Physiological Tolerance to Uncompensable Heat Stress: Effects of Exercise Intensity, Protective Clothing, and Climate

1994 ◽  
Author(s):  
Scott J. Montain ◽  
Michael N. Sawka ◽  
Bruce S. Cadarette ◽  
Mark D. Quigley ◽  
James M. McKay
Keyword(s):  
Heat Stress ◽  
Exercise Intensity ◽  
Protective Clothing ◽  
Physiological Tolerance ◽  
Stress Effects ◽  
Uncompensable Heat Stress

Physiological tolerance to uncompensable heat stress: effects of exercise intensity, protective clothing, and climate

1994 ◽  
Vol 77 (1) ◽  
pp. 216-222 ◽  
Author(s):  
S. J. Montain ◽  
M. N. Sawka ◽  
B. S. Cadarette ◽  
M. D. Quigley ◽  
J. M. McKay
Keyword(s):  
Heat Stress ◽  
Relative Humidity ◽  
Core Temperature ◽  
Exercise Intensity ◽  
Protective Clothing ◽  
Heat Exposure ◽  
Heat Strain ◽  
Published Data ◽  
Physiological Tolerance ◽  
Uncompensable Heat Stress

This study determined the influence of exercise intensity, protective clothing level, and climate on physiological tolerance to uncompensable heat stress. It also compared the relationship between core temperature and the incidence of exhaustion from heat strain for persons wearing protective clothing to previously published data of unclothed persons during uncompensable heat stress. Seven heat-acclimated men attempted 180-min treadmill walks at metabolic rates of approximately 425 and 600 W while wearing full (clo = 1.5) or partial (clo = 1.3) protective clothing in both a desert (43 degrees C dry bulb, 20% relative humidity, wind 2.2 m/s) and tropical (35 degrees C dry bulb, 50% relative humidity, wind 2.2 m/s) climate. During these trials, the evaporative cooling required to maintain thermal balance exceeded the maximal evaporative capacity of the environment and core temperature continued to rise until exhaustion from heat strain occurred. Our findings concerning exhaustion from heat strain are 1) full encapsulation in protective clothing reduces physiological tolerance as core temperature at exhaustion was lower (P < 0.05) in fully than in partially clothed persons, 2) partial encapsulation results in physiological tolerance similar to that reported for unclothed persons, 3) raising metabolic rate from 400 to 600 W does not alter physiological tolerance when subjects are fully clothed, and 4) physiological tolerance is similar when subjects are wearing protective clothing in desert and tropical climates having the same wet bulb globe thermometer. These findings can improve occupational safety guidelines for human heat exposure, as they provide further evidence that the incidence of exhaustion from heat strain can be predicted from core temperature.

Heat acclimation, aerobic fitness, and hydration effects on tolerance during uncompensable heat stress

1998 ◽  
Vol 84 (5) ◽  
pp. 1731-1739 ◽  
Author(s):  
Stephen S. Cheung ◽  
Tom M. McLellan
Keyword(s):  
Heart Rate ◽  
Heat Stress ◽  
Aerobic Fitness ◽  
Protective Clothing ◽  
Sweat Rate ◽  
Heat Acclimation ◽  
Short Term ◽  
Chemical Protective Clothing ◽  
Uncompensable Heat Stress ◽  
C 30

—The purpose of the present study was to determine the separate and combined effects of aerobic fitness, short-term heat acclimation, and hypohydration on tolerance during light exercise while wearing nuclear, biological, and chemical protective clothing in the heat (40°C, 30% relative humidity). Men who were moderately fit [(MF); <50 ml ⋅ kg−1 ⋅ min−1maximal O2 consumption; n = 7] and highly fit [(HF); >55 ml ⋅ kg−1 ⋅ min−1maximal O2 consumption; n = 8] were tested while they were euhydrated or hypohydrated by ∼2.5% of body mass through exercise and fluid restriction the day preceding the trials. Tests were conducted before and after 2 wk of daily heat acclimation (1-h treadmill exercise at 40°C, 30% relative humidity, while wearing the nuclear, biological, and chemical protective clothing). Heat acclimation increased sweat rate and decreased skin temperature and rectal temperature (Tre) in HF subjects but had no effect on tolerance time (TT). MF subjects increased sweat rate but did not alter heart rate, Tre, or TT. In both MF and HF groups, hypohydration significantly increased Tre and heart rate and decreased the respiratory exchange ratio and the TT regardless of acclimation state. Overall, the rate of rise of skin temperature was less, while ΔTre, the rate of rise of Tre, and the TT were greater in HF than in MF subjects. It was concluded that exercise-heat tolerance in this uncompensable heat-stress environment is not influenced by short-term heat acclimation but is significantly improved by long-term aerobic fitness.

