A comparison of drinking behavior using a harmonized methodology (Liq.In 7 ) in six countries.

PURPOSE: To assess drinking occasions (volume and type) according to consumption with food in or outside meals, and location, for six countries. METHODS: A total of 10,521 participants aged 4-65 years from Argentina, Brazil, China, Indonesia, Mexico and Uruguay completed a validated 7-day fluid intake record. For each drinking event, the volume consumed, the fluid type, the location of intake, and whether the drink was accompanied by food (meal or snack) or not, was recorded. RESULTS: Similar drinking behaviors were found in Mexico and Argentina; fluid intake during meals was 48 and 45% of total fluid intake (TFI), respectively. In Brazil (55%), Indonesia (58%) and China (66%) most fluid was consumed without food. In Uruguay, 34% of TFI was with a main meal, 31% with food between meals and 35% without food. Indonesia had the highest median (25-75th percentile) TFI; 2520 (1750-3347) mL/day, and China the lowest 1138 (818-3347) mL/day. Water was consumed with meals for 37% of Chinese and 87% of Indonesian participants, while the four Latin-American American countries showed a preference for sweet drinks; 54% in Mexico, 67% in Brazil, 55% in Argentina and 59% in Uruguay. Diversity in fluid type was noted when drinking with food between meals. Apart from China, most drinking occasions (> 75%) occurred at home. CONCLUSIONS: Three distinct drinking behaviors were identified, namely, drinking with meals, drinking as a stand-alone activity, and a type of 'grazing' (i.e., frequent drinks throughout the day) behavior. Most drinking occasions occurred at home.

Fluid intake of children, adolescents and adults in Indonesia: results of the 2016 Liq.In7 national cross-sectional survey.

PURPOSE: To report daily total fluid intake (TFI) and fluid types in Indonesia according to age, sex, socio-economic status (SES) and geographic region, and compare TFI with the Indonesian adequate fluid intake (AI) recommendations. METHODS: Data were collected in 32 cities over nine regions from children (4-9 years, n = 388), adolescents, (10-17 years, n = 478) and adults (18-65 years, n = 2778) using a fluid intake 7-day record (Liq.In7); socio-economic status was also recorded. The 7-day mean TFIs were compared with the AI of water set by the Ministry of Health of the Republic of Indonesia. RESULTS: Total median fluid intakes for all age groups exceeded 2000 mL/day. At population level, TFI was associated with household income (P < 0.001), education (P < 0.001) and Indonesian geographical regions (P < 0.001). More than 67% of participants met the AI of water from fluids. A higher percentage of children and adolescents met the AI (78 and 80%, respectively), compared with adults (72%). Drinking water was the main contributor to TFI in all age groups (76-81%). Sugar-sweetened beverages (SSB) were consumed by 62% children, 72% adolescents and 61% of adults. An SSB intake ≥ 1 serving per day was observed for 24% children, 41% adolescents and 33% adults. CONCLUSIONS: A high percentage of the population drank enough to meet the AI of water from fluids. Water was the most frequently consumed drink; however, many participants consumed at least one serving of SSB per day. This study provides data to help direct targeted intervention programs.

Fluid intake of Latin American children and adolescents: results of four 2016 LIQ.IN 7 National Cross-Sectional Surveys.

PURPOSE: The primary aim of this survey was to report total fluid intake (TFI) and different fluid types for children (4-9 years) and adolescents (10-17 years) in Mexico, Brazil, Argentina and Uruguay. The second aim was to compare TFI with the adequate intake (AI) of water from fluids as recommended by the USA Institute of Medicine. METHODS: Data were collected using a validated liquid intake 7-day record (Liq.In 7 ). Participants' characteristics, including age, sex and anthropometric measurements were recorded. RESULTS: A total of 733 children and 933 adolescents were recruited. Over 75% of children in Uruguay met the IOM's recommended intake. Fewer children in Argentina (64-72%) and Brazil (41-50%) obtained AI and the lowest values were recorded in Mexico (33-44%), where 16% of boys and 14% girls drank 50% or less of the AI. More adolescents in Argentina (42%) met the AIs than other countries; the lowest was in Mexico (28%). Children and adolescents in Mexico and Argentina drank more sugar sweetened beverages than water. CONCLUSIONS: Large numbers of children and adolescents did not meet AI recommendations for TFI, raising concerns about their hydration status and potential effects on mental and physical well-being. Given the negative effects on children's health, the levels of SSB consumption are worrying.

