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PURPOSE:: This study examined the impact of 10 d of exercise-heat acclimation on sweat mineral concentrations. METHODS:: Eight male subjects walked on a treadmill at 3.5 mph, 4% grade for 100 continuous minutes or until rectal temperature reached 39.5 degrees C on 10 consecutive days in an environmental chamber set at 45 degrees C, 20% relative humidity. Arm sweat samples were collected during the first 30 min of exercise-heat stress on days 1 and 10 using a polyethylene arm glove. RESULTS:: Final core temperature and HR values were significantly lower (P < 0.05) on day 10 versus day 1. Whole-body sweating rates increased by approximately 6% (P = 0.12). Sweat sodium concentration on day 10 (36.22 +/- 7.22 mM) was significantly lower than day 1 (54.49 +/- 16.18 mM) (P < 0.05). Sweat mineral concentrations of calcium ( 29%), copper ( 50%), and magnesium ( 43%) were also significantly lower on day 10 versus day 1 of heat acclimation (P < 0.05). A trend for lower sweat iron ( 75%; P = 0.07) and zinc ( 23%; P = 0.10) concentrations were observed from day 1 to day 10. The estimated hourly sweat mineral losses (arm concentration x whole-body sweat rate) were reduced for calcium ( 27%), copper ( 46%), and magnesium ( 42%) (P < 0.05), but not iron (75%) or zinc ( 16%) (P > 0.05), from day 1 to day 10. CONCLUSION:: Exercise-heat acclimation conserves arm sweat mineral concentrations and possibly whole-body sweat losses of calcium, copper, and magnesium, and may reduce sweat iron and zinc concentrations. [ABSTRACT FROM AUTHOR]

PURPOSE: The purpose of this study was to 1) determine the effect of hypohydration (HYPO) on thirst sensations during moderate exercise in the cold and 2) determine a possible mechanism for a cold-induced decline in thirst. METHODS: In the first phase of the study, eight males walked on four occasions, in T-shirts, shorts, and shoes, at 50% VO2max, for 60 min in either a 4 degrees C (cold) or 27 degrees C (temperate) environment in a state of HYPO or euhydration (EU). In the second phase, nine males in states of EU or HYPO randomly performed four trials consisting of 30 min standing at 27 degrees C, followed by 30 min of standing and 30 min of treadmill exercise at 50% of VO2max, in either 4 degrees C or 27 degrees C air. RESULTS: In phase 1, thirst sensations were lower throughout 60 min of exercise (P < 0.05) in both HYPO and EU conditions during the cold trials. In phase 2, despite elevated plasma osmolality (P < 0.05), perception of thirst and plasma arginine vasopressin [AVP] similarly decreased (P < 0.05) after 30-min standing rest and 30-min exercise in the HYPO-cold trial, compared with the HYPO-temperate, EU-cold, and EU-temperate trials. CONCLUSIONS: When either euhydrated or hypohydrated, cold exposure attenuated thirst by up to 40% at rest and during moderate-intensity exercise. The attenuated thirst when hypohydrated during cold exposure was associated with lower plasma [AVP] despite an elevated plasma osmolality. This decline in thirst and AVP in the cold may be the result of peripheral vasoconstriction, mediating an increase in central blood volume and stimulation of central volume receptors. [ABSTRACT FROM AUTHOR]

Exercise alone or in combination with environmental heat stress can elevate blood S-100beta protein concentrations. However, the explanatory power of exercise with marked environmental heat stress on the appearance of S-100beta is questionable. It is possible that the process of heat acclimation might afford additional insight. PURPOSE:: Determine the S-100beta response to moderate-intensity exercise with heat strain before and after heat acclimation. METHODS:: Nine healthy male volunteers completed 10 consecutive days of heat acclimation consisting of up to 100 min of treadmill walking (1.56 m.s, 4% grade) in the heat (45 degrees C, 20% relative humidity). Changes in HR, rectal temperature (Tre), and sweat rate (SR) were examined to determine successful acclimation. Area under the curve (AUC) for Tre greater than 38.5 degrees C was calculated to assess cumulative hyperthermia. Blood samples were taken before and after exercise on days 1 and 10 and were analyzed for serum osmolality and S-100beta concentration. RESULTS:: All subjects displayed physiological adaptations to heat acclimation including a significant (P < 0.05) reduction in final HR (161 to 145 bpm) and Tre (39.0 to 38.4 degrees C), as well as a modest ( 10%) increase in SR (1.10 to 1.20 L.h; P = 0.09). No differences were observed in pre- to postexercise serum S-100beta concentrations on day 1 or 10, and no differences were observed in S-100beta values between days 1 and 10. No significant correlations were found between S-100beta values and any variable of interest. CONCLUSIONS:: S-100beta concentrations do not necessarily increase in response to exercise-heat strain, and no effect of heat acclimation on S-100beta could be observed despite other quantifiable physiological adaptations. [ABSTRACT FROM AUTHOR]