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Introduction: Exertional hyponatremia (EH) during prolonged exercise involves all avenues of fluid-electrolyte gain and loss. Although previous research implicates retention of excess fluid, EH may involve either loss, gain, or no change of body mass. Thus, the etiology, predisposing factors, and recommendations for prevention are vague--except for advice to avoid excessive drinking. Purpose: This retrospective field study presents case reports of two unacquainted recreational cyclists (LC, 31y and AM, 39 years) who began exercise with normal serum electrolytes but finished a summer 164-km ride (ambient, 34±5°C) with a serum [Na+] of 130 mmol/L. Methods: To clarify the etiology of EH, their pre- and post-exercise measurements were compared to a control group (CON) of 31 normonatremic cyclists (mean ± SD; 37±6 years; 141±3 mmol Na+/L). Results: Anthropomorphic characteristics, exercise time, and post-exercise ratings of thermal sensation, perceived exertion and muscle cramp were similar for LC, AM and CON. These two hyponatremic cyclists consumed a large and similar volume of fluid (191 and 189 ml/kg), experienced an 11 mmol/L decrease of serum [Na+], reported low thirst sensations; however, LC gained 3.1 kg (+4.3% of body mass) during 8.9 hr of exercise and AM maintained body mass (+0.1kg, +0.1%, 10.6h). In the entire cohort (n = 33), post-event serum [Na+] was strongly correlated with total fluid intake (R² = 0.45, p < .0001), and correlated moderately with dietary sodium intake (R²=0.28, p = .004) and body mass change (R² = 0.22, p = .02). Linear regression analyses predicted the threshold of EH onset (<135 mmol Na+/L) as 168 ml fluid/kg. Conclusions: The wide range of serum [Na+] changes (+6 to -11 mmol/L) led us to recommend an individualized rehydration plan to athletes because the interactions of factors were complex and idiosyncratic. [ABSTRACT FROM AUTHOR]

This field investigation assessed differences (e.g., drinking behavior, hydration status, perceptual ratings) between female and male endurance cyclists who completed a 164-km event in a hot environment (35 °C mean dry bulb) to inform rehydration recommendations for athletes. Three years of data were pooled to create 2 groups of cyclists: women (n = 15) and men (n = 88). Women were significantly smaller (p < .001) than men in height (166 ± 5 vs. 179 ± 7 cm), body mass (64.6 ± 7.3 vs. 86.4 ± 12.3 kg), and body mass index (BMI; 23.3 ±1.8 vs. 26.9 ± 3.4) and had lower preevent urinary indices of hydration status, but were similar to men in age (43 ± 7 years vs. 44 ± 9 years) and exercise time (7.77 ± 1.24 hr vs. 7.23 ± 1.75 hr). During the 164-km ride, women lost less body mass (-0.7 ± 1.0 vs. -1.7 ± 1.5 kg; -1.1 ± 1.6% vs. -1.9 ± 1.8% of body weight; p < .005) and consumed less fluid than men (4.80 ± 1.28 L vs. 5.59 ± 2.13 L; p < .005). Women consumed a similar volume of fluid as men, relative to body mass (milliliters/kilogram). To control for performance and anthropomorphic characteristics, 15 women were pair-matched with 15 men on the basis of exercise time on the course and BMI; urine-specific gravity, urine color, and body mass change (kilograms and percentage) were different (p < .05) in 4 of 6 comparisons. No gender differences were observed for ratings of thirst, thermal sensation, or perceived exertion. In conclusion, differences in relative fluid volume consumed and hydration indices suggest that professional sports medicine organizations should consider gender and individualized drinking plans when formulating pronouncements regarding rehydration during exercise. [ABSTRACT FROM AUTHOR]

Purpose: An increasing body of evidence suggests that excreting a generous volume of diluted urine is associated with short- and long-term beneficial health effects, especially for kidney and metabolic function. However, water intake and hydration remain under-investigated and optimal hydration is poorly and inconsistently defined. This review tests the hypothesis that optimal chronic water intake positively impacts various aspects of health and proposes an evidence-based definition of optimal hydration. Methods: Search strategy included PubMed and Google Scholar using relevant keywords for each health outcome, complemented by manual search of article reference lists and the expertise of relevant practitioners for each area studied. Results: The available literature suggest the effects of increased water intake on health may be direct, due to increased urine flow or urine dilution, or indirect, mediated by a reduction in osmotically -stimulated vasopressin (AVP). Urine flow affects the formation of kidney stones and recurrence of urinary tract infection, while increased circulating AVP is implicated in metabolic disease, chronic kidney disease, and autosomal dominant polycystic kidney disease. Conclusion: In order to ensure optimal hydration, it is proposed that optimal total water intake should approach 2.5 to 3.5 L day−1 to allow for the daily excretion of 2 to 3 L of dilute (< 500 mOsm kg−1) urine. Simple urinary markers of hydration such as urine color or void frequency may be used to monitor and adjust intake. [ABSTRACT FROM AUTHOR]

