Fitness-related differences in the rate of whole-body total heat loss in exercising young healthy women are heat-load dependent.

New Findings: What is the central question of this study? Aerobic fitness modulates heat loss, albeit the heat load at which fitness-related differences occur in young healthy women remains unclear. What is the main finding and its importance? We demonstrate using direct calorimetry that fitness modulates heat loss in a heat-load dependent manner, with differences occurring between young women of low and high fitness and matched physical characteristics when the metabolic heat load is at least 400 W in hot, dry conditions. Although fitness has been known for some time to modulate heat loss, our findings define the metabolic heat load at which fitness-related differences occur.

Voltage-gated potassium channels and NOS contribute to a sustained cutaneous vasodilation elicited by local heating in an interactive manner in young adults.

Local skin heating to 42°C causes rapid increases in cutaneous perfusion (initial peak), followed by a brief nadir and subsequent sustained elevation (plateau). Several studies have demonstrated that nitric oxide synthase (NOS) largely contributes to the plateau response during local heating. In this study, we tested the hypothesis that voltage-gated potassium (Kv) channels contribute to the plateau of the cutaneous vasodilation during local heating through NOS-dependent mechanisms.

Type 2 diabetes specifically attenuates purinergic skin vasodilatation without affecting muscarinic and nicotinic skin vasodilatation and sweating.

New Findings: What is the central question of this study? It remains to be determined whether type 2 diabetes attenuates muscarinic and nicotinic cutaneous vasodilatation and sweating as well as purinergic cutaneous vasodilatation. What is the main finding and its importance? We show that type 2 diabetes specifically attenuates purinergic cutaneous vasodilatation without influencing muscarinic and nicotinic cutaneous vasodilatation and sweating. Our results provide valuable new information regarding the receptor-specific influence of type 2 diabetes on microvascular and sudomotor function.

Oxidative stress does not influence local sweat rate during high-intensity exercise.

What is the central question of this study? We evaluated whether oxidative stress attenuates the contribution of nitric oxide to sweating during high-intensity exercise. What is the main finding and its importance? In contrast to our previous report of an oxidative stress-mediated reduction in nitric oxide-dependent cutaneous vasodilatation in this cohort during intense exercise, we demonstrated no influence of local ascorbate administration on the sweating response during moderate- (∼51% peak oxygen uptake) or high-intensity exercise (∼72% peak oxygen uptake). These new findings provide important mechanistic insight into how exercise-induced oxidative stress impacts sudomotor activity.

Body temperature and cold sensation during and following exercise under temperate room conditions in cold-sensitive young trained females.

We evaluated cold sensation at rest and in response to exercise-induced changes in core and skin temperatures in cold-sensitive exercise trained females. Fifty-eight trained young females were screened by a questionnaire, selecting cold-sensitive (Cold-sensitive,  = 7) and non-cold-sensitive (Control,  = 7) individuals. Participants rested in a room at 29.

Fitness-related differences in the rate of whole-body evaporative heat loss in exercising men are heat-load dependent.

What is the central question of this study? Aerobic fitness modulates heat loss, but the heat-load threshold at which fitness-related differences in heat loss occur in young healthy men remains unclear. What is the main finding and its importance? We demonstrate using direct calorimetry that aerobic fitness modulates heat loss in a heat-load-dependent manner, with fitness-related differences occurring between young men who have low and high fitness when the heat load is ∼≥500 W. Although aerobic fitness has been known for some time to modulate heat loss, our findings define the precise heat-load threshold at which fitness-related differences occur.

Aging Impairs Whole-Body Heat Loss in Women under Both Dry and Humid Heat Stress.

Purpose: This study was designed to determine whether age-related impairments in whole-body heat loss, which are known to exist in dry heat, also occur in humid heat in women.

Methods: To evaluate this possibility, 10 young (25 ± 4 yr) and 10 older (51 ± 7 yr) women matched for body surface area (young, 1.69 ± 0.

Thermographic imaging in sports and exercise medicine: A Delphi study and consensus statement on the measurement of human skin temperature.

The importance of using infrared thermography (IRT) to assess skin temperature (t) is increasing in clinical settings. Recently, its use has been increasing in sports and exercise medicine; however, no consensus guideline exists to address the methods for collecting data in such situations. The aim of this study was to develop a checklist for the collection of t using IRT in sports and exercise medicine.

