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Reduction in body temperature using hand cooling versus passive rest after exercise in the heat.
Adams, WM, Hosokawa, Y, Adams, EL, Belval, LN, Huggins, RA, Casa, DJ
Journal of science and medicine in sport. 2016;(11):936-940
Abstract
OBJECTIVES To examine the effects of hydration and hand cooling on lowering body temperature after exercise in the heat. DESIGN Randomized cross-over design. METHODS Nine recreationally active male participants (mean±SD; age, 24±4; height, 177.3±9.9cm; body mass, 76.7±11.6kg; body fat, 14.7±5.8%) completed a bout of treadmill exercise in a hot environment. After completion of exercise, participants were assigned to the following trials for post-exercise cooling: (1) hydrated with passive rest (HY), (2) hydrated with hand cooling on both hands (HY+2HC), (3) dehydrated with passive rest (DY), and (4) dehydrated with hand cooling on both hands (DY+2HC). Within subject differences were assessed using a three-way (Hydration×Condition×Time) repeated measures ANOVA with Tukey's post hoc analysis if significant interactions were found. RESULTS Irrespective of hydration status, hand cooling on both hands resulted in significantly greater reductions in TREC than passive cooling at minute 20 (0.27°C [0.05, 0.49], ES=2.08, p=0.017) (Fig. 1). The reduction in TREC at minute 18 trended towards statistical significance (0.21°C [.003, .42], ES=1.59, p=0.053). Hydration status alone and when differentiated among modes of cooling showed no differences on changes of TREC or heart rate across all conditions during post exercise recovery (p>0.05). CONCLUSIONS Hand cooling on both hands reduced TREC more than passive cooling, however, the cooling rates observed render hand cooling a poor option for cooling. Greater reductions in TREC after exercise or between bouts of exercise may enhance recovery and subsequent performance.
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Adenosine receptor inhibition with theophylline attenuates the skin blood flow response to local heating in humans.
Fieger, SM, Wong, BJ
Experimental physiology. 2010;(9):946-54
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Abstract
Mechanisms underlying the robust cutaneous vasodilatation in response to local heating of human skin remain unresolved. Adenosine receptor activation has been shown to induce vasodilatation via nitric oxide, and a substantial portion of the plateau phase to local heating of human skin has been shown to be dependent on nitric oxide. The purpose of this study was to investigate a potential role for adenosine receptor activation in cutaneous thermal hyperaemia in humans. Six subjects were equipped with four microdialysis fibres on the ventral forearm. Sites were randomly assigned to receive one of the following four treatments: (1) lactated Ringer solution to serve as a control; (2) 4 mM theophylline, a competitive, non-selective A(1)/A(2) adenosine receptor antagonist; (3) 10 mM Nomega(-)-nitro-L-arginine methyl ester (L-NAME) to inhibit NO synthase; or (4) combined 4 mm theophylline + 10 mM L-NAME. Following baseline measurements, each site was locally heated from a baseline temperature of 33 degrees C to 42 degrees C at a rate of 1 degrees C (10 s)(-1), and skin blood flow was monitored via laser-Doppler flowmetry (LDF). Cutaneous vascular conductance (CVC) was calculated as LDF divided by mean arterial pressure and normalized to maximal values (CVC(max)) via local heating to 43 degrees C and infusion of 28 mM sodium nitroprusside. The initial peak was significantly reduced in theophylline (68 +/- 2% CVC(max)) and L-NAME sites (54 +/- 5% CVC(max)) compared with control sites (81 +/- 2% CVC(max); P < 0.01 and P < 0.001, respectively). Combined theophylline + L-NAME (52 +/- 5% CVC(max)) reduced the initial peak compared with control and theophylline sites, but was not significantly different compared with L-NAME sites. The secondary plateau was attenuated in theophylline (77 +/- 2% CVC(max)), L-NAME (60 +/- 2% CVC(max)) and theophylline + L-NAME (53 +/- 1% CVC(max)) compared with control sites (94 +/- 2% CVC(max); P < 0.001 for all conditions). The secondary plateau was reduced in L-NAME compared with theophylline sites (P < 0.001), and combined theophylline + L-NAME further reduced the secondary plateau compared with theophylline- (P < 0.001) and L-NAME-only sites (P < 0.05). These data suggest that adenosine receptor activation directly contributes to cutaneous thermal hyperaemia, as evidenced by the reduced initial peak and secondary plateau in theophylline sites. These data further suggest that a portion of the NO response may be explained by adenosine receptor activation; however, a substantial portion of the NO response is independent of adenosine receptor activation.
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A comparison of thermal stress in the submarine escape using immersion half- and full suit in tropical weather operations.