Context: Exertional heat exhaustion (HEX) is the most common form of heat illness experienced by athletes, laborers, and military personnel. Both dehydration stemming from a water and/or salt deficiency and a high ambient temperature must exist for HEX to occur. In the field, appropriate therapy can reduce recovery time. Objective: This manuscript provides clinical guidance regarding return to activity. The primary focus of this paper is to describe the evaluation of residual effects and the underlying personal characteristics that initially predispose the athlete to HEX. Attention to these factors will reduce the risk of future episodes. [ABSTRACT FROM AUTHOR]

This investigation determined if 3 levels of controlled caffeine consumption affected fluid-electrolyte balance and renal function differently. Healthy males (mean ± standard deviation; age, 21.6 ± 3.3 y) consumed 3 mg caffeine · kg-1 · d-1 on days 1 to 6 (equilibration phase). On days 7 to 11 (treatment phase), subjects consumed either 0 mg (C0; placebo; n = 20), 3 mg (C3; n = 20), or 6 mg (C6; n = 19) caffeine · kg-1 · d-1 in capsules, with no other dietary caffeine intake. The following variables were unaffected (P > 0.05) by different caffeine doses on days 1, 3, 6, 9, and 11 and were within normal clinical ranges: body mass, urine osmolality, urine specific gravity, urine color, 24-h urine volume, 24-h Na+ and K+ excretion, 24-h creatinine, blood urea nitrogen, serum Na+ and K+, serum osmolality, hematocrit, and total plasma protein. Therefore, C0, C3, and C6 exhibited no evidence of hypohydration. These findings question the widely accepted notion that caffeine consumption acts chronically as a diuretic. [ABSTRACT FROM AUTHOR]

Presents a review which aimed to critique controlled investigations regarding the effects of caffeine on dehydration and exercise performance and ascertain whether abstaining from caffeinated beverages is scientifically and physiologically justifiable. Consumption of caffeine; Discussion on caffeine pharmacology; Metabolic and ergogenic properties of caffeine; Regulations of sports governing bodies.

Provides information on a study which assessed the plasma glucose and hormonal responses to carbohydrate ingestion, prior to exercise in the heat, in a hypohydrated state versus partial rehydration with intravenous solutions. Methodology; Plasma osmolality throughout the experimental protocol; Plasma glucose concentrations throughout the experimental protocol after correction for plasma volume changes.

The micro-organisms which inhabit the human gut (i.e. the intestinal microbiota) influence numerous human biochemical pathways and physiological functions. The present review focuses on two questions, 'Are intestinal microbiota effects measurable and meaningful?' and 'What research methods and variables are influenced by intestinal microbiota effects?'. These questions are considered with respect to doubly labelled water measurements of energy expenditure, heat balance calculations and models, measurements of RMR via indirect calorimetry, and diet-induced energy expenditure. Several lines of evidence suggest that the intestinal microbiota introduces measurement variability and measurement errors which have been overlooked in research studies involving nutrition, bioenergetics, physiology and temperature regulation. Therefore, we recommend that present conceptual models and research techniques be updated via future experiments, to account for the metabolic processes and regulatory influences of the intestinal microbiota. [ABSTRACT FROM AUTHOR]

Background: Urine osmolality (UOSM) reflects the renal regulation of excess fluid or deficit fluid, and therefore, serves as a marker of hydration status. Little is known about monitoring hydration in pregnant and lactating women despite significant physiological challenges to body water balance during that time. Therefore, we designed a study to assess if urine color (UCOL), an inexpensive and practical method, was a valid means of assessing urine concentration. Twenty-four hour UCOL was significantly correlated with 24 h UOSM in all women: pregnant, lactating, and control (r = 0.61-0.84, all p < 0.001). Utilizing a receiver operating characteristic statistical analysis, we found that 24 h and single sample UCOL had excellent diagnostic accuracy for identifying UOSM ≥ 500 mOsm·kg-1 in all women (area under the curve = 0.68-0.95, p < 0.001-0.46), and the UCOL that reflected this cut off was ≥ 4 on the UCOL chart. Summary: Therefore, UCOL is a valid marker of urine concentration and ultimately hydration status in pregnant, lactating, and non-pregnant, non-lactating women. For pregnant, lactating, and control women, the UCOL chart is a valid tool that can be used to monitor urine concentration in a single sample or over the course of the day via a 24 h sample. Key Message: Women who present with a UCOL of 4 or more likely have a UOSM ≥ 500 mOsm·kg-1. Given the positive health benefits associated with UOSM <500 mOsm·kg-1, women should aim for a 1, 2, or 3 on the UCOL chart. If a UCOL of ≥ 4 is observed, women should consider increasing fluid consumption to improve hydration status. [ABSTRACT FROM AUTHOR]

An introduction to the journal is presented which includes articles on topics including a review of water drinking habits and barriers to optimal drinking at school, an initiative that seeks to increase awareness of healthy hydration practices among dietitians and increase in kidney disorders.

The article discusses a study which determines adequate drink to be consumed by athletes in a hot climate during ultra endurance cycling to compensate fluid loss due to sweating and urination. The study was conducted on 26 male cyclists and measurements were taken at the start, 52 km, 97 km, 136 km and at the finish point. The study found no universal drinking plan and that each athlete has to develop a plan based on specific needs as per body mass, exercise time and field requirements.

