Publications by authors named "Adam W Potter"

24 Publications

  • Page 1 of 1

Heat Stress Management in the Military: Wet-Bulb Globe Temperature Offsets for Modern Body Armor Systems.

Hum Factors 2021 Apr 16:187208211005220. Epub 2021 Apr 16.

139261 Queensland University of Technology, Brisbane, Australia.

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.
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http://dx.doi.org/10.1177/00187208211005220DOI Listing
April 2021

A digital tool for prevention and management of cold weather injuries-Cold Weather Ensemble Decision Aid (CoWEDA).

Int J Biometeorol 2021 Apr 4. Epub 2021 Apr 4.

Biophysics and Biomedical Modeling Division, U.S. Army Research Institute of Environmental Medicine, 10 General Greene Avenue, Natick, MA, 01760-5007, USA.

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.
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http://dx.doi.org/10.1007/s00484-021-02113-0DOI Listing
April 2021

Effects of modern military backpack loads on walking speed and cardiometabolic responses of US Army Soldiers.

Appl Ergon 2021 Feb 27;94:103395. Epub 2021 Feb 27.

US Army Research Institute of Environmental Medicine (USARIEM), 10 General Greene Avenue, Natick, MA, 01760, USA. Electronic address:

Introduction: Military leaders must understand how modern military equipment loads affect trade-offs between movement speed and physiological strain to optimize pacing strategies.

Purpose: To evaluate the effects of load carried in a recently developed military backpack on the walking speed and cardiometabolic responses of dismounted warfighters.

Methods: Fifteen soldiers (1 woman, 14 men; age, 22 ± 2 years; height, 173 ± 7 cm; body mass (BM), 73 ± 10 kg) completed incremental walking tests with four external load conditions (0, 22, 44, or 66% BM) using the US Army's newest backpack: the Modular Lightweight Load-Carrying Equipment 4000 (MOLLE 4000). Oxygen uptake (V̇O) and heart rate (HR) were evaluated relative to maximal values (V̇O and HR respectively). Testing ceased when participants completed the highest tested speed (1.97 m s), exceeded a respiratory exchange ratio (RER) of 1.00, or reached volitional exhaustion.

Results: Peak speed significantly decreased (p < 0.03) with successively heavier loads (0% BM, 1.95 ± 0.06 m s; 22% BM, 1.87 ± 0.10 m s; 44% BM, 1.69 ± 0.13 m s; 66% BM, 1.48 ± 0.13 m s). Peak V̇O was significantly lower (p < 0.01) with 0% BM (47 ± 5% V̇O) than each load (22% BM, 58 ± 8% V̇O; 44% BM, 63 ± 10% V̇O; 66% BM, 61 ± 11% V̇O). Peak HR was significantly lower (p < 0.01) with 0% BM (71 ± 5% HR) versus each load (22% BM, 83 ± 6% HR; 44% BM, 87 ± 6% HR; 66% BM, 88 ± 6% HR).

Conclusion: Overburdened warfighters suffer severe impairments in walking speed even when carrying recently developed military load carriage equipment. Our results suggest that the relative work intensity of heavy load carriage may be better described when expressed relative to HR versus V̇O.
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http://dx.doi.org/10.1016/j.apergo.2021.103395DOI Listing
February 2021

Verification Testing to Confirm V˙O2max in a Hot Environment.

Med Sci Sports Exerc 2021 04;53(4):763-769

Department of Health and Human Performance, Concordia University, Chicago, IL.

Purpose: This study aimed to evaluate the validity and reliability of a verification test to confirm GXT V˙O2max in a hot environment.

Methods: Twelve recreationally trained cyclists completed a two-test protocol that included a GXT progressing 20 W·min-1 followed by a biphasic supramaximal-load verification test (1 min at 60% increasing to 110% maximal GXT wattage until failure) in a hot environment (39°C, 32% relative humidity). Rest between tests occurred in a thermoneutral room and was anchored to the duration required for gastrointestinal temperature to return to baseline.

Results: Mean verification test V˙O2max (51.3 ± 8.8 mL·kg-1·min-1) was lower than GXT (55.9 ± 7.6 mL·kg-1·min-1, P = 0.02). Verification tests confirmed GXT V˙O2max in 92% of participants using individual analysis thresholds. Bland-Altman analysis revealed a sizable mean bias (-4.6 ± 4.9 mL·kg-1·min-1) with wide 95% limits of agreement (-14.0 to 5.0 mL·kg-1·min-1) across a range of V˙O2max values. The high coefficient of variation (9.6%) and typical error (±3.48 mL·kg-1·min-1) indicate potential issues of test-retest reliability in the heat.

