Search

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 "non-combat 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.

Introduction The incidence of and risk factors for exertional heat illness (EHI) and cold weather injury (CWI) in the U.S. Army have been well documented. The “heat season”, when the risk of EHI is highest and application of risk mitigation procedures is mandatory, has been arbitrarily defined as May 1 through September 30, while the “cold season” is understood to occur from October 1 to April 30 each year. The proportions of EHI and CWI that occur outside of the traditional heat and cold seasons are unknown. Additionally, it is unknown if either of the seasonal definitions are appropriate. The primary purpose of this study was to determine the proportion of EHI and of CWI that occur within the commonly accepted seasonal definitions. We also report the location-specific variability, seasonal definitions, and the demographic characteristics of the populations. Methods The U.S. Army installations with the highest frequency of EHI and of CWI from 2008 to 2013 were identified and used for analysis. In total there were 15 installations included in the study, with five installations used for analysis in both the EHI and CWI projects. In- and out-patient EHI and CWI data (ICD-9-CM codes 992.0 to 992.9 and ICD codes 991.0 to 991.9, respectively) were obtained from the Defense Medical Surveillance System. Installation-specific denominator data were obtained from the Defense Manpower Data Center, and incidence rates were calculated by week, for each installation. Segmental (piecewise) regression analysis was used to determine the start and end of the heat and cold seasons. Results Our analysis indicates that the heat season starts around April 22 and ends around September 9. The cold season starts on October 3 and ends on March 24. The majority (n = 6,445, 82.3%) of EHIs were diagnosed during the “heat season” of May 1 to September 30, while 10.3% occurred before the heat season started (January1 to April 30) and 7.3% occurred after the heat season ended (October 1 to December 31). Similar to EHI, 90.5% of all CWIs occurred within the traditionally defined cold season, while 5.7% occurred before and 3.8% occurred after the cold season. The locations with the greatest EHI frequency were Ft Bragg (n = 2,129), Ft Benning (n = 1,560), and Ft Jackson (n = 1,538). The bases with the largest proportion of CWI in this sample were Ft Bragg (17.8%), Ft Wainwright (17.2%), and Ft Jackson (12.7%). There were considerable inter-installation differences for the start and end dates of the respective seasons. Conclusions The present study indicates that the traditional heat season definition should be revised to begin ∼3 weeks earlier than the current date of May 1; our data indicate that the current cold season definition is appropriate. Inter-installation variability in the start of the cold season was much larger than that for the heat season. Exertional heat illnesses are a year-round problem, with ∼17% of all cases occurring during non-summer months, when environmental heat strain and vigilance are lower. This suggests that EHI mitigation policies and procedures require greater year-round emphasis, particularly at certain locations.

The purpose of this consensus document was to develop feasible, evidence‐based occupational heat safety recommendations to protect the US workers that experience heat stress. Heat safety recommendations were created to protect worker health and to avoid productivity losses associated with occupational heat stress. Recommendations were tailored to be utilized by safety managers, industrial hygienists, and the employers who bear responsibility for implementing heat safety plans. An interdisciplinary roundtable comprised of 51 experts was assembled to create a narrative review summarizing current data and gaps in knowledge within eight heat safety topics: (a) heat hygiene, (b) hydration, (c) heat acclimatization, (d) environmental monitoring, (e) physiological monitoring, (f) body cooling, (g) textiles and personal protective gear, and (h) emergency action plan implementation. The consensus‐based recommendations for each topic were created using the Delphi method and evaluated based on scientific evidence, feasibility, and clarity. The current document presents 40 occupational heat safety recommendations across all eight topics. Establishing these recommendations will help organizations and employers create effective heat safety plans for their workplaces, address factors that limit the implementation of heat safety best‐practices and protect worker health and productivity., Key Points This document presents feasible, evidenced‐based occupational heat safety recommendations to protect workers from the dangers of heatA roundtable of 51 experts created 40 heat safety recommendations within eight heat safety topics: heat hygiene, hydration, heat acclimatization, environmental monitoring, physiological monitoring, body cooling, textiles and personal protective gear, and emergency action plan implementationImplementing feasible and effective heat safety plans in the workplace will protect worker health and mitigate productivity losses

Introduction Pregnancy profoundly affects cardiovascular and musculoskeletal performance requiring up to 12 months for recovery in healthy individuals. Objective To assess the effects of extending postpartum convalescence from 6 to 12 weeks on the physical fitness of Active Duty (AD) soldiers as measured by the Army Physical Fitness Test (APFT) and Body Mass Index (BMI). Methods We conducted a retrospective study of AD soldiers who delivered their singleton pregnancy of ≥ 32weeks gestation at a tertiary medical center. Pre- and post-pregnancy APFT results as well as demographic, pregnancy, and postpartum data were collected. Changes in APFT raw scores, body composition measures, and failure rates across the 6-week and 12-week convalescent cohorts were assessed. Multivariable regressions were utilized to associate risk factors with failure. Results Four hundred sixty women met inclusion criteria; N = 358 in the 6 week cohort and N = 102 in the 12 week cohort. Demographic variables were similar between the cohorts. APFT failure rates across pregnancy increased more than 3-fold in both groups, but no significant differences were found between groups in the decrement of performance or weight gain. With the combined cohort, multivariable regression analysis showed failure on the postpartum APFT to be independently associated with failure on the pre-pregnancy APFT (OR = 16.92, 95% CI 4.96–57.77), failure on pre-pregnancy BMI (OR = 8.44, 95% CI 2.23–31.92), elevated BMI at 6–8 weeks postpartum (OR = 4.02, 95% CI 1.42–11.35) and not breastfeeding at 2 months (OR = 3.23, 95% CI 1.48–7.02). Within 36 months of delivery date, 75% of women had achieved pre-pregnancy levels of fitness. Conclusion An additional 6 weeks of convalescence did not adversely affect physical performance or BMI measures in AD Army women following pregnancy. Modifiable factors such as pre- and post-pregnancy conditioning and weight, weight gain in pregnancy and always breastfeeding were found to be significant in recovery of physical fitness postpartum.

