Sex Differences in Voluntary Fluid Intake by Older Adults during Exercise

Analysis of Hydration Habits Before and During a Specific Training Session in Male Padel Athletes Aged over 65: Physiological and Psychological Implications

(1) Background: Since older adults are more susceptible to dehydration and there is a lack of information on older athletes, this study observed a group of 12 male padel players in this age group (70.42 ± 3.50 years) to characterize their hydration habits, physiological demands, and psychological responses before and during a 90 min padel training (PT). (2) Methods: After approval from the Ethics Committee (CE/FCDEF-UC/00022023) and the provision of signed informed consent, participants' body mass, height, waist and hip circumferences, body mass index, waist-to-hip ratio, and waist-to-height ratio were measured. Habitual fluid intake was monitored by diary from the evening until before the PT; the subjects completed a Profile of Mood States questionnaire (POMS) and a satiety scale (SLIM). To assess hydration levels at different moments, we used a portable osmometer and an eight-point urine color chart and weighed the participants immediately before and after the PT. During the PT, heart rate (HR) and hydration were monitored. After the PT, subjects completed another POMS and SLIM. (3) Results: Subjects trained at 73.2 ± 12.3% of their maximum HR, with brief peaks at the anaerobic threshold or higher (130.00 ± 18.78 bpm). The mean urine osmolality indicated normal hydration or minimal dehydration. However, the urine color values indicated dehydration after the training. Subjects drank 438 mL of liquids at night, 333 mL before PT, and 900 mL during the PT, with a good repartition of the liquids. POMS and SLIM were not affected by the training. (4) Conclusions: Older male padel athletes achieved challenging yet safe training, staying within healthy intensity zones; their hydration patterns nearly met the recommendations for exercise and should be slightly increased.

Experimental research in environmentally induced hyperthermic older persons: A systematic quantitative literature review mapping the available evidence

The heat-related health burden is expected to persist and worsen in the coming years due to an aging global population and climate change. Defining the breadth and depth of our understanding of age-related changes in thermoregulation can identify underlying causes and strategies to protect vulnerable individuals from heat. We conducted the first systematic quantitative literature review to provide context to the historical experimental research of healthy older adults - compared to younger adults or unhealthy age matched cases - during exogenous heat strain, focusing on factors that influence thermoregulatory function (e.g. co-morbidities). We identified 4,455 articles, with 147 meeting eligibility criteria. Most studies were conducted in the US (39%), Canada (29%), or Japan (12%), with 71% of the 3,411 participants being male. About 71% of the studies compared younger and older adults, while 34% compared two groups of older adults with and without factors influencing thermoregulation. Key factors included age combined with another factor (23%), underlying biological mechanisms (18%), age independently (15%), influencing health conditions (15%), adaptation potential (12%), environmental conditions (9%), and therapeutic/pharmacological interventions (7%). Our results suggest that controlled experimental research should focus on the age-related changes in thermoregulation in the very old, females, those with overlooked chronic heat-sensitive health conditions (e.g. pulmonary, renal, mental disorders), the impact of multimorbidity, prolonged and cumulative effects of extreme heat, evidence-based policy of control measures (e.g. personal cooling strategies), pharmaceutical interactions, and interventions stimulating protective physiological adaptation. These controlled studies will inform the directions and use of limited resources in ecologically valid fieldwork studies.

International society of sports nutrition position stand: nutritional concerns of the female athlete

