Evidence against a 40°C core temperature threshold for fatigue in humans

2009 ◽  
Vol 107 (5) ◽  
pp. 1519-1525 ◽  
Author(s):  
Brett R. Ely ◽  
Matthew R. Ely ◽  
Samuel N. Cheuvront ◽  
Robert W. Kenefick ◽  
David W. DeGroot ◽  
...  
Keyword(s):  
Heart Rate ◽  
Field Study ◽  
Skin Temperature ◽  
Core Temperature ◽  
Rectal Temperature ◽  
Temperature Limit ◽  
Temperature Threshold ◽  
Elapsed Time ◽  
Skin Temperatures ◽  
Cardiovascular Strain

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 Tre <40°C for each runner. Changes in running velocity over the last 600 m were compared between runners with Tre >40°C and <40°C. Twelve runners achieved Tre >40.0°C with ≥600 m remaining (range 600–3,400 m). Average running velocity for Tre <40°C (282 ± 27 m/min) was not different from that for Tre >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 <40°C ( P = 0.16). Chest skin temperature ranged from 30 to 34°C, and heart rate was >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.

Quantifying Occupational Stress in Intensive Care Unit Nurses: An Applied Naturalistic Study of Correlations Among Stress, Heart Rate, Electrodermal Activity, and Skin Temperature

2021 ◽  
pp. 001872082110408
Author(s):  
Nima Ahmadi ◽  
Farzan Sasangohar ◽  
Tariq Nisar ◽  
Valerie Danesh ◽  
Ethan Larsen ◽  
...  
Keyword(s):  
Intensive Care Unit ◽  
Heart Rate ◽  
Intensive Care ◽  
Skin Temperature ◽  
Electrodermal Activity ◽  
Laboratory Research ◽  
Prior Literature ◽  
High Level ◽  
Intensive Care Unit Nurses ◽  
Skin Temperatures

Objective To identify physiological correlates to stress in intensive care unit nurses. Background Most research on stress correlates are done in laboratory environments; naturalistic investigation of stress remains a general gap. Method Electrodermal activity, heart rate, and skin temperatures were recorded continuously for 12-hr nursing shifts (23 participants) using a wrist-worn wearable technology (Empatica E4). Results Positive correlations included stress and heart rate (ρ = .35, p < .001), stress and skin temperature (ρ = .49, p < .05), and heart rate and skin temperatures (ρ = .54, p = .0008). Discussion The presence and direction of some correlations found in this study differ from those anticipated from prior literature, illustrating the importance of complementing laboratory research with naturalistic studies. Further work is warranted to recognize nursing activities associated with a high level of stress and the underlying reasons associated with changes in physiological responses. Application Heart rate and skin temperature may be used for real-time detection of stress, but more work is needed to validate such surrogate measures.

Age and sex difference in response to short exposure to extreme dry heat

1978 ◽  
Vol 44 (1) ◽  
pp. 1-4 ◽  
Author(s):  
Y. Shoenfeld ◽  
R. Udassin ◽  
Y. Shapiro ◽  
A. Ohri ◽  
E. Sohar
Keyword(s):  
Skin Temperature ◽  
Rectal Temperature ◽  
Short Exposure ◽  
Large Individual ◽  
Elderly Male ◽  
Dry Heat ◽  
Heat Response ◽  
Male Subjects ◽  
Skin Temperatures ◽  
Age And Sex

Sixty volunteers, 33 males and 27 females (18–63 yr), were divided according to age and sex. They were exposed for 10 min to extreme dry heat: 80–90 degrees C dry bulb temperature and 3–4% relative humidity. Their rectal temperature, skin temperature at eight different points, weight, and heart rate were recorded prior to and immediately following the exposure. A mean rise of only 0.5 degrees C in rectal temperature was recorded following exposure as compared to a mean rise of 5.2 degrees C in mean weighted skin temperature (MWST). Female subjects showed a significantly higher rise in MWST than the male subjects. Similarly, a significantly higher rise in MWST was observed in elderly male subjects as compared to the youngest male group (P less than 0.05). The differences in MWST possibly resulted from differences in mean skin blood flow causing differences in skin conductance. Large individual variation in heat response was recorded in rectal temperature, as well as in weighted skin temperatures. The increase in skin temperature during the first 10 min of exposure to extreme dry heat may serve as an indicator for heat tolerance time, and may help predicting heatstroke susceptible individuals.

