scholarly journals Effect of hypohydration on thermoregulatory responses in men with low and high body fat exercising in the heat

2017 ◽  
Vol 122 (1) ◽  
pp. 142-152 ◽  
Author(s):  
Matthew A. Tucker ◽  
Aaron R. Caldwell ◽  
Cory L. Butts ◽  
Forrest B. Robinson ◽  
Haley C. Reynebeau ◽  
...  
Keyword(s):  
Heat Stress ◽  
Body Fat ◽  
Rectal Temperature ◽  
Sweat Rate ◽  
Core Body Temperature ◽  
Hydration Status ◽  
High Body ◽  
Thermoregulatory Responses ◽  
Heat Production Rate ◽  
Local Sweat Rate

It is unclear whether men with low body fat (LO-BF) have impaired thermoregulation during exercise heat stress compared with those with high body fat (HI-BF) when euhydration (EU) is maintained. Furthermore, in LO-BF individuals, hypohydration (HY) impairs thermoregulatory responses during exercise heat stress, but it is unknown whether this occurs in HI-BF counterparts. The purpose of this study was to test the hypotheses that men with HI-BF have impaired thermoregulatory responses to exercise heat stress and that HY further exacerbates these impairments vs. LO-BF. Men with LO-BF [ n = 11, body mass (BM) 73.9 ± 8.5 kg, BF% 13.6 ± 3.8] and HI-BF ( n = 9, BM 89.6 ± 6.9 kg, BF% 30.2 ± 4.1), in a randomized crossover design, performed 60 min of upright cycling in a hot environment (40.3 ± 0.4°C, relative humidity 32.5 ± 1.9%) at a metabolic heat production rate of 6 W/kg BM and finished exercise either euhydrated (EU; 0.3 ± 1.2 vs. 0.3 ± 0.9% BM loss) or HY (−2.5 ± 1.1 vs. −1.7 ± 1.5% BM loss). Changes in rectal temperature (ΔTrec), local sweat rate (ΔLSR), and cutaneous vascular conductance (ΔCVC; %max) were measured throughout. When EU, LO-BF and HI-BF had similar CVC and LSR responses ( P > 0.05); however, LO-BF had a lower ΔTrec vs. HI-BF (0.92 ± 0.35 vs. 1.31 ± 0.32°C, P = 0.021). Compared with EU, HY increased end-exercise ΔTrec in LO-BF (0.47 ± 0.37°C, P < 0.01) but not in HI-BF (−0.06 ± 0.29°C, P > 0.05). HY, compared with EU, did not affect ΔLSR and ΔCVC in either group ( P > 0.05). We conclude that, when euhydrated, men with HI-BF have a greater increase in Trec vs. LO-BF but similar CVC and LSR. HY exacerbates increases in Trec in LO-BF but not HI-BF. NEW & NOTEWORTHY This is the first known investigation to compare thermoregulatory responses to exercise heat stress between men with high and low body fat (BF) in a physiologically uncompensable environment while simultaneously examining the confounding influence of hydration status. Both groups demonstrated similar sweating and cutaneous vasodilatory responses when euhydrated, despite vast differences in rectal temperature. Furthermore, in contrast to low BF, individuals with high BF demonstrated similar increases in core body temperature when either euhydrated or hypohydrated.

scholarly journals A comparison of thermoregulatory responses to exercise between mass-matched groups with large differences in body fat

2016 ◽  
Vol 120 (6) ◽  
pp. 615-623 ◽  
Author(s):  
Sheila Dervis ◽  
Geoff B. Coombs ◽  
Georgia K. Chaseling ◽  
Davide Filingeri ◽  
Jovana Smoljanic ◽  
...  
Keyword(s):  
Lean Body Mass ◽  
Body Mass ◽  
Body Fat ◽  
Sweat Rate ◽  
Whole Body ◽  
Total Body Mass ◽  
Percentage Body Fat ◽  
Thermoregulatory Responses ◽  
Local Sweat Rate ◽  
Total Body