Chng, J, Wan, MC, Lim, CL, Kang, WL
Undersea & hyperbaric medicine : journal of the Undersea and Hyperbaric Medical Society, Inc. 2010;(6):447-54
Abstract
OBJECTIVE Submariners of disabled submarines are subject to drastic weather changes as they are awaiting rescue on the sea surface. Hyperthermia and hypothermia are just two of the adverse conditions that they can experience. The purpose of this study was to investigate the effectiveness of two models of submarine escape and the protective capabilities of immersion suits from environmental changes. METHOD A randomized study involving 24 male subjects was conducted to compare the thermal capabilities of the full- versus half-configuration suit in a climate-controlled chamber. RESULTS The full-configuration suits tested for a higher mean maximal core temperature (37.76 degrees C / 99.97 degrees F) than the mean maximal core temperature of the half-suits (37.52 degrees C / 99.54 degrees F). The full suits also tested for a higher mean minimal core temperature (36.13 degrees C / 97.03 degrees F) than the mean minimal core temperature (35.95 degrees C / 96.71 degrees F) of the half-suits. CONCLUSION Results showed that the full-suit configuration did not induce clinically significant high levels of heat stress as compared to the half-suits, but instead provided better thermal protection against hypothermia than the half-suits.
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Core temperature cooling in healthy volunteers after rapid intravenous infusion of cold and room temperature saline solution.
Moore, TM, Callaway, CW, Hostler, D
Annals of emergency medicine. 2008;(2):153-9
Abstract
STUDY OBJECTIVE Studies have suggested that inducing mild hypothermia improves neurologic outcomes after traumatic brain injury, major stroke, traumatic hemorrhage, and cardiac arrest. Although infusion of cold normal saline solution is a simple and inexpensive method for initiating hypothermia, human cold-defense mechanisms potentially make this route stressful or ineffective. We hypothesize that rapid infusion of 30 mL/kg of cold (4 degrees C, 39.2 degrees F) 0.9% saline solution during 30 minutes to healthy subjects (aged 27 [standard deviation (SD) 4] years) will reduce core body temperature to the therapeutic range of 33 degrees C to 35 degrees C (91.4 degrees F to 95 degrees F). METHODS Sixteen subjects were randomly assigned to receive either cold (4 degrees C, 39.2 degrees F) or room temperature (23 degrees C, 73.4 degrees F) normal saline solution. Subjects were not informed of their assignment, but blinding was not possible after initiation of the infusion. Core temperature, skin temperature, and vital signs were recorded every 2 minutes. Subjects indicated global discomfort during the infusion on a 100-mm visual analog scale at 5-minute intervals. RESULTS Core temperature decreased in both the cold saline solution (1.0 degrees C [SD 0.4 degrees C]/1.8 degrees F [0.7 degrees F]) and room temperature saline solution (0.5 degrees C [SD 0.1 degrees C]/0.9 degrees F [0.2 degrees F]) groups, whereas skin temperature was unchanged. Slopes calculated from the core temperature cooling curves indicate that the majority of cooling occurred during the first half of the infusion. Examination of the core temperature cooling curves revealed a 2-phase temporal pattern in 30-minute cooling curves. The early phase, spanning 0 to 14 minutes, demonstrated rapid cooling in both groups, with a larger effect observed in subjects receiving cold saline solution. CONCLUSION In this pilot study of healthy volunteers, rapid administration of cold saline solution to awake normothermic volunteers resulted in 1 degrees C (1.8 degrees F) cooling but did not induce a therapeutic plane of hypothermia. This change in core temperature was not accompanied by significant changes in skin temperature. These data suggest that a reduction in core temperature of about 1 degrees C (1.8 degrees F) can be achieved in healthy humans before a thermoregulatory response is triggered and that rapid infusion of cold intravenous fluids is insufficient by itself to overcome this response. The clinically relevant control arm of room temperature saline solution also resulted in mild core cooling.
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Hydration, thermoregulation, and performance effects of two sport drinks during soccer training sessions.
Siegler, JC, Mermier, CM, Amorim, FT, Lovell, RJ, McNaughton, LR, Robergs, RA
Journal of strength and conditioning research. 2008;(5):1394-401
Abstract
In the present study, we aimed to compare the thermoregulatory response and soccer-specific training performance aspects of two commercially available sport drinks, both of similar carbohydrate concentration, but one containing 5.2% glycerol. Ten players participated in two similar outdoor training sessions and were randomly assigned to each of two drinks: a carbohydrate (C) beverage or a carbohydrate-glycerol (CG) beverage. Players consumed 500 mL of C or CG 30 minutes pre-exercise and at half-time. Pre- and postexercise body mass, core temperature (CT), and heart rate (HR) were recorded, and urine and blood samples were taken. No difference was observed between days for wet bulb globe temperature (session 1: 17.0 +/- 1.1 degrees C, session 2: 16.9 +/- 1.1 degrees C; P = 0.944). The degree of dehydration (% Delta BM) was greater after the C trial (P = 0.041). Similarly, percent change in plasma volume was greater in the C trial (P = 0.049). No overall main affect was observed between CT and mean exercise HRs during either training session (CT: P = 0.350; mean HR: P = 0.256), and there was no difference observed between groups in time to failure during the session-ending fatigue test (P = 0.547). Ingestion of a CG beverage provided players with better hydration than C alone. However, if training sessions are short (<75 minute), with adequate time for recovery, both drinks are sufficient for maintaining performance intensities during soccer-specific training.
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Thermic effect of food and beta-adrenergic thermogenic responsiveness in habitually exercising and sedentary healthy adult humans.
Stob, NR, Bell, C, van Baak, MA, Seals, DR
Journal of applied physiology (Bethesda, Md. : 1985). 2007;(2):616-22
Abstract
The thermic effect of food (TEF) is an important physiological determinant of total daily energy expenditure (EE) and energy balance. TEF is believed to be mediated in part by sympathetic nervous system activation and consequent beta-adrenergic receptor (beta-AR) stimulation of metabolism. TEF is greater in habitually exercising than in sedentary adults, despite similar postprandial sympathetic nervous system activation. We determined whether augmented TEF in habitually exercising adults is associated with enhanced peripheral thermogenic responsiveness to beta-AR stimulation. In separate experiments in 22 sedentary and 29 habitually exercising adults, we measured the increase in EE (indirect calorimetry, ventilated hood) during beta-AR stimulation (intravenous isoproterenol: 6, 12, and 24 ng x kg fat-free mass(-1) x min(-1)) and EE before and after a liquid meal (40% of resting EE; 53% carbohydrate, 32% fat, 15% protein). The increase in EE during incremental isoproterenol administration was greater (P = 0.01) in habitual exercisers (0.34 +/- 0.03, 0.54 +/- 0.04, 0.81 +/- 0.05 kJ/min; means +/- SE) than in sedentary adults (0.26 +/- 0.03, 0.40 +/- 0.03, 0.64 +/- 0.04 kJ/min). The area under the TEF response curve was also greater (P = 0.04) in habitual exercisers (160 +/- 9 kJ) than in sedentary adults (130 +/- 11 kJ) and was positively related to beta-AR thermogenic responsiveness (r = 0.32, P = 0.02). We conclude that TEF is related to beta-AR thermogenic responsiveness and that the greater TEF in habitual exercisers is attributable in part to their augmented beta-AR thermogenic responsiveness. Our results also suggest that peripheral thermogenic responsiveness to beta-AR stimulation is a physiological determinant of TEF and hence energy balance in healthy adult humans.
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Effects of exercise in the heat on thermoregulation of Japanese and Malaysian males.
Saat, M, Tochihara, Y, Hashiguchi, N, Sirisinghe, RG, Fujita, M, Chou, CM
Journal of physiological anthropology and applied human science. 2005;(4):267-75
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Abstract
The effect of low-intensity exercise in the heat on thermoregulation and certain biochemical changes in temperate and tropical subjects under poorly and well-hydrated states was examined. Two VO2max matched groups of subjects consisting of 8 Japanese (JS) and 8 Malaysians (MS) participated in this study under two conditions: poorly-hydrated (no water was given) and well-hydrated (3 mL x Kg(-1) body weight of water was provided at onset of exercise, and the 15th, 35th and 55th min of exercise). The experimental room in both countries was adjusted to a constant level (Ta: 31.6+/-0.03 degrees C, rh: 72.3+/-0.13%). Subjects spent an initial 10 min rest, 60 min of cycling at 40% VO2max and then 40 min recovery in the experimental room. Rectal temperatures (Tre) skin temperatures (Tsk), heart rate (HR), heat-activated sweat glands density (HASG), local sweat rate (M sw-back) and percent dehydration were recorded during the test. Blood samples were analysed for plasma glucose and lactate levels.The extent of dehydration was significantly higher in the combined groups of JS (1.43+/-0.08%) compared to MS (1.15+/-0.05%). During exercise M sw-back was significantly higher in JS compared to MS in the well-hydrated condition. The HASG was significantly more in JS compared to MS at rest and recovery. Tre was higher in MS during the test. Tsk was significantly higher starting at the 5th min of exercise until the end of the recovery period in MS compared to JS. In conclusion, tropical natives have lower M sw-back associated with higher Tsk and Tre during the rest, exercise and recovery periods. However, temperate natives have higher M sw-back and lower Tsk and Tre during experiments in a hot environment. This phenomenon occurs in both poorly-hydrated and well-hydrated states with low intensity exercise. The differences in M sw-back, Tsk and Tre are probably due to a setting of the core temperature at a higher level and enhancement of dry heat loss, which occurred during passive heat exposure.
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Thermoregulation during cold exposure after several days of exhaustive exercise.
Castellani, JW, Young, AJ, Degroot, DW, Stulz, DA, Cadarette, BS, Rhind, SG, Zamecnik, J, Shek, PN, Sawka, MN
Journal of applied physiology (Bethesda, Md. : 1985). 2001;(3):939-46
Abstract
This study examined the hypothesis that several days of exhaustive exercise would impair thermoregulatory effector responses to cold exposure, leading to an accentuated core temperature reduction compared with exposure of the same individual to cold in a rested condition. Thirteen men (10 experimental and 3 control) performed a cold-wet walk (CW) for up to 6 h (6 rest-work cycles, each 1 h in duration) in 5 degrees C air on three occasions. One cycle of CW consisted of 10 min of standing in the rain (5.4 cm/h) followed by 45 min of walking (1.34 m/s, 5.4 m/s wind). Clothing was water saturated at the start of each walking period (0.75 clo vs. 1.1 clo when dry). The initial CW trial (day 0) was performed (afternoon) with subjects rested before initiation of exercise-cold exposure. During the next 7 days, exhaustive exercise (aerobic, anaerobic, resistive) was performed for 4 h each morning. Two subsequent CW trials were performed on the afternoon of days 3 and 7, approximately 2.5 h after cessation of fatiguing exercise. For controls, no exhaustive exercise was performed on any day. Thermoregulatory responses and body temperature during CW were not different on days 0, 3, and 7 in the controls. In the experimental group, mean skin temperature was higher (P < 0.05) during CW on days 3 and 7 than on day 0. Rectal temperature was lower (P < 0.05) and the change in rectal temperature was greater (P < 0.05) during the 6th h of CW on day 3. Metabolic heat production during CW was similar among trials. Warmer skin temperatures during CW after days 3 and 7 indicate that vasoconstrictor responses to cold, but not shivering responses, are impaired after multiple days of severe physical exertion. These findings suggest that susceptibility to hypothermia is increased by exertional fatigue.
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Rapid cooling techniques in joggers experiencing heat strain.
Clapp, AJ, Bishop, PA, Muir, I, Walker, JL
Journal of science and medicine in sport. 2001;(2):160-7
Abstract
This study examined subjects that exercised on three occasions in a heated environment (WBGT = 39 degrees C] until they experienced heat strain. Since morbidity and mortality due to heat injury increase with the duration of elevated core temperature, it is important that techniques to lower core temperature be evaluated. Following three exercise sessions, subjects underwent each of three core cooling treatments in random order: 1) Torso immersion in cool water, 2) Hands and feet immersion in cool water, and 3) Sit-in-shade with a 1.5mph breeze provided. Subjects (n=5) consistently reached peak rectal temperatures of 38.8 (+/-0.1) degrees C following each exercise bout in the heated environment. Torso immersion produced a significantly (p<0.05) greater rate of decline in rectal temperature (0.25+/-0.10 degrees C/min) than the hands and feet immersion technique (0.16+/-0.05 degrees C/min) and the sit in the shade technique (0.11+/-0.04 degrees C/min). After only 10 minutes of cooling, the differences among cooling techniques were evident. Similar trends were observed for mean heart rate readings, albeit not significant (p>0.05). It was concluded that rectal temperatures can be reduced rapidly through the use of a cool water torso-immersion technique.
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Hyperhydration and glycerol: thermoregulatory effects during exercise in hot climates.
Latzka, WA, Sawka, MN
Canadian journal of applied physiology = Revue canadienne de physiologie appliquee. 2000;(6):536-45
Abstract
Hyperhydration or increasing body water content above normal (euhydration) level was thought to have some benefit during exercise heat-stress; however, attempts to overdrink have been minimized by a rapid diuretic response. The perception that hyperhydration might be beneficial for exercise performance and for thermoregulation arose from the adverse consequences of hypohydration. Many studies had examined the effects of hyperhydration on thermoregulation in the heat; however, most of them suffer from design problems that confound their results. The design problems included control conditions not representing euhydration but hypohydration, control conditions not adequately described, cold fluid ingestion that reduced core temperature, and/or changing heat acclimation status. Several investigators reported lower core temperatures during exercise after hyperhydration, while other studies do not. Some investigators reported higher sweating rates with hyperhydration, while other studies do not. Recent research that controlled for these confounding variables reported that hyperhydration (water or glycerol) did not alter core temperature, skin temperature, whole body sweating rate, local sweating rate, sweating threshold temperature, sweating sensitivity, or heart rate responses compared to euhydration trial. If euhydration is maintained during exercise-heat stress then hyperhydration appears to have no meaningful advantage.