Fluid intake in urban China: results of the 2016 Liq.In 7 national cross-sectional surveys.

PURPOSE: To describe total fluid intake (TFI) and types of fluid consumed in urban China by age, gender, regions and city socioeconomic status relative to the adequate intakes (AI) set by the Chinese Nutrition Society. METHODS: In 2016, participants aged 4-9, 10-17 and 18-55 years were recruited via a door-to-door approach in 27 cities in China. In total, 2233 participants were included. The volumes and sources of TFI were collected using the Liq.In 7 record, assisted by a photographic booklet of standard fluid containers. RESULTS: The mean daily TFI among children, adolescents and adults were 966, 1177 and 1387 mL, respectively. In each age group, TFI was significantly higher in male vs female (981 vs 949, 1240 vs 1113, 1442 vs 1332; mL). Approximately 45, 36 and 28% of children, adolescents and adults reached the AI. Although plain water was the highest contributor to TFI, the contribution of sugar sweetened beverages (SSB) was ranked in the top three together with water and milk and derivatives. Approximately 27, 48 and 47% of children, adolescents and adults consumed more than one serving of SSB per day, respectively. CONCLUSIONS: A relatively large proportion of participants did not drink enough to meet the AI in urban China. Many children, adolescents and adults consumed more than one serving of SSB per day. A majority of children, adolescents and adults in the study population do not meet both quantitative and qualitative fluid intake requirements, and signal socioeconomic disparities.

Fluid intake of Latin American adults: results of four 2016 Liq.In7 national cross-sectional surveys.

PURPOSE: To report total fluid intake (TFI) and the intake of different fluid types in adults (≥ 18 years old) from Mexico, Argentina, Brazil and Uruguay. To compare intakes between countries and with recommended adequate intake (AI) of water from fluids. METHODS: Cross-sectional data were collected using a validated liquid intake 7-day record (Liq.In 7 ) in populations from Argentina (n = 1089), Brazil (n = 477), Mexico (n = 1677) and Uruguay (n = 554). Population characteristics, including age, gender, body mass index and socioeconomic level were recorded. Mean TFI was compared with the AI of water from fluids set by the USA Institute of Medicine. RESULTS: The lowest TFI was recorded in Mexican women (1748 mL/day) and the highest in Argentinean men (2318 mL/day). Median daily TFI was significantly different between countries; Uruguay and Argentina had higher values than Mexico and Brazil. In the former, plain water contributed to only 25% of TFI, the remainder being predominantly from hot beverages. Approximately, a third of adults did not drink enough fluid to meet the recommended AI. High SSB consumption was reported, which was significantly different between countries (p < 0.05), the highest being in Mexico (median 25-75th percentiles): 531 (300-895 mL/day. CONCLUSIONS: This survey highlights the need to increase water consumption and reduce SSB intake in this region to avoid potential associated health risks. These findings may be useful information in monitoring public health policy strategies.

Fluid intake patterns of children and adolescents: results of six Liq.In7 national cross-sectional surveys.