An introduction is presented in which the editor discusses various articles within the issue pregnancy and breastfeeding; scientific literature regarding the effects of dehydration on cognitive function and mood in children, adolescents; and childhood obesity.

Because body mass change (ΔMb) does not represent all water losses and gains, the present field investigation determined if (a) ΔMbequalled the net effective body water change during ultra-endurance exercise and (b) ground speed and exercise duration influenced these variables. Thirty-two male cyclists (age range, 35–52 years) completed a 164-km event in a hot environment, were retrospectively triplet matched and placed into one of three groups based on exercise duration (4.8, 6.3, 9.6 h). Net effective body water loss was computed from measurements (body mass, total fluid intake and urine excreted) and calculations (water evolved and mass loss due to substrate oxidation, solid food mass and sweat loss), including (ΔEBWgly) and excluding (ΔEBW) water bound to glycogen. With all cyclists combined, the mean ΔMb(i.e. loss) was greater than that of ΔEBWglyby 1200 ± 200 g (P= 1.4 × 10–18), was similar to ΔEBW (difference, 0 ± 200 g;P= .21) and was strongly correlated with both (R2= .98). Analysis of equivalence indicated that ΔMbwas not equivalent to ΔEBWgly, but was equivalent to ΔEBW. Due to measurement complexity, we concluded that (a) athletes will not calculate the effective body water calculations routinely and (b) body mass change remains a useful field-expedient estimate of net effective body water change. [ABSTRACT FROM AUTHOR]

Context: The sensation of thirst is different from the complex behavior of drinking ad libitum. Rehydration recommendations to athletes differ, depending on the source, yet no previous researchers have systematically compared drinking to thirst (DTT) versus ad libitum drinking behavior (DAL). Objective: To compare 2 groups of trained cyclists (DTT and DAL) who had similar physical characteristics and training programs (P > .05). The DTT group (n = 12, age = 47 6 7 years) drank only when thirsty, whereas the DAL group (n = 12, age = 44 6 7 years) consumed fluid ad libitum (ie, whenever and in whatever volume desired). Design: Cohort study. Setting: Road cycling (164 km) in the heat (36.18C ± 6.58C). Patients or Other Participants: Ultraendurance cyclists (4 women, 20 men). Intervention(s): We recorded measurements 1 day before the event, on event day before the start, at 3 roadside aid stations, at the finish line, and 1 day after the event. Main Outcome Measure(s): Body mass, urinary hydration indices, and food and fluids consumed. Results: No between-groups differences were seen on event day for total exercise time (DTT = 6.69 6 0.89 hours, DAL = 6.66 6 0.77 hours), urinary indices (specific gravity, color), body mass change (DTT = -2.22% 6 1.73%, DAL = -2.29% 6 1.62%), fluid intake (DTT=5.63 6 2.59 L/6.7 h, DAL= 6.04 6 2.37 L/6.7 h), dietary energy intake, macronutrient intake, ratings of thirst (DTT start=2 ± 1, DTT finish=6 ± 1, DAL start = 2 ± 1, DAL finish = 6 6 1), pain, perceived exertion, or thermal sensation. Total fluid intake on recovery dayþ1 was the primary significant difference (DAL = 5.13 ± 1.87 L/24 h, DTT = 3.13 6 1.53 L/24 h, t18 = 2.59, P = .02). Conclusions: Observations on event day indicated that drinking to thirst and drinking ad libitum resulted in similar physiologic and perceptual outcomes. This suggests that specific instructions to "drink to thirst" were unnecessary. Indeed, if athletes drink ad libitum, they can focus on training and competition rather than being distracted by ongoing evaluation of thirst sensations. [ABSTRACT FROM AUTHOR]

Exploring novel hydration indices is important because no human biomarker has been shown to be incontrovertibly valid in all life situations. The present investigation was designed to identify inexpensive, nontechnical methods to use when self-assessing hydration status. This investigation evaluated the validity and efficacy of 2 novel techniques (i.e., thirst sensation and urine volume) to assess hydration state of 29 active men (mean ± SD; age, 23 ± 4 years; body mass, 76.02 ± 11.94 kg) at rest. Eight combinations of 4 water challenges (4.8, 9.3, 11.0, or 14 mL·kg−1) and 2 hydration states (mildly hypohydrated (HY), -2.0%; euhydrated (EU), -0.2% body mass) were employed. First, thirst was linearly related to body water loss, and ratings of thirst distinguished HY from EU ( p < 0.001) subsequent to 19 h of controlled food and fluid intake. Second, measurements of urine volume 60 min after consuming a water bolus (11.0 or 14 mL·kg−1) were strongly and inversely correlated with entering hydration state, assessed by urine specific gravity ( r2 = 0.76, p < 0.0001) and urine osmolality ( r2 = 0.77, p < 0.0001). We concluded that healthy men can employ simple measurements of morning thirst sensation and urine volume to identify the presence of mild hypohydration and to guide fluid replacement. These 2 techniques are relevant because HY (-2% body mass) is the approximate threshold for the onset of thirst, reduced endurance exercise performance, and decrements of working memory and mood. [ABSTRACT FROM AUTHOR]

Normal human water intake spans a large range owing to the body's ability to excrete large volumes of water in times of excess and conserve in times of scarcity. Recently, chronic intakes of either large volumes (HIGH) or small volumes (LOW) of water have been investigated. Adaptations within the renal regulation of water through the secretion and reabsorptive actions of the hormone arginine vasopressin and the thirst mechanism have been observed to differentiate these 2 groups during normal living. Increases or decreases in daily fluid intake in LOW and HIGH resulted in appropriate arginine vasopressin and perception of thirst changes, which enabled fluid balance in both of these populations. However, future research should establish if the chronic adaptive mechanisms, by which fluid is regulated have long-term negative outcomes. [ABSTRACT FROM AUTHOR]

The purpose of this article is to review the effects of chronic mild dehydration and fluid consumption on specific health outcomes including obesity. The electronic databases PubMed and Google Scholar were searched for relevant literature published from the time of their inception to 2011, with results restricted to studies performed on human subjects and reports in the English language. Key words included the following: dehydration, hypohydration, water intake, fluid intake, disease, and the names of specific disease states. Strength of evidence categories were described for 1) medical conditions associated with chronic dehydration or low daily water intake, and 2) randomized-controlled trials regarding the effects of increased water consumption on caloric intake, weight gain, and satiety. This process determined that urolithiasis is the only disorder that has been consistently associated (i.e., 11 of 13 publications) with chronic low daily water intake. Regarding obesity and type 2 diabetes, evidence suggests that increased water intake may reduce caloric intake for some individuals. Recommendations for future investigations include measuring total fluid intake (water + beverages + water in solid food), conducting randomized-controlled experiments, identifying novel hydration biomarkers, and delineating hydration categories. [ABSTRACT FROM AUTHOR]

Abstract: Normative values and confidence intervals for the hydration indices of women do not exist. Also, few publications have precisely described the fluid types and volumes that women consume. This investigation computed seven numerical reference categories for widely used hydration biomarkers (eg, serum and urine osmolality) and the dietary fluid preferences of self-reported healthy, active women. Participants (n=32; age 20±1 years; body mass 59.6±8.5 kg; body mass index [calculated as kg/m2] 21.1±2.4) were counseled in the methods to record daily food and fluid intake on 2 consecutive days. To reduce day-to-day body water fluctuations, participants were tested only during the placebo phase of the oral contraceptive pill pack. Euhydration was represented by the following ranges: serum osmolality=293 to 294 mOsm/kg; mean 24-hour total fluid intake=2,109 to 2,506 mL/24 hours; mean 24-hour total beverage intake=1,300 to 1,831 mL/24 hours; urine volume=951 to 1,239 mL/24 hours; urine specific gravity=1.016 to 1.020; urine osmolality=549 to 705 mOsm/kg; and urine color=5. However, only 3% of women experienced a urine specific gravity <1.005, and only 6% exhibited a urine color of 1 or 2. Water (representing 45.3% and 47.9% of 24-hour total fluid intake), tea, milk, coffee, and fruit juice were consumed in largest volumes. In conclusion, these data provide objective normative values for hyperhydration, euhydration, and dehydration that can be used by registered dietitians and clinicians to counsel women about their hydration status. [Copyright &y& Elsevier]

The article examines hydration biomarkers used to assess mild dehydration in daily living and discusses advances in the understanding of invasive and non-invasive hydration techniques. According to the article, dynamic complexity in human fluid electrolyte regulation such as neuro-endocrine responses complicate the likelihood that any single biomarker will validly describe hydration status. It suggests future directions to explore novel hydration indices yet to be discovered.

Limited information is available regarding the effects of mild dehydration on cognitive function. Therefore, mild dehydration was produced by intermittent moderate exercise without hyperthermia and its effects on cognitive function of women were investigated. Twenty-five females (age 23.0 ± 0.6 y) participated in three 8-h, placebo-controlled experiments involving a different hydration state each day: exercise-induced dehydration with no diuretic (DNI, exerciseinduced dehydration plus diuretic (DD; furosemide, 40 mg), and euhydration (EU(. Cognitive performance, mood, and symptoms of dehydration were assessed during each experiment, 3 times at rest and during each of 3 exercise sessions. The DN and DD trials in which a volunteer attained a ⩾ 1 % level of dehydration were pooled and compared to that volunteer's equivalent EU trials. Mean dehydration achieved during these DN and DD trials was -1.36 ± 0.16% of body mass. Significant adverse effects of dehydration were present at rest and during exercise for vigor-activity, fatigue-inertia, and total mood disturbance scores of the Profile of Mood States and for task difficulty, concentration, and headache as assessed by questionnaire. Most aspects of cognitive performance were not affected by dehydration. Serum osmolality, a marker of hydration, was greater in the mean of the dehydrated trials in which a ⩾ 1 % level of dehydration was achieved IP = 0.006) compared to EU. In conclusion, degraded mood, increased perception of task difficulty, lower concentration, and headache symptoms resulted from 1.36% dehydration in females. Increased emphasis on optimal hydration is warranted, especially during and after moderate exercise. [ABSTRACT FROM AUTHOR]

The article presents the results of a study which investigated the dietary, metabolic, and behavioral responses of nonelite ultraendurance cyclists. An overview of related previous research is provided, detailing cyclist dietary intake and dehydration factors relative to body mass. Details of the experiment protocol are also presented, including interval thermal, fluid electrolyte, and perceptual variable measurements of male and female cyclists.