Conclusions: Verification testing in a hot condition confirmed GXT V˙O2max in virtually all participants, indicating robust utility. To enhance test-retest reliability in this environment, protocol recommendations for work rate and recovery between tests are provided.
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http://dx.doi.org/10.1249/MSS.0000000000002520DOI Listing
April 2021

Formulae for calculating body surface area in modern U.S. Army Soldiers.

J Therm Biol 2020 Aug 30;92:102650. Epub 2020 Jun 30.

Biophysics and Biomedical Modeling Division, U.S. Army Research Institute of Environmental Medicine (USARIEM), 10 General Greene Avenue, Bldg 42, Natick, MA, 01760, USA. Electronic address:

Purpose: Body surface area (BSA) is an important measurement for many thermophysiological, pharmaceutical, toxicological, environmental, and military applications. Unfortunately, BSA is difficult to quantify, and existing prediction methods are not optimized for contemporary populations.

Methods: The present study analyzed data body measurements from 5603 male and female participants of a US Army Anthropometric Survey to determine optimal methods for estimating BSA in modern US Army Soldiers. This data included 94 individual body measurements as well as three dimensional (3D) whole body scans for each participant. We used this data to assess and compared 15 existing equations to the measured data. We also derived best fitting nonlinear regression models for estimating BSA from different combinations of sex, height, and weight and iteratively included the remaining 91 measurements to determine which combinations resulted in the highest goodness-of-fit.

Results: We found that inclusion of armspan measurements as a third body dimension maximized the model goodness-of-fit.

Conclusion: Some of the existing formulae provide reasonable estimates of 3D-scanner derived BSA; while our new formulae derived from this study allows for more accurate estimates of BSA using one or more common input variables.
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http://dx.doi.org/10.1016/j.jtherbio.2020.102650DOI Listing
August 2020

A canine thermal model for simulating temperature responses of military working dogs.

J Therm Biol 2020 Jul 29;91:102651. Epub 2020 Jun 29.

Thermal and Mountain Medicine Division, U.S. Army Research Institute of Environmental Medicine, 10 General Greene Avenue, Bldg 42, Natick, MA, 01760-5007, USA. Electronic address:

Military working dogs (MWDs) are often required to operate in dangerous or extreme environments, to include hot and humid climate conditions. These scenarios can put MWD at significant risk of heat injury. To address this concern, a two-compartment (core, skin) rational thermophysiological model was developed to predict the temperature of a MWD during rest, exercise, and recovery. The Canine Thermal Model (CTM) uses inputs of MWD mass and length to determine a basal metabolic rate and body surface area. These calculations are used along with time series inputs of environmental conditions (air temperature, relative humidity, solar radiation and wind velocity) and level of metabolic intensity (MET) to predict MWD thermoregulatory responses. Default initial values of core and skin temperatures are set at neutral values representative of an average MWD; however, these can be adjusted to match known or expected individual temperatures. The rational principles of the CTM describe the heat exchange from the metabolic energy of the core compartment to the skin compartment by passive conduction as well as the application of an active control for skin blood flow and to tongue and lingual tissues. The CTM also mathematically describes heat loss directly to the environment via respiration, including panting. Thermal insulation properties of MWD fur are also used to influence heat loss from skin and gain from the environment. This paper describes the CTM in detail, outlining the equations used to calculate avenues of heat transfer (convective, conductive, radiative and evaporative), overall heat storage, and predicted responses of the MWD. Additionally, this paper outlines examples of how the CTM can be used to predict recovery from exertional heat strain, plan work/rest cycles, and estimate work duration to avoid overheating.
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http://dx.doi.org/10.1016/j.jtherbio.2020.102651DOI Listing
July 2020

Divers risk accelerated fatigue and core temperature rise during fully-immersed exercise in warmer water temperature extremes.

Temperature (Austin) 2019 13;6(2):150-157. Epub 2019 Apr 13.

Navy Experimental Diving Unit (NEDU), Panama City, Florida, USA.