Role of skin and of core temperatures in man's temperature regulation

1965 ◽  
Vol 20 (1) ◽  
pp. 31-36 ◽  
Author(s):  
C. H. Wyndham
Keyword(s):  
Skin Temperature ◽  
Rectal Temperature ◽  
Temperature Regulation ◽  
Passive Control ◽  
Sweat Rate ◽  
Heat Conductance ◽  
Response Characteristics ◽  
Highly Nonlinear ◽  
The Right ◽  
Skin Temperatures

The response characteristics have been studied of the curves relating heat conductance and sweat rate to change in rectal temperature at different levels of skin temperature, and vice versa. The increase in these responses with deviation in rectal temperature from the “neutral” setting is highly nonlinear; the neutral point and the curve shift to the right and the slope decreases with lowering of skin temperature and vice versa when it is raised. With further deviation of rectal temperature these responses reach maximum values, i.e., become “saturated.” All of these features are analogous to servomechanisms with negative feedback, giving sensitive and stable control. Control of these responses by skin temperature is more linear, characterizing passive control systems which are insensitive and less stable. Quantitatively, the effect at skin temperature of 26 C of 1 C rise in rectal temperature on heat conductance and sweat rate is 10 times greater than the same rise in skin temperature; at a neutral skin temperature of 33–34 C, a rise of 1 C in rectal temperature is 6–7 times greater; at a high skin temperature of 36 C, a rise in rectal temperature of 1 C is 4–5 times greater. relationship between heat conductance and a change in either rectal or skin temperatures; relationship between sweat rate and a change in either rectal or skin temperatures; response characteristics of curves relating heat conductance to change in either rectal or skin temperatures; response characteristics of curves relating sweat rate to change in either rectal or skin temperatures; assessment of the contribution of skin and rectal temperatures to man's temperature regulation Submitted on October 22, 1963

scholarly journals Core Temperature in Triathletes during Swimming with Wetsuit in 10 °C Cold Water

Sports ◽  
2019 ◽  
Vol 7 (6) ◽  
pp. 130 ◽  
Author(s):  
Jørgen Melau ◽  
Maria Mathiassen ◽  
Trine Stensrud ◽  
Mike Tipton ◽  
Jonny Hisdal
Keyword(s):  
Water Temperature ◽  
Skin Temperature ◽  
Core Temperature ◽  
Rectal Temperature ◽  
Physiological Response ◽  
Cold Water ◽  
Temperature Response ◽  
Open Water ◽  
Open Water Swimming ◽  
Ironman Distance

Low water temperature (<15 °C) has been faced by many organizers of triathlons and swim-runs in the northern part of Europe during recent years. More knowledge about how cold water affects athletes swimming in wetsuits in cold water is warranted. The aim of the present study was therefore to investigate the physiological response when swimming a full Ironman distance (3800 m) in a wetsuit in 10 °C water. Twenty triathletes, 37.6 ± 9 years (12 males and 8 females) were recruited to perform open water swimming in 10 °C seawater; while rectal temperature (Tre) and skin temperature (Tskin) were recorded. The results showed that for all participants, Tre was maintained for the first 10–15 min of the swim; and no participants dropped more than 2 °C in Tre during the first 30 min of swimming in 10 °C water. However; according to extrapolations of the results, during a swim time above 135 min; 47% (8/17) of the participants in the present study would fall more than 2 °C in Tre during the swim. The results show that the temperature response to swimming in a wetsuit in 10 °C water is highly individual. However, no participant in the present study dropped more than 2 °C in Tre during the first 30 min of the swim in 10 °C water.

Effects of caffeine on blood pressure, heart rate, and forearm blood flow during dynamic leg exercise

1998 ◽  
Vol 85 (1) ◽  
pp. 154-159 ◽  
Author(s):  
Jason W. Daniels ◽  
Paul A. Molé ◽  
James D. Shaffrath ◽  
Charles L. Stebbins
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Blood Flow ◽  
Systolic Blood Pressure ◽  
Skin Temperature ◽  
Rectal Temperature ◽  
Forearm Blood Flow ◽  
Dynamic Exercise ◽  
Ang Ii ◽  
Leg Exercise