We sought to determine 1) the influence of adiposity on thermoregulatory responses independently of the confounding biophysical factors of body mass and metabolic heat production (Hprod); and 2) whether differences in adiposity should be accounted for by prescribing an exercise intensity eliciting a fixed Hprod per kilogram of lean body mass (LBM). Nine low (LO-BF) and nine high (HI-BF) body fat males matched in pairs for total body mass (TBM; LO-BF: 88.7 ± 8.4 kg, HI-BF: 90.1 ± 7.9 kg; P = 0.72), but with distinctly different percentage body fat (%BF; LO-BF: 10.8 ± 3.6%; HI-BF: 32.0 ± 5.6%; P < 0.001), cycled for 60 min at 28.1 ± 0.2°C, 26 ± 8% relative humidity (RH), at a target Hprod of 1) 550 W (FHP trial) and 2) 7.5 W/kg LBM (LBM trial). Changes in rectal temperature (ΔTre) and local sweat rate (LSR) were measured continuously while whole body sweat loss (WBSL) and net heat loss (Hloss) were estimated over 60 min. In the FHP trial, ΔTre (LO-BF: 0.66 ± 0.21°C, HI-BF: 0.87 ± 0.18°C; P = 0.02) was greater in HI-BF, whereas mean LSR (LO-BF 0.52 ± 0.19, HI-BF 0.43 ± 0.15 mg·cm−2·min−1; P = 0.19), WBSL (LO-BF 586 ± 82 ml, HI-BF 559 ± 75 ml; P = 0.47) and Hloss (LO-BF 1,867 ± 208 kJ, HI-BF 1,826 ± 224 kJ; P = 0.69) were all similar. In the LBM trial, ΔTre (LO-BF 0.82 ± 0.18°C, HI-BF 0.54 ± 0.19°C; P < 0.001), mean LSR (LO-BF 0.59 ± 0.20, HI-BF 0.38 ± 0.12 mg·cm−2·min−1; P = 0.04), WBSL (LO-BF 580 ± 106 ml, HI-BF 381 ± 68 ml; P < 0.001), and Hloss (LO-BF 1,884 ± 277 kJ, HI-BF 1,341 ± 184 kJ; P < 0.001) were all greater at end-exercise in LO-BF. In conclusion, high %BF individuals demonstrate a greater ΔTre independently of differences in mass and Hprod, possibly due to a lower mean specific heat capacity or impaired sudomotor control. However, thermoregulatory responses of groups with different adiposity levels should not be compared using a fixed Hprod in watts per kilogram lean body mass.

Forearm cutaneous vascular and sudomotor responses to whole body passive heat stress in young smokers

2015 ◽  
Vol 309 (1) ◽  
pp. R36-R42 ◽  
Author(s):  
Nicole E. Moyen ◽  
Hannah M. Anderson ◽  
Jenna M. Burchfield ◽  
Matthew A. Tucker ◽  
Melina A. Gonzalez ◽  
...  
Keyword(s):  
Heat Stress ◽  
Sweat Gland ◽  
Sweat Rate ◽  
Whole Body ◽  
Mean Body Temperature ◽  
Doppler Flowmetry ◽  
Cutaneous Vasodilation ◽  
Local Sweat Rate ◽  
Vasomotor Activity ◽  
Young Smokers

The purpose of this study was to compare smokers and nonsmokers' sudomotor and cutaneous vascular responses to whole body passive heat stress. Nine regularly smoking (SMK: 29 ± 9 yr; 10 ± 6 cigarettes/day) and 13 nonsmoking (N-SMK: 27 ± 8 yr) males were passively heated until core temperature (TC) increased 1.5°C from baseline. Forearm local sweat rate (LSR) via ventilated capsule, sweat gland activation (SGA), sweat gland output (SGO), and cutaneous vasomotor activity via laser-Doppler flowmetry (CVC) were measured as mean body temperature increased (ΔTb) during passive heating using a water-perfused suit. Compared with N-SMK, SMK had a smaller ΔTb at the onset of sweating (0.52 ± 0.19 vs. 0.35 ± 0.14°C, respectively; P = 0.03) and cutaneous vasodilation (0.61 ± 0.21 vs. 0.31 ± 0.12°C, respectively; P < 0.01). Increases in LSR and CVC per °C ΔTb (i.e., sensitivity) were similar in N-SMK and SMK (LSR: 0.63 ± 0.21 vs. 0.60 ± 0.40 Δmg/cm2/min/°C ΔTb, respectively, P = 0.81; CVC: 82.5 ± 46.2 vs. 58.9 ± 23.3 Δ%max/°C ΔTb, respectively; P = 0.19). However, the plateau in LSR during whole body heating was higher in N-SMK vs. SMK (1.00 ± 0.13 vs. 0.79 ± 0.26 mg·cm−2·min−1; P = 0.03), which was likely a result of higher SGO (8.94 ± 3.99 vs. 5.94 ± 3.49 μg·gland−1·min−1, respectively; P = 0.08) and not number of SGA (104 ± 7 vs. 121 ± 9 glands/cm2, respectively; P = 0.58). During whole body passive heat stress, smokers had an earlier onset for forearm sweating and cutaneous vasodilation, but a lower local sweat rate that was likely due to lower sweat output per gland. These data provide insight into local (i.e., forearm) thermoregulatory responses of young smokers during uncompensatory whole body passive heat stress.