Recent research indicates that a simplified approach to urban planning in Sub-Saharan African cities can address the challenges of rapid urban growth. Current plans focus too heavily on the existing area of the city and offer unrealistic agendas for future urban growth, such as densification, containment and high-rise development; plans that are often too complicated and too costly to be deployed in a developing-world context. In response, New York University and the Government of Ethiopia have created a programme to deploy a simple methodology called Making Room for Urban Expansion in 18 Ethiopian cities that are experiencing rapid growth. The programme is called the Ethiopia Urban Expansion Initiative. The Initiative set aside a number of standard planning objectives and instead focused only on expanding city boundaries to include adequate land for expansion, designing and protecting a network of arterial roads spaced approximately 1 km apart, and identifying and protecting environmentally sensitive open spaces. These efforts focused on areas that had not yet been occupied by development. This article reports on the preliminary results from the four Ethiopian cities participating in the Initiative that began in 2013. The results from the first four participating cities show that simple plans can lead to the creation of new arterial roads, increasing access to peripheral land and potentially bringing the available land supply in line with projected growth. These activities can be done at the local level and implemented with limited support from consultants and from the regional and national government, and it requires minimal public investment.

Objectives Army body composition standards are based upon validated criteria; however, certain field-expedient methodologies (e.g., weight-for-height, body mass index [BMI]) may disqualify individuals from service who may otherwise excel on physical performance and military-relevant tasks. The purpose was to assess soldier physical performance and military-specific task/fitness performance stratified by BMI. Design Cross-sectional observational study. Methods Male (n = 275) and female (n = 46) soldiers performed a wide-array of physical fitness tests and military-specific tasks, including the Army physical fitness test (APFT). Within-sex performance data were analyzed by BMI tertile stratification or by Army Body Composition Program (ABCP) weight-for-height (calculated BMI) screening standards using ANOVA/Tukey post-hoc or independent t-tests, respectively. Results BMI stratification (higher vs. lower BMI) was associated with significant improvements in muscular strength and power, but also with decrements in speed/agility in male and female soldiers. Within the military specific tasks, a higher BMI was associated with an increased APFT 2-Mile Run time; however, performance on a 1600-m Loaded March or a Warrior Task and Battle Drill obstacle course was not related to BMI in either sex. Male and Female soldiers who did not meet ABCP screening standards demonstrated a slower 2-Mile Run time; however, not meeting the ABCP BMI standard only affected a minimal number (∼6%) of soldiers’ ability to pass the APFT. Conclusions Military body composition standards require a careful balance between physical performance, health, and military readiness. Allowances should be considered where tradeoffs exist between body composition classifications and performance on physical tasks with high military relevance.

The severity of exertional heat illnesses (EHI) ranges from relatively minor heat exhaustion to potentially life-threatening heat stroke. Epidemiological surveillance of the types of and trends in EHI incidence depends on application of the appropriate International Classification of Disease, 9th Revision (ICD-9) diagnostic code. However, data examining whether the appropriate EHI ICD-9 code is selected are lacking. The purpose of this study was to determine whether the appropriate ICD-9 code is selected in a cohort of EHI casualties.Chart reviews of 290 EHI casualties that occurred in U.S. Army soldiers from 2009 to 2012 were conducted. The ICD-9 diagnostic code was extracted, as were the initial and peak values for aspartate transaminase, alanine transaminase, creatine kinase, and creatinine. Diagnostic criteria for heat injury and heat stroke include evidence of organ and/or tissue damage; 2 out of 3 of the following must have been met to be considered heat injury (ICD-9 code 992.8) or heat stroke (ICD-9 code 992.0): aspartate transaminase/ alanine transaminase fold increase3, creatine kinase fold increase5, and/or creatinine ≥1.5mg/dL. Contingency tables were constructed from which sensitivity, specificity, and positive and negative predictive value were calculated.The 290 cases in this cohort represent ∼29% of all EHI at Fort Benning and ∼6% of all EHI Army-wide during the study period. There were 80 cases that met the laboratory diagnostic criteria for heat injury/stroke, however of those, 28 cases were diagnosed as an EHI other than heat injury/stroke (sensitivity = 0.65). 210 cases did not meet the laboratory diagnostic criteria, but 66 of those were incorrectly diagnosed as heat injury or heat stroke (specificity = 0.69). Positive and negative predictive values were 0.44 and 0.84, respectively. In total, the incorrect ICD-9 code was applied to 94 of 290 total cases.Our data suggest that caution is warranted when examining epidemiological surveillance data on EHI severity, as there was disagreement between the laboratory data and the selected ICD-9 code in ∼1/3 of all cases in this cohort. Of note is the lack of an ICD-9 or -10 code for heat injury; we recommend coding for heat exhaustion as the primary diagnosis and additional codes to capture the accompanying muscle, tissue, and/or organ damage.

