: For men and women, respectively, %BF averaged 16.2 ± 4.1 (median 15.3), 24.3 ± 4.5 (median 23.8); fat‐free mass (FFM): 67.7 ± 7.2, 49.4 ± 5.3 kg; FFM index: 21.5 ± 1.8, 18.3 ± 1.6 kg/m2; and body mass index (BMI): 25.5 ± 1.9, 24.1 ± 2.2 kg/m2. Bone mineral content (BMC) was 5% of FFM; total body water (TBW) was 70%–72% of FFM. Physique remained similar between median and higher percentiles of %BF. Only small changes in key measures were noted across the six‐month training program. Conclusions: Mean %BF of healthy active men and women in 2021 remains very similar to the 15% and 25% posited in 1980, suggesting that relative body fat has a normal fat‐lean relationship in physically mature humans. These data may bring new attention to sex‐appropriate %BF. [ABSTRACT FROM AUTHOR]

Biomathematical models quantitatively describe human physiological responses to environmental and operational stressors and have been used for planning and real-time prevention of cold injury. These same models can be applied from a military tactical perspective to gain valuable insights into the health status of opponent soldiers. This paper describes a use case for predicting physiological status of Russian soldiers invading Ukraine using open-source information. In March 2022, media outlets reported Russian soldiers in a stalled convoy invading Ukraine were at serious risk of hypothermia and predicted these soldiers would be "freezing to death" within days because of declining temperatures (down to −20°C). Using existing Army models, clothing data and open-source intelligence, modelling and analyses were conducted within hours to quantitatively assess the conditions and provide science-based predictions. These predictions projected a significant increase in risks of frostbite for exposed skin and toes and feet, with a very low (negligible) risk of hypothermia. Several days later, media outlets confirmed these predictions, reporting a steep rise in evacuations for foot frostbite injuries in these Russian forces. This demonstrated what can be done today with the existing mathematical physiology and how models traditionally focused on health risk can be used for tactical intelligence. [ABSTRACT FROM AUTHOR]

Global climate change has resulted in an increase in the number and intensity of environmental heat waves, both in areas traditionally associated with hot temperatures and in areas where heat waves did not previously occur. For military communities around the world, these changes pose progressively increasing risks of heat-related illnesses and interference with training sessions. This is a significant and persistent "noncombat threat" to both training and operational activities of military personnel. In addition to these important health and safety concerns, there are broader implications in terms of the ability of worldwide security forces to effectively do their job (particularly in areas that historically already have high ambient temperatures). In the present review, we attempt to quantify the impact of climate change on various aspects of military training and performance. We also summarize ongoing research efforts designed to minimize and/or prevent heat injuries and illness. In terms of future approaches, we propose the need to "think outside the box" for a more effective training/schedule paradigm. One approach may be to investigate potential impacts of a reversal of sleep-wake cycles during basic training during the hot months of the year, to minimize the usual increase in heat-related injuries, and to enhance the capacity for physical training and combat performance. Regardless of which approaches are taken, a central feature of successful present and future interventions will be that they are rigorously tested using integrative physiological approaches. [ABSTRACT FROM AUTHOR]

The article discusses the use of antiobesity medications (AOMs) in active-duty military personnel. It highlights the high prevalence of obesity among soldiers and the significant costs associated with obesity-related health care. The study found that only 0.1% of active-duty service members use AOMs, despite a 100-fold increase in prescriptions since their authorization in 2018. The article also discusses the administrative barriers to AOM treatment in the Military Health System and the need for further research on the effects of AOMs on body composition and physical performance in military populations. [Extracted from the article]