Context: In hot environments, the American football uniform predisposes athletes to exertional heat exhaustion or exerciseinduced hyperthermia at the threshold for heat stroke (rectal temperature [Tre] > 39°C). Objective: To evaluate the differential effects of 2 American football uniform configurations on exercise, thermal, cardiovascular, hematologic, and perceptual responses in a hot, humid environment. Design: Randomized controlled trial. Setting: Human Performance Laboratory. Patients or Other Participants: Ten men with more than 3 years of competitive experience as football linemen (age = 23.8 ± 4.3 years, height = 183.9 ± 6.3 cm, mass = 117.41 ± 12.59 kg, body fat = 30.1% ± 5.5%). Intervention(s): Participants completed 3 controlled exercise protocols consisting of repetitive box lifting (lifting, carrying, and depositing a 20.4-kg box at a rate of 10 lifts per minute for 10 minutes), seated recovery (10 minutes), and up to 60 minutes of treadmill walking. They wore one of the following: a partial uniform (PART) that included the National Football League (NFL) uniform without a helmet and shoulder pads; a full uniform (FULL) that included the full NFL uniform; or control clothing (CON) that included socks, sneakers, and shorts. Exercise, meals, and hydration status were controlled. Main Outcome Measure(s): We assessed sweat rate, Tre, heart rate, blood pressure, treadmill exercise time, perceptual measurements, plasma volume, plasma lactate, plasma glucose, plasma osmolality, body mass, and fat mass. Results: During 19 of 30 experiments, participants halted exercise as a result of volitional exhaustion. Mean sweat rate, Tre, heart rate, and treadmill exercise time during the CON condition were different from those measures during the PART (P range, .04-.001; d range, 0.42-0.92) and FULL (P range, .04-.003; d range, 1.04-1.17) conditions; no differences were detected for perceptual measurements, plasma volume, plasma lactate, plasma glucose, or plasma osmolality. Exhaustion occurred during the FULL and PART conditions at the same Tre (39.2°C). Systolic and diastolic blood pressures (n = 9) indicated that hypotension developed throughout exercise (all treatments). Compared with the PART condition, the FULL condition resulted in a faster rate of Tre increase (P < .001, d = 0.79), decreased treadmill exercise time (P = .005, d = 0.48), and fewer completed exercise bouts. Interestingly, Tre increase was correlated with lean body mass during the FULL condition (R2 = 0.71, P = .005), and treadmill exercise time was correlated with total fat mass during the CON (R2 = 0.90, P < .001) and PART (R2 = 0.69, P = .005) conditions. Conclusions: The FULL and PART conditions resulted in greater physiologic strain than the CON condition. These findings indicated that critical internal temperature and hypotension were concurrent with exhaustion during uncompensable (FULL) or nearly uncompensable (PART) heat stress and that anthropomorphic characteristics influenced heat storage and exercise time to exhaustion. [ABSTRACT FROM AUTHOR]

The purpose of this research was to characterize the movement of ingested water through body fluids, during exercise-heat stress. Deuterium oxide ((2)H(2)O) accumulation in plasma and eccrine sweat was measured at two sites (back and forehead). The exercise of 14 males was controlled via cycle ergometry in a warm environment (60 min; 28.7 degrees C, 51%rh). Subjects consumed (2)H(2)O (0.15 mg kg(-1), 99.9% purity) mixed in flavored, non-caloric, colored water before exercise, then consumed 3.0 ml kg(-1) containing no (2)H(2)O every 15 min during exercise. We hypothesized that water transit from mouth to skin would occur before 15 min. (2)H(2)O appeared rapidly in both plasma and sweat (P < 0.05), within 10 min of water consumption. The ratio (2)H(2)O/H(2)O (D:H) was 47.3-55.0 times greater in plasma than in back sweat at minutes 10, 20, and 30 (DeltaD:H relative to baseline). At elapsed minute 20, the mean rate of deuterium accumulation (DeltaD:H min(-1)) in plasma was 14.9 and 23.7 times greater than in forehead and back sweat samples, respectively. Mean (+/-SE) whole-body sweat rate was 1.04 +/- 0.05 L h(-1) and subjects with the greatest whole-body sweat rate exhibited the greatest peak deuterium enrichment in sweat (r(2) = 0.87, exponential function); the peak (2)H(2)O enrichment in sweat was not proportional (P > 0.05) to body mass, volume of the deuterium dose, or total volume of fluid consumed. These findings clarify the time course of fluid movement from mouth to eccrine sweat glands, and demonstrate considerable differences of (2)H(2)O enrichment in plasma versus sweat. [ABSTRACT FROM AUTHOR]

The article reports that few caffeine studies have been published which include cognitive and physiologic considerations for the athlete. Lower doses of caffeine can be as effective as higher doses during exercise performance without any negative coincidence. Caffeine can improve the cognitive aspects of performance when an athlete has not slept well.