PURPOSE: This study aimed to identify and characterize patterns of fluid intake in children and adolescents from six countries: Argentina, Brazil, China, Indonesia, Mexico and Uruguay. METHODS: Data on fluid intake volume and type amongst children (4-9 years; N = 1400) and adolescents (10-17 years; N = 1781) were collected using the validated 7-day fluid-specific record (Liq.In7 record). To identify relatively distinct clusters of subjects based on eight fluid types (water, milk and its derivatives, hot beverages, sugar-sweetened beverages (SSB), 100% fruit juices, artificial/non-nutritive sweetened beverages, alcoholic beverages, other beverages), a cluster analysis (partitioning around k-medoids algorithm) was used. Clusters were then characterized according to their socio-demographics and lifestyle indicators. RESULTS: The six interpretable clusters identified were: low drinkers-SSB (n 523), low drinkers-water and milk (n 615), medium mixed drinkers (n 914), high drinkers-SSB (n 513), high drinkers-water (n 352) and very high drinkers-water (n 264). Country of residence was the dominant characteristic, followed by socioeconomic level, in all six patterns. CONCLUSIONS: This analysis showed that consumption of water and SSB were the primary drivers of the clusters. In addition to country, socio-demographic and lifestyle factors played a role in determining the characteristics of each cluster. This information highlights the need to target interventions in particular populations aimed at changing fluid intake behavior and improving health in children and adolescents.

Incremental effects of 28 days of beta-alanine supplementation on high-intensity cycling performance and blood lactate in masters female cyclists.

Within the aging population, there exists a subset of individuals termed masters athletes (MA). As masters-level competition increases in popularity, MA must find methods to enhance individual athletic performance. Longitudinal beta-alanine (BA) supplementation is suggested to enhance physical capability during exercise; however, these effects have not been evaluated in MA. To examine the longitudinal effects of BA on time to exhaustion (TTE), total work completed (TWC), and lactate clearance in female MA cyclists. Twenty-two female MA (age = 53.3 ± 1.0) participated in this double-blind design. Subjects were randomly assigned to BA (n = 11; 800 mg BA + 8 g dextrose) or placebo (PLA; n = 11; 8 g dextrose) groups and supplemented 4 doses/day over 28 days. Every 7 days, subjects completed a cycling TTE at 120% VO2max, and TWC was calculated. Blood lactate was measured at baseline, immediate post, and 20-min post each TTE. No significant differences existed between groups for any variable at baseline (p > 0.05). After 28 days supplementation, BA had greater TTE (23 vs 1% change) and TWC (21 vs 2% change) than PLA (p < 0.05). Following the 20-min TTE recovery, lactate was 24% lower in BA compared to PLA (4.35 vs. 5.76 mmol/L, respectively). No differences existed for variables during intermittent weeks. 28 days of BA supplementation increased cycling performance via an enhanced time to exhaustion and total work completed with associated lactate clearance during passive rest in female MA.

Total fluid intake and its determinants: cross-sectional surveys among adults in 13 countries worldwide.

PURPOSE: To evaluate the total fluid intake from drinking water and beverages in adult populations from different countries and assess the percentage of individuals complying with the European Food Safety Agency (EFSA) adequate intake (AI) of water from fluids. METHODS: A total of 16,276 adults (7580 men and 8696 women) aged between 18 and 70 years (mean age 39.8 years) were randomly recruited from 13 different countries from three continents. Information about the total daily fluid intake (sum of drinking water and beverages) was collected using a 24-h fluid-specific record over seven consecutive days. RESULTS: Important differences in total fluid intake between countries were found; however, few differences between men and women were reported in most of the countries. Less than 50 % of the women and approximately 60 % of the men do not comply with the EFSA AI of water from fluids. Women were more than twice as likely as men to meet these AI (OR 2.15; 95 % CI 2.02-2.29). The odds of meeting the AI of water from fluids were lower in individuals over 50 years (OR 0.88; 95 % CI 0.80-0.96). Nine percent of the total population consumed less than half of the AI, 40.5 % between 50 and 100 %, and 50.5 % more than the AI. CONCLUSIONS: There were considerable differences in total fluid intake between countries but not between genders. Only 40 % of men and 60 % of women comply with the EFSA AI of water from fluids. Men and elderly individuals had an increased risk of not complying with this reference value.

