Short-term cocoa bioflavanol supplementation does not improve cold-induced vasodilation in young healthy adults.

PURPOSE: Cold-induced vasodilation (CIVD) is an oscillatory rise in blood flow to glabrous skin that occurs in cold-exposed extremities. Dietary flavanols increase bioavailable nitric oxide, a proposed mediator of CIVD through active vasodilation and/or withdrawal of sympathetic vascular smooth muscle tone. However, no studies have examined the effects of flavanol intake on extremity skin perfusion during cold exposure. We tested the hypothesis that acute and 8-day flavanol supplementation would augment CIVD during single-digit cold water immersion (CWI). METHODS: Eleven healthy adults (24 ± 6 years; 10 M/1F) ingested cocoa flavanols (900 mg/day) or caffeine- and theobromine-matched placebo for 8 days in a double-blind, randomized, crossover design. On Days 1 and 8, CIVD was assessed 2 h post-treatment. Subjects immersed their 3rd finger in warm water (42 °C) for 15 min before CWI (4 °C) for 30 min, during which nail bed and finger pad skin temperature were measured. RESULTS: Flavanol ingestion had no effect on CIVD frequency (Day 1, Flavanol: 3 ± 2 vs. Placebo: 3 ± 2; Day 8, Flavanol: 3 ± 2 vs. Placebo: 3 ± 1) or amplitude (Day 1, Flavanol: 4.3 ± 1.7 vs. Placebo: 4.9 ± 2.6 °C; Day 8, Flavanol: 3.9 ± 1.9 vs. Placebo: 3.9 ± 2.0 °C) in the finger pad following acute or 8-day supplementation (P > 0.05). Furthermore, average, nadir, and apex finger pad temperatures during CWI were not different between treatments on Days 1 or 8 of supplementation (P > 0.05). Similarly, no differences in CIVD parameters were observed in the nail bed following supplementation (P > 0.05). CONCLUSION: These data suggest that cocoa flavanol ingestion does not alter finger CIVD. Clinical Trial Registration Clinicaltrials.gov Identifier: NCT04359082. April 24, 2020.

Finite element model of female thermoregulation with geometry based on medical images.

INTRODUCTION: this study describes the development of a female finite element thermoregulatory model (FETM) METHOD: the female body model was developed from medical image datasets of a median U.S. female and was constructed to be anatomically correct. The body model preserves the geometric shapes of 13 organs and tissues, including skin, muscles, fat, bones, heart, lungs, brain, bladder, intestines, stomach, kidneys, liver, and eyes. Heat balance within the body is described by the bio-heat transfer equation. Heat exchange at the skin surface includes conduction, convection, radiation, and sweat evaporation. Vasodilation, vasoconstriction, sweating, and shivering are controlled by afferent and efferent signals to and from the skin and hypothalamus. RESULTS: the model was validated with measured physiological data during exercise and rest in thermoneutral, hot, and cold conditions. Validations show the model predicted the core temperature (rectal and tympanic temperatures) and mean skin temperatures with acceptable accuracy (within 0.5 °C and 1.6 °C, respectively) CONCLUSION: this female FETM predicted high spatial resolution temperature distribution across the female body, which provides quantitative insights into human thermoregulatory responses in females to non-uniform and transient environmental exposure.

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

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.

ACSM Expert Consensus Statement: Injury Prevention and Exercise Performance during Cold-Weather Exercise.

ABSTRACT: Cold injury can result from exercising at low temperatures and can impair exercise performance or cause lifelong debility or death. This consensus statement provides up-to-date information on the pathogenesis, nature, impacts, prevention, and treatment of the most common cold injuries.

Cold-induced cutaneous vasoconstriction in humans: Function, dysfunction and the distinctly counterproductive.