The article evaluated the effects of a nutritional supplement in rehydration solutions, with and without carbohydrate and electrolytes for a sample of male runners. The rehydration with fluids containing betaine resulted in significant differences in plasma volume, oxygen consumption, plasma lactate concentration and thermal sensation. The increases of both aerobic and anaerobic metabolism mean that further investigation of betaine as a nutritional supplement is needed.

The article presents a study which investigates the effects of hypohydration on running and physiological responses. One study performed four experiments on euhydrated and hypohydration state with ten highly trained collegiate distance runners participants. The results show that there was no between-treatment differences on running economy, concentration on plasma lactate, and perceived exertion's rating. In addition, hypohydration indicates greater heart rate, rectal temperature, and concentration on plasma norepinephrine. The study concludes further that hypohydration did not change the running economy or lactate accumulation of endurance athletes which indicates that running economy was not affected by hypohydration.

Abstract: The stimulatory effects of acute caffeine intake on choice reaction time, mood state, and visual vigilance are well established. Little research exists, however, on the effects of chronic caffeine ingestion on psychomotor tasks. Therefore, the purpose of this study was to evaluate the effects of 5 days of controlled caffeine intake on cognitive and psychomotor performance. Three groups of 20 healthy males (age=22±3 years, mass=75.4±7.9 kg, body fat percentage=11.2±5.1%) twice completed a battery of cognitive and psychomotor tasks: after 6 days of 3 mg·kg−1 day−1 caffeine equilibration (Day 6), and after 5 days of experimental (0 [G0], 3 [G3], or 6 [G6] mg·kg−1 day−1) caffeine intake (Day 11). Groups were randomized and stratified for age, mass, and body composition; all procedures were double-blind. Cognitive analyses involved a visual four-choice reaction time test, a mood state questionnaire, and a visual vigilance task. Experimental chronic caffeine intake did not significantly alter the number of correct responses or the mean latency of response for either the four-choice reaction time or the visual vigilance tasks. The Vigor–Activity subset of the mood state questionnaire was significantly greater in G3 than G0 or G6 on Day 11. All other mood constructs were unaffected by caffeine intake. In conclusion, few cognitive and psychomotor differences existed after 5 days of controlled caffeine ingestion between subjects consuming 0, 3, or 6 mg·kg−1 day−1 of caffeine, suggesting that chronic caffeine intake (1) has few perceptible effects on cognitive and psychomotor well-being and (2) may lead to a tolerance to some aspects of caffeine''s acute effects. [Copyright &y& Elsevier]

Water in the human body is essential for metabolism, temperature regulation, and numerous other physiological processes that are consistent with good health. Accurate, precise, and reliable methods to assess body fluid compartments are needed. This review describes the hydration assessment techniques of isotope dilution, neutron activation analysis, bioelectrical impedance, body mass change, thirst, tracer appearance, hematologic indices, and urinary markers. It also provides guidance for selecting techniques that are appropriate for use with unique individuals and situations. [ABSTRACT FROM AUTHOR]

Although endogenous and exogenous steroid hormones affect numerous physiological processes, the interactions of reproductive hormones, chronic exercise training, and heat acclimation are unknown. This investigation evaluated the re- sponges and adaptations of 36 inactive females [age 21 ± 3 (SD) yr] as they undertook a 7- to 8-wk program [heat acclimation and physical training (HAPT)J of indoor heat acclimation (90 mm/day, 3 day s/wk) and outdoor physical training (3 days/wk) while using either an oral estradiol-progestin contraceptive (ORAL, n = 15), a contraceptive injection of depot medroxyprogesterone acetate (DEPO, n = 7), or no contraceptive (EU-OV, n = 14; control). Standardized physical fitness and exercise-heat tolerance tests (36.5°C, 37% relative humidity), administered before and after HAPT, demonstrated that the three subject groups successfully (P < 0.05) acclimated to heat (i.e., rectal temperature, heart rate) and improved muscular endurance (i.e., sit- ups, push-ups, 4.6-km run time) and body composition characteristics. The stress of HAPT did not disrupt the menstrual cycle length/phase characteristics, ovulation, or plasma hormone concentrations of EU- OV. No between-group differences (P> 0.05) existed for rectal and skin temperatures or metabolic, cardiorespiratory, muscular endurance, or body composition variables. A significant difference post- HAPT in the onset temperature of local sweating, ORAL (37.2 ± 0.4°C) vs. DEPO (37.7 ± 0.2°C), suggested that steroid hormones influenced this adaptation. In summary, virtually all adaptations of ORAL and DEPO were similar to EU-OV, suggesting that exogenous reproductive hormones neither enhanced nor impaired the ability of women to complete 7-8 wk of strenuous physical training and heat acclimation. [ABSTRACT FROM AUTHOR]