Based on a comprehensive review and critical analysis of the literature regarding the nutritional concerns of female athletes, conducted by experts in the field and selected members of the International Society of Sports Nutrition (ISSN), the following conclusions represent the official Position of the Society: 1. Female athletes have unique and unpredictable hormone profiles, which influence their physiology and nutritional needs across their lifespan. To understand how perturbations in these hormones affect the individual, we recommend that female athletes of reproductive age should track their hormonal status (natural, hormone driven) against training and recovery to determine their individual patterns and needs and peri and post-menopausal athletes should track against training and recovery metrics to determine the individuals' unique patterns. 2. The primary nutritional consideration for all athletes, and in particular, female athletes, should be achieving adequate energy intake to meet their energy requirements and to achieve an optimal energy availability (EA); with a focus on the timing of meals in relation to exercise to improve training adaptations, performance, and athlete health. 3. Significant sex differences and sex hormone influences on carbohydrate and lipid metabolism are apparent, therefore we recommend first ensuring athletes meet their carbohydrate needs across all phases of the menstrual cycle. Secondly, tailoring carbohydrate intake to hormonal status with an emphasis on greater carbohydrate intake and availability during the active pill weeks of oral contraceptive users and during the luteal phase of the menstrual cycle where there is a greater effect of sex hormone suppression on gluconogenesis output during exercise. 4. Based upon the limited research available, we recommend that pre-menopausal, eumenorrheic, and oral contraceptives using female athletes should aim to consume a source of high-quality protein as close to beginning and/or after completion of exercise as possible to reduce exercise-induced amino acid oxidative losses and initiate muscle protein remodeling and repair at a dose of 0.32-0.38 g·kg-1. For eumenorrheic women, ingestion during the luteal phase should aim for the upper end of the range due to the catabolic actions of progesterone and greater need for amino acids. 5. Close to the beginning and/or after completion of exercise, peri- and post-menopausal athletes should aim for a bolus of high EAA-containing (~10 g) intact protein sources or supplements to overcome anabolic resistance. 6. Daily protein intake should fall within the mid- to upper ranges of current sport nutrition guidelines (1.4-2.2 g·kg-1·day-1) for women at all stages of menstrual function (pre-, peri-, post-menopausal, and contraceptive users) with protein doses evenly distributed, every 3-4 h, across the day. Eumenorrheic athletes in the luteal phase and peri/post-menopausal athletes, regardless of sport, should aim for the upper end of the range. 7. Female sex hormones affect fluid dynamics and electrolyte handling. A greater predisposition to hyponatremia occurs in times of elevated progesterone, and in menopausal women, who are slower to excrete water. Additionally, females have less absolute and relative fluid available to lose via sweating than males, making the physiological consequences of fluid loss more severe, particularly in the luteal phase. 8. Evidence for sex-specific supplementation is lacking due to the paucity of female-specific research and any differential effects in females. Caffeine, iron, and creatine have the most evidence for use in females. Both iron and creatine are highly efficacious for female athletes. Creatine supplementation of 3 to 5 g per day is recommended for the mechanistic support of creatine supplementation with regard to muscle protein kinetics, growth factors, satellite cells, myogenic transcription factors, glycogen and calcium regulation, oxidative stress, and inflammation. Post-menopausal females benefit from bone health, mental health, and skeletal muscle size and function when consuming higher doses of creatine (0.3 g·kg-1·d-1). 9. To foster and promote high-quality research investigations involving female athletes, researchers are first encouraged to stop excluding females unless the primary endpoints are directly influenced by sex-specific mechanisms. In all investigative scenarios, researchers across the globe are encouraged to inquire and report upon more detailed information surrounding the athlete's hormonal status, including menstrual status (days since menses, length of period, duration of cycle, etc.) and/or hormonal contraceptive details and/or menopausal status.

Impact of dehydration on perceived exertion during endurance exercise: A systematic review with meta-analysis

Background

Understanding the impact of stressors on the rating of perceived exertion (RPE) is relevant from a performance and exercise adherence/participation standpoint. Athletes and recreationally active individuals dehydrate during exercise. No attempt has been made to systematically determine the impact of exercise-induced dehydration (EID) on RPE.

Objective

The present meta-analysis aimed to determine the effect of EID on RPE during endurance exercise and examine the moderating effect of potential confounders.

Data analyses

Performed on raw RPE values using random-effects models weighted mean effect summaries and meta-regressions with robust standard errors, and with a practical meaningful effect set at 1 point difference between euhydration (EUH) and EID. Only controlled crossover studies measuring RPE with a Borg scale in healthy adults performing ≥30 min of continuous endurance exercise while dehydrating or drinking to maintain EUH were included.

Results

Sixteen studies were included, representing 147 individuals. Mean body mass loss with EUH was 0.5 ± 0.4%, compared to 2.3 ± 0.5% with EID (range 1.7-3.1%). Within an EID of 0.5-3% body mass, a maximum difference in RPE of 0.81 points (95% CI: 0.36-1.27) was observed between conditions. A meta-regression revealed that RPE increases by 0.21 points for each 1% increase in EID (95% CI: 0.12-0.31). Humidity, ambient temperature and aerobic capacity did not alter the relationship between EID and RPE.

Conclusion

Therefore, the effect of EID on RPE is unlikely to be practically meaningful until a body mass loss of at least 3%.

Programmed vs. Thirst-Driven Drinking during Prolonged Cycling in a Warm Environment

We compared the effect of programmed (PFI) and thirst-driven (TDFI) fluid intake on prolonged cycling performance and exercise associated muscle cramps (EAMC). Eight male endurance athletes (26 ± 6 years) completed two trials consisting of 5 h of cycling at 61% V˙O2peak followed by a 20 km time-trial (TT) in a randomized crossover sequence at 30 °C, 35% relative humidity. EAMC was assessed after the TT with maximal voluntary isometric contractions of the shortened right plantar flexors. Water intake was either programmed to limit body mass loss to 1% (PFI) or consumed based on perceived thirst (TDFI). Body mass loss reached 1.5 ± 1.0% for PFI and 2.5 ± 0.9% for TDFI (p = 0.10). Power output during the 20 km TT was higher (p < 0.05) for PFI (278 ± 41 W) than TDFI (263 ± 39 W), but the total performance time, including the breaks to urinate, was similar (p = 0.48) between conditions. The prevalence of EAMC of the plantar flexors was similar between the drinking conditions. Cyclists competing in the heat for over 5 h may benefit from PFI aiming to limit body mass loss to <2% when a high intensity effort is required in the later phase of the race and when time lost for urination is not a consideration.