Intake of water and different beverages in adults across 13 countries.

PURPOSE: To describe the intake of water and all other fluids and to evaluate the proportion of adults exceeding the World Health Organisation (WHO) recommendations on energy intake from free sugar, solely from fluids. METHODS: A total of 16,276 adults (46 % men, mean age 39.8 years) were recruited in 13 countries from 3 continents. A 24-h fluid-specific record over 7 days was used for fluid assessment. RESULTS: In Spain, France, Turkey, Iran, Indonesia and China, fluid intake was characterised by a high contribution of water (47-78 %) to total fluid intake (TFI), with a mean water intake between 0.76 and 1.78 L/day, and a mean energy intake from fluids from 182 to 428 kcal/day. Between 11 and 49 % of adults exceeded the free sugar WHO recommendations, considering solely fluids. In Germany, UK, Poland and Japan, the largest contributors to TFI were hot beverages (28-50 %) and water (18-32 %). Mean energy intake from fluids ranged from 415 to 817 kcal/day, and 48-62 % of adults exceeded free sugar WHO recommendations. In Mexico, Brazil and Argentina, the contribution of juices and regular sugar beverages (28-41 %) was as important as the water contribution to TFI (17-39 %). Mean energy intake from fluids ranged 565-694 kcal/day, and 60-66 % of the adults exceeded the free sugar WHO recommendation. CONCLUSIONS: The highest volumes recorded in most of the countries were for water, mean energy intake from fluids was up to 694 kcal/day, and 66 % of adults exceeded the free sugar WHO recommendation solely by fluids. Actions to create an environment in favour of water consumption and reduce sugar intake from fluids therefore are warranted.

Intake of water and beverages of children and adolescents in 13 countries.

PURPOSE: To describe the intake of water and all other beverages in children and adolescents in 13 countries of three continents. METHODS: Data of 3611 children (4-9 years) and 8109 adolescents (10-17 years) were retrieved from 13 cross-sectional surveys (47 % males). In three countries, stratified cluster sampling design was applied to randomly recruit schools classes. A quota method was applied in the other countries to randomly recruit participants. Details on the intake of all fluid types were obtained with a fluid-specific record over 7 consecutive days. RESULTS: In the total sample, the highest mean intakes were observed for water (738 ± 567 mL/day), followed by milk (212 ± 209 mL/day), regular soft beverages (RSB) (168 ± 290 mL/day) and juices (128 ± 228 mL/day). Patterns characterized by a high contribution of water, RSB or hot beverages to total fluid intake were identified among the countries with close geographical location. Adolescents had a significantly lower milk intake and higher intake of RSB and hot beverages than children in most countries. The most consistent gender difference observed was that in both age groups males reported a significantly higher RSB consumption than females. CONCLUSION: On average, water was the fluid consumed in the largest volume by children and adolescents, but the intake of the different fluid types varied substantially between countries. Since the RSB intake was as large, or even larger, than water intake in some countries, undertaking actions to improve fluid intake habits of children and adolescents are warranted.

Assessing Hydration in Children: From Science to Practice.

Raising children's awareness about their hydration status could be done through a noninvasive biomarker. Urine color (UC) has been validated as a biomarker of hydration in adults and children aged 8-14 years. The aim of this survey was to design and to evaluate the level of understanding and attractiveness of a self-assessment, UC-based hydration tool for children aged 6-11 years. The first phase of the survey consisted of face-to-face interviews during which 84 children identified those graphical elements necessary to understand the hydration message from 6 illustration-based designs containing the UC chart. The graphic elements selected were the basis to create 3 new designs. During the 2nd phase, the level of understanding and attractiveness of these 3 new designs was then evaluated via an online questionnaire by a total of 1,231 children in 3 countries. The design with the highest level of understanding was totally or partially understood by 76% of the participants, independent of age and gender. The levels of understanding, however, differed in the countries. In Indonesia, the levels of understanding of the 3 designs were comparable; whereas in both France (74%) and Mexico (78%), significantly more participants totally and partially understood one of the 3 designs. The levels of attractiveness of the 3 designs were comparable, independent of country, age, and gender. On average, 80% of all participants liked the 3 designs a bit or a lot. Only 14% did not like the designs, and 5% of participants had no opinion regarding attractiveness. These results indicated that three out of four children like and understand the correct hydration message from a strictly illustration-based tool containing the eight-point UC scale.