Recent trends in weight loss diets have led to a substantial increase in protein intake by individuals. As a result, the safety of habitually consuming dietary protein in excess of recommended intakes has been questioned. In particular, there is concern that high protein intake may promote renal damage by chronically increasing glomerular pressure and hyperfiltration. There is, however, a serious question as to whether there is significant evidence to support this relationship in healthy individuals. In fact, some studies suggest that hyperfiltration, the purported mechanism for renal damage, is a normal adaptative mechanism that occurs in response to several physiological conditions. This paper reviews the available evidence that increased dietary protein intake is a health concern in terms of the potential to initiate or promote renal disease. While protein restriction may be appropriate for treatment of existing kidney disease, we find no significant evidence for a detrimental effect of high protein intakes on kidney function in healthy persons after centuries of a high protein Western diet. [ABSTRACT FROM AUTHOR]

For a person undertaking regular exercise, any fluid deficit that is incurred during one exercise session can potentially compromise the next exercise session if adequate fluid replacement does not occur. Fluid replacement after exercise can, therefore, frequently be thought of as hydration before the next exercise bout. The importance of ensuring euhydration before exercise and the potential benefits of temporary hyperhydration with sodium salts or glycerol solutions are also important issues. Post-exercise restoration of fluid balance after sweat-induced dehydration avoids the detrimental effects of a body water deficit on physiological function and subsequent exercise performance. For effective restoration of fluid balance, the consumption of a volume of fluid in excess of the sweat loss and replacement of electrolyte, particularly sodium, losses are essential. Intravenous fluid replacement after exercise has been investigated to a lesser extent and its role for fluid replacement in the dehydrated but otherwise well athlete remains equivocal. [ABSTRACT FROM AUTHOR]

Examines the relationship between vitamin and mineral supplements as nutritional aids to exercise performance and health. Recommended dietary allowance and intake; Nature, classification, and functions of vitamins and minerals; Role of vitamin and mineral supplements in vitality and health; Vitamins as antioxidants.

• This research assessed perceptions during controlled changes of hydration status. [81]. • 18 men rated 17 perceptions during 24 h euhydration, 24 h dehydration and rehydration. [84]. • Mild dehydration induced perceptual/mood effects beginning at ∼0.5% body mass loss. [83]. • Perceptual interrelationships varied as controlled hydration status changed. [76]. • Unique aversive moods motivated drinking and discouraged overdrinking. [70]. Thirst motivates consumption of water necessary for optimal health and cognitive-physiological functions. Other than thirst, little is known about coexisting perceptions and moods that provide information to the brain and participate in body water homeostasis. The purpose of this investigation was to observe perceptions, somatic sensations, and moods during controlled changes of hydration status. During routine daily activities interspersed with laboratory visits, 18 healthy young men (age, 23±3 y; body mass, 80.13±10.61 kg) self-reported hourly ratings (visual analog scales, VAS) of 17 subjective perceptions, across two 24-h periods (ad libitum food and water intake while euhydrated; water restriction with dry food intake [WR]) and during a 30-min rehydration session (R 30 , 1.46±0.47 L water intake). At the end of WR, body mass loss reached 1.67 kg (2.12%). Distinct perceptions were identified during euhydration, WR and immediately after R 30. Starting approximately 4 h after WR began (body mass loss of ∼0.5%), perceptual changes included progressively intensifying ratings of thirst, mouth dryness, desire for water, and pleasantness of drinking. In comparison, immediately after R 30 , participants reported a reversal of the perceptions observed during WR (above) plus cooler thermal sensation, increased satisfaction, and stomach fullness. These VAS ratings suggested that aversive moods contributed to drinking behavior and supported previously published animal studies. In conclusion, this investigation delineates previously unreported perceptions and their evolution (e.g., appearance, extinction, time course) that motivated drinking during WR and discouraged overdrinking after R 30. [ABSTRACT FROM AUTHOR]

The article discusses the importance of dietary water intake for the human health which is discovered by various studies. It states that the use of water as a healthy hydration program is recommended by a panel of experts to adults and children. It mentions a study which discovers that water consumption before or during meals is helpful for overweight individuals. It also cites another study which finds that mean resting heart rate of healthy men is lessened by water intake.

A letter to the editor is presented in response to the article "Toward ending fatal heat stroke in football players," by E. Randy Eichner.

Comments on the protein and amino acid requirements of athletes and exertional hyponatraemia. Role of extra dietary protein in muscle hypertrophy, and muscle growth; Impact on the nitrogen balance due to high protein intakes; Effect of high protein diets in untrained individuals; Aspects of fluid-electrolyte imbalance and symptoms of exertional hyponatraemia; Rate of maximal renal diuresis; Need for optimizing and maximizing fluid intake.

The article introduces various reports published within the issue, including one about kidney diseases, the role of arginine vasopressin (AVP) in the brain and peripheral organs and another on global initiatives to fight chronic kidney disease (CKD).

Presents a study that characterized metabolic response to provision of mixed protein-carbohydrate supplementation during endurance exercise. Method of the study; Results and discussion; Conclusion.

Investigates the effects of intravenous versus oral rehydration, during a brief period on stress hormone concentrations during subsequent exhaustive exercise in the heat. Effects of dehydration on the physiological function and performance of athletes; Methodology of the study; Stress hormone responses.