Edema-like symptoms are common in ultra-distance cyclists and driven by overdrinking, use of analgesics and female sex - a study of 919 athletes

Background

Ultra-endurance cyclists regularly report various extents of bodily decline during long-distance bicycle rides, including potential kidney function-related symptoms such as swelling of body parts and urine changes. This study aimed to assess the prevalence of these symptoms in a representative cohort of ultra-endurance cyclists and shed light on potential predictors related to the ride, the rider and the rider’s behavior.

Methods

Between November 26 and December 14, 2020, 1350 people participated in an online survey investigating potential kidney-related symptoms of ultra-distance cycling. Frequency and severity of edema-like (“swelling”) symptoms and perceived changes in urine output, concentration and quality were associated with ride-related factors, demographic parameters and rider behavior-related variables.

Results

A total of 919 participants met the predefined inclusion criteria. The majority (N = 603, 65.6%) stated that they suffered from at least one potential kidney function-related symptom, out of which 498 (54.2%) stated one or more edema-like (“swelling”) symptoms. In correlational and multiple regression analyses, female sex, intake of analgesics and drinking strategies correlated with swelling symptoms. Further analyses indicated that drinking due to thirst and/or drinking adapted to ambient sweating and temperature negatively correlated with swelling symptoms, whereas “drinking as much as possible” enhanced these. Intake of analgesics was moderately positively correlated with swelling symptoms.

Conclusions

According to our survey, edema-like symptoms occur in the majority of ultra-distance cyclists and female sex, drinking strategy and intake of analgesic drugs are major predictors thereof. Studies are needed to investigate the underlying pathophysiological processes of such symptoms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12970-021-00470-0.

Gender-Specific Differences of Renal Heat Tolerance in Older Adults during Heat Waves

BACKGROUND

Heat waves are known to cause increased morbidity and mortality in susceptible populations like old and functionally impaired people. The objective of the study was to assess renal tubular stress, a predictor for development of acute kidney injury, during heat waves in Central Europe. As a marker of renal tubular stress tissue inhibitor of metalloproteinases-2 [TIMP-2]·insulin-like growth factor binding protein-7 [IGFBP7], a new FDA-cleared renal tubular stress biomarker, was used.

MATERIALS AND METHODS

68 residents from facilities of sheltered housing with urine samples collected at heat waves in 2015 and at control visits were included. Urinary [TIMP-2]·[IGFBP7] was compared between the heat waves and the control visits. Multivariate linear models were adjusted for age, frailty index, and functional comorbidity index.

RESULTS

The median age was 82.0 years, 82.3% were women. The percentage of elevated levels of urinary [TIMP-2]·[IGFBP7] (>0.3 [ng/mL]2/1,000) in the total study population was higher at the heat waves than at the control visits (25.0% vs. 17.7%). The effect of the heat waves on urinary [TIMP-2]·[IGFBP7] was stronger in men than in women: The percentage of elevated levels was 75.0% in men and 14.3% in women. In the multivariate analysis, the mean urinary [TIMP-2]·[IGFBP7] was 0.48 (95% CI 0.25; 0.70) (ng/mL)2/1,000 higher in men than in women. Except gender, a number of additional variables did not show an association with urinary [TIMP-2]·[IGFBP7] at the heat waves or the control visits.

CONCLUSIONS

At heat waves, urinary [TIMP-2]·[IGFBP7] was elevated and higher in men than in women. This suggests gender-specific differences in renal heat tolerance in older people.

Maintaining serum ionized calcium during brisk walking attenuates the increase in bone resorption in older adults

BACKGROUND

Endurance exercise can cause a decrease in serum ionized calcium (iCa) and increases in parathyroid hormone (PTH) and bone resorption, reflected by serum carboxy-terminal collagen crosslinks (CTX). We developed a calcium clamp to prevent the decrease in iCa during exercise, which attenuated increases in PTH and CTX during vigorous cycling in young men. The goal was to determine whether this occurs in older adults during brisk walking.