Educational intervention on water intake improves hydration status and enhances exercise performance in athletic youth.

We aimed to evaluate whether an intervention program emphasizing in increased fluid intake can improve exercise performance in children exercising in the heat. Ninety-two young athletes participated in the study (age: 13.8 ± 0.4 years, weight: 54.9 ± 1.5 kg). Thirty-one (boys: 13, girls: 18) children served as the control group (CON) and 61 (boys: 30, girls: 31) as the intervention (INT). Volunteers had free access to fluids. Hydration was assessed on the basis of first morning urine. A series of field tests were used to evaluate exercise performance. All tests occurred outdoors in the morning (mean ambient temperature=28°C). After baseline testing, INT attended a lecture on hydration, and urine color charts were mounted in all bathrooms. Additionally, water accessibility was facilitated in training, dining and resting areas. Hydration status was improved significantly in the INT [USG: pre=1.031 ± 0.09, post=1.023 ± 0.012, P<0.05; urine osmolality (mOsm/kg water): pre=941 ± 30, post=782 ± 34, P<0.05], while no statistically significant changes were found in the CON [USG: pre=1.033 ± 0.011, post=1.032 ± 0.013, P>0.05; urine osmolality (mOsm/kg water) 970 ± 38 vs 961 ± 38, P>0.05]. Performance in an endurance run was improved significantly only in INT (time for 600 m: pre=189 ± 5 s, post=167 ± 4 s, P<0.05). Improving hydration status by ad libitum consumption of water can enhance performance in young children exercising in the heat.

Estimated liver weight is directly related to hepatic very low-density lipoprotein-triglyceride secretion rate in men.

BACKGROUND: Animal studies suggest that liver weight is directly related to hepatic very low-density lipoprotein-triglyceride (VLDL-TG) secretion, independently of body size. This relationship has never been examined in humans. MATERIALS AND METHODS: We measured VLDL-TG secretion rate by using stable isotope-labelled tracers in 21 healthy, non-obese men (age: 25 +/- 3 years; body mass index: 24.8 +/- 1.6 kg m(-2)), and evaluated the relationship between VLDL-TG secretion and indices of total and regional adiposity (body mass index, total body fat, trunk fat), metabolic parameters (free fatty acid, glucose, and insulin concentrations, homeostasis model assessment index of insulin resistance, resting energy expenditure), and estimated liver weight. RESULTS: Correlation analysis showed that estimated liver weight was positively associated with total VLDL-TG secretion rate (r = 0.722, P < 0.001), VLDL-TG secretion rate per liter of plasma (r = 0.562, P = 0.008), VLDL-TG secretion rate per kilogram of body weight (r = 0.555, P = 0.009), and VLDL-TG secretion rate per kilogram of liver weight (r = 0.620, P = 0.003). In multiple regression analysis, estimated liver weight was the only significant predictor of VLDL-TG secretion rate regardless of units of expression, explaining 31-52% of total variance; none of the metabolic parameters and indices of body fatness entered the regression models. CONCLUSIONS: We conclude that estimated liver weight is directly related to hepatic VLDL-TG secretion rate in healthy non-obese men; this relationship is likely not mediated by interindividual variation in body size.

Water intake and urinary hydration biomarkers in children.

BACKGROUND/OBJECTIVES: The aims of the study were as follows: (1) examine fluid intake and urinary hydration markers of children in Greece, (2) determine the calculated relative risk of hypohydration in children who did not meet the recommendations for daily water intake provided by the Institute of Medicine and the European Food Safety Authority compared with those who did and (3) analyze the efficacy of the recommendations as a method to achieve euhydration in children. SUBJECTS/METHODS: One hundred and fifty Greek boys and girls (age 9-13) recorded their fluid intake for 2 consecutive days. A 24-h urine collection was obtained during the second day. Fluid intake records were analyzed for total water intake from fluids (TWI-F), and urine samples were analyzed for osmolality, color, specific gravity and volume. Urine osmolality ⩾800 mmol/kg H2O was defined as hypohydration. RESULTS: Water intake from fluids was 1729 (1555-1905) and 1550 (1406-1686) ml/d for boys and girls, respectively. Prevalence of hypohydration was 33% (44% of boys, 23% of girls). Children who failed to meet TWI-F recommendations demonstrated a risk of hypohydration that was 1.99-2.12 times higher than those who met recommendations (P⩽0.01). Boys between 9 and 13 years displayed urine osmolality of 777 (725-830) mmol/kg, and urine specific gravity of 1.021 (1.019-1.022), which was higher than those in girls between 9-13 years (P⩽0.015), and >27% were classified as hypohydrated despite meeting water intake recommendations. CONCLUSIONS: Failure to meet TWI-F guidelines increased calculated relative risk of hypohydration in children. Boys between 9 and 13 years are at greater hazard regardless of meeting guidelines and may require greater water intake to avoid elevated urine concentration and ensure adequate hydration.

Intracellular diglycerides in relation to glycaemic control in the myocardium: A pilot study in humans.

AIM: Intramyocellular diglycerides have been implicated in the development of insulin resistance in skeletal muscle. In the myocardium, excess lipid storage may also contribute to the appearance of diabetic cardiomyopathy, while diglycerides may have certain cardio-protective functions. However, little is known on intracellular diglyceride accumulation in the human heart. We aimed to determine diglyceride accumulation in the human myocardium in relation to diabetes status. METHODS: Six diabetic and six non-diabetic aged human subjects undergoing by-pass surgery participated in the study. Subjects were matched for age and body mass index. Intracellular diglyceride levels were measured in heart biopsy samples. Additional samples were taken from pectoralis major muscle that served as control. Whole body glycaemic control was assessed as the percent glycated haemoglobin. RESULTS: Intracellular diglycerides were significantly higher in the myocardium compared to pectoralis major (P<0.05). Although not statistically significant, diabetic subjects tended to accumulate smaller amounts of diglycerides compared to non-diabetic subjects in the myocardium. A linear negative correlation was observed between myocardial diglycerides and glycaemic control (r=0.632, P<0.05). CONCLUSIONS: Our data suggest that poor glycaemic control and diabetes may be associated with a defective accumulation of myocardial diglycerides, possibly blunting intracellular processes and contributing to the development of cardiomyopathy.

24-h Void number as an indicator of hydration status.

BACKGROUND/OBJECTIVES: Few user-friendly hydration assessment techniques exist for the general population to use on a daily basis. The present study evaluated void number over 24 h as a potential hydration assessment tool. SUBJECTS/METHODS: Male and female subjects collected urine for 24 h while adequately hydrated (n=44; 22 ± 4 years, 168 ± 16 cm, 73 ± 15 kg) or fluid restricted (n=43; 22 ± 3 years, 175 ± 10 cm, 81 ± 24 kg). As a control, participants were asked to void when feeling the 'first urge to void' on a commonly used urge scale and noted the volume of each void. For each sample, 24-h urine volume, osmolality (U(OSM)), specific gravity (U(SG)) and color were measured in the laboratory. RESULTS: As designed, the level of urge upon voiding was consistent throughout the study (2 ± 0; 'first urge to void'). Samples were classified by U(SG) as either euhydrated (U(SG)<1.020) or hypohydrated (U(SG) ⩾ 1.020). Grouping by U(OSM) did not change results. Euhydrated versus hypohydrated individuals had greater 24-h urine volume (1933 ± 864 versus 967 ± 306 ml, respectively) and lower urine color (2 ± 1 versus 5 ± 1), U(SG) (1.012 ± 0.004 versus 1.025 ± 0.004) and UOSM (457 ± 180 versus 874 ± 175 mOsm/kg H2O; all P<0.001). Euhydrated individuals voided more than hypohydrated individuals over the 24-h period (5 ± 2 versus 3 ± 1 voids; P<0.001). Additionally, void number inversely correlated with hydration status as identified by U(SG) (r=-0.50; P<0.05) and U(OSM) (r=-0.56; P<0.05). CONCLUSIONS: In conclusion, over 24 h, individuals with a higher void number were euhydrated (that is, had less concentrated hydration biomarkers) than those with a lower void number. Based on these data, void number might be utilized as a simple and feasible hydration assessment for the general public, as it utilizes no equipment or technical expertise.

Increased renal tubular sodium reabsorption during exercise-induced hypervolemia in humans.

We tested the hypothesis that renal tubular Na(+) reabsorption increased during the first 24 h of exercise-induced plasma volume expansion. Renal function was assessed 1 day after no-exercise control (C) or intermittent cycle ergometer exercise (Ex, 85% of peak O(2) uptake) for 2 h before and 3 h after saline loading (12.5 ml/kg over 30 min) in seven subjects. Ex reduced renal blood flow (p-aminohippurate clearance) compared with C (0.83 +/- 0.12 vs. 1.49 +/- 0.24 l/min, P < 0.05) but did not influence glomerular filtration rates (97 +/- 10 ml/min, inulin clearance). Fractional tubular reabsorption of Na(+) in the proximal tubules was higher in Ex than in C (P < 0.05). Saline loading decreased fractional tubular reabsorption of Na(+) from 99.1 +/- 0.1 to 98.7 +/- 0.1% (P < 0.05) in C but not in Ex (99.3 +/- 0.1 to 99.4 +/- 0.1%). Saline loading reduced plasma renin activity and plasma arginine vasopressin levels in C and Ex, although the magnitude of decrease was greater in C (P < 0.05). These results indicate that, during the acute phase of exercise-induced plasma volume expansion, increased tubular Na(+) reabsorption is directed primarily to the proximal tubules and is associated with a decrease in renal blood flow. In addition, saline infusion caused a smaller reduction in fluid-regulating hormones in Ex. The attenuated volume-regulatory response acts to preserve distal tubular Na(+) reabsorption during saline infusion 24 h after exercise.

Thermal and circulatory responses during exercise: effects of hypohydration, dehydration, and water intake.

This investigation examined the distinct and interactive effects of initial hydration state, exercise-induced dehydration, and water rehydration in a hot environment. On four occasions, 10 men performed a 90-min heat stress test (treadmill walking at 5.6 km/h, 5% grade, 33 degrees C, 56% relative humidity). These heat stress tests differed in pretest hydration [2 euhydrated (EU) and 2 hypohydrated (HY) trials] and water intake during exercise [2 water ad libitum (W) and 2 no water (NW) trials]. HY+NW indicated greater physiological strain than all other trials (P < 0.05-0.001) in heart rate, plasma osmolality (Posm), sweat sensitivity (g/degrees C.min), and rectal temperature. Unexpectedly, final HY+W and EU+W responses for rectal temperature, heart rate, and Posm were similar, despite the initial 3.9 +/- 0.2% hypohydration in HY+W. We concluded that differences in pretest Posm (295 +/- 7 and 287 +/- 5 mosmol/kg for HY+W and EU+W, respectively) resulted in greater water consumption (1.65 and 0.31 liter for HY+W and EU+W, respectively), no voluntary dehydration (0.9% body mass increase), and attenuated thermal and circulatory strain during HY+W.