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 (Tw, Tw, Tw, and Tw 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 (Tw, 174 ± 12 min; Tw, 115 ± 13 min; Tw, 50 ± 13 min; Tw, 34 ± 14 min). Peak core body temperature during work was significantly lower in Tw water (38.31 ± 0.49°C) than in warmer temperatures (Tw, 38.60 ± 0.55°C; Tw, 38.82 ± 0.76°C; Tw, 38.97 ± 0.65°C). Core body temperature rate of change increased significantly with warmer water temperature (Tw, 0.39 ± 0.28°C·h; Tw, 0.80 ± 0.19°C·h; Tw, 2.02 ± 0.31°C·h; Tw, 3.54 ± 0.41°C·h). 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.
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http://dx.doi.org/10.1080/23328940.2019.1599182DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6620004PMC
April 2019

Response.

Med Sci Sports Exerc 2019 07;51(7):1567

U.S. Army Research Institute of Environmental Medicine Natick, MA.

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http://dx.doi.org/10.1249/MSS.0000000000001918DOI Listing
July 2019

Estimating Energy Expenditure during Level, Uphill, and Downhill Walking.

Med Sci Sports Exerc 2019 09;51(9):1954-1960

United States Army Research Institute of Environmental Medicine, Natick, MA.

Introduction: The load carriage decision aid (LCDA) walking equation was developed from literature-aggregated group mean data to calculate standing and level walking energy expenditures in healthy, military-age adults. The LCDA walking equation has not been validated for use in individuals or graded walking.

Purpose: We aimed to validate the LCDA walking equation as a predictor of standing and level walking energy expenditure in individuals and expand to a new graded walking equation for uphill and downhill walking.

Methods: We compiled standing, level walking, and graded walking energy expenditures measured in 95 participants from 11 studies. Walking speeds reached up to 1.96 m·s with grades ranging between -40% and 45%. The LCDA walking equation was validated against the aggregated standing and level walking data. The new LCDA graded walking equation was developed and cross-validated on the graded walking trials. We compared each equation against four reference predictive equations with the standard error of estimation (SEE) as the primary criterion.

Results: The LCDA walking equation accurately estimated standing and level walking energy expenditure (bias, -0.02 ± 0.20 W·kg; SEE, 0.20 W·kg). Addition of the novel grade term resulted in precise estimates of uphill and downhill walking energy expenditure (bias, 0.09 ± 0.40 W·kg; SEE, 0.42 W·kg).

Conclusions: The LCDA walking equation is a valid predictor of standing and walking energy expenditure in healthy, military-age individuals. We developed a novel grade term for estimating both uphill and downhill walking energy expenditure with a single equation. Practitioners can use the new LCDA graded walking equation to calculate energy expenditure during standing as well as walking on level, uphill, and downhill slopes.
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http://dx.doi.org/10.1249/MSS.0000000000002002DOI Listing
September 2019

Heat Strain Decision Aid (HSDA) accurately predicts individual-based core body temperature rise while wearing chemical protective clothing.

Comput Biol Med 2019 04 16;107:131-136. Epub 2019 Feb 16.

Biophysics and Biomedical Modeling Division, U.S. Army Research Institute of Environmental Medicine, 10 General Greene Avenue, Bldg 42, Natick, MA 01760, USA. Electronic address:

Purpose: We examined the accuracy of the Heat Strain Decision Aid (HSDA) as a predictor of core body temperature in healthy individuals wearing chemical protective clothing during laboratory and field exercises in hot and humid conditions.

Methods: The laboratory experiment examined three chemical protective clothing ensembles in eight male volunteers (age 24 ± 6 years; height 178 ± 5 cm; body mass 76.6 ± 8.4 kg) during intermittent treadmill marching in an environmental chamber (air temperature 29.3 ± 0.1 °C; relative humidity 56 ± 1%; wind speed 0.4 ± 0.1 m s). The field experiment examined four different chemical protective clothing ensembles in twenty activity military volunteers (26 ± 5 years; 175 ± 8 cm; 80.2 ± 12.1 kg) during a prolonged road march (26.0 ± 0.5 °C; 55 ± 3%; 4.3 ± 0.7 m s). Predictive accuracy and precision were evaluated by the bias, mean absolute error (MAE), and root mean square error (RMSE). Additionally, accuracy was evaluated using a prediction bias of ±0.27 °C as an acceptable limit and by comparing predictions to observations within the standard deviation (SD) of the observed data.