Warfighters complete strenuous physical activity on their feet throughout their military careers. While greater physiologic costs of walking have been demonstrated with older models of military combat boots versus running shoes, these quantitative differences may not be applicable for contemporary military footwear. The purpose of this study was to quantify and compare physiological responses to walking when wearing modern military combat boots versus running shoes. In this randomized, counterbalanced crossover experiment, 34 active military personnel (29 men and 5 women; age, 26 ± 7 years; height, 1.74 ± 0.08 m; body mass, 77.9 ± 15.1 kg) completed an incremental walking test (4.18–7.08 km.h−1) on separate visits in running shoes (mass, 0.6 ± 0.1 kg) and military combat boots (mass, 1.2 ± 0.3 kg). Oxygen uptake (V̇O2), carbon dioxide production (V̇CO2), heart rate (HR), respiration rate (RR), and metabolic energy expenditure (Ṁ) measurements were collected and averaged over the final minute of each walking speed. The oxygen costs of walking were 6–9% higher when wearing combat boots versus running shoes (p < 0.01 for each comparison). Other cardiorespiratory indicators of exercise intensity, specifically V̇CO2, Ṁ, HR, and RR, increased by 2.7–9.9% (p < 0.02 for each indicator). Walking in modern military combat boots incurs noticeably increased metabolic and cardiorespiratory strain as compared to walking in running shoes. These physiological consequences emphasize the trade-off between the intended versatility and protective characteristics of military footwear and the economy of traditional running shoes. This strain must be considered when selecting footwear to maximize warfighter health and performance during military exercise interventions. [ABSTRACT FROM AUTHOR]

Objectives: To improve predictive formulae for estimating body surface area (BSA) in healthy men and women using a modern three‐dimensional scanner technology. Methods: Body surface areas were obtained from a convenience sample of 1267 US Marines (464 women and 803 men) using a whole body surface scanner (Size Stream SS20). The reliability of SS20 measures of total and regional BSA within participants was compared across triplicate scans. We then derived a series of formulae to estimate SS20‐measured BSA using various combinations of sex, height, and mass. We also assessed relationships between percent body fat measured by dual‐energy x‐ray absorptiometry and sex‐specific formulae errors in Marines. Results: Body surface areas recorded by the SS20 were highly reliable whether measured for the total body or by region (ICC ≥.962). Formulae estimates of BSA from sex, height, and mass were precise (root‐mean‐square deviation, 0.031 m2). Errors from the Marine Corps formulae were positively associated with percent body fat for men (p =.001) but not women (p =.843). Conclusions: Clinicians, military leaders, and researchers can use the newly developed BSA formulae for precise estimates in healthy physically active men and women. Users should be aware that height‐ and mass‐based BSA estimates are less accurate for individuals with extremely low or high percent body fat. [ABSTRACT FROM AUTHOR]

Objective: The aim of this study was to model the effect of body armor coverage on body core temperature elevation and wet-bulb globe temperature (WBGT) offset. Background: Heat stress is a critical factor influencing the health and safety of military populations. Work duration limits can be imposed to mitigate the risk of exertional heat illness and are derived based on the environmental conditions (WBGT). Traditionally a 3°C offset to WBGT is recommended when wearing body armor; however, modern body armor systems provide a range of coverage options, which may influence thermal strain imposed on the wearer. Method: The biophysical properties of four military clothing ensembles of increasing ballistic protection coverage were measured on a heated sweating manikin in accordance with standard international criteria. Body core temperature elevation during light, moderate, and heavy work was modeled in environmental conditions from 16°C to 34°C WBGT using the heat strain decision aid. Results: Increasing ballistic protection resulted in shorter work durations to reach a critical core temperature limit of 38.5°C. Environmental conditions, armor coverage, and work intensity had a significant influence on WBGT offset. Conclusion: Contrary to the traditional recommendation, the required WBGT offset was >3°C in temperate conditions (<27°C WBGT), particularly for moderate and heavy work. In contrast, a lower WBGT offset could be applied during light work and moderate work in low levels of coverage. Application: Correct WBGT offsets are important for enabling adequate risk management strategies for mitigating risks of exertional heat illness. [ABSTRACT FROM AUTHOR]

