Thermoregulatory responses of heat production and heat loss were measured in seven adult volunteers (four women and three men, aged 21–57 yr) during 45‐min dorsal exposures of the whole body to 450 MHz continuous wave radio frequency (RF) fields. Two power densities (PD) (local peak PD = 18 and 24 mW/cm2; local peak specific absorption rate = 0.320 [W/kg]/[mW/cm2]) were tested in each of three ambient temperatures (Ta = 24, 28, and 31 °C) plus Ta controls (no RF). No changes in metabolic heat production occurred under any exposure conditions. Vigorous increases in sweating rate on back and chest, directly related to both Ta and PD, cooled the skin and ensured efficient regulation of the deep body (esophageal) temperature to within 0.1 °C of the normal level. Category judgments of thermal sensation, comfort, sweating, and thermal preference usually matched the measured changes in physiological responses. Some subtle effects related to gender were noted that confirm classic physiological data. Our results indicate that dorsal exposures of humans to a supra‐resonant frequency of 450 MHz at local peak specific absorption rates up to 7.68 W/kg are mildly thermogenic and are counteracted efficiently by normal thermophysiologic heat loss mechanisms, principally sweating. Bioelectromagnetics 19:232–245, 1998. Published 1998 Wiley‐Liss, Inc.
These data indicate that the inability to induce adaptations in CPBR function may limit BV expansion during training in older women. In addition, the absence of these specific adaptations may contribute to the relatively poor improvements in VO2peak in older women during short (10-12 wk) periods of training.
This study investigated the hypothesis that addition of to a rehydration beverage would stimulate drinking and augment restoration of body water in individuals dehydrated during 90 min of continuous treadmill exercise in the heat. Following a 3.0 ± 0.2% decrease in body weight (BW), 6 subjects sat in a thermoneutral environment for 30 min to allow body fluid compartments to stabilize. Over the next 3 hr, subjects rehydrated ad libitum using either flavored/artificially sweetened water (H20-R) or a flavored, 6% sucrose drink containing either or 50 mmol/L NaCl. Results demonstrated that rapid removal of the osmotic stimulus, during 0-R, and the volume-dependent dipsogenic stimuli, during , are important factors in limiting fluid intake during rehydration, compared to . It was also found that the pattern of fluid replacement and restoration of fluid balance following dehydration is influenced by the dehydration protocol used to induce the loss in total body water and the sodium content of the rehydration beverage.
This study examined the change in plasma volume (% delta PV) in response to consecutive Wingate tests (30 sec Anaerobic Power test). Twelve active men (21 +/- 1.6 yr, 81.3 +/- 6.6 kg) performed two Wingate tests (W1 and W2, separated by 10 min) on three occasions (T1-T3, tests were two weeks apart). Exercise resistance was maintained at 75 g.kg-1 body weight during testing. Blood samples were taken immediately before (Pre) and after (IP) W1 and W2. There were no significant differences in hematocrit, hemoglobin, mean power (MP) or peak power (PP) between T1-T3. There was a marked hemoconcentration in response to W1 (IP W1, -17.4 +/- 2.6% delta PV), with a further, but not significantly greater, hemoconcentration following W2 (IP W2, -8.2 +/- 1.1% delta PV). The % delta PV, between PRE W1 and IP W2 was-20.1 +/- 3.1%. These results suggest that an existing hemoconcentration (W1) may affect the magnitude of the % delta PV response to subsequent supramaximal exercise (W2).
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