Does a Prolonged Work Day in the Heat Impair Heat Loss on the Next Day in Young Men?

Purpose: Heat strain is known to be exacerbated on the second of consecutive work days. We therefore evaluated whether prolonged work in the heat would impair whole-body heat loss capacity on the next day.

Methods: To evaluate this possibility, we assessed changes in whole-body heat exchange and heat storage in eight young (26 ± 4 yr) men during heat stress tests performed on the same day before (day 1) and on the day after (day 2) a prolonged work simulation.

Depressive symptoms, perceived stress, self-efficacy, and outcome expectations: Predict fitness among adolescents with obesity.

The objective of the present study was to test if outcome expectancy mediated the relationship between fitness and self-efficacy, perceived stress, and depressive symptoms.Adolescents with obesity ( = 228) completed measures of perceived stress and depressive symptoms at baseline, self-efficacy and outcome expectancy at baseline and 3 months, and fitness at baseline and 6 months. Structural equation modeling was used to analyze the data.

Time-motion analysis as a novel approach for evaluating the impact of environmental heat exposure on labor loss in agriculture workers.

: In this study we (i) introduced time-motion analysis for assessing the impact of workplace heat on the work shift time spent doing labor (WTL) of grape-picking workers, (ii) examined whether seasonal environmental differences can influence their WTL, and (iii) investigated whether their WTL can be assessed by monitoring productivity or the vineyard manager's estimate of WTL. : Seven grape-picking workers were assessed during the summer and/or autumn via video throughout four work shifts. : Air temperature (26.

Fluid replacement modulates oxidative stress- but not nitric oxide-mediated cutaneous vasodilation and sweating during prolonged exercise in the heat.

The roles of nitric oxide synthase (NOS), reactive oxygen species (ROS), and angiotensin II type 1 receptor (ATR) activation in regulating cutaneous vasodilation and sweating during prolonged (≥60 min) exercise are currently unclear. Moreover, it remains to be determined whether fluid replacement (FR) modulates the above thermoeffector responses. To investigate, 11 young men completed 90 min of continuous moderate intensity (46% V̇o) cycling performed at a fixed rate of metabolic heat production of 600 W (No FR condition).

Work Rate during Self-paced Exercise is not Mediated by the Rate of Heat Storage.

Purpose: To date, there have been mixed findings on whether greater anticipatory reductions in self-paced exercise intensity in the heat are mediated by early differences in rate of body heat storage. The disparity may be due to an inability to accurately measure minute-to-minute changes in whole-body heat loss. Thus, we evaluated whether early differences in rate of heat storage can mediate exercise intensity during self-paced cycling at a fixed rate of perceived exertion (RPE of 16; hard-to-very-hard work effort) in COOL (15°C), NORMAL (25°C), and HOT (35°C) ambient conditions.

Do nitric oxide synthase and cyclooxygenase contribute to sweating response during passive heating in endurance-trained athletes?

The aim of our study was to determine if habitual endurance training can influence the relative contribution of nitric oxide synthase (NOS) and cyclooxygenase (COX) in the regulation of sweating during a passive heat stress in young adults. Ten trained athletes and nine untrained counterparts were passively heated until oral temperature (as estimated by sublingual temperature, T) increased by 1.5°C above baseline resting.

The physiological strain incurred during electrical utilities work over consecutive work shifts in hot environments: A case report.

Purpose: In this article, we evaluated physiological strain in electrical utilities workers during consecutive work shifts in hot outdoor conditions.

Methods: Four highly experienced electrical utilities workers were monitored during regularly scheduled work performed in hot conditions (∼34°C) on two consecutive days. Worker hydration (urine specific gravity) was assessed prior to and following work.

Heat shock protein 90 contributes to cutaneous vasodilation through activating nitric oxide synthase in young male adults exercising in the heat.