Intravenous versus oral rehydration during a brief period: responses to subsequent exercise in the heat.

PURPOSE: The purpose of this study was to assess whether a brief period (20 min) of intravenous (i.v.) fluid rehydration versus oral rehydration differentially affects cardiovascular, thermoregulatory, and performance factors during exhaustive exercise in the heat. METHODS: Following dehydration (-4% of body weight), eight nonacclimated highly trained cyclists (age = 23.5 +/- 1.2 yr; VO2peak = 61.4 +/- 0.8 mL x kg x min(-1); body fat = 13.5 +/- 0.6%) rehydrated and then cycled at 70% VO2peak to exhaustion in 37 degrees C. Rehydration (randomized, cross-over design) included: 1) CONTROL (no fluid), 2) DRINK (oral rehydration, 0.45% NaCl) equal to 50% of prior dehydration, and 3) IV (intravenous rehydration, 0.45% NaCl), equal to 50% of prior dehydration. Thus, in the DRINK and IV treatments subjects began exercise (EX) at -2% of body weight. RESULTS: Exercise time to exhaustion was not different (P = 0.07) between DRINK (34.9 +/- 4 min) and IV (29.5 +/- 3.5 min), but both were significantly (P < 0.05) longer than CONTROL (18.9 +/- 2.7 min). Plasma volume was better (P < 0.05) restored during IV than CONTROL and DRINK at pre-exercise and 5 min EX, but different (P < 0.05) from only CONTROL at 15 min EX. Plasma lactate during DRINK was lower (P < 0.05) than IV at 15 min EX and postexercise. Heart rate during CONTROL was greater (P < 0.05) than DRINK and IV from 0-8 min EX, and greater (P < 0.05) than DRINK from 10-14 min EX. Rectal temperature during DRINK was less (P < 0.05) than IV from 0-24 min EX. Mean weighted skin temperature during DRINK was less (P < 0.05) than IV from 4-12 min EX. CONCLUSIONS: Thus, despite no statistically significant performance differences between DRINK and IV, it appears that certain physiological parameters were better maintained in the DRINK trial, and the trend toward performance differences may be important to elite athletes.

Bioimpedance spectroscopy technique: intra-, extracellular, and total body water.

The purpose of this study was to test the validity of a multiple frequency bioimpedance spectroscopy (BIS) technique that estimates extracellular fluid volume (ECV), intracellular fluid volume (ICV), and total body water (TBW). Thirteen healthy males (mean +/- SD: age, 23 +/- 3 yr; body mass, 80.6 +/- 14.7 kg) had their TBW and ECV measured by ingesting dilution tracers (7.27 g deuterium oxide, 1.70 g sodium bromide; blood samples at 0 and 4 h). ICV was calculated as TBW minus ECV. Impedance was measured (50-500 kHz) at rest, on a nonconducting surface, with a BIS analyzer. Electrode placement, posture, exercise, food/fluid intake, and ambient temperature were controlled. Dilution measures (TBW, 51.00 +/- 9.30; ECV, 19.88 +/- 3.14; ICV, 31.12 +/- 6.80 L) and BIS volumes (TBW, 50.03 +/- 7.67; ECV, 20.95 +/- 3.33; ICV, 29.04 +/- 4.51 L) were significantly different for ECV (P < 0.01) and ICV (P < 0.05); some individual differences were large. The correlation coefficients of dilution versus BIS volumes (r = 0.93 to 0.96) were significant at P < 0.0001; SEEs were: TBW, 2.23 L; ECV, 1.26 L; and ICV, 1.71 L. We concluded that BIS is valid for between-subject comparisons of body fluid compartments, is appropriate in clinical settings where change in ECV/ICV ratio is important, and should be used by comparing the required level of accuracy to the inherent technique error/variance.