NEW FINDINGS: What is the topic of this review? This review presents an update and synthesis of normal mechanisms of human cutaneous vasoconstriction in response to cold stress. It then discusses conditions in which cutaneous vasoconstrictor responses are excessive or insufficient and cases in which cold-induced vasoconstrictor responses become counter to maintaining thermal and haemodynamic homeostasis. What advances does it highlight? The review highlights our current understanding of the mechanisms that mediate alterations in cold-induced cutaneous vasoconstriction in pathology and environmental extremes, which has important clinical implications for preventing cold- and cardiovascular-related deaths. ABSTRACT: In humans, cold-induced peripheral vasoconstriction is an essential element of body temperature regulation. Given that the thermoregulatory system responds rapidly to changes in skin temperature, sympathetically mediated cutaneous vasoconstriction represents a crucial 'first line of defense' against excessive reduction in body temperature. Sympathetic noradrenergic vasoconstrictor nerves cause a rapid decrease in skin blood flow, thus increasing the insulative capacity of the skin and decreasing heat loss from the body. Small changes in the activity of these nerves are also responsible for the subtle changes in skin blood flow that occur with normal daily activities or minor changes in environmental temperature. With ageing, hypertension and other conditions, the cutaneous reflex vasoconstrictor response can become excessive or insufficient. Healthy older adults have impaired reflex vasoconstriction, which may result in an impaired ability to defend body temperature in some circumstances. Hypertension is associated with augmented vasoconstriction, which could have pathological implications for left ventricular afterload in individuals already at risk for cardiovascular events. Finally, in some cases, the reflex vasoconstrictor response becomes distinctly counterproductive to its own goals of maintaining cardiovascular and thermoregulatory homeostasis. Examples include Raynaud's phenomenon, in which exaggerated vasoconstriction can produce ischaemia in the periphery, and the cutaneous vasoconstrictor response to therapeutic body cooling in severe hyperthermia, which can limit the heat exchange necessary to prevent serious heat illness.

Changes in intestinal microbiota composition and metabolism coincide with increased intestinal permeability in young adults under prolonged physiological stress.

The magnitude, temporal dynamics, and physiological effects of intestinal microbiome responses to physiological stress are poorly characterized. This study used a systems biology approach and a multiple-stressor military training environment to determine the effects of physiological stress on intestinal microbiota composition and metabolic activity, as well as intestinal permeability (IP). Soldiers (n = 73) were provided three rations per day with or without protein- or carbohydrate-based supplements during a 4-day cross-country ski-march (STRESS). IP was measured before and during STRESS. Blood and stool samples were collected before and after STRESS to measure inflammation, stool microbiota, and stool and plasma global metabolite profiles. IP increased 62 ± 57% (mean ± SD, P < 0.001) during STRESS independent of diet group and was associated with increased inflammation. Intestinal microbiota responses were characterized by increased α-diversity and changes in the relative abundance of >50% of identified genera, including increased abundance of less dominant taxa at the expense of more dominant taxa such as Bacteroides Changes in intestinal microbiota composition were linked to 23% of metabolites that were significantly altered in stool after STRESS. Together, pre-STRESS Actinobacteria relative abundance and changes in serum IL-6 and stool cysteine concentrations accounted for 84% of the variability in the change in IP. Findings demonstrate that a multiple-stressor military training environment induced increases in IP that were associated with alterations in markers of inflammation and with intestinal microbiota composition and metabolism. Associations between IP, the pre-STRESS microbiota, and microbiota metabolites suggest that targeting the intestinal microbiota could provide novel strategies for preserving IP during physiological stress.NEW & NOTEWORTHY Military training, a unique model for studying temporal dynamics of intestinal barrier and intestinal microbiota responses to stress, resulted in increased intestinal permeability concomitant with changes in intestinal microbiota composition and metabolism. Prestress intestinal microbiota composition and changes in fecal concentrations of metabolites linked to the microbiota were associated with increased intestinal permeability. Findings suggest that targeting the intestinal microbiota could provide novel strategies for mitigating increases in intestinal permeability during stress.

Heat removal using microclimate foot cooling: a thermal foot manikin study.

BACKGROUND: It has been proposed that microclimate cooling systems exploit the peripheral extremities because of more efficient heat transfer. The purpose of this study was to quantify, using a patented microclimate cooling technique, the heat transfer from the plantar surface of the foot for comparison to other commonly cooled body regions. METHODS: A military boot was fitted with an insole embedded with a coiled, 1.27 m length of hollow tubing terminating in inlet and outlet valves. A thermal foot manikin with a surface temperature of 34 degrees C was placed in the boot and the valves were connected to a system that circulated water through the insole at a temperature of 20 degrees C and flow rate of 120 ml x min(-1). The manikin foot served as a constant heat source to determine heat transfer provided by the insole. Testing was done with the foot model dry and sweating at a rate of 500 ml x h(- 1) x m(-2). Climatic chamber conditions were 30 degrees C with 30% RH. RESULTS: Heat loss was approximately 4.1 +/- 0.1 and approximately 7.7 +/- 0.3 W from the dry and sweating foot models, respectively. On a relative scale, the heat loss was 3.0 W and 5.5 W per 1% (unit) body surface area, respectively, for the dry and sweating conditions. DISCUSSION: The relative heat loss afforded by plantar foot cooling was similar compared to other body regions, but the absolute amount of heat removal is unlikely to make an impact on whole body heat balance.

Energy Expenditure during Physical Work in Cold Environments: Physiology and Performance Considerations for Military Service Members.

Effective execution of military missions in cold environments requires highly trained, well-equipped, and operationally ready service members. Understanding the metabolic energetic demands of performing physical work in extreme cold conditions is critical for individual medical readiness of service members. In this narrative review, we describe 1) the extreme energy costs of performing militarily relevant physical work in cold environments, 2) key factors specific to cold environments that explain these additional energy costs, 3) additional environmental factors that modulate the metabolic burden, 4) medical readiness consequences associated with these circumstances, and 5) potential countermeasures to be developed to aid future military personnel. Key characteristics of the cold operational environment that cause excessive energy expenditure in military personnel include thermoregulatory mechanisms, winter apparel, inspiration of cold air, inclement weather, and activities specific to cold weather. The combination of cold temperatures with other environmental stressors, including altitude, wind, and wet environments exacerbates the overall metabolic strain on military service members. The high energy cost of working in these environments increases the risk of undesirable consequences, including negative energy balance, dehydration, and subsequent decrements in physical and cognitive performance. Such consequences may be mitigated by the application of enhanced clothing and equipment design, wearable technologies for biomechanical assistance and localized heating, thermogenic pharmaceuticals, and cold habituation and training guidance. Altogether, the reduction in energy expenditure of modern military personnel during physical work in cold environments would promote desirable operational outcomes and optimize the health and performance of service members.

Wet Military Uniforms Pose Low Risk of Hypothermia while Static in Mild Cold Air.

Wet clothing is less insulative than dry clothing and increases heat loss in cold air. Tactical necessity can render removal of wet clothing impossible and/or require Warfighters to remain static to avoid detection, limiting heat production and posing a threat of hypothermia (core temperature <35°C). This study aimed to characterize body temperatures and evaluate hypothermia risk while statically exposed to 5°C air wearing three wet military uniforms. Further, low-speed loaded walking was evaluated as a strategy to raise end-static temperatures. Twelve adults (11M, 1F) randomly completed three wet-cold trials wearing either the Improved Hot Weather Combat Uniform (IHWCU), Army Combat Uniform (ACU), or ACU with silk-weight base layer (ACU+). Each trial involved 180 minutes of cold air (5.3±0.3°C, 0.8 m·s-1) exposure after a clothed 2-minute head-out immersion (34.0 ± 0.2°C). Volunteers were static for 60 minutes followed by 120 minutes of loaded walking. Rectal temperature (Tre) area under the curve did not differ among the three wet uniforms when static (p=0.431) with Tre increasing, rather than decreasing, across the 60 minutes (IHWCU: +0.26±0.19°C, ACU: +0.37±0.21°C, ACU+: +0.36±0.20°C). Hypothermia risk with 60-minute static wet-cold exposure therefore appears minimal, regardless of the military uniform worn. End-static finger temperatures (IHWCU: 9.48±2.30°C, ACU: 9.99±1.82°C, ACU+: 9.27±1.66°C, p >0.999) were reduced by ~20-23°C posing a considerable dexterity concern. Heat production of ~210 W·m2 appeared sufficient to begin to reverse negative cumulative heat storage and initiate slight elevation of rectal and peripheral temperatures, although finger temperatures increased < 2°C after 120 minutes. ClinicalTrials.gov ID:NCT05409937.

Physiological Employment Standards III: physiological challenges and consequences encountered during international military deployments.

Modern international military deployments in austere environments (i.e., Iraq and Afghanistan) place considerable physiological demands on soldiers. Significant physiological challenges exist: maintenance of physical fitness and body composition, rigors of external load carriage, environmental extremes (heat, cold, and altitude), medical illnesses, musculoskeletal injuries, traumatic brain injuries, post-traumatic stress disorder, and environmental exposure hazards (i.e., burn pits, vehicle exhaust, etc.). To date there is very little published research and no comprehensive reviews on the physiological effects of deployments. The purpose of this paper is to overview what is currently known from the literature related mainly to current military conflicts with regard to the challenges and consequences from deployments. Summary findings include: (1) aerobic capacity declines while muscle strength, power and muscular endurance appear to be maintained, (2) load carriage continues to tax the physical capacities of the Soldier, (3) musculoskeletal injuries comprise the highest proportion of all injury categories, (4) environmental insults occur from both terrestrial extremes and pollutant exposure, and (5) post-deployment concerns linger for traumatic brain injury and post-traumatic stress disorder. A full understanding of these responses will assist in identifying the most effective risk mitigation strategies to ensure deployment readiness and to assist in establishment of military employment standards.

Validation of a human thermoregulatory model during prolonged immersion in warm water.

This study validates the Six Cylinder Thermoregulatory Model (SCTM) during prolonged warm water immersion, which underpins the Probability of Survival Decision Aid (PSDA) currently in use by the United States Coast Guard (USCG). PSDA predicts survival time for hypothermia and dehydration. USCG has been using PSDA for search and rescue operation since 2010. In 2019, USCG organized a workshop to review PSDA performance and concluded that PSDA is an essential tool for operation, although it occasionally overestimates survival times in warm waters above 16 °C. Forty-six human subjects were immersed from the neck down in 18, 22, and 26 °C water for 45 min up to 10 h. Rectal temperature (Tcore), 10-site mean skin temperature (Tsk), and water loss were measured. At the end of immersion, Tcore ranged from 35.2 to 38.0 °C, and Tsk ranged from 19.7 to 27.4 °C. The SCTM-predicted Tcore, Tsk and water loss were compared to the measured values. Root mean squared deviation (RMSD) was used to test for acceptable predictions. Tcore RMSDs were 0.2, 0.14, and 0.3 °C in 18, 22, and 26 °C water respectively. Tsk RMSDs were 1.44, 0.76, and 1.1 °C in 18, 22, and 26 °C water respectively. SCTM underpredicted water loss by 84%. Overall, SCTM predicted Tcore and Tsk with acceptable accuracy in 18 and 22 °C water for up to 10 h, but overpredicted in 26 °C water. Future studies and algorithm development are required to improve water loss prediction as well as Tcore and Tsk prediction in 26 °C water.

Human cold habituation: Physiology, timeline, and modifiers.

Habituation is an adaptation seen in many organisms, defined by a reduction in the response to repeated stimuli. Evolutionarily, habituation is thought to benefit the organism by allowing conservation of metabolic resources otherwise spent on sub-lethal provocations including repeated cold exposure. Hypermetabolic and/or insulative adaptations may occur after prolonged and severe cold exposures, resulting in enhanced cold defense mechanisms such as increased thermogenesis and peripheral vasoconstriction, respectively. Habituation occurs prior to these adaptations in response to short duration mild cold exposures, and, perhaps counterintuitively, elicits a reduction in cold defense mechanisms demonstrated through higher skin temperatures, attenuated shivering, and reduced cold sensations. These habituated responses likely serve to preserve peripheral tissue temperature and conserve energy during non-life threatening cold stress. The purpose of this review is to define habituation in general terms, present evidence for the response in non-human species, and provide an up-to-date, critical examination of past studies and the potential physiological mechanisms underlying human cold habituation. Our aim is to stimulate interest in this area of study and promote further experiments to understand this physiological adaptation.

Human vulnerability and variability in the cold: Establishing individual risks for cold weather injuries.

Human tolerance to cold environments is extremely limited and responses between individuals is highly variable. Such physiological and morphological predispositions place them at high risk of developing cold weather injuries [CWI; including hypothermia and/or non-freezing (NFCI) and freezing cold injuries (FCI)]. The present manuscript highlights current knowledge on the vulnerability and variability of human cold responses and associated risks of developing CWI. This review 1) defines and categorizes cold stress and CWI, 2) presents cold defense mechanisms including biological adaptations, acute responses and acclimatization/acclimation and, 3) proposes mitigation strategies for CWI. This body of evidence clearly indicates that all humans are at risk of developing CWI without adequate knowledge and protective equipment. In addition, we show that while body mass plays a key role in mitigating risks of hypothermia between individuals and populations, NFCI and FCI depend mainly on changes in peripheral blood flow and associated decrease in skin temperature. Clearly, understanding the large interindividual variability in morphology, insulation, and metabolism is essential to reduce potential risks for CWI between and within populations.

Thermal face protection delays finger cooling and improves thermal comfort during cold air exposure.

When people dress for cold weather, the face often remains exposed. Facial cooling can decrease finger blood flow, reducing finger temperature (T (f)). This study examined whether thermal face protection limits finger cooling and thereby improves thermal comfort and manual dexterity during prolonged cold exposure. T (f) was measured in ten volunteers dressed in cold-weather clothing as they stood for 60 min facing the wind (-15°C, 3 m s(-1)), once while wearing a balaclava and goggles (BAL), and once with the balaclava pulled down and without goggles (CON). Subjects removed mitts, wearing only thin gloves to perform Purdue Pegboard (PP) tests at 15 and 50 min, and Minnesota Rate of Manipulation (MRM) tests at 30 and 55 min. Subjects rated their thermal sensation and comfort just before the dexterity tests. T (f) decreased (p < 0.05 for time × trial interaction) by 15 min of cold exposure during CON (33.6 ± 1.4-28.7 ± 2.0°C), but not during BAL (33.2 ± 1.4-30.6 ± 3.2°C); and after 30 min T (f) remained warmer during BAL (23.3 ± 5.9°C) than CON (19.2 ± 3.5); however, by 50 min, T (f) was no different between trials (14.1 ± 2.7°C). Performance on PP fell (p < 0.05) by 25% after 50 min in both trials; MRM performance was not altered by cold on either trial. Subjects felt colder (p < 0.05) and more uncomfortable (p < 0.05) during CON, compared to BAL. Thermal face protection was effective for maintaining warmer T (f) and thermal comfort during cold exposure; however, local cooling of the hands during manual dexterity tests reduced this physiological advantage, and performance was not improved.

A geometrically accurate 3 dimensional model of human thermoregulation for transient cold and hot environments.

This paper outlines the development of a finite element human thermoregulatory model using an anatomically and geometrically correct human body model. The finite element body model was constructed from digital Phantoms and is anatomically realistic, including 13 organs and tissues: skin, muscles, fat, bones, heart, lungs, brain, bladder, intestines, stomach, kidneys, liver, and eyes. The model simulates thermal responses through a passive and active system. The passive system describes heat balance within the body and between the skin surface and environment. The active system describes thermoregulatory mechanisms, i.e., vasodilation, vasoconstriction, sweating, and shivering heat production. This model predicts temperature distribution across the body at high spatial resolution, and provides insight into human thermoregulatory responses to non-uniform and transient environments. Predicted temperatures (i.e., core, skin, muscle and fat) at 29 sites were compared with measured values in comfort, hot, and cold conditions. The comprehensive validation shows predictions are accurate and acceptable.

Hypohydration reduces vertical ground reaction impulse but not jump height.

This study examined vertical jump performance using a force platform and weighted vest to determine why hypohydration (approximately 4% body mass) does not improve jump height. Measures of functional performance from a force platform were determined for 15 healthy and active males when euhydrated (EUH), hypohydrated (HYP) and hypohydrated while wearing a weighted vest (HYP(v)) adjusted to precisely match water mass losses. HYP produced a significant loss of body mass [-3.2 +/- 0.5 kg (-3.8 +/- 0.6%); P < 0.05], but body mass in HYP(v) was not different from EUH. There were no differences in absolute or relative peak force or power among trials. Jump height was not different between EUH (0.380 +/- 0.048 m) and HYP (0.384 +/- 0.050 m), but was 4% lower (P < 0.05) in HYP(v) (0.365 +/- 0.52 m) than EUH due to a lower jump velocity between HYP(v) and EUH only (P < 0.05). However, vertical ground reaction impulse (VGRI) was reduced in both HYP and HYP(v) (2-3%) compared with EUH (P < 0.05). In conclusion, this study demonstrates the failure to improve jump height when HYP can be explained by offsetting reductions in both VGRI and body mass.

Frostbite: Pathophysiology, Epidemiology, Diagnosis, Treatment, and Prevention.

Frostbite can occur during cold-weather operations when the temperature is <0°C (<32°F). When skin temperature is =-4°C (=25°F), ice crystals form in the blood, causing mechanical damage, inflammation, thrombosis, and cellular death. Lower temperatures, higher wind speeds, and moisture exacerbate the process. The frozen part or area should not be rewarmed unless the patient can remain in a warm environment; repeated freeze/thaw cycles cause further injury. Treatment involves rapid rewarming in a warm, circulating water bath 37°C to 39°C (99°F-102°F) or, if this is not possible, then contact with another human body. Thrombolytics show promise in the early treatment of frostbite. In the field, the depth and severity of the injury can be determined with laser Doppler ultrasound devices or thermography. In hospital settings, bone scintigraphy with single-photon emission computed tomography (SPECT) 2 to 4 days postinjury provides detailed information on the depth of the injury. Prevention is focused primarily on covering exposed skin with proper clothing and minimizing exposure to wind and moisture. The Generation III Extended Cold Weather Clothing System is an interchangeable 12-piece clothing ensemble designed for low temperatures and is compatible with other military systems. The Extreme Cold Vapor Barrier Boot has outer and inner layers composed of seamless rubber with wool insulation between, rated for low temperatures. The Generation 3 Modular Glove System consists of 11 different gloves and mitts with design features that assist in enhancing grip, aid in the use of mobile devices, and allow shooting firearms. Besides clothing, physical activity also increases body heat, reducing the risk of frostbite.

Cognitive function and mood during acute cold stress after extended military training and recovery.

INTRODUCTION: Acute cold stress is often accompanied by exposure to other adverse factors, such as sleep loss, under-nutrition, and psychological stress that singly and together may affect cognitive function. METHODS: The effect of moderate cold stress on cognitive function was investigated in 15 male volunteers exposed to cold air (10 degrees C) for 4 h after they had completed an intense, 61-d regimen (U.S. Army Ranger training). The single cohort of volunteers was tested on three separate occasions: (1) immediately after completing Ranger training; (2) 2 d later when they had partially recovered from training; (3) 108 d later after full recovery. Documented training stressors included limited sleep (approximately 4 h sleep/night), caloric deficit (approximately 850 kcal x d(-1), intense physical activity, and psychological stress. RESULTS: Baseline rectal temperature fell significantly due to training alone (from 36.6 degrees C +/- 0.1 to 36.3 degrees C +/- 0.1) and was lower still with acute cold exposure (35.9 degrees C +/- 0.2). Cognitive function was affected by training alone, as indicated by significant decreases in vigilance, four-choice reaction time, pattern recognition, symbol-digit substitution, word-list learning, grammatical reasoning, and mood prior to exposure to acute cold stress. Mood states were also adversely affected, including tension, depression, anger, fatigue, confusion, and vigor. Acute cold exposure itself significantly degraded vigilance, overall mood, and increased tension. DISCUSSION: Chronic multifactorial stress impaired cognitive function and mood; the addition of moderate, acute cold stress further degraded vigilance and mood. When such circumstances occur, such as during disasters or military operations, measures to prevent adverse cognitive and physiological outcomes are recommended.

Hydration effects on cognitive performance during military tasks in temperate and cold environments.

Body water deficits or hypohydration (HYP) may degrade cognitive performance during heat exposure and perhaps temperate conditions. Cold exposure often induces HYP, but the combined effects of cold and HYP on cognitive performance are unknown. This study investigated whether HYP degrades cognitive performance during cold exposure and if physical exercise could mitigate any cold-induced performance decline. On four occasions, eight volunteers completed one hour of militarily-relevant cognitive testing: 30 min of simulated sentry duty/marksmanship, 20 min of a visual vigilance task, a self-report workload assessment, and a mood questionnaire. Testing was conducted in a cold (2 degrees C) or temperate (20 degrees C) environment before and after cycle ergometer (60 min at 60% of VO(2peak)) exercise. Each trial was preceded by 3 h of passive heat stress (45 degrees C) in the early morning with (euhydration, EUH) or without (hypohydration, HYP; 3% body mass) fluid replacement followed by prolonged recovery. HYP did not alter any cognitive, psychomotor, or self-report parameter in either environment before or after exercise. Cold exposure increased (p<0.05) target detection latency in the sentry duty task, adversely affected mood and workload ratings, but had no impact on any other cognitive or psychomotor measure. After completing the exercise bout, there were modest improvements in friend-foe discrimination and total response latency in the sentry duty task, but not on any other performance measures. Moderate HYP had no effect on cognitive and psychomotor performance in either environment, cold exposure produced equivocal effects, and aerobic exercise improved some aspects of military task performance.