Robert W. Kenefick

U.S. Army Research Institute of Environmental Medicine

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Samuel N. Cheuvront

U.S. Army Research Institute of Environmental Medicine

Michael N. Sawka

Georgia Institute of Technology

John W. Castellani

U.S. Army Research Institute of Environmental Medicine

Samuel N. Cheuvront

Synergy University

Lawrence E. Armstrong

University of Connecticut

Nisha Charkoudian

U.S. Army Research Institute of Environmental Medicine

Brett R. Ely

U.S. Army Research Institute of Environmental Medicine

Deborah Riebe

University of Rhode Island

Katherine Mitchell

Children's Hospital of Philadelphia

Carl M. Maresh

The Ohio State University

Cooperative Institutions

U.S. Army Research Institute of Environmental Medicine

115

United States Army

100

University of Connecticut

University of New Hampshire

United States Department of the Army

American College of Surgeons

Harvard University

Oak Ridge Institute for Science and Education

University of Florida

Oak Ridge Associated Universities

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Use of the heat tolerance test to assess recovery from exertional heat stroke

Temperature (2019)

Katherine Mitchell Samuel N. Cheuvront Michelle A. King Thomas A. Mayer Lisa R. Leon

Exercise or work in hot environments increases susceptibility to exertional heat illnesses such as exertional heat stroke (EHS). EHS occurs when body heat gain exceeds body heat dissipation, resulting in rapid body heat storage and potentially life-threatening consequences. EHS poses a dangerous threat for athletes, agriculture workers, and military personnel, as they are often exposed to hot environmental conditions that restrict body heat loss or contribute to body heat gain. Currently, there is limited guidance on return to activity (RTA) after an episode of EHS. While examining biomarkers in the blood is thought to be beneficial for determining RTA, they are not sensitive or specific enough to be a final determining factor as organ damage may persist despite blood biomarkers returning to baseline levels. As such, additional assessment tests to more accurately determine RTA are desired. One method used for determining RTA is the heat tolerance test (HTT, 120 minutes treadmill walking; 40°C, 40% relative humidity). Unfortunately, the HTT provides even less information about EHS recovery since it offers no test sensitivity or specificity even after years of implementation. We provide an overview of the HTT and the controversy of this test with respect to assessment criteria, applicability to tasks involving high metabolic workloads, and the lack of follow-up analyses to determine its accuracy for determining recovery in order to diminish the likelihood of a second EHS occurrence.

Heat illness

Heat exhaustion

Stroke

Treadmill

10.1080/23328940.2019.1574199

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Citations (35)

Hypohydration Adversely Affects Lactate Threshold in Endurance Athletes

The Journal of Strength and Conditioning Research (2002)

Robert W. Kenefick NICHOLAS V. MAHOOD Craig O. Mattern Robert Kertzer Timothy J. Quinn

The purpose of this investigation was to observe the effect of hypohydration (-4% body mass) on lactate threshold (LAT) in 14 collegiate athletes (8 men and 6 women; age, 20.9 +/- 0.5 years; height, 171.1 +/- 2.4 cm; weight, 64.8 +/- 2.3 kg; V(O)2 max, 62.8 +/- 1.9 ml x kg(-1) x min(-1); percentage of fat, 11.4 +/- 1.5%). Subjects performed 2 randomized, discontinuous treadmill bouts at a dry bulb temperature (T(db)) of 22 degrees C to volitional exhaustion in 2 states of hydration, euhydrated and hypohydrated. The hypohydrated condition was achieved in a thermally neutral environment (T(db), 22 degrees C; humidity, 45%), with exercise conducted at a moderate intensity as defined by rating of perceived exertion (RPE, approximately 12) 12-16 hours before testing. On average, subjects decreased 3.9% of their body mass before the hypohydration test. Blood lactate, hematocrit, V(O)2, minute ventilation (VE), R value, heart rate (HR), and RPE were measured during each 4-minute stage of testing. In the hypohydrated condition, LAT occurred significantly earlier during exercise and at a lower absolute V(O)2, VE, respiratory exchange ratio, RPE, and blood lactate concentration. Also, the blood lactate concentration was significantly lower in the hypohydrated condition (6.7 +/- 0.8 mmol) compared with the euhydrated condition (10.2 +/- 0.9 mmol) at peak exercise. There were no differences in HR or percentage of maximum HR at LAT nor did plots of V(CO2):V(O)2 reveal differences in bicarbonate buffering during exercise between the 2 conditions. From these results, we speculate that hypohydration did not significantly alter cardiovascular function or buffering capacity but did cause LAT to occur at a lower absolute exercise intensity.