METHODS

Twelve older adults (6 men, 6 women) performed two identical 60-min treadmill walking bouts with Ca gluconate or half-normal saline infusion. Blood sampling for iCa, total calcium (tCa), phosphate (P), PTH, and CTX, occurred before, during, and for 4 h after exercise.

RESULTS

iCa decreased during exercise with the saline infusion (p = 0.04) and this provoked increases in PTH and CTX (both p < 0.01). The Ca clamp prevented the decrease in serum iCa during exercise and attenuated the PTH and CTX responses.

CONCLUSIONS

Preventing the exercise-induced decrease in iCa markedly attenuated the increases in PTH and CTX. The cause of the decrease in iCa during exercise remains unclear, but the increases in PTH and CTX are likely counter-regulatory responses to defend serum iCa. This contention is supported by previous observations that the disruption of Ca homeostasis during exercise occurs regardless of training status. It will be important to establish whether this acute catabolic effect of exercise diminishes the potential chronic anabolic effects of exercise on bone.

Post-Exercise Sweat Loss Estimation Accuracy of Athletes and Physically Active Adults: A Review

The main purposes of this review were to provide a qualitative description of nine investigations in which sweat losses were estimated by participants following exercise and to perform a quantitative analysis of the collective data. Unique estimations (n = 297) were made by 127 men and 116 women after a variety of exercise modalities in moderate to hot environmental conditions. Actual sweat loss exceeded estimated sweat loss (p < 0.001) for women (1.072 ± 0.473 vs. 0.481 ± 0.372 L), men (1.778 ± 0.907 vs. 0.908 ± 0.666 L) and when all data were combined (1.428 ± 0.806 vs. 0.697 ± 0.581 L), respectively. However, estimation accuracy did not differ between women (55.2 ± 51.5%) and men (62.4 ± 54.5%). Underestimation of 50% or more of sweat losses were exhibited in 168 (54%) of estimation scenarios with heavier sweaters displaying a higher prevalence and trend of greater underestimations in general. Most modern guidelines for fluid intake during and between training bouts are based on approximate sweat loss estimation knowledge. These guidelines will likely have minimal efficacy if greater awareness of how to determine sweat losses and accurate recognition of sweat losses is not increased by coaches and athletes.

Exercise-Associated Hyponatremia in Endurance and Ultra-Endurance Performance-Aspects of Sex, Race Location, Ambient Temperature, Sports Discipline, and Length of Performance: A Narrative Review

Exercise-associated hyponatremia (EAH) is defined as a plasma sodium concentration of <135 mmol/L during or after endurance and ultra-endurance performance and was first described by Timothy Noakes when observed in ultra-marathoners competing in the Comrades Marathon in South Africa in the mid-1980s. It is well-established that a decrease in plasma sodium concentration <135 mmol/L occurs with excessive fluid intake. Clinically, a mild hyponatremia will lead to no or very unspecific symptoms. A pronounced hyponatremia (<120 mmol/L) will lead to central nervous symptoms due to cerebral edema, and respiratory failure can lead to death when plasma sodium concentration reaches values of <110-115 mmol/L. The objective of this narrative review is to present new findings about the aspects of sex, race location, sports discipline, and length of performance. The prevalence of EAH depends on the duration of an endurance performance (i.e., low in marathon running, high to very high in ultra-marathon running), the sports discipline (i.e., rather rare in cycling, more frequent in running and triathlon, and very frequent in swimming), sex (i.e., increased in women with several reported deaths), the ambient temperature (i.e., very high in hot temperatures) and the country where competition takes place (i.e., very common in the USA, very little in Europe, practically never in Africa, Asia, and Oceania). A possible explanation for the increased prevalence of EAH in women could be the so-called Varon-Ayus syndrome with severe hyponatremia, lung and cerebral edema, which was first observed in marathon runners. Regarding the race location, races in Europe seemed to be held under rather moderate conditions whereas races held in the USA were often performed under thermally stressing conditions (i.e., greater heat or greater cold).

[Exercise-Associated Hyponatremia in Endurance Performance]

Exercise-Associated Hyponatremia in Endurance Performance Abstract. Exercise-associated hyponatremia is defined as a plasma sodium concentration of <135 mmol/l and was first described by Timothy Noakes at the Comrades Marathon in South Africa in the mid-1980s. A decrease in plasma sodium <135 mmol/l occurs with excessive fluid intake. Risk factors include long to very long endurance performance, extreme climatic conditions, female gender and competitions in the USA. Regarding its prevalence by sport, exercise-associated hyponatraemia tends to occur while swimming and running, but rarely when cycling. While mild exercise-associated hyponatremia does not lead to clinical symptoms, severe hyponatremia due to cerebral edema can lead to neurological deficits and even death. The best prevention of exercise-associated hyponatremia is the reduction of fluid intