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Daniel S. Moran, Tomer Erlich and Yoram Epstein

Context:

Individuals in the population who are not able to sustain heat and whose body temperature will start rising earlier and at a higher rate than that of others, under the same conditions, are defined as “heat intolerant.”

Objectives:

The applicability of the heat tolerance test (HTT) in identifying individuals’ tolerance/intolerance to heat is presented.

Setting:

HTT is performed according to the following protocol: 120 minutes exposure to 40°C and 40% relative humidity in a climatic chamber while walking on a treadmill, dressed in shorts and T-shirt, at a pace of 5 km/h and 2% elevation. Rectal temperature and heart rate are continuously monitored, and sweat rate is calculated.

Results and Conclusion:

The HTT that is based on controlled exposure to an exercise-heat stress is an applicable and an efficient tool in differentiating between a temporary and permanent state of heat susceptibility.

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Brendon P. McDermott, Douglas J. Casa, Susan W. Yeargin, Matthew S. Ganio, Lawrence E. Armstrong and Carl M. Maresh

Objective:

To describe the current scientific evidence of recovery and return to activity following exertional heat stroke (EHS).

Data Sources:

Information was collected using MEDLINE and SPORTDiscus databases in English using combinations of key words, exertional heat stroke, recovery, rehabilitation, residual symptoms, heat tolerance, return to activity, and heat illness.

Study Selection:

Relevant peer-reviewed, military, and published text materials were reviewed.

Data Extraction:

Inclusion criteria were based on the article’s coverage of return to activity, residual symptoms, or testing for long-term treatment. Fifty-two out of the original 554 sources met these criteria and were included in data synthesis.

Data Synthesis:

The recovery time following EHS is dependent on numerous factors, and recovery length is individually based and largely dependent on the initial care provided.

Conclusion:

Future research should focus on developing a structured return-to-activity strategy following EHS.

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João C. Dias, Melissa W. Roti, Amy C. Pumerantz, Greig Watson, Daniel A. Judelson, Douglas J. Casa and Lawrence E. Armstrong

Context:

Dieticians, physiologists, athletic trainers, and physicians have recommended refraining from caffeine intake when exercising because of possible fluid-electrolyte imbalances and dehydration.

Objective:

To assess how 16-hour rehydration is affected by caffeine ingestion.

Design:

Dose–response.

Setting:

Environmental chamber.

Participants:

59 college-age men.

Intervention:

Subjects consumed a chronic caffeine dose of 0 (placebo), 3, or 6 mg · kg−1 · day−1 and performed an exercise heat-tolerance test (EHT) consisting of 90 minutes of walking on a treadmill (5.6 km/h) in the heat (37.7 °C).

Outcome Measures:

Fluid-electrolyte measures.

Results:

There were no between-group differences immediately after and 16 hours after EHT in total plasma protein, hematocrit, urine osmolality, specific gravity, color, and volume. Body weights after EHT and the following day (16 hours) were not different between groups (P > .05).

Conclusion:

Hydration status 16 hours after EHT did not change with chronic caffeine ingestion.

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Francis G. O’Connor, Aaron D. Williams, Steve Blivin, Yuval Heled, Patricia Deuster and Scott D. Flinn

Since Biblical times, heat injuries have been a major focus of military medical personnel. Heat illness accounts for considerable morbidity during recruit training and remains a common cause of preventable nontraumatic exertional death in the United States military. This brief report describes current regulations used by Army, Air Force, and Navy medical personnel to return active duty warfighters who are affected by a heat illness back to full duty. In addition, a description of the profile system used in evaluating the different body systems, and how it relates to military return to duty, are detailed. Current guidelines require clinical resolution, as well as a profile that that protects a soldier through repeated heat cycles, prior to returning to full duty. The Israeli Defense Force, in contrast, incorporates a heat tolerance test to return to duty those soldiers afflicted by heat stroke, which is briefly described. Future directions for U.S. military medicine are discussed.

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Tal Marom, David Itskoviz, Haim Lavon and Ishay Ostfeld

Introduction:

Exertional heat stroke (EHS) is a major concern in military trainees performing intense physical exercise, with substantial morbidity rates. Prehospital diagnosis of EHS is essentially clinical. Thus, soldiers, command personnel, and medical staff are taught to recognize this injury and immediately begin aggressive treatment to prevent further deterioration.

Patients and Methods:

During 2007, 5 otherwise healthy Israeli Defense Forces (IDF) soldiers were diagnosed with EHS while performing strenuous exercise. They were treated vigorously according to the IDF EHS-treatment protocol and were referred to the emergency department.

Results:

On arrival at the emergency department, physical examination including rectal temperature was unremarkable in all soldiers. Blood and urine workup showed near-normal values. No other medical conditions that could have explained the clinical presentation were found. All soldiers were discharged shortly afterward, with no further consequences. A heat-tolerance test was performed several weeks after the event and was interpreted as normal. All soldiers returned to active service.

Conclusion:

Because the initial clinical findings were very suggestive of EHS and because no other condition could have explained the prehospital transient hyperthermia, we suggest that these soldiers were correctly diagnosed with EHS, and we propose that rapid vigorous cooling prevented further deterioration and complications. We suggest calling this condition aborted heat stroke.

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Erin L. McCleave, Katie M. Slattery, Rob Duffield, Philo U. Saunders, Avish P. Sharma, Stephen Crowcroft and Aaron J. Coutts

Purpose: To determine whether combining training in heat with “Live High, Train Low” hypoxia (LHTL) further improves thermoregulatory and cardiovascular responses to a heat-tolerance test compared with independent heat training. Methods: A total of 25 trained runners (peak oxygen uptake = 64.1 [8.0] mL·min−1·kg−1) completed 3-wk training in 1 of 3 conditions: (1) heat training combined with “LHTL” hypoxia (H+H; FiO2 = 14.4% [3000 m], 13 h·d−1; train at <600 m, 33°C, 55% relative humidity [RH]), (2) heat training (HOT; live and train <600 m, 33°C, 55% RH), and (3) temperate training (CONT; live and train <600 m, 13°C, 55% RH). Heat adaptations were determined from a 45-min heat-response test (33°C, 55% RH, 65% velocity corresponding to the peak oxygen uptake) at baseline and immediately and 1 and 3 wk postexposure (baseline, post, 1 wkP, and 3 wkP, respectively). Core temperature, heart rate, sweat rate, sodium concentration, plasma volume, and perceptual responses were analyzed using magnitude-based inferences. Results: Submaximal heart rate (effect size [ES] = −0.60 [−0.89; −0.32]) and core temperature (ES = −0.55 [−0.99; −0.10]) were reduced in HOT until 1 wkP. Sweat rate (ES = 0.36 [0.12; 0.59]) and sweat sodium concentration (ES = −0.82 [−1.48; −0.16]) were, respectively, increased and decreased until 3 wkP in HOT. Submaximal heart rate (ES = −0.38 [−0.85; 0.08]) was likely reduced in H+H at 3 wkP, whereas CONT had unclear physiological changes. Perceived exertion and thermal sensation were reduced across all groups. Conclusions: Despite greater physiological stress from combined heat training and “LHTL” hypoxia, thermoregulatory adaptations are limited in comparison with independent heat training. The combined stimuli provide no additional physiological benefit during exercise in hot environments.

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Michelle Cleary * 8 2007 16 3 204 214 10.1123/jsr.16.3.204 The Heat Tolerance Test: An Efficient Screening Tool for Evaluating Susceptibility to Heat Daniel S. Moran * Tomer Erlich * Yoram Epstein * 8 2007 16 3 215 221 10.1123/jsr.16.3.215 Identification of Risk Factors for Exertional Heat Illness

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Margaret C. Morrissey, Michael R. Szymanski, Andrew J. Grundstein and Douglas J. Casa

dysfunction ( Davis, Genebriera, Sandroni, & Fealey, 2006 ; Flavahan, 2008 ; Leibowitz et al., 1991 ). For example, Leibowitz et al. ( 1991 ) reported that males with psoriasis covering approximately 4.9% of their body surface area had significantly higher rectal temperatures at the end of a heat tolerance