Many epidemiological studies rely on valid physical fitness data. The purpose of this investigation was to assess the validity of self-reported Army Physical Fitness Test (APFT) data and determine whether men and women recall APFT performance differently. U.S. Army soldiers (N = 1,047) completed a survey, including questions on height, weight, and most recent APFT performance. Height, weight, and APFT performance were also obtained from unit records. The mean ± SDs for unit and self-reported push-up repetitions were 63.5 ± 13.1 and 66.3 ± 14.0 for men and 37.7 ± 12.8 and 40.2 ± 12.8 for women, respectively. The mean ± SD for unit- and self-reported sit-up repetitions were 66.3 ± 11.4 and 68.1 ± 12.1 for men and 64.2 ± 13.6 and 66.5 ± 12.9 for women, respectively. The mean ± SD unit- and self-reported 2-mile run times were 15.2 ± 1.8 and 14.9 ± 1.6 minutes for men, and 18.0 ± 2.9 and 17.4 ± 1.9 minutes for women, respectively. Unit- and self-reported body mass indices (BMIs) (calculated by height and weight) were 26.4 ± 3.4 and 26.3 ± 3.6 for men and 24.6 ± 2.8 and 24.2 ± 3.3 for women. Correlations between unit- and self-reported scores for push-ups, sit-ups, 2-mile run, height, weight, and BMI were 0.82, 0.78, 0.85, 0.87, 0.97, and 0.88 for men and 0.86, 0.84, 0.87, 0.78, 0.98, and 0.78 for women, respectively. On average, men and women slightly overreported performance on the APFT and overestimated height, resulting in underestimated BMI. There was no difference in recall ability between men and women (p > 0.05). The very good to excellent correlations (r = 0.78-0.98) between unit- and self-reported scores indicate that self-reported data are valid for capturing physical fitness performance in this population.

This article reviews current prehospital treatment for heat casualties and introduces a retrospective study on the addition of cold (4 °C) intravenous (IV) saline to prehospital treatment and its effect on morbidity. The study is a retrospective cohort reviewing electronic medical records of 290 heat casualties admitted to Martin Army Community Hospital, Ft. Benning, GA, comparing two treatment groups; U.S. Army Training and Doctrine Command (ice-sheeting and ambient temperature IV saline) versus Benning (ice-sheeting and cold IV saline). U.S. Army Training and Doctrine Command group significantly differed from Benning group on a number of measures, the median length of stay in the hospital was 3 and 2 d, respectively (P < 0.0001); pCr were 1.8 to 1.4 mg·dL, respectively (difference of 0.4 mg·dL pCr, P < 0.0001). However, creatine phosphokinase, aspartate aminotransferase, and alanine aminotransferase were not significantly different across groups. Findings demonstrate that adding cold IV saline to ice-sheeting as a protocol reduces the length of hospitalization of heat casualties and lowers their peak creatinine values.

Physical work, high ambient temperature and wearing protective clothing can elevate body temperature and cardiovascular strain sufficiently to degrade performance and induce heat-related illnesses. We have recently developed an Arm Immersion Cooling System (AICS) for use in military training environments and this paper will review literature supporting such an approach and provide details regarding its construction. Extremity cooling in cool or cold water can accelerate body (core temperature) cooling from 0.2 to 1.0 °C/10 min vs. control conditions, depending on the size/surface area of the extremity immersed. Arm immersion up to the elbow results in greater heat loss than hand- or foot-only immersion and may reduce cardiovascular strain by lowering heart rate by 10–25 beats/min and increase work tolerance time by up to 60%. The findings from studies in this paper support the use of AICS prototypes, which have been incorporated as part of the heat stress mitigation procedures employed in US Army Ranger Training and may have great application for sports and occupational use.

Physically demanding occupations (ie, military, firefighter, law enforcement) often use fitness tests for job selection or retention. Despite numerous individual studies, the relationship of these tests to job performance is not always clear. : This review examined the relationship by aggregating previously reported correlations between different fitness tests and common occupational tasks. : Search criteria were applied to PUBMED, EBSCO, EMBASE and military sources; scoring yielded 27 original studies providing 533 Pearson correlation coefficients (r) between fitness tests and 12 common physical job task categories. Fitness tests were grouped into predominant health-related fitness components and body regions: cardiorespiratory endurance (CRe); upper body, lower body and trunk muscular strength and muscular endurance (UBs, LBs, TRs, UBe, LBe, TRe) and flexibility (FLX). Meta-analyses provided pooled r's between each fitness component and task category. : The CRe tests had the strongest pooled correlations with most tasks (eight pooled r values 0.80-0.52). Next were LBs (six pooled r values >0.50) and UBe (four pooled r values >0.50). UBs and LBe correlated strongly to three tasks. TRs, TRe and FLX did not strongly correlate to tasks. : Employers can maximise the relevancy of assessing workforce health by using fitness tests with strong correlations between fitness components and job performance, especially those that are also indicators for injury risk. Potentially useful field-expedient tests include timed-runs (CRe), jump tests (LBs) and push-ups (UBe). Impacts of gender and physiological characteristics (eg, lean body mass) should be considered in future study and when implementing tests.

Total force fitness is an emerging concept defined as a state in which the individual, family, and organization can sustain optimal well-being and performance under all conditions. Medical and environmental fitness are two of the component domains in the total force fitness framework. These domains have purposely been combined as they are inextricably intertwined: a warfighter must be able to function, free of any anticipated medical condition that could compromise either individual or unit effectiveness, while potentially confronting multiple environmental challenges. Medical fitness, best described as a state of general mental and physical well-being, is determined by medical metrics. Environmental fitness is defined as the ability to perform mission-specific duties in any environment and withstand the multiple stressors of deployment and war. This article defines the domains of medical and environmental fitness, describes the benefits of a medically and environmentally fit force, and identifies...

Aged humans often exhibit an impaired defense of core temperature during cold stress. However, research documenting this response has typically used small subject samples and strong cold stimuli. The purpose of this study was to determine the responses of young and older subjects, matched for anthropometric characteristics, during mild cold stress. Thirty-six young (YS; 23 ± 1 years, range 18–30) and 46 older (OS; 71 ± 1 years, range 65–89) subjects underwent a slow transient cold air exposure from a thermoneutral baseline, during which esophageal (Tes) and mean skin temperatures (Tsk), O2 consumption, and skin blood flow (SkBF; laser-Doppler flowmetry) were measured. Cold exposure was terminated at the onset of visible sustained shivering. Net metabolic heat production (Mnet), heat debt, predicted change in midregion temperature (ΔTmid), and tissue insulation (It) were calculated. Cutaneous vascular conductance (CVC) was calculated as laser-Doppler flux/mean arterial pressure and expressed as percent change from baseline (ΔCVC%base). There were no baseline group differences for Tes, but OS Mnet was lower (OS: 38.0 ± 1.1; YS: 41.9 ± 1.1 W · m−2, P < 0.05). Tes was well maintained in YS but fell progressively in OS ( P < 0.01 for all timepoints after 35 min). The skin vasoconstrictor response to mild cold stress was attenuated in OS (42 ± 3 vs. 53 ± 4 ΔCVC%base, P < 0.01). There were no group differences for Tsk or It, while Mnet remained lower in OS ( P < 0.05). The ΔTmid did not account for the drop in Tes in OS. Healthy aged humans failed to maintain Tes; however, the mechanisms underlying this response are not clear.

Ranger training includes strenuous physical activities and despite heat mitigations strategies, numerous cases of serious exertional heat illness (EHI) occur. We developed an Arm Immersion Cooling (AIC) system that is not logistically burdensome and may be easily employed in training environments.To examine the effect of AIC on EHI incidence, severity, and treatment costs during Ranger School.The training program was standardized for physical exertion and heat stress factors throughout the study period. AIC was employed summer months of 2010-2012 (n = 3,930 Soldiers) and Control (CON; n = 6,650 Soldiers) data were obtained for summer months of 2007-2009. Descriptive characteristics of all EHI casualties were obtained, including hospitalization status (treated and released [Treat], evacuated [Evac] or admitted [Admit] to the hospital), which served as proxy indicator of illness/injury severity. Medical cost savings were calculated from hospital records.Incidence rates were not different (CON 4.06 vs. AIC 4.00/1,000 person-days). Treat increased during AIC (18.43 vs. 4.84/1,000 person-days) accompanied by marked but non-significant decreases in Evac and Admit rates. AIC use was associated with a medical cost savings of $1,719 per casualty.AIC implementation during strenuous physical training in summer months can reduce EHI severity and associated medical treatment costs.

The incidence of and risk factors for exertional heat illness (EHI) in the US Army have been well documented. The heat season, when the risk of EHI is highest and application of risk mitigation procedures is mandatory, has been arbitrarily defined as 1 May through 30 September. The proportion of EHI that occur outside of the traditional heat season is unknown. Additionally, it is unknown if the heat season definition is appropriate. Purpose: To determine the proportion of EHI that occur within the traditional definition of the heat season at select US Army installations and to examine whether the heat season definition requires revision, Army-wide or on an installation-specific basis. Methods: The 10 US Army installations with the highest frequency of EHI from 2008-2012 were identified and used for analysis. In- and out-patient EHI data (ICD-9-CM codes 992-992.9, first or second diagnoses only) were obtained from the Defense Medical Surveillance System. The summer heat season was operationally defined as 1 May through 30 September; the proportional distribution of EHI within the heat season, overall and by installation was determined. In order to assess the relation between ambient weather conditions and EHI incidence, weather data were downloaded from the National Centers for Environmental Information website and overlaid with weekly EHI incidence plots. Piecewise segmental regression analysis was conducted in order to determine the beginning and end of the heat season for all locations combined and by individual location. Results: During the investigation period there were 7,827 EHIs, 79% of which occurred during the heat season. However, between locations there was considerable variability in within heat season EHI frequency, ranging from 70.1% at Ft Bragg to 95.3% at Ft Sill. The locations with the greatest EHI frequency were Ft Bragg (n=2,129), Ft Benning (n=1,560), and Ft Jackson (n=1,538).

Older individuals' ability to maintain core temperature during cold stress is impaired; however, the relative importance of individual characteristics that influence this response are unknown. The purpose of this study was to determine the relative influence of individual characteristics on core temperature and tissue insulation (I(t)) during mild cold stress. Forty-two young (23 +/- 1 yr, range 18-30 yr) and 46 older (71 +/- 1 yr, range 65-89 yr) subjects, varying widely in muscularity, adiposity, and body size, underwent a transient cooling protocol during which esophageal temperature (T(es)) was measured continuously and I(t) was calculated using standard equations. Multiple-regression analyses were performed to determine predictors of T(es) and I(t), and standardized regression coefficients were analyzed to determine the relative influence of each predictor. Candidate predictors included age, sex, weight, body surface area, body surface area-to-mass ratio, sum of skinfolds, percent fat, appendicular skeletal muscle mass, and thyroid hormone concentrations (triiodothyronine, thyronine). The sum of skinfolds explained 67% (P0.01) of the T(es) variance in young subjects vs. 2% (P = 0.30) in older subjects. Conversely, appendicular skeletal muscle mass explained a greater portion of the variance in older subjects for both T(es) (older: 28%, P0.01; young: 8%, not significant) and I(t) (older: 46%, P0.01; young: 17%, P0.01). The T(es) residual variance was considerably larger in older subjects (59-72% vs. 14-42% in young subjects), possibly due to varying rates of physiological aging. These results suggest that the relative influence of individual characteristics changes with aging.

1. Human life is sustainable only below an internal temperature of roughly 42–44 °C. Yet our ability to survive at severe environmental extremes is testimony to the marvels of integrative human physiology. 2. One approach to understanding human thermoregulatory capacity is to examine the upper limits of thermal balance between man and the air environment, i.e. the maximal environmental conditions under which humans can maintain a steady-state core temperature. Heat acclimation expands the zone of thermal balance. 3. Human beings can and do, often willingly, tolerate extreme heat stresses well above these thermal balance limits. Survival in all such cases is limited to abbreviated exposure times, which in turn are limited by the robustness of the thermoregulatory response. 4. Figures are provided that relate tolerance time and the rate of change in core temperature to environmental characteristics based on data compiled from the literature.

Purpose: To help evaluate the Army Physical Fitness Test (APFT) and ensure a future test is associated with Soldiers performance of common physical job requirements, the USAPHC applied a Systematic Review (SR) methodology to identify and synthesize published correlations between military task performance and physical fitness tests. Methods: A preliminary step to our SR was to identify key military-relevant tasks and physical fitness components of interest. Starting with the Army's Warrior Tasks and Battle Drills (WTBDs), twelve task categories were identified, including some tasks performed by both military and civilian occupations (e.g., firefighters, police, and athletes). Physical fitness tests were sorted into four physical fitness groups: cardiorespiratory endurance (e.g., aerobic fitness), muscle strength, muscle endurance, and flexibility. Tests of muscular strength and muscular endurance were further subcategorized into Upper and Lower Body, Core, or Whole Body regions. Physical tests included the APFT events (2-mile run, sit ups, push-ups) as well as other equipment and non-equipment physical fitness tests (e.g., jump tests, squats, sprints, pull-ups, grip tests, arm lifts, curls, and various extension machine tests). To synthesize the data, a series of meta-analyses provided pooled correlation coefficients for the twelve tasks and eleven physical fitness test groups. Results: Flexibility tests were the least frequently identified, while upper body strength tests were most frequently identified in studies that met our inclusion criteria. Correlations with aerobic tests were fairly well studied, with a few notable gaps (e.g., the Loaded March task). Pooled r coefficients for specific physical tests (e.g., run tests, push-ups, sit-ups, grip tests, and vertical and broad jump tests) were also calculated. Of the physical fitness component groups evaluated, aerobic capacity is most strongly correlated across the greatest number of military tasks.

This study examined the hypothesis that several days of exhaustive exercise would impair thermoregulatory effector responses to cold exposure, leading to an accentuated core temperature reduction compared with exposure of the same individual to cold in a rested condition. Thirteen men (10 experimental and 3 control) performed a cold-wet walk (CW) for up to 6 h (6 rest-work cycles, each 1 h in duration) in 5°C air on three occasions. One cycle of CW consisted of 10 min of standing in the rain (5.4 cm/h) followed by 45 min of walking (1.34 m/s, 5.4 m/s wind). Clothing was water saturated at the start of each walking period (0.75 clo vs. 1.1 clo when dry). The initial CW trial ( day 0) was performed (afternoon) with subjects rested before initiation of exercise-cold exposure. During the next 7 days, exhaustive exercise (aerobic, anaerobic, resistive) was performed for 4 h each morning. Two subsequent CW trials were performed on the afternoon of days 3 and 7, ∼2.5 h after cessation of fatiguing exercise. For controls, no exhaustive exercise was performed on any day. Thermoregulatory responses and body temperature during CW were not different on days 0, 3, and 7 in the controls. In the experimental group, mean skin temperature was higher ( P< 0.05) during CW on days 3 and 7 than on day 0. Rectal temperature was lower ( P < 0.05) and the change in rectal temperature was greater ( P < 0.05) during the 6th h of CW on day 3. Metabolic heat production during CW was similar among trials. Warmer skin temperatures during CW after days 3 and 7indicate that vasoconstrictor responses to cold, but not shivering responses, are impaired after multiple days of severe physical exertion. These findings suggest that susceptibility to hypothermia is increased by exertional fatigue.

Participants in prolonged, physically demanding cold-weather activities are at risk for a condition called "thermoregulatory fatigue". During cold exposure, the increased gradient favoring body heat loss to the environment is opposed by physiological responses and clothing and behavioral strategies that conserve body heat stores to defend body temperature. The primary human physiological responses elicited by cold exposure are shivering and peripheral vasoconstriction. Shivering increases thermogenesis and replaces body heat losses, while peripheral vasoconstriction improves thermal insulation of the body and retards the rate of heat loss. A body of scientific literature supports the concept that prolonged and/or repeated cold exposure, fatigue induced by sustained physical exertion, or both together, can impair the shivering and vasoconstrictor responses to cold ("thermoregulatory fatigue"). The mechanisms accounting for this thermoregulatory impairment are not clear, but there is evidence to suggest that changes in central thermoregulatory control or peripheral sympathetic responsiveness to cold lead to thermoregulatory fatigue and increased susceptibility to hypothermia.

Evidence suggests that core temperatures of ∼40°C can induce fatigue, although this may be confounded by coincident elevations in skin temperatures and maximal cardiovascular strain. In an observational field study to examine core temperature threshold for fatigue, we investigated whether running performance is impaired when rectal temperature (Tre) is >40°C and skin temperature remains modest. Seventeen competitive runners (7/10 women/men: 8 km best 1,759 ± 78/1,531 ± 60 s) completed 8-km track time trials in cool (WBGT ∼13°C; n = 6), warm (WBGT ∼27°C; n = 4), or both ( n = 7) conditions. Tre, chest skin temperature, and heart rate were logged continuously; elapsed time was recorded every 200 m. Running velocity for Tre>40°C was compared with that for Trere>40°C and re>40.0°C with ≥600 m remaining (range 600–3,400 m). Average running velocity for Trere>40°C (279 ± 28 m/min; P = 0.82). There were no differences in running velocity during the final 600 m between runners with final Tre>40°C or 95% of age-predicted maximum. Our observation that runners were able to sustain running velocity despite Tre>40°C is evidence against 40°C representing a “critical” core temperature limit to performance.

Sweating threshold temperature and sweating sensitivity responses are measured to evaluate thermoregulatory control. However, analytic approaches vary, and no standardized methodology has been validated. This study validated a simple and standardized method, segmented linear regression (SReg), for determination of sweating threshold temperature and sensitivity. Archived data were extracted for analysis from studies in which local arm sweat rate (ṁsw; ventilated dew-point temperature sensor) and esophageal temperature (Tes) were measured under a variety of conditions. The relationship ṁsw/Tes from 16 experiments was analyzed by seven experienced raters (Rater), using a variety of empirical methods, and compared against SReg for the determination of sweating threshold temperature and sweating sensitivity values. Individual interrater differences ( n = 324 comparisons) and differences between Rater and SReg ( n = 110 comparisons) were evaluated within the context of biologically important limits of magnitude (LOM) via a modified Bland-Altman approach. The average Rater and SReg outputs for threshold temperature and sensitivity were compared ( n = 16) using inferential statistics. Rater employed a very diverse set of criteria to determine the sweating threshold temperature and sweating sensitivity for the 16 data sets, but interrater differences were within the LOM for 95% (threshold) and 73% (sensitivity) of observations, respectively. Differences between mean Rater and SReg were within the LOM 90% (threshold) and 83% (sensitivity) of the time, respectively. Rater and SReg were not different by conventional t-test ( P > 0.05). SReg provides a simple, valid, and standardized way to determine sweating threshold temperature and sweating sensitivity values for thermoregulatory studies.

Background There are limited data concerning the physiological responses to long-duration exercise collected under field conditions, and less data under harsh environmental conditions. This paper describes select environmental conditions and physiological responses of three runners attempting to run across the entire Sahara desert over a 111-d period. Methods The runners started in Saint-Louis, Senegal, and we collected data on 2 d at the start of the expedition. Core temperature was measured via telemetry pill (Tpill), heart rate via Polar monitor, and metabolic rate (M) was estimated from two equations. The Pandolf equation uses movement speed and grade while Berglund's equation predicts M from heart rate and dry-bulb temperature. Data are presented as mean +/- SD (range). Results The runners intermittently ran 8.0 km x h(-1) over 6 h during Night (warm-humid) conditions and 6.9 km x h(-1) over 7 h 40 min during Day (hot-dry) desert conditions. Mean Tpill was similar for both days (37.8 +/- 10.34 vs. 37.82 +/- 0.50 degrees C) while range was greater during the day (Day: 36.69-38.91 vs. Night: 37.11-38.48 degrees C). Heart rate was 128 +/- 16 (72-156) and 119 +/- 17 (75-147) bpm for Night and Day, respectively. Mmean was 299 +/- 66 (65-418) W x m(-2) and 364 +/- 117 (58-542) W x m(-2) during Night and 239 +/- 60 (67-356) and 244 +/- 139 (54-464) W x m(-2) during Day, estimated by Berglund and Pandolf, respectively. Conclusions During Day, the athletes ran slower than during Night, though Tpill was similar, indicative of the greater environmental strain. Mean predicted M was similar between equations, though maximum and minimal values were more extreme and rate-of-change dynamics faster according to Pandolf's equation.