Purpose: Diving in warm water increases thermal risk during exercise compared to thermoneutral waters. The purpose of this study was to evaluate exercise endurance in warm- and hot-water conditions in divers habituated to wet or dry heat. Methods: Nineteen male divers completed this study at the Navy Experimental Diving Unit. Subjects were assigned DRY or WET heat habituation groups. The DRY group (n=9) cycled at 125-150W for one hour in a non-immersed condition (34.4 ̊C, 50%RH), while the WET group (n=10) cycled at 50W for one hour while immersed in 34.4 ̊C water. Exercise time to exhaustion was tested on an underwater cycle ergometer in 35.8 ̊C (WARM) and 37.2 ̊C (HOT) water at 50W. Core temperature (T c ) was continuously recorded and for all dives. Results: Time to exhaustion was reduced in HOT compared to WARM water (p<0.01) in both DRY (92.7±41.6 minutes in 35.8 ̊C vs. 43.4±17.5 minutes in 37.2 ̊C) and WET (95.9±39.2 minutes in 35.8 ̊C vs. 53.4±27.5 minutes in 37.2 ̊C) groups, but did not differ between groups (p=0.62). Rate of T c rise was greater with higher water temperature (p<0.01), but was not different between groups (p=0.68). Maximum Tc (p=0.94 and p=0.95) and T c change from baseline (p=0.38 and p=0.34) was not different between water temperatures or habituation group, respectively.. Conclusion: Endurance decreased with increased water temperature but was not different between WET and DRY. Divers became exhausted at a similar core temperature during WARM- and HOT-water exercise. Mechanisms and applications of heat acclimation for warm-water diving should be further explored. [ABSTRACT FROM AUTHOR]

Figueiredo, PS, Looney, DP, Pryor, JL, Doughty, EM, McClung, HL, Vangala, SV, Santee, WR, Beidleman, BA, and Potter, AW. Verification of maximal oxygen uptake in active military personnel during treadmill running. J Strength Cond Res 36(4): 1053-1058, 2022-It is unclear whether verification tests are required to confirm "true" maximal oxygen uptake (V[Combining Dot Above]O2max) in modern warfighter populations. Our study investigated the prevalence of V[Combining Dot Above]O2max attainment in U.S. Army soldiers performing a traditional incremental running test. In addition, we examined the utility of supramaximal verification testing as well as repeated trials for familiarization for accurate V[Combining Dot Above]O2max assessment. Sixteen U.S. Army soldiers (1 woman, 15 men; age, 21 +/- 2 years; height, 1.73 +/- 0.06 m; body mass, 71.6 +/- 10.1 kg) completed 2 laboratory visits, each with an incremental running test (modified Astrand protocol) and a verification test (110% maximal incremental test speed) on a motorized treadmill. We evaluated V[Combining Dot Above]O2max attainment during incremental testing by testing for the definitive V[Combining Dot Above]O2 plateau using a linear least-squares regression approach. Peak oxygen uptake (V[Combining Dot Above]O2peak) was considered statistically equivalent between tests if the 90% confidence interval around the mean difference was within +/-2.1 ml[middle dot]kg-1[middle dot]min-1. Oxygen uptake plateaus were identified in 14 of 16 volunteers for visit 1 (87.5%) and all 16 volunteers for visit 2 (100%). Peak oxygen uptake was not statistically equivalent, apparent from the mean difference in V[Combining Dot Above]O2peak measures between the incremental test and verification test on visit 1 (2.3 ml[middle dot]kg-1[middle dot]min-1, [1.3-3.2]) or visit 2 (1.1 ml[middle dot]kg-1[middle dot]min-1 [0.2-2.1]). Interestingly, V[Combining Dot Above]O2peak was equivalent, apparent from the mean difference in V[Combining Dot Above]O2peak measures between visits for the incremental tests (0.0 ml[middle dot]kg-1[middle dot]min-1 [-0.8 to 0.9]) but not the verification tests (-1.2 ml[middle dot]kg-1[middle dot]min-1 [-2.2 to -0.2]). Modern U.S. Army soldiers can attain V[Combining Dot Above]O2max by performing a modified Astrand treadmill running test. Additional familiarization and verification tests for confirming V[Combining Dot Above]O2max in healthy active military personnel may be unnecessary. [ABSTRACT FROM AUTHOR]