Active cutaneous vasodilation in resting humans during mild heat stress

2005 ◽  
Vol 98 (3) ◽  
pp. 829-837 ◽  
Author(s):  
Yoshi-Ichiro Kamijo ◽  
Kichang Lee ◽  
Gary W. Mack
Keyword(s):  
Blood Flow ◽  
Heat Stress ◽  
Skin Temperature ◽  
Skin Blood Flow ◽  
Sweat Rate ◽  
Mean Skin Temperature ◽  
Local Skin ◽  
Mild Heat ◽  
Normal Core ◽  
Local Sweat Rate

The role of skin temperature in reflex control of the active cutaneous vasodilator system was examined in six subjects during mild graded heat stress imposed by perfusing water at 34, 36, 38, and 40°C through a tube-lined garment. Skin sympathetic nerve activity (SSNA) was recorded from the peroneal nerve with microneurography. While monitoring esophageal, mean skin, and local skin temperatures, we recorded skin blood flow at bretylium-treated and untreated skin sites by using laser-Doppler velocimetry and local sweat rate by using capacitance hygrometry on the dorsal foot. Cutaneous vascular conductance (CVC) was calculated by dividing skin blood flow by mean arterial pressure. Mild heat stress increased mean skin temperature by 0.2 or 0.3°C every stage, but esophageal and local skin temperature did not change during the first three stages. CVC at the bretylium tosylate-treated site (CVCBT) and sweat expulsion number increased at 38 and 40°C compared with 34°C ( P < 0.05); however, CVC at the untreated site did not change. SSNA increased at 40°C ( P < 0.05, different from 34°C). However, SSNA burst amplitude increased ( P < 0.05), whereas SSNA burst duration decreased ( P < 0.05), at the same time as we observed the increase in CVCBT and sweat expulsion number. These data support the hypothesis that the active vasodilator system is activated by changes in mean skin temperature, even at normal core temperature, and illustrate the intricate competition between active vasodilator and the vasoconstrictor system for control of skin blood flow during mild heat stress.

scholarly journals Core Temperature and Metabolic Responses After Carbohydrate Intake During Exercise at 30°C

2008 ◽  
Vol 43 (6) ◽  
pp. 585-591 ◽  
Author(s):  
Craig A. Horswill ◽  
John R. Stofan ◽  
Shannon C. Lovett ◽  
Chris Hannasch
Keyword(s):  
Steady State ◽  
Metabolic Rate ◽  
Core Temperature ◽  
Rectal Temperature ◽  
Repeated Measures ◽  
Sweat Rate ◽  
Fluid Replacement ◽  
Metabolic Responses ◽  
Hydration Status ◽  
Carbohydrate Ingestion

Abstract Context: Carbohydrate ingestion has recently been associated with elevated core temperature during exercise in the heat when testing for ergogenic effects. Whether the association holds when metabolic rate is controlled is unclear. Such an effect would have undesirable consequences for the safety of the athlete. Objective: To examine whether ingesting fluids containing carbohydrate contributed to an accelerated rise in core temperature and greater overall body heat production during 1 hour of exercise at 30°C when the effort was maintained at steady state. Design: Crossover design (repeated measures) in randomized order of treatments of drinking fluids with carbohydrate and electrolytes (CHO) or flavored-water placebo with electrolytes (PLA). The beverages were identical except for the carbohydrate content: CHO  =  93.7 ± 11.2 g, PLA  =  0 g. Setting: Research laboratory. Patients or Other Participants: Nine physically fit, endurance-trained adult males. Intervention(s): Using rectal temperature sensors, we measured core temperature during 30 minutes of rest and 60 minutes of exercise at 65% of maximal oxygen uptake (V˙o2 max) in the heat (30.6°C, 51.8% relative humidity). Participants drank equal volumes (1.6 L) of 2 beverages in aliquots 30 minutes before and every 15 minutes during exercise. Volumes were fixed to approximate sweat rates and minimize dehydration. Main Outcome Measure(s): Rectal temperature and metabolic response (V˙o2, heart rate). Results: Peak temperature, rate of temperature increase, and metabolic responses did not differ between beverage treatments. Initial hydration status, sweat rate, and fluid replacement were also not different between trials, as planned. Conclusions: Ingestion of carbohydrate in fluid volumes that minimized dehydration during 1 hour of steady-state exercise at 30°C did not elicit an increase in metabolic rate or core temperature.