While the mechanisms underlying the control of cutaneous vasodilation have been extensively studied, there remains a lack of understanding of the different factors that may modulate cutaneous perfusion during an exercise-induced heat stress. We evaluated the hypothesis that heat shock protein 90 (HSP90) contributes to the heat loss response of cutaneous vasodilation via the activation of nitric oxide synthase (NOS) during exercise in the heat. In 11 young males (25 ± 5 yr), cutaneous vascular conductance (CVC) was measured at four forearm skin sites that were continuously treated with ) lactated Ringer solution (control), ) NOS inhibition with 10 mM -nitro-l-arginine methyl ester (l-NAME), ) HSP90 inhibition with 178 μM geldanamycin, or ) a combination of 10 mM l-NAME and 178 μM geldanamycin.

Increasing age is a major risk factor for susceptibility to heat stress during physical activity.

We evaluated the extent to which age, cardiorespiratory fitness, and body fat can independently determine whole-body heat loss (WBHL) in 87 otherwise healthy adults. We show that increasing age is a major predictor for decreasing WBHL in otherwise healthy adults (aged 20-70 years), accounting for 40% of the variation in the largest study to date. While greater body fat also had a minor detrimental impact on WBHL, there was no significant role for cardiorespiratory fitness.

Direct calorimetry: a brief historical review of its use in the study of human metabolism and thermoregulation.

Direct calorimetry is the gold standard means of measuring human metabolic rate and its use has been fundamental for understanding metabolism in health and disease. While metabolic rate is now more commonly estimated indirectly from measures of the oxygen consumed during respiration, direct calorimetry provides the user with the unique capacity to quantify the heat produced from aerobic and anaerobic metabolism by measuring heat exchange between the body and the environment. This review provides a brief historical overview of the fundamental concepts which underlie direct calorimetry, of pioneer scientists which developed these concepts into functional pieces of equipment and the subsequent use of direct calorimetry to advance our understanding of energy balance, nutrition, and the pathogenesis of metabolic diseases.

The recommended Threshold Limit Values for heat exposure fail to maintain body core temperature within safe limits in older working adults.

Purpose: The American Conference of Governmental and Industrial Hygienists (ACGIH®) Threshold Limit Values (TLV® guidelines) for work in the heat consist of work-rest (WR) allocations designed to ensure a stable core temperature that does not exceed 38°C. However, the TLV® guidelines have not been validated in older workers. This is an important shortcoming given that adults as young as 40 years demonstrate impairments in their ability to dissipate heat.

Wearing graduated compression stockings augments cutaneous vasodilation but not sweating during exercise in the heat.

The activation of cutaneous vasodilation and sweating are essential to the regulation of core temperature during exercise in the heat. We assessed the effect of graduated compression induced by wearing stockings on cutaneous vasodilation and sweating during exercise in the heat (30°C). On two separate occasions, nine young males exercised for 45 min or until core temperature reached ~1.

Are All Heat Loads Created Equal?

Purpose: We evaluated physiological responses during exercise at a fixed evaporative requirement for heat balance (Ereq) but varying combinations of metabolic and environmental heat load.

Methods: Nine healthy, physically active males (age: 46 ± 8 yr) performed four experimental sessions consisting of 75 min of semirecumbent cycling at various ambient temperatures. Whole-body dry heat loss (direct calorimetry) was monitored continuously as was heat production (indirect calorimetry), which was adjusted to achieve an Ereq of 400 W.

Heat remains unaccounted for in thermal physiology and climate change research.

In the aftermath of the Paris Agreement, there is a crucial need for scientists in both thermal physiology and climate change research to develop the integrated approaches necessary to evaluate the health, economic, technological, social, and cultural impacts of 1.5°C warming. Our aim was to explore the fidelity of remote temperature measurements for quantitatively identifying the continuous redistribution of heat within both the Earth and the human body.

Hyperthermia and cardiovascular strain during an extreme heat exposure in young versus older adults.

We examined whether older individuals experience greater levels of hyperthermia and cardiovascular strain during an extreme heat exposure compared to young adults. During a 3-hour extreme heat exposure (44°C, 30% relative humidity), we compared body heat storage, core temperature (rectal, visceral) and cardiovascular (heart rate, cardiac output, mean arterial pressure, limb blood flow) responses of young adults (n = 30, 19-28 years) against those of older adults (n = 30, 55-73 years). Direct calorimetry measured whole-body evaporative and dry heat exchange.