Purpose: Body composition assessment methods are dependent on their underlying principles, and assumptions of each method may be affected by age and sex. This study compared an abdominal circumference-focused method of percent body fat estimation (AC %BF) to a criterion method of dual-energy x-ray absorptiometry (DXA), and a comparative assessment with bioelectrical impedance (BIA), in younger (≤30 years) and older (>age 30 years) physically fit (meeting/exceeding annual US Marine Corps fitness testing requirements) men and women. Methods: Fit healthy US Marines (430 men, 179 women; 18–57 years) were assessed for body composition by DXA (iDXA, GE Lunar), anthropometry, and BIA (Quantum IV, RJL Systems). Results: Compared to DXA %BF, male AC %BF underestimated for both ≤30 and >30 years age groups (bias, -2.6 ± 3.7 and -2.5 ± 3.7%); while female AC %BF overestimated for both ≤30 and >30 years age groups (2.3 ± 4.3 and 1.3 ± 4.8%). On an individual basis, lean men and women were overestimated and higher %BF individuals were underestimated. Predictions from BIA were more accurate and reflected less relationship to adiposity for each age and sex group (males: ≤30, 0.4 ± 3.2, >30 years, -0.5 ± 3.5; women: ≤30, 1.4 ± 3.1, >30 years, 0.0 ± 3.3). Total body water (hydration) and bone mineral content (BMC) as a proportion of fat-free mass (FFM) remained consistent across the age range; however, women had a higher proportion of %BMC/FFM than men. Older men and women (>age 30 years) were larger and carried more fat but had similar FFM compared to younger men and women. Conclusion: The AC %BF provides a field expedient method for the US Marine Corps to classify individuals for obesity prevention, but does not provide research-grade quantitative body composition data. [ABSTRACT FROM AUTHOR]

This paper describes a Cold Weather Ensemble Decision Aid (CoWEDA) that provides guidance for cold weather injury prevention, mission planning, and clothing selection. CoWEDA incorporates current science from the disciplines of physiology, meteorology, clothing, and computer modeling. The thermal performance of a cold weather ensemble is defined by endurance times, which are the time intervals from initial exposure until the safety limits are reached. These safety limits correspond to conservative temperature thresholds that provide a warning of the approaching onset of frostbite and/or hypothermia. A validated six-cylinder thermoregulatory model is used to predict human thermal responses to cold while wearing different ensembles. The performance metrics, model, and a database of clothing properties were integrated into a user-friendly software application. CoWEDA is the first tool that allows users to build their own ensembles from the clothing menu (i.e., jackets, footwear, and accessories) for each body region (i.e., head, torso, lower body, hands, feet) and view their selections in the context of physiological strain and the operational consequences. Comparison of predicted values to skin and core temperatures, measured during 17 cold exposures ranging from 0 to −40°C, indicated that the accuracy of CoWEDA prediction is acceptable, and most predictions are within measured mean ± SD. CoWEDA predicts the risk of frostbite and hypothermia and ensures that a selected clothing ensemble is appropriate for expected weather conditions and activities. CoWEDA represents a significant enhancement of required clothing insulation (IREQ, ISO 11079) and wind chill index-based guidance for cold weather safety and survival. [ABSTRACT FROM AUTHOR]