scholarly journals Effect of hypohydration on postsynaptic cutaneous vasodilation and sweating in healthy men

2017 ◽  
Vol 312 (5) ◽  
pp. R637-R642 ◽  
Author(s):  
Matthew A. Tucker ◽  
Ashley Six ◽  
Nicole E. Moyen ◽  
Alf Z. Satterfield ◽  
Matthew S. Ganio
Keyword(s):  
Heat Stress ◽  
Sweat Rate ◽  
Local Heating ◽  
Maximal Response ◽  
Fluid Restriction ◽  
Doppler Flowmetry ◽  
Healthy Men ◽  
Cutaneous Vasodilation ◽  
Stress Changes ◽  
Local Sweat Rate

Hypohydration decreases cutaneous vasodilation and sweating during heat stress, but it is unknown if these decrements are from postsynaptic (i.e., sweat gland/blood vessel) alterations. The purpose of this study was to determine if hypohydration affects postsynaptic cutaneous vasodilation and sweating responses. Twelve healthy men participated in euhydrated (EU) and hypohydrated (HY) trials, with hypohydration induced via fluid restriction and passive heat stress. Changes in cutaneous vascular conductance (CVC; %max) in response to incremental intradermal infusion of the endothelium-independent vasodilator sodium nitroprusside (SNP) and the endothelium-dependent vasodilator methacholine chloride (MCh) were assessed by laser Doppler flowmetry. Local sweat rate (LSR) was simultaneously assessed at the MCh site via ventilated capsule. At the end of the last dose, maximal CVC was elicited by delivering a maximal dose of SNP (5 × 10−2 M) for 30 min to both sites with simultaneous local heating (~44°C) at the SNP site. The concentration of drug needed to elicit 50% of the maximal response (log EC50) was compared between hydration conditions. The percent body mass loss was greater with HY vs. EU (−2.2 ± 0.7 vs. −0.1 ± 0.7%, P < 0.001). Log EC50 of endothelium-dependent CVC was lower with EU (−3.62 ± 0.22) vs. HY (−2.93 ± 0.08; P = 0.044). Hypohydration did not significantly alter endothelium-independent CVC or LSR (both P > 0.05). In conclusion, hypohydration attenuated endothelium-dependent CVC but did not affect endothelium-independent CVC or LSR responses. These data suggest that reductions in skin blood flow accompanying hypohydration can be partially attributed to altered postsynaptic function.

Comparison of estimated core body temperature measured with the BioHarness and rectal temperature under several heat stress conditions

2016 ◽  
Vol 13 (8) ◽  
pp. 612-620 ◽  
Author(s):  
Yongsuk Seo ◽  
Travis DiLeo ◽  
Jeffrey B. Powell ◽  
Jung-Hyun Kim ◽  
Raymond J. Roberge ◽  
...  
Keyword(s):  
Heat Stress ◽  
Body Temperature ◽  
Rectal Temperature ◽  
Core Body Temperature ◽  
Stress Conditions ◽  
Core Body

scholarly journals Aspirin ingestion does not alter the onset or slope of local sweat rate during whole‐body passive heat stress (1104.12)

2014 ◽  
Vol 28 (S1) ◽  
Author(s):  
Stephen J. Carter ◽  
Robert L. Herron ◽  
S. Zeb Akers ◽  
Ann B. Collins ◽  
Jonathan E. Wingo
Keyword(s):  
Heat Stress ◽  
Sweat Rate ◽  
Whole Body ◽  
Local Sweat Rate ◽  
Aspirin Ingestion

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

scholarly journals An Occupational Heat Stress and Hydration Assessment of Agricultural Workers in North Mexico

2020 ◽  
Vol 17 (6) ◽  
pp. 2102
Author(s):  
Rietta S. Wagoner ◽  
Nicolas I. López-Gálvez ◽  
Jill G. de Zapien ◽  
Stephanie C. Griffin ◽  
Robert A. Canales ◽  
...  
Keyword(s):  
Heat Stress ◽  
Core Body Temperature ◽  
Heat Exposure ◽  
Agricultural Workers ◽  
Hydration Status ◽  
Southern Mexico ◽  
Agricultural Industry ◽  
Targeted Interventions ◽  
Northern Mexico ◽  
Core Body

Expanding agribusiness in Northern Mexico has increased demand for workers from Southern Mexico, with hundreds of thousands migrating for work annually. Extreme temperatures, physical labor, and low fluid consumption place workers at risk for heat strain and dehydration, commonly underreported hazards in the agricultural industry. The objectives of this pilot study were to assess heat exposure and hydration status of a population of migratory agricultural workers in Northern Mexico throughout the grape harvest season. In addition to demographic information, environmental conditions, hydration status, and core body temperatures were collected. The majority listed Chiapas as their home state, nearly half spoke an Indigenous language, and none had completed high school. The wet-bulb globe temperature was significantly higher during the harvest and post-harvest seasons compared to the pre-harvest season. Across the different seasons, the majority were dehydrated post-shift, and mean core body temperature of workers was not significantly different. This project highlights the need for targeted interventions to improve hydration and prevent heat stress in this region. As the number of warm days is expected to rise each year worldwide, it will be increasingly important to engage in practices to protect vulnerable populations, such as migratory agriculture workers.

scholarly journals Effects of cooled floor pads combined with chilled drinking water on behavior and performance of lactating sows under heat stress

2021 ◽  
Vol 99 (3) ◽  
Author(s):  
Y Zhu ◽  
L J Johnston ◽  
M H Reese ◽  
E S Buchanan ◽  
J E Tallaksen ◽  
...  
Keyword(s):  
Drinking Water ◽  
Heat Stress ◽  
Respiration Rate ◽  
Rectal Temperature ◽  
Time Budget ◽  
Video Recording ◽  
Lactating Sows ◽  
Before And After ◽  
And Performance ◽  
Drinking Frequency

Abstract This study was conducted to evaluate whether cooled floor pads combined with chilled drinking water could alleviate negative impacts of heat stress on lactating sows. Thirty sows (Landrace × Yorkshire, Parity = 1 to 6) were housed in individual farrowing stalls in two rooms with temperatures being controlled at 29.4°C (0700–1900 hours) and 23.9°C (1900–0700 hours). Sows in one room (Cool), but not in the other room (Control) were provided cooled floor pads (21–22°C) and chilled drinking water (13–15°C). Behavior of sows (15 sows/treatment) was video recorded during farrowing, and days 1, 3, 7, 14, and 21 after farrowing. Videos were viewed continuously to register the birth time of each piglet, from which total farrowing duration and birth intervals were calculated. The number of drinking bouts and the duration of each drinking bout were registered for each sow through viewing videos continuously for 2 h (1530–1730 hours) each video-recording day. Postures (lying laterally, lying ventrally, sitting, and standing) were recorded by scanning video recordings at 5-min intervals for 24 h each video-recording day, and time budget for each posture was calculated. Rectal temperature and respiration rate were measured for all sows the day before and after farrowing, and then once weekly. Sow and litter performance was recorded. Data were analyzed using the Glimmix procedure of SAS. The cooling treatment did not affect sow behavior or litter performance. Sows in the Cool room had lower rectal temperature (P = 0.03) and lower respiration rate (P &lt; 0.001), consumed more feed (P = 0.03), tended to have reduced weight loss (P = 0.07), and backfat loss (P = 0.07) during lactation than sows in the Control room. As lactation progressed, sows increased drinking frequency (P &lt; 0.001) and time spent lying ventrally (P &lt; 0.0001), standing (P &lt; 0.001), and sitting (P &lt; 0.0001), and decreased time spent lying laterally (P &lt; 0.0001) in both Cool and Control rooms. While cooled floor pads combined with chilled drinking water did not affect sow behavior, they did alleviate heat stress partially, as indicated by decreased rectal temperature, respiration rate, weight, and backfat loss, and increased feed intake in lactating sows.

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