Results: Core body temperature predictions were accurate for each chemical protective clothing ensemble in laboratory (Bias -0.10 ± 0.36 °C; MAE 0.28 ± 0.24 °C; RMSE 0.37 ± 0.24 °C) and field experiments (Bias 0.23 ± 0.32 °C; MAE 0.30 ± 0.25 °C; RMSE 0.40 ± 0.25 °C). From all modeled data, 72% of all predictions were within one standard deviation of the observed data including 92% of predictions for the laboratory experiment (SD ± 0.64 °C) and 67% for the field experiment (SD ± 0.38 °C). Individual-based predictions showed modest errors outside the SD range with 98% of predictions falling <1 °C; while, 81% of all errors were within 0.5 °C of observed data.

Conclusion: The HSDA acceptably predicts core body temperature when wearing chemical protective clothing during laboratory and field exercises in hot and humid conditions.
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http://dx.doi.org/10.1016/j.compbiomed.2019.02.004DOI Listing
April 2019

Metabolic Costs of Standing and Walking in Healthy Military-Age Adults: A Meta-regression.

Med Sci Sports Exerc 2019 02;51(2):346-351

U.S. Army Research Institute of Environmental Medicine (USARIEM), Natick, MA.

Introduction: The Load Carriage Decision Aid (LCDA) is a U.S. Army planning tool that predicts physiological responses of soldiers during different dismounted troop scenarios. We aimed to develop an equation that calculates standing and walking metabolic rates in healthy military-age adults for the LCDA using a meta-regression.

Methods: We searched for studies that measured the energetic cost of standing and treadmill walking in healthy men and women via indirect calorimetry. We used mixed effects meta-regression to determine an optimal equation to calculate standing and walking metabolic rates as a function of walking speed (S, m·s). The optimal equation was used to determine the economical speed at which the metabolic cost per distance walked is minimized. The estimation precision of the new LCDA walking equation was compared with that of seven reference predictive equations.

Results: The meta-regression included 48 studies. The optimal equation for calculating normal standing and walking metabolic rates (W·kg) was 1.44 + 1.94S + 0.24S. The economical speed for level walking was 1.39 m·s (~ 3.1 mph). The LCDA walking equation was more precise across all walking speeds (bias ± SD, 0.01 ± 0.33 W·kg) than the reference predictive equations.

Conclusion: Practitioners can use the new LCDA walking equation to calculate energy expenditure during standing and walking at speeds <2 m·s in healthy, military-age adults. The LCDA walking equation avoids the errors estimated by other equations at lower and higher walking speeds.
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http://dx.doi.org/10.1249/MSS.0000000000001779DOI Listing
February 2019

Terrain coefficients for predicting energy costs of walking over snow.

Appl Ergon 2019 Jan 15;74:48-54. Epub 2018 Aug 15.

Oak Ridge Institute for Science and Education (ORISE), 1299 Bethel Valley Rd, Oak Ridge, TN, 37830, USA; Biophysics and Biomedical Modeling Division, United States Army Research Institute of Environmental Medicine, Natick, MA, 01760, USA.

Background: Predicting the energy costs of human travel over snow can be of significant value to the military and other agencies planning work efforts when snow is present. The ability to quantify, and predict, those costs can help planners determine if snow will be a factor in the execution of dismounted tasks and operations. To adjust predictive models for the effect of terrain, and more specifically for surface conditions, on energy costs, terrain coefficients (ƞ) have been developed. The physiological demands of foot travel over snow have been studied previously, and there are well established methods of predicting metabolic costs of locomotion. By applying knowledge gained from prior studies of the effects of terrain and snow, and by leveraging those existing dismounted locomotion models, this paper seeks to outline the steps in developing an improved terrain coefficient (ƞ) for snow to be used in predictive modeling.

Methods: Using published data, methods, and a well-informed understanding of the physical elements of terrain, e.g., characterization of snow sinkage (z), this study made adjustments to ƞ-values specific to snow.

Results: This review of published metabolic cost methods suggest that an improved ƞ-value could be developed for use with the Pandolf equation, where z = depth (h)*(1 - (snow density (ρ)/1.186)) and ƞ = 0.0005z + 0.0001z + 0.1072z + 1.2604.

Conclusion: While the complexity of variables related to characteristics of snow, speed of movement, and individuals confound efforts to develop a simple, predictive model, this paper provides data-driven improvements to models that are used to predict the energy costs of dismounted movements over snow.
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http://dx.doi.org/10.1016/j.apergo.2018.08.017DOI Listing
January 2019

Cardiorespiratory responses to heavy military load carriage over complex terrain.

Appl Ergon 2018 Nov 24;73:194-198. Epub 2018 Jul 24.

US Army Research Institute of Environmental Medicine (USARIEM), 10 General Green Ave, Natick, MA, 01760, USA.

This study examined complex terrain march performance and cardiorespiratory responses when carrying different Soldier loads. Nine active duty military personnel (age, 21 ± 3 yr; height, 1.72 ± 0.07 m; body mass (BM), 83.4 ± 12.9 kg) attended two test visits during which they completed consecutive laps around a 2.5-km mixed terrain course with either a fighting load (30% BM) or an approach load (45% BM). Respiratory rate and heart rate data were collected using physiological status monitors. Training impulse (TRIMP) scores were calculated using Banister's formula to provide an integrated measure of both time and cardiorespiratory demands. Completion times were not significantly different between the fighting and approach loads for either Lap 1 (p = 0.38) or Lap 2 (p = 0.09). Respiration rate was not significantly higher with the approach load than the fighting load during Lap 1 (p = 0.17) but was significantly higher for Lap 2 (p = 0.04). However, heart rate was significantly higher with the approach load versus the fighting load during both Lap 1 (p = 0.03) and Lap 2 (p = 0.04). Furthermore, TRIMP was significantly greater with the approach load versus the fighting load during both Lap 1 (p = 0.02) and Lap 2 (p = 0.02). Trained military personnel can maintain similar pacing while carrying either fighting or approach loads during short mixed terrain marches. However, cardiorespiratory demands are greatly elevated with the approach load and will likely continue to rise during longer distance marches.
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http://dx.doi.org/10.1016/j.apergo.2018.07.010DOI Listing
November 2018

Complex Terrain Load Carriage Energy Expenditure Estimation Using Global Positioning System Devices.

Med Sci Sports Exerc 2018 Oct;50(10):2145-2149

United States Army Research Institute of Environmental Medicine, Natick, MA.

Introduction: Military load carriage can cause extreme energy expenditure (EE) that is difficult to estimate due to complex terrain grades and surfaces. Global Positioning System (GPS) devices capture rapid changes in walking speed and terrain but the delayed respiratory response to movement is problematic. We investigated the accuracy using GPS data in three different equations to estimate EE during complex terrain load carriage.

Methods: Twelve active duty military personnel (age, 20 ± 3 yr; height, 174 ± 8 cm; body mass, 85 ± 13 kg) hiked a complex terrain trail on multiple visits under different external load conditions. Energy expenditure was estimated by inputting GPS data into three different equations: the Pandolf-Santee equation, a recent GPS-based equation from de Müllenheim et al.; and the Minimum Mechanics model. Minute-by-minute EE estimates were exponentially smoothed using smoothing factors between 0.05 and 0.95 and compared with mobile metabolic sensor EE measurements.

Results: The Pandolf-Santee equation had no significant estimation bias (-2 ± 12 W; P = 0.89). Significant biases were detected for the de Müllenheim equation (38 ± 13 W; P = 0.004) and the Minimum Mechanics model (-101 ± 7 W; P < 0.001).

Conclusions: Energy expenditure can be accurately estimated from GPS data using the Pandolf-Santee equation. Applying a basic exponential smoothing factor of 0.5 to GPS data enables more precise tracking of EE during non-steady-state exercise.
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http://dx.doi.org/10.1249/MSS.0000000000001669DOI Listing
October 2018

Metabolic Costs of Military Load Carriage over Complex Terrain.

Mil Med 2018 09;183(9-10):e357-e362

United States Army Research Institute of Environmental Medicine (USARIEM), 10 General Greene Avenue, Natick, MA.

Introduction: Dismounted military operations often involve prolonged load carriage over complex terrain, which can result in excessive metabolic costs that can directly impair soldiers' performance. Although estimating these demands is a critical interest for mission planning purposes, it is unclear whether existing estimation equations developed from controlled laboratory- and field-based studies accurately account for energy costs of traveling over complex terrain. This study investigated the accuracy of the following equations for military populations when applied to data collected over complex terrain with two different levels of load carriage: American College of Sports Medicine (2002), Givoni and Goldman (1971), Jobe and White (2009), Minetti et al (2002), Pandolf et al (1977), and Santee et al (2003).

Materials And Methods: Nine active duty military personnel (age 21 ± 3 yr; height 1.72 ± 0.07 m; body mass 83.4 ± 12.9 kg; VO2 max 47.8 ± 3.9 mL/kg/min) were monitored during load carriage (with loads equal to 30% and 45% of body mass) over a 10-km mixed terrain course on two separate test days. The course was divided into four 2.5-km laps of 40 segments based on distance, grade, and/or surface factors. Timing gates and radio-frequency identification cards (SportIdent; Scarborough Orienteering, Huntington Beach, CA) were used to record completion times for each course segment. Breath-by-breath measures of energy expenditure were collected using portable oxygen exchange devices (COSMED Sri., Rome, Italy) and compared model estimates.

Results: The Santee et al equation performed best, demonstrating the smallest estimation bias (-13 ± 87 W) and lowest root mean square error (99 W).

Conclusion: Current predictive equations underestimate the metabolic cost of load carriage by military personnel over complex terrain. Applying the Santee et al correction factor to the Pandolf et al equation may be the most suitable approach for estimating metabolic demands in these circumstances. However, this work also outlines the need for improvements to these methods, new method development and validation, or the use of a multi-model approach to account for mixed terrain.
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http://dx.doi.org/10.1093/milmed/usx099DOI Listing
September 2018

Estimation of core body temperature from skin temperature, heat flux, and heart rate using a Kalman filter.

Comput Biol Med 2018 08 18;99:1-6. Epub 2018 May 18.

Biophysics and Biomedical Modeling Division, U.S. Army Research Institute of Environmental Medicine, 10 General Greene Avenue, Natick, MA, 01760-5007, USA. Electronic address:

Core body temperature (T) is a key physiological metric of thermal heat-strain yet it remains difficult to measure non-invasively in the field. This work used combinations of observations of skin temperature (T), heat flux (HF), and heart rate (HR) to accurately estimate T using a Kalman Filter (KF). Data were collected from eight volunteers (age 22 ± 4 yr, height 1.75 ± 0.10 m, body mass 76.4 ± 10.7 kg, and body fat 23.4 ± 5.8%, mean ± standard deviation) while walking at two different metabolic rates (∼350 and ∼550 W) under three conditions (warm: 25 °C, 50% relative humidity (RH); hot-humid: 35 °C, 70% RH; and hot-dry: 40 °C, 20% RH). Skin temperature and HF data were collected from six locations: pectoralis, inner thigh, scapula, sternum, rib cage, and forehead. Kalman filter variables were learned via linear regression and covariance calculations between T and T, HF, and HR. Root mean square error (RMSE) and bias were calculated to identify the best performing models. The pectoralis (RMSE 0.18 ± 0.04 °C; bias -0.01 ± 0.09 °C), rib (RMSE 0.18 ± 0.09 °C; bias -0.03 ± 0.09 °C), and sternum (RMSE 0.20 ± 0.10 °C; bias -0.04 ± 0.13 °C) were found to have the lowest error values when using T, HF, and HR but, using only two of these measures provided similar accuracy.
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http://dx.doi.org/10.1016/j.compbiomed.2018.05.021DOI Listing
August 2018

Talk to the Hand: U.S. Army Biophysical Testing.

Mil Med 2017 07;182(7):e1702-e1705

Biophysics and Biomedical Modeling Division, U.S. Army Research Institute of Environmental Medicine, 10 General Greene Avenue, Building 42, Natick, MA 01760-5007.

Background: Many people are unaware of the science underlying the biophysical properties of Soldier clothing and personal protective equipment, yet there is a well-refined biomedical methodology initiated by Army physiologists in World War II. This involves a methodical progression of systematic material testing technologies, computer modeling, and human testing that enables more efficient development and rapid evaluation of new concepts for Soldier health and performance. Sophisticated manikins that sweat and move are a central part of this testing continuum. This report briefly summarizes the evolution and use of one specialized form of the manikin technologies, the thermal hand model, and its use in research on Soldier hand-wear items that sustain dexterity and protect the hand in extreme environments.

Methods: Thermal manikin testing methodologies were developed to provide an efficient and consistent analytical tool for the rapid evaluation of new clothing concepts. These methods have been upgraded since the original World War II and Korean War eras to include articulation and sweating capabilities, as characterized and illustrated in this article. The earlier "retired" versions of thermal hand models have now been transferred to the National Museum of Health and Science.

Findings: The biophysical values from manikin testing are critical inputs to the U.S. Army Research Institute of Environmental Medicine mathematical models that provide predictions of soldier comfort, duration of exposure before loss of manual dexterity, and time to significant risk of freezing (skin temperature <-1°C) and nonfreezing cold injuries (skin temperature <5°C). The greater thickness of better insulated handwear reduces dexterity and also increases surface area which makes added insulation increasingly less effective in retaining heat. Measurements of both thermal resistance (insulation) and evaporative resistance (permeability) collectively characterize the biophysical properties and enable mathematical modeling of the human thermophysiological responses. This information can help guide the hand-wear development and selection process which often requires trade-offs between factors such as material, cost, and sizing.

Impact: Soldier hands provide fine motor dexterity in tactical functions, ranging from pulling a trigger to pulling a parachute ripcord; thus, protecting hand function is critical to soldier readiness. Also, the importance of protection against nonbattle cold injuries was highlighted during World War II in northern Europe, in the Aleutian Islands, and later in Korea. The U.S. Army has been on the forefront of the biophysical analysis of clothing including gloves since environmental research was established at the Armored Medical Research Laboratory and Climatic Research Laboratory during World War II. U.S. Army Research Institute of Environmental Medicine does not make the equipment but works with their Natick Soldier Research, Development, and Engineering Center partners to make the equipment better.
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http://dx.doi.org/10.7205/MILMED-D-16-00156DOI Listing
July 2017

Mathematical prediction of core body temperature from environment, activity, and clothing: The heat strain decision aid (HSDA).

J Therm Biol 2017 Feb 16;64:78-85. Epub 2017 Jan 16.

Biophysics and Biomedical Modeling Division, US Army Research Institute of Environmental Medicine, 10 General Greene Avenue, Bldg 42, Natick, MA 01760-5007, USA. Electronic address:

Physiological models provide useful summaries of complex interrelated regulatory functions. These can often be reduced to simple input requirements and simple predictions for pragmatic applications. This paper demonstrates this modeling efficiency by tracing the development of one such simple model, the Heat Strain Decision Aid (HSDA), originally developed to address Army needs. The HSDA, which derives from the Givoni-Goldman equilibrium body core temperature prediction model, uses 16 inputs from four elements: individual characteristics, physical activity, clothing biophysics, and environmental conditions. These inputs are used to mathematically predict core temperature (T) rise over time and can estimate water turnover from sweat loss. Based on a history of military applications such as derivation of training and mission planning tools, we conclude that the HSDA model is a robust integration of physiological rules that can guide a variety of useful predictions. The HSDA model is limited to generalized predictions of thermal strain and does not provide individualized predictions that could be obtained from physiological sensor data-driven predictive models. This fully transparent physiological model should be improved and extended with new findings and new challenging scenarios.
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http://dx.doi.org/10.1016/j.jtherbio.2017.01.003DOI Listing
February 2017

Measured body composition and geometrical data of four "virtual family" members for thermoregulatory modeling.

Int J Biometeorol 2017 Mar 19;61(3):477-486. Epub 2016 Aug 19.

US Army Research Institute of Environmental Medicine, Biophysics and Biomedical Modeling Division, 10 General Greene Avenue, Natick, MA, 01760, USA.

The purpose of this paper is to develop a database of tissue composition, distribution, volume, surface area, and skin thickness from anatomically correct human models, the virtual family. These models were based on high-resolution magnetic resonance imaging (MRI) of human volunteers, including two adults (male and female) and two children (boy and girl). In the segmented image dataset, each voxel is associated with a label which refers to a tissue type that occupies up that specific cubic millimeter of the body. The tissue volume was calculated from the number of the voxels with the same label. Volumes of 24 organs in body and volumes of 7 tissues in 10 specific body regions were calculated. Surface area was calculated from the collection of voxels that are touching the exterior air. Skin thicknesses were estimated from its volume and surface area. The differences between the calculated and original masses were about 3 % or less for tissues or organs that are important to thermoregulatory modeling, e.g., muscle, skin, and fat. This accurate database of body tissue distributions and geometry is essential for the development of human thermoregulatory models. Data derived from medical imaging provide new effective tools to enhance thermal physiology research and gain deeper insight into the mechanisms of how the human body maintains heat balance.
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http://dx.doi.org/10.1007/s00484-016-1227-7DOI Listing
March 2017

Ebola Response: Modeling the Risk of Heat Stress from Personal Protective Clothing.