Physiological responses to work in cold water have been well studied but little is known about the effects of exercise in warm water; an overlooked but critical issue for certain military, scientific, recreational, and professional diving operations. This investigation examined core temperature responses to fatiguing, fully-immersed exercise in extremely warm waters. Twenty-one male U.S. Navy divers (body mass, 87.3 ± 12.3 kg) were monitored during rest and fatiguing exercise while fully-immersed in four different water temperatures (Tw): 34.4, 35.8, 37.2, and 38.6°C (Tw34.4, Tw35.8, Tw37.2, and Tw38.6 respectively). Participants exercised on an underwater cycle ergometer until volitional fatigue or core temperature limits were reached. Core body temperature and heart rate were monitored continuously. Trial performance time decreased significantly as water temperature increased (Tw34.4, 174 ± 12 min; Tw35.8, 115 ± 13 min; Tw37.2, 50 ± 13 min; Tw38.6, 34 ± 14 min). Peak core body temperature during work was significantly lower in Tw34.4 water (38.31 ± 0.49°C) than in warmer temperatures (Tw35.8, 38.60 ± 0.55°C; Tw37.2, 38.82 ± 0.76°C; Tw38.6, 38.97 ± 0.65°C). Core body temperature rate of change increased significantly with warmer water temperature (Tw34.4, 0.39 ± 0.28°C·h−1; Tw35.8, 0.80 ± 0.19°C·h−1; Tw37.2, 2.02 ± 0.31°C·h−1; Tw38.6, 3.54 ± 0.41°C·h−1). Physically active divers risk severe hyperthermia in warmer waters. Increases in water temperature drastically increase the rate of core body temperature rise during work in warm water. New predictive models for core temperature based on workload and duration of warm water exposure are needed to ensure warm water diving safety. [ABSTRACT FROM AUTHOR]

Introduction: A significant number of healthcare workers have responded to aid in the relief and containment of the 2013 Ebola virus disease (EVD) outbreak in West Africa. Healthcare workers are required to wear personal protective clothing (PPC) to impede the transmission of the virus; however, the impermeable design and the hot humid environment lead to risk of heat stress. Objective: Provide healthcare workers quantitative modeling and analysis to aid in the prevention of heat stress while wearing PPC in West Africa. Methods: A sweating thermal manikin was used to measure the thermal (Rct) and evaporative resistance (Ret) of the five currently used levels of PPC for healthcare workers in the West Africa EVD response. Mathematical methods of predicting the rise in core body temperature (Tc) in response to clothing, activity, and environment was used to simulate different responses to PPC levels, individual body sizes, and two hot humid conditions: morning/evening (air temperature: 25°C, relative humidity: 40%, mean radiant temperature: 35°C, wind velocity: 1 m/s) and mid-day (30°C, 60%, 70°C, 1 m/s). Results: Nearly still air (0.4 m/s) measures of Rct ranged from 0.18 to 0.26 m2 K/W and Ret ranged from 25.53 to 340.26 m2 Pa/W. Conclusion: Biophysical assessments and modeling in this study provide quantitative guidance for prevention of heat stress of healthcare workers wearing PPC responding to the EVD outbreak in West Africa. [ABSTRACT FROM AUTHOR]

Introduction: Military personnel are often required to wear ballistic protection in order to defend against enemies. However, this added protection increases mass carried and imposes additional thermal burden on the individual. Body armor (BA) is known to reduce combat casualties, but the effects of BA mass and insulation on the physical performance of soldiers are less well documented. Until recently, the emphasis has been increasing personal protection, with little consideration of the adverse impacts on human performance. Objective: The purpose of this work was to use sweating thermal manikin and mathematical modeling techniques to quantify the tradeoff between increased BA protection, the accompanying mass, and thermal effects on human performance. Methods: Using a sweating thermal manikin, total insulation (IT, clo) and vapor permeability indexes (im) were measured for a baseline clothing ensemble with and without one of seven increasingly protective U.S. Army BA configurations. Using mathematical modeling, predictions were made of thermal impact on humans wearing each configuration while working in hot/dry (desert), hot/humid (jungle), and temperate environmental conditions. Results: In nearly still air (0.4 m/s), IT ranged from 1.57 to 1.63 clo and im from 0.35 to 0.42 for the seven BA conditions, compared to IT and im values of 1.37 clo and 0.45 respectively, for the baseline condition (no BA). Conclusion: Biophysical assessments and predictive modeling show a quantifiable relationship exists among increased protection and increased thermal burden and decreased work capacity. This approach enables quantitative analysis of the tradeoffs between ballistic protection, thermal-work strain, and physical work performance. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented that discusses the concepts of fabric thermal resistance and ensemble thermal resistances.