This study examined the acute effects of caffeine on the cardiovascular system during dynamic leg exercise. Ten trained, caffeine-naive cyclists (7 women and 3 men) were studied at rest and during bicycle ergometry before and after the ingestion of 6 mg/kg caffeine or 6 mg/kg fructose (placebo) with 250 ml of water. After consumption of caffeine or placebo, subjects either rested for 100 min (rest protocol) or rested for 45 min followed by 55 min of cycle ergometry at 65% of maximal oxygen consumption (exercise protocol). Measurement of mean arterial pressure (MAP), forearm blood flow (FBF), heart rate, skin temperature, and rectal temperature and calculation of forearm vascular conductance (FVC) were made at baseline and at 20-min intervals. Plasma ANG II was measured at baseline and at 60 min postingestion in the two exercise protocols. Before exercise, caffeine increased both systolic blood pressure (17%) and MAP (11%) without affecting FBF or FVC. During dynamic exercise, caffeine attenuated the increase in FBF (53%) and FVC (50%) and accentuated exercise-induced increases in ANG II (44%). Systolic blood pressure and MAP were also higher during exercise plus caffeine; however, these increases were secondary to the effects of caffeine on resting blood pressure. No significant differences were observed in heart rate, skin temperature, or rectal temperature. These findings indicate that caffeine can alter the cardiovascular response to dynamic exercise in a manner that may modify regional blood flow and conductance.

Circadian rhythm of heat production, heart rate, and skin and core temperature under unmasking conditions in men

1994 ◽  
Vol 267 (3) ◽  
pp. R819-R829 ◽  
Author(s):  
K. Krauchi ◽  
A. Wirz-Justice
Keyword(s):  
Heart Rate ◽  
Circadian Rhythm ◽  
Heat Loss ◽  
Rectal Temperature ◽  
Heat Production ◽  
Circadian Variation ◽  
Bed Rest ◽  
Sodium Potassium ◽  
Hands And Feet ◽  
Skin Temperatures

Seven healthy men were studied in a 34-h constant routine protocol to investigate whether the daily rhythm of heat production and heat loss has an endogenous circadian component. Under these unmasking conditions (constant bed rest, no sleep allowed, regular food and fluid intake), a significant circadian rhythm could be demonstrated for heat production, heart rate, and skin temperatures but not for the respiratory quotient. Heat production and heart rate were phase locked with a maximum at 1100-1200 h. Proximal skin temperatures (infraclavicular region, thigh, and forehead) followed the same circadian rhythm as rectal temperature, whereas distal skin temperatures (hands and feet) were opposite in phase. These physiological circadian rhythm parameters, as well as biochemical parameters (urinary sodium, potassium, urea, and urine flow), were phase advanced by 25-180 min with respect to the circadian rhythm in rectal temperature. Our findings under unmasking conditions show that the circadian variation in rectal temperature is a consequence of endogenous circadian rhythms in both heat production and heat loss.

Observations on the effect of salicylate in fever and the regulation of body temperature against cold

1976 ◽  
Vol 54 (2) ◽  
pp. 101-106 ◽  
Author(s):  
Q. J. Pittman ◽  
W. L. Veale ◽  
K. E. Cooper
Keyword(s):  
Body Temperature ◽  
Skin Temperature ◽  
Rectal Temperature ◽  
Heat Production ◽  
Intravenous Infusion ◽  
Sodium Salicylate ◽  
Single Injection ◽  
Continuous Intravenous Infusion ◽  
Skin Temperatures

Prostaglandins appear to be mediators, within the hypothalamus, of heat production and conservation during fever. We have investigated a possible role of prostaglandins in the nonfebrile rabbit during thermoregulation in the cold. Shorn rabbits were placed in an environment of 20 °C, and rectal and ear skin temperatures, shivering and respiratory rates were measured. A continuous intravenous infusion of leucocyte pyrogen was given to establish a constant fever of approximately 1 °C, and after observation of a stable febrile temperature for 90 min, a single injection of 300 mg of sodium salicylate, followed by a 1.5 mg/min infusion was then given. After the salicylate infusion was begun, rectal temperature began to fall, and reached nonfebrile levels within 90 min. Shivering activity ceased, respiratory rates increased, and in two animals, ear skin temperature increased. When these same rabbits were placed in an environment of 10 °C, at a time they were not febrile, and an identical amount of salicylate was given, rectal and ear skin temperatures, shivering and respiratory rates did not change. These results indicate that prostaglandins do not appear to be involved in heat production and conservation in the nonfebrile rabbit.