Low doses of melatonin and diurnal effects on thermoregulation and tolerance to uncompensable heat stress

1999 ◽  
Vol 87 (1) ◽  
pp. 308-316 ◽  
Author(s):  
Tom M. McLellan ◽  
Greg A. Gannon ◽  
Jiri Zamecnik ◽  
Valerie Gil ◽  
Greg M. Brown
Keyword(s):  
Heat Stress ◽  
Protective Clothing ◽  
Low Dose ◽  
Heart Rate Response ◽  
Heat Storage ◽  
Stress Exposure ◽  
Double Blind ◽  
Early Afternoon ◽  
Hypothermic Effect ◽  
Uncompensable Heat Stress

This study examined whether the reported hypothermic effect of melatonin ingestion increased tolerance to exercise at 40°C, for trials conducted either in the morning or afternoon, while subjects were wearing protective clothing. Nine men performed four randomly ordered trials; two each in the morning (0930) and afternoon (1330) after the double-blind ingestion of either two placebo capsules or two 1-mg capsules of melatonin. Despite significant elevations in plasma melatonin to over 1,000 ng/ml 1 h after the ingestion of the first 1-mg dose, rectal temperature (Tre) was unchanged before or during the heat-stress exposure. Also, all other indexes of temperature regulation and the heart rate response during the uncompensable heat stress were unaffected by the ingestion of melatonin. Initial Tre was increased during the afternoon (37.1 ± 0.2°C), compared with the morning (36.8 ± 0.2°C) exposures, and these differences remained throughout the uncompensable heat stress, such that final Tre was also increased for the afternoon (39.2 ± 0.2°C) vs. the morning (39.0 ± 0.3°C) trials. Tolerance times and heat storage were not different among the exposures at ∼110 min and 16 kJ/kg, respectively. It was concluded that this low dose of melatonin had no impact on tolerance to uncompensable heat stress and that trials conducted in the early afternoon were associated with an increased Tre tolerated at exhaustion that offset the circadian influence on resting Tre and thus maintained tolerance times similar to those of trials conducted in the morning.

Effects of Dehydration, Hypohydration, and Hyperhydration on Tolerance During Uncompensable Heat Stress

1999 ◽  
Vol 24 (4) ◽  
pp. 349-361 ◽  
Author(s):  
Tom M. Mclellan ◽  
Stephen S. Cheung ◽  
William A. Latzka ◽  
Mike N. Sawka ◽  
Kent B. Pandolf ◽  
...  
Keyword(s):  
Body Weight ◽  
Heat Stress ◽  
Rectal Temperature ◽  
Protective Clothing ◽  
Cardiovascular Responses ◽  
Hydration Status ◽  
Fluid Restriction ◽  
Prior Exercise ◽  
Key Words Thermoregulation ◽  
Uncompensable Heat Stress

The present study examined the effects of dehydration from prior exercise on subsequent exercise tolerance time (TT) that involved wearing nuclear, biological, and chemical (NBC) protective clothing. It was hypothesised that TT would be reduced in the dehydrated state. Ten men undertook continuous treadmill walking at 4.8 km • h−1 at 35 °C and 50% relative humidity, wearing NBC clothing while euhydrated (EU) or dehydrated (D) by 2.3% of body weight. Hydration status had no impact on thermoregulatory or cardiovascular responses during exercise. Also rectal temperature at exhaustion did not differ between EU (38.52 ± 0.39 °C) and D (38.43 ± 0.45 °C). Exercise TT during this uncompensable heat stress was reduced significantly for D (47.7 ± 15.3 min) compared with EU (59.0 ± 13.6 min). It was concluded that prior exercise leading to levels of dehydration to 2.3% of body weight, together with subsequent fluid restriction during exposure to uncompensable heat stress, impaired TT while wearing the NBC protective clothing. The integration of these findings together with other comparable studies that have examined the influence of hypo- and hyperhydration on TT while wearing NBC protective clothing revealed that hydration status has less effect on TT as the severity of uncompensable heat stress increases. Key words: thermoregulation, protective clothing, heat tolerance, rectal temperature

Heat Stress Effects of a Navy/USMC vs. Army Aviator Ensemble in a UH-6O Helicopter Simulator

1998 ◽  
Author(s):  
Matthew J. Reardon ◽  
E. B. Fraser ◽  
Lawrence Katz ◽  
Patricia LeDuc ◽  
Pooria Morovati
Keyword(s):  
Heat Stress ◽  
Stress Effects

Protective clothing and heat stress

Ergonomics ◽  
1995 ◽  
Vol 38 (1) ◽  
pp. 166-182 ◽  
Author(s):  
INGVAR HOLMÉR
Keyword(s):  
Heat Stress ◽  
Protective Clothing

scholarly journals Nutritional strategies to alleviate heat stress effects through feed restrictions and feed additives (vitamins and minerals) in broilers under summer conditions

2019 ◽  
Vol 7 (3) ◽  
pp. 123-131 ◽  
Author(s):  
Mohamed Abdelhameed Salah Abdelhameed ◽  
◽  
Lozovskiy Alexander Robertovich ◽  
Ali Amany Muhammad Ahmed ◽  
◽  
...  
Keyword(s):  
Heat Stress ◽  
Feed Additives ◽  
Stress Effects ◽  
Nutritional Strategies
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