PLoS One 2015 17;10(11):e0143461. Epub 2015 Nov 17.

Biophysics and Biomedical Modeling Division, United States Army Research Institute of Environmental Medicine, Natick, Massachusetts, 01760, United States of America.

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.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0143461PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4648492PMC
June 2016

Biophysical Assessment and Predicted Thermophysiologic Effects of Body Armor.

PLoS One 2015 22;10(7):e0132698. Epub 2015 Jul 22.

Biophysics and Biomedical Modeling Division, United States Army Research Institute of Environmental Medicine, Natick, Massachusetts, United States of America.

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.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0132698PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4511810PMC
April 2016

Fabric thermal resistance and ensemble thermal resistances are two different concepts.

J Occup Environ Hyg 2014 ;11(11):D187-8

a Biophysics and Biomedical Modeling Division , U.S. Army Research Institute of Environmental Medicine , Natick , Massachusetts.

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http://dx.doi.org/10.1080/15459624.2014.946517DOI Listing
June 2015

Primitive reflexes associated with delirium: a prospective trial.

Psychosomatics 2011 Nov-Dec;52(6):507-12

Department of Psychiatry and Behavioral Sciences, Montefiore Medical Center, Albert Einstein College of Medicine, Bronx, NY 10467, USA.

Background: The presence of primitive reflexes (PRs) may have diagnostic or prognostic value in the evaluation of cognitive impairment.

Objective: We hypothesized that the presence of preoperative PRs would predict the development of postoperative delirium and that the emergence of PRs postoperatively would be positively associated with the emergence of delirium.

Methods: Patients participating in a larger study on the prophylaxis of postoperative delirium were evaluated for the presence of six PRs (grasp reflex [left and right], palmomental reflex [left and right], glabellar tap, and snout reflex), preoperatively and postoperatively. The presence of PRs was then correlated with the development of delirium.

Results: Of the 79 patients studied, 29% (n = 23) developed delirium during the postoperative period. The preoperative presence of one PR did not predict the development of delirium, but the only patient with >1 PR preoperatively went on to develop delirium in the postoperative period. Similarly, having one frontal release sign in the postoperative period did not correlate with delirium, while the appearance of more than one PR was associated with a greater likelihood of delirium. Of the 11 patients who had two or more frontal release signs during one postoperative examination, six (55%) developed delirium. Of the five patients who showed three or more frontal release signs, 4 (80%) developed delirium.

Conclusion: Our study is the first to investigate the relationship between the appearance of PRs and the development of delirium. We have provided some evidence that PRs are associated with acute CNS dysfunction.
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http://dx.doi.org/10.1016/j.psym.2011.06.008DOI Listing
February 2012

Administration of olanzapine to prevent postoperative delirium in elderly joint-replacement patients: a randomized, controlled trial.

Psychosomatics 2010 Sep-Oct;51(5):409-18

Beth Israel Deaconess Medical Center, New England Baptist Hospital, Boston, MA, USA.

Background: Delirium is a serious postoperative condition for which few pharmacologic prevention trials have been conducted.

Objective: The authors tested the efficacy of perioperative olanzapine administration to prevent postoperative delirium in elderly patients after joint-replacement surgery.

Method: The authors conducted a randomized, double-blind, placebo-controlled, prophylaxis trial at an orthopedic teaching hospital, enrolling 495 elderly patients age ≥65 years, who were undergoing elective knee- or hip-replacement surgery; 400 patients received either 5 mg of orally-disintegrating olanzapine or placebo just before and after surgery. The primary efficacy outcome was the incidence of (DSM-III-R) delirium.

Results: The incidence of delirium was significantly lower in the olanzapine group than in the placebo group; this held true for both knee- and hip-replacement surgery. However, delirium lasted longer and was more severe in the olanzapine group. Advanced age, a high level of medical comorbidity, an abnormal albumin level, and having knee-replacement surgery were independent risk factors for postoperative delirium (Clinicaltrials.gov Identifier: NCT000699946).

Conclusion: Administration of 10 mg of oral olanzapine perioperatively, versus placebo, was associated with a significantly lower incidence of delirium. These findings suggest that olanzapine prophylaxis of postoperative delirium may be an effective strategy.
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http://dx.doi.org/10.1176/appi.psy.51.5.409DOI Listing
January 2011