The article presents a recap of conference presentations on the importance of hydration for health. Studies discover that sugar-containing beverages encourage obesity, while water does not stimulate insulin and does not influence metabolism. They also suggest that there is relation between increased carbonated soft-drink consumption and increased incidence of obesity and type 2 diabetes. Furthermore, a study suggests that kidney is more effective than a fluid deficit in fluid excess regulation.

The article focuses on the findings of a study concerning preseason heat-acclimatization guidelines for secondary school athletics. The study reveals that the guidelines should be used for all preseason conditioning, training and practice activities in a warm or hot environment whether it may be an indoor or an outdoor activities. It suggests that all student athletes should undergo a participation medical examination administered by a physician or as required by state law. Moreover, it notes that the goal of the acclimatization period is to enhance exercise heat tolerance and the ability to exercise effectively.

A review of the article "Artifacts in Plasma Volume Change Due to Hematology Analyzer-derived Hematocrit," by P. Watson et al., which appears within this issue of "Medicine & Science in Sports & Exercise" is presented.

Objective: To present evidence-based recommendations that promote optimized fluid-maintenance practices for physically active individuals. Background: Both a lack of adequate fluid replacement (hypohydration) and excessive intake (hyperhydration) can compromise athletic performance and increase health risks. Athletes need access to water to prevent hypohydration during physical activity but must be aware of the risks of overdrinking and hyponatremia. Drinking behavior can be modified by education, accessibility, experience, and palatability. This statement updates practical recommendations regarding fluid-replacement strategies for physically active individuals. Recommendations: Educate physically active people regarding the benefits of fluid replacement to promote performance and safety and the potential risks of both hypohydration and hyperhydration on health and physical performance. Quantify sweat rates for physically active individuals during exercise in various environments. Work with individuals to develop fluid-replacement practices that promote sufficient but not excessive hydration before, during, and after physical activity. [ABSTRACT FROM AUTHOR]

The article offers information on the international conference organised by International Life Sciences Institute (ILSI) North America Hydration Committee, held on November15 and 16, 2011 at Miami Beach, Florida. The conference presented new research on fluid intake and the impact of hydration status on mental and physical markers of health and well-being.

Context: Clinicians and athletes can benefit from field-expedient measurement tools, such as urine color, to assess hydration state; however, the diagnostic efficacy of this tool has not been established. Objective: To determine the diagnostic accuracy of urine color assessment to distinguish a hypohydrated state (≥2% body mass loss [BML]) from a euhydrated state (<2% BML) after exercise in a hot environment. Design: Controlled laboratory study. Setting: Environmental chamber in a laboratory. Patients or Other Participants: Twenty-two healthy men (age = 22 ± 3 years, height = 180.4 ± 8.7 cm, mass = 77.9 ± 12.8 kg, body fat = 10.6% ± 4.6%). Intervention(s): Participants cycled at 68% ± 6% of their maximal heart rates in a hot environment (36°C ± 1°C) for 5 hours or until 5% BML was achieved. At the point of each 1% BML, we assessed urine color. Main Outcome Measure(s): Diagnostic efficacy of urine color was assessed using receiver operating characteristic curve analysis, sensitivity, specificity, and likelihood ratios. Results: Urine color was useful as a diagnostic tool to identify hypohydration after exercise in the heat (area under the curve = 0.951, standard error = 0.022; P < .001). A urine color of 5 or greater identified BML ≥2% with 88.9% sensitivity and 84.8% specificity (positive likelihood ratio = 5.87, negative likelihood ratio = 0.13). Conclusions: Under the conditions of acute dehydration due to exercise in a hot environment, urine color assessment can be a valid, practical, inexpensive tool for assessing hydration status. Researchers should examine the utility of urine color to identify a hypohydrated state under different BML conditions. [ABSTRACT FROM AUTHOR]

This study investigated the effects of environmental temperature on repetitive box lifting (RBL) performance, associated stress hormone and creatine kinase (CK) responses. Ten healthy males performed two experimental trials in a random crossover design. The trials consisted of three 40 min (10 min sitting, 20 min standing, and 10 min RBL) circuits performed in either 23°C or 38°C followed by a 180 min seated recovery period in 23°C. RBL performance (i.e., number of boxes lifted) was reduced (p ≤ 0.05) in 38°C compared to the 23°C trial. Physiological Strain Index was significantly different between trials (38°C: 8.5 ± 1.1 versus 23°C: 7.2 ± 0.7; p ≤ 0.01). Plasma testosterone was elevated (p ≤ 0.05) across both trials and then decreased at 60 min recovery, compared to pre-exercise (PRE) measures, but was higher (p ≤ 0.05) during the 38°C trial. Plasma cortisol increased (p ≤ 0.05) at 60 min during both trials and remained elevated until 120 min in 23°C, and until 60 min recovery in 38°C. Serum CK was greater through 48 hr post compared to PRE values in both trials. Thus, 10 min RBL performance was reduced in 38°C despite the 30-min rest periods between RBL intervals. Plasma testosterone and cortisol were generally higher during the 38°C trial, suggesting a greater stress response. Additional research is needed to determine optimal work:rest cycles for maximizing work performance in thermally oppressive environments. [ABSTRACT FROM AUTHOR]