The combination of cold exposure and exercise performed in this environment elicits profound physiological responses. These include increases in metabolic heat production and vasoconstriction in order to maintain body temperature, changes in fluid balance and changes in substrate mobilization in order to fuel increased metabolic activity. Many of these physiological responses are associated with endocrine secretion and concentration changes. It is acknowledged that differences in plasma levels as a result of cold exposure could be due to secretion, clearance and volume of distribution that cannot be differentiated in these studies. Most of the studies examining the role of cold exposure on hormone responses have been completed during resting exposure and these are still relatively few in number. The interaction of exercise and cold on the endocrine system is even less studied. The primary purpose of this chapter is to survey the endocrine responses to exercise-cold stress in humans. Animal studies will not be considered. Sedentary cold exposure responses are also reviewed to provide background information and for use as a point of comparison to exercise studies. Table 33.% presents the hormones that will be discussed and presents a general overview of the changes caused by resting and exercise-cold stress.

Adverse reactions during hypobaric chamber operations result from changes in barometric pressure per se and to the related reductions in the partial pressure of inspired oxygen. Previous studies have indicated that an adverse reaction may occur in approximately 6% of exposures in chambers used for flight training. The purpose of this study was to determine the rate of adverse reactions in a chamber used exclusively for terrestrial altitude research studies.Data for incidence of ear block, sinus block, toothache, and other adverse reactions were analyzed using a master history file that contained information such as annual and total number of studies and human exposures, and onset and outcome of adverse reactions. Incidence for a given time period was calculated as (# of reactions x 100)/(# of exposures).In 33 yr, there have been 23,656 human exposures and 296 adverse reactions. The overall incidence was 1.25 reactions per 100 exposures (0.72 for research volunteers and 0.53 for staff). The majority (75% of all reactions) were ear blocks (0.93 reactions per 100 exposures). Staff members were more likely than research volunteers to have more than one reaction.The incidence of 1.25 reactions per 100 exposures for our chamber is considerably lower than that reported in the literature. This is due primarily to our use of lower altitudes and slower rates of ascent and descent compared with other facilities whose emphasis is on aircraft flight training.

Cold weather injuries (CWI) are of great military concern due to their wide-ranging impact on military readiness. Previous short-term studies have identified CWI to be more prevalent in African-Americans, infantrymen, and lower-ranking soldiers. The purpose of this cross-sectional study was to determine the occurrence of CWI hospitalizations in the U.S. Army from 1980 to 1999, and to identify possible trends, high-risk groups and/or activities.The U.S. Army Research Institute of Environmental Medicine Total Army Injury and Health Outcomes Database was searched for hospitalizations with ICD-9-CM codes for frostbite, hypothermia, immersion foot, chilblains, and other. Information concerning each soldier included: gender, age, ethnicity, rank, occupation, type of injury, home of record, duty station, principle diagnosis, trauma code, and cause of injury. Data was available on the demographic composition of the Army, by year, and was used as the denominator when calculating the frequency of occurrence.During the study period there were 2143 hospitalizations due to CWI. African-American men and women were injured approximately 4 times and 2.2 times as often as their Caucasian counterparts, respectively. Trauma and cause of injury codes indicate that about 80% of all CWI hospitalizations result on-duty and during organized training. The yearly rate of CWI hospitalization has declined from 38.2/100,000 in 1985 to 0.2/100,000 in 1999.Our data are consistent with previous research concerning the increased rate of CWI among African-Americans though further investigation appears warranted. The occurrence of most CWI during on-duty training suggests preventability. The decline in the overall rate of CWI hospitalizations is multifactorial.

UNLABELLED PURPOSE; This study examined the effects of short-term (3.5 d) sustained military operations (SUSOPS) on thermoregulatory responses to cold stress. METHODS Ten men (22.8 +/- 1.4 yr) were assessed during a cold-air test (CAT) after a control week (control) and again after an 84-h SUSOPS (sleep = 2 h.d (-1), energy intake = approximately 1650 kcal.d(-1), and energy expenditure = approximately 4500 kcal.d(-1). CAT consisted of a resting subject (seminude) being exposed to an ambient temperature ramp from 25 degrees C to 10 degrees C during the initial 30 min of CAT, with the ambient temperature then remaining at 10 degrees C for an additional 150 min. RESULTS SUSOPS decreased (P< 0.05) body weight, % body fat, and fat-free mass by 3.9 kg, 1.6%, and 1.8 kg, respectively. During CAT, rectal temperature decreased to a greater extent (P< 0.05) after SUSOPS (0.52 +/- 0.09 degrees C) versus control (0.45 +/- 0.12 degrees C). Metabolic heat production was lower (P< 0.05) after SUSOPS at min 30 (55.4 +/- 3.3 W.m (-2)) versus control (66.9 +/- 4.4 W.m(-2)). Examination of the mean body temperature-metabolic heat production relationship indicated that the threshold for shivering was lower (P< 0.05) after SUSOPS (34.8 +/- 0.2 degrees C) versus control (35.8 +/- 0.2 degrees C). Mean weighted skin temperatures ( degrees C) were lower during the initial 1.5 h of CAT in SUSOPS versus control. Heat debt was similar between trials. CONCLUSION These results indicate that sustained (84-h) military operations leads to greater declines in core temperature, due to either a lag in the initial shivering response or heat redistribution secondary to an insulative acclimation.

After several days of exhaustive exercise in mild-warm environments, cutaneous vasoconstrictor responses to cold exposure are less effective in conserving body heat than in the rested condition. Hypothalamic-pituitary-adrenal and hypothalamic-pituitary-thyroid axes hormones could mediate this response since they may affect vasoconstriction. The effects of exertional fatigue on pituitary-adrenal hormones and thyroid hormone responses to exercise-cold stress are unknown.We hypothesized that 7 consecutive days of exercise would decrease adrenocorticotropin (ACTH) and cortisol, while elevating thyroid stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) and that these hormones would be related to a blunted vasoconstrictor response to cold.Nine male volunteers walked, completely wetted, for up to 6 h in 5 degrees C air, when rested (day 0, control) and after 7 consecutive days (day 7) of exhaustive exercise (4 h each day of mixed aerobic and anaerobic activities in thermoneutral conditions). Blood was sampled on day 0 and day 7 at baseline (0700 hours), and before and immediately after cold exposure.At 0700 hours, ACTH and cortisol were elevated (p0.05) after 7 d of exercise, compared with control conditions. Following exercise-cold exposure, cortisol, T3, and T4 increased (p0.05) similarly on both day 0 and day 7. ACTH and TSH did not increase as a result of exercise-cold exposure on either day.These data indicate that 7 d of exercise elevates basal (0700 hours) pituitary-adrenal stress hormones (ACTH, cortisol). However, 7 d of exercise did not modify adrenal or thyroid hormone responses, relative to the day 0 cold exposure, suggesting that they are not responsible for the blunted vasoconstriction during exercise-cold exposure following 7 consecutive days of exercise.

In order to simulate the expected environmental conditions in a submarine that has become disabled (i.e., loss of electrical power and subsequent inability to control temperature, humidity, and oxygen and carbon dioxide levels), a system was created to control the oxygen and carbon dioxide concentration of an environmental chamber. The study protocol called for a baseline testing period of ambient environmental conditions for 2 days (20 deg C, 50% RH, 20.93% O2, 0.04% CO2), followed by a 24-hour transition phase to the disabled conditions (4 deg C, 80% RH, 16.75% O2, 2.50% CO2), which where maintained for 5 days. Due to numerous design factors, the hypobaric chamber facility was chosen to conduct this study, since the facility met all of the needs of the study except for the ability to control oxygen and carbon dioxide levels, which none of the institute's chambers are normally capable of. Reduced oxygen content was achieved by displacement with nitrogen, and increased carbon dioxide content was achieved by injection of 100% carbon dioxide and metabolic carbon dioxide production. The oxygen and carbon dioxide content of the chamber was continually monitored and controlled by a custom designed software system. During the 5 day 'disabled' portion of the study, chamber conditions were as follows: temp 4.51 +/- 0.56 deg C; relative humidity 80.48 +/- 5.27% RH; oxygen 16.73 +/- 0.06% and carbon dioxide 2.49 +/- 0.04%. Variations in temperature, oxygen and carbon dioxide levels, as indicated by the standard deviation, were all within desired limits (+/- 1.0 deg C; +/- 0.10% concentration). Relative humidity was outside the desired limit of +/- 3.0% R.

Because blood lactic acid (LA) levels may be important in prescribing exercise for cardiac patients, this study documented the LA response to four different circuit weight training (CWT) protocols and compared these responses to both maximal treadmill and LA threshold values.Intervention study following a crossover trial design.A phase III community-based setting.All subjects had documented cardiac disease and were volunteers.We used 40% and 60% of the one-repetition maximum (1-RM) for six exercises and 30 or 60sec of rest between each station, resulting in four protocols, performed in random order. A discontinuous treadmill test was conducted, and the LA threshold was determined.The main dependent variable was LA after each CWT protocol.No signs or symptoms suggestive of cardiovascular distress during any of the four CWT protocols were reported. A repeated-measures analysis of variance showed that the LA threshold value was significantly less than all four CWT protocols (p.05). The CWT responses were also compared with the traditional LA threshold value of 4.0mmol/L, and both 60% protocols were significantly elevated (p.05).Because no positive signs or symptoms were reported, we recommend starting stable cardiac patients on a CWT program with an initial load between 40% and 60% 1-RM and allowing at least 60sec of rest between exercises.