Acclimatization of calves to a hot humid environment

1959 ◽  
Vol 52 (3) ◽  
pp. 305-312 ◽  
Author(s):  
W. Bianca
Keyword(s):  
Heart Rate ◽  
Body Temperature ◽  
Respiratory Rate ◽  
Skin Temperature ◽  
Rectal Temperature ◽  
Heat Production ◽  
Metabolic Heat ◽  
Hot Environment ◽  
Humid Environment ◽  
Physiological Reactions

1. Three calves were exposed in a climatic room to an environment of 40° C. dry-bulb and 38° C. wet-bulb temperature for up to 110 min. each day for 1-2 weeks.2. These exposures produced progressive changes in the physiological reactions of the animals to heat:(a) Rectal temperature and skin temperature (for a given time of exposure) declined. In consequence there was a marked increase in the tolerance time, i.e. in the time for which the animals could withstand the hot environment before reaching a rectal temperature of 42° C.(b) Respiratory rate rose earlier and assumed higher levels (for given levels of body temperature).(c) Heart rate decreased markedly.3. These changes are discussed in relation to heat loss and heat production and have been interpreted as reflecting chiefly a reduction in the metabolic heat production of the animals.

Responses of Zebu, Jersey, and Zebu X Jersey crossbred heifers to rising temperature, with particular reference to sweating

1962 ◽  
Vol 13 (1) ◽  
pp. 165 ◽  
Author(s):  
TE Allen
Keyword(s):  
Skin Temperature ◽  
Air Temperature ◽  
Rectal Temperature ◽  
Temperature Regime ◽  
Linear Increase ◽  
The Other ◽  
Sweating Rate ◽  
Respiration Rates ◽  
Breed Differences ◽  
Skin Temperatures

Zebu, Jersey, and Zebu x Jersey crossbred heifers were subjected to a rising temperature regime over the range 65 to 105°F. Sweating rates, respiration rates, skin temperatures, and rectal temperatures were measured. All breeds showed similar responses in skin temperature and rectal temperature to increase in air temperature. The increase in skin temperature was approximately linear with rise in air temperature. Rectal temperature did not commence to rise until an air temperature of 90°F and a skin temperature of 98° was reached. Breed differences in sweating and respiratory rates with increase in air and skin temperature were observed. The Jersey heifers showed an early and almost linear increase in sweating rate with rise in air and skin temperature, whereas the sweating rate of the Zebu heifers did not increase until air temperature had risen to at least 85°F and skin temperature to 95°. Two crossbreds began to increase their sweating rates at temperatures intermediate between those recorded for Zebus arid Jerseys. The remaining two behaved similarly to Jerseys. All three breeds showed similar maximum sweating rates in response to this rising temperature regime. The respiratory rate of' the Jerseys was higher than that of the Zebus at all temperatures, and particularly at high temperatures. Crossbreds respired at rates comparable to the Jerseys until an air temperature of 90°F and a skin temperature of 97°F were exceeded, when their respiration rates became intermediate between the other two breeds. The significance of these differences is discussed.

Predicting indoor thermal sensation for the elderly in welfare centres in Korea using local skin temperatures

2016 ◽  
Vol 26 (8) ◽  
pp. 1155-1167 ◽  
Author(s):  
Chihye Bae ◽  
Hyunjung Lee ◽  
Chungyoon Chun
Keyword(s):  
Field Study ◽  
Skin Temperature ◽  
Elderly People ◽  
Thermal Sensation ◽  
The Elderly ◽  
The Body ◽  
Elderly Subjects ◽  
Climate Chamber ◽  
Local Skin ◽  
Skin Temperatures

This study aims to develop a method to predict thermal sensation in elderly people. To identify the point on the body where skin temperature can best predict thermal sensation in elderly people aged 65 or older and develop a thermal comfort measurement model that can replace the psychological scale, experiments were conducted in a stainless steel wall finish climate chamber and at the seven senior welfare centres in Korea. The results of the climate chamber experiment with 30 healthy elderly people (15 males, 15 females) showed that there was a correlation between thermal sensation and local skin temperature on the back of the hand, the upper arm, the top of the foot and the cheek. This developed thermal sensation prediction model was then applied in a field study at senior welfare centres to verify whether the model could be applied to a large number of elderly subjects in different locations. The field study with 294 elderly people (111 males, 183 females) shows that cheek and back of the hand skin temperatures were useful in predicting thermal sensation in the elderly, and predicted thermal sensation based on the skin temperature of the cheek had the strongest correlation with thermal sensation among the participants.

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