Treadmill

Respiratory exchange ratio

10.1519/1533-4287(2002)016<0038:haalti>2.0.co;2

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Citations (24)

Personalized fluid and fuel intake for performance optimization in the heat

Journal of science and medicine in sport (2021)

Samuel N. Cheuvront Robert W. Kenefick

Fluid intake

10.1016/j.jsams.2021.01.004

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Citations (10)

Two-Day Residence at 2500 m to 4300 m Does Not Affect Subsequent Exercise Performance at 4300 m

Medicine & Science in Sports & Exercise (2018)

Robert W. Kenefick Beth A. Beidleman Sean P. Andrew Bruce S. Cadarette Stephen R. Muza

To determine the efficacy residing for 2 d at various altitudes while sedentary (S) or active (A; ~90 min hiking 2 d) on exercise performance at 4300 m.Sea-level (SL) resident men (n = 45) and women (n = 21) (mean ± SD; 23 ± 5 yr; 173 ± 9 cm; 73 ± 12 kg; V˙O2peak = 49 ± 7 mL·kg·min) were randomly assigned to a residence group and, S or A within each group: 2500 m (n = 11S, 8A), 3000 m (n = 6S, 12A), 3500 m (n = 6S, 8A), or 4300 m (n = 7S, 8A). Exercise assessments occurred at SL and 4300 m after 2-d residence and consisted of 20 min of steady-state (SS) treadmill walking (45% ± 3% SL V˙O2peak) and a 5-mile, self-paced running time trial (TT). Arterial oxygen saturation (SpO2) and HR were recorded throughout exercise. Resting SpO2 was recorded at SL, at 4 and 46 h of residence, and at 4300 m before exercise assessment. To determine if 2-d altitude residence improved 4300 m TT performance, results were compared with estimated performances using a validated prediction model.For all groups, resting SpO2 was reduced (P < 0.01) after 4 h of residence relative to SL inversely to the elevation and did not improve after 46 h. Resting SpO2 (~83%) did not differ among groups at 4300 m. Although SL and 4300 m SS exercise SpO2 (97% ± 2% to 74% ± 4%), HR (123 ± 10 bpm to 140 ± 12 bpm) and TT duration (51 ± 9 to 73 ± 16 min) were different (P < 0.01), responses at 4300 m were similar among all groups, as was actual and predicted 4300 m TT performances (74 ± 12 min).Residing for 2 d at 2500 to 4300 m, with or without daily activity, did not improve resting SpO2, SS exercise responses, or TT performance at 4300 m.

Affect

10.1249/mss.0000000000001843

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Citations (2)

Efficacy of Glucose or Amino Acid–Based Commercial Beverages in Meeting Oral Rehydration Therapy Goals After Acute Hypertonic and Isotonic Dehydration

Journal of Parenteral and Enteral Nutrition (2018)

Samuel N. Cheuvront Robert W. Kenefick Nisha Charkoudian Katherine Mitchell Adam J. Luippold

Abstract Background The efficacy of different commercial beverage compositions for meeting oral rehydration therapy (ORT) goals in the treatment of acute dehydration in healthy humans has not been systematically tested. The objective of the study was to compare fluid retention, plasma volume (PV), and interstitial fluid (ISF) volume restoration when using 1 popular glucose‐based and 1 novel amino acid–based (AA) commercial ORT beverage following experimental hypertonic or isotonic dehydration. Methods Twenty‐six healthy adults (21 males, 5 females) underwent either a controlled bout of hypertonic (n = 13) or isotonic (n = 13) dehydration (3%–4% body mass) via eccrine or renal body water and electrolyte losses induced using exercise‐heat stress (EHS) or Lasix administration (LAS), respectively. Rehydration was achieved over 90 minutes by matching fluid intake to water losses (1:1) using a sports drink (SP) or AA commercial ORT beverage. Fluid retention (water and electrolytes), PV, and ISF volume changes were tracked for 180 minutes. Results AA produced significantly ( P <0.05) greater fluid retention (75% vs 57%), ISF volume restoration, and tended ( P = 0.06) to produce greater PV restoration in trial EHS. In trial LAS, neither beverage exceeded 65% retention, but AA replaced electrolytes and preserved ISF volume better than SP ( P <0.05). Conclusion The results of this study demonstrate superior rehydration when using AA compared with SP for both hypertonic and isotonic dehydration.

Isotonic Solutions

Plasma volume

Body fluid

10.1002/jpen.1142

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Citations (11)

Skin temperature modifies the impact of hypohydration on aerobic performance

Journal of Applied Physiology (2010)

Robert W. Kenefick Samuel N. Cheuvront Laura J. Palombo Brett R. Ely Michael N. Sawka

This study determined the effects of hypohydration on aerobic performance in compensable [evaporative cooling requirement (E(req)) < maximal evaporative cooling (E(max))] conditions of 10 degrees C [7 degrees C wet bulb globe temperature (WBGT)], 20 degrees C (16 degrees C WBGT), 30 degrees C (22 degrees C WBGT), and 40 degrees C (27 degrees C WBGT) ambient temperature (T(a)). Our hypothesis was that 4% hypohydration would impair aerobic performance to a greater extent with increasing heat stress. Thirty-two men [22 +/- 4 yr old, 45 +/- 8 ml.kg(-1).min(-1) peak O(2) uptake (Vo(2 peak))] were divided into four matched cohorts (n = 8) and tested at one of four T(a) in euhydrated (EU) and hypohydrated (HYPO, -4% body mass) conditions. Subjects completed 30 min of preload exercise (cycle ergometer, 50% Vo(2 peak)) followed by a 15 min self-paced time trial. Time-trial performance (total work, change from EU) was -3% (P = 0.1), -5% (P = 0.06), -12% (P < 0.05), and -23% (P < 0.05) in 10 degrees C, 20 degrees C, 30 degrees C, and 40 degrees C T(a), respectively. During preload exercise, skin temperature (T(sk)) increased by approximately 4 degrees C per 10 degrees C T(a), while core (rectal) temperature (T(re)) values were similar within EU and HYPO conditions across all T(a). A significant relationship (P < 0.05, r = 0.61) was found between T(sk) and the percent decrement in time-trial performance. During preload exercise, hypohydration generally blunted the increases in cardiac output and blood pressure while reducing blood volume over time in 30 degrees C and 40 degrees C T(a). Our conclusions are as follows: 1) hypohydration degrades aerobic performance to a greater extent with increasing heat stress; 2) when T(sk) is >29 degrees C, 4% hypohydration degrades aerobic performance by approximately 1.6% for each additional 1 degrees C T(sk); and 3) cardiovascular strain from high skin blood flow requirements combined with blood volume reductions induced by hypohydration is an important contributor to impaired performance.

Wet-bulb globe temperature

Preload

Time trial

Rectal temperature

10.1152/japplphysiol.00135.2010

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Citations (142)

Impact Of Heat Acclimation On Steady-State Exercise And Time-Trial Performance In Hypobaric Hypoxia (3500m)

Medicine & Science in Sports & Exercise (2020)

Beau R. Yurkevicius Kirsten E. Coffman Karleigh E. Bradbury Adam J. Luippold Katherine Mitchell

Heat acclimation (HA) has been reported to improve endurance exercise performance in normobaric hypoxia. However, the impact of prior HA on exercise performance in hypobaric hypoxia (HH) is unclear. PURPOSE: To determine whether HA alters steady-state (SS) exercise responses and time-trial (TT) cycle performance during a 30 hour exposure to HH. METHODS: Thirteen sea level (SL) resident men (mean ± SD; age: 21 ± 3 years; height: 173 ± 8 cm; weight: 75 ± 12 kg; SL cycle ergometer VO2peak: 43 ± 5 ml·kg-1·min-1) participated in two 30 hour HH exposures in a hypobaric chamber (496mmHg or ~3500m, 20°C, 20% RH). The HH exposures were separated by a 14 day washout period during which volunteers completed an 8-day exercise-HA protocol (2 hours of treadmill walking: 5km·h-1, 2% grade; 40°C, 40% RH). During each HH exposure, volunteers completed 30 min of SS exercise followed by a 15 min cycle TT at ~2 and 24 hours of exposure. SS exercise consisted of cycling at ~50% SL VO2peak while gas exchange (oxygen consumption (VO2), minute ventilation (VE), end tidal partial pressure of oxygen (PETO2)), and oxygen saturation (SpO2) were recorded. For the TT, volunteers completed as much work (kJ) as possible in 15 min, with heart rate (HR), SpO2, and Rating of Perceived Exertion (RPE, Borg Scale) recorded at the end of exercise. A two way repeated measures ANOVA was used to compare the effects of condition (Pre HA and Post HA) and time (~2 and 24 hours). RESULTS: There were no condition x time interaction effects among the SS or TT variables. For main effect of condition, from Pre HA vs. Post HA, SS VO2 tended to be lower (1.63 ± 0.00 L·min-1 vs. 1.60 ± 0.01 L·min-1; p = 0.05), PETO2 was higher (75.7 ± 1.0 mmHg vs. 76.8 ± 0.7 mmHg; p < 0.01), and VE and SpO2 did not differ (p > 0.05 for both). For the TT, there was no main effect of HA on total work completed (106.8 ± 23.0 kJ vs. 103.8 ± 21.3 kJ), HR (159 ± 13 bpm vs. 158 ± 13 bpm), SpO2 (83 ± 3% vs. 83 ± 3%), or RPE (17 ± 2 vs. 17 ± 2) (p > 0.05, for all). CONCLUSIONS: Our results suggest that although HA may augment some aspects of ventilation during low-intensity SS exercise, exercise performance measured by a 15 min cycle TT in HH is not affected by HA. Supported by USAMRDC; author views not official US Army or DoD policy

Time trial

Respiratory exchange ratio

Cycling

Treadmill

Endurance Training

Repeated measures design

Hypoxia

Ventilatory threshold

10.1249/01.mss.0000675568.90043.b0

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Citations (0)

Pathophysiology of Heat-Related Illnesses

Lisa R. Leon Robert W. Kenefick

Abstract : Heat illnesses are best viewed as existing along a continuum, transitioning from the mild conditions of heat cramps and heat exhaustion to the life-threatening condition of heatstroke. Environmental heat exposure is one of the most deadly natural hazards in the United States, with approximately 200 heatstroke deaths per year. Although the majority of heatstroke deaths are observed in vulnerable populations during annual heat waves, young fit individuals may also succumb to heatstroke while engaging in strenuous activities such as athletic competitions, military operations, or occupational tasks. Multiorgan system failure is the ultimate cause of heatstroke death, and there is complex interplay among the physiologic and environmental factors that compromise an individuals' ability to adequately respond to heat stress. The pathophysiology of heatstroke is thought to be caused by a systemic inflammatory response that occurs in response to endotoxin leakage from the gut, but there remains limited understanding of the mechanisms that mediate morbidity and mortality. This chapter provides an overview of the pathophysiologic responses that are observed in patients and experimental animal models at the time of heatstroke collapse and during long-term recovery. A brief discussion is provided on current clinical heatstroke treatments and promising avenues of research that may aid in the development of more effective interventions and/or treatments to prevent this debilitating illness.

Heatstroke

Heat illness

Pathophysiology

Heat exhaustion

Source

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Citations (18)

The Effect of Exposure to High Altitude and Heat on Speech Articulatory Coordination

Interspeech 2022 (2018)

James R. Williamson Thomas F. Quatieri Adam Lammert Katherine Mitchell Katherine Finkelstein

10.21437/interspeech.2018-2372

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Citations (5)

Effect of Environmental Temperature and Humidity on Permethrin Biomarkers of Exposure in U.S. Soldiers Wearing Permethrin-Treated Uniforms

American Journal of Tropical Medicine and Hygiene (2020)

Alexis L. Maule Kristin J. Heaton Bruce S. Cadarette Kathryn M. Taylor Katelyn I. Guerriere

Environmental factors, including high temperature and humidity, can influence dermal absorption of chemicals. Soldiers can be dermally exposed to permethrin while wearing permethrin-treated uniforms. This study aimed at examining the effects of high temperature and a combined high temperature and humid environment on permethrin absorption compared with ambient conditions when wearing a permethrin-treated uniform. Twenty-seven male enlisted soldiers wore study-issued permethrin-treated army uniforms for 33 consecutive hours in three different environments: 1) simulated high temperature (35°C, 40% relative humidity [rh]) (n = 10), 2) simulated high temperature and humidity (30°C, 70% rh) (n = 10), and 3) ambient conditions (13°C, 60% rh) (n = 7). Spot urine samples, collected at 21 scheduled time points before, during, and after wearing the study uniforms, were analyzed for permethrin exposure biomarkers (3-phenoxybenzoic acid, cis- and trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid) and creatinine. Biomarker concentrations were 60–90% higher in the heat and combined heat/humidity groups (P < 0.001–0.022) than the ambient group. Also, the average daily permethrin dose, calculated 12 hours after removing the treated uniforms, was significantly higher in the heat (P = 0.01) and the heat/humidity (P = 0.03) groups than the ambient group. There were no significant differences in biomarker concentrations or computed average daily dose between the heat and the heat/humidity groups. Both hot and combined hot and humid environmental conditions significantly increased permethrin absorption in soldiers wearing permethrin-treated uniforms.

10.4269/ajtmh.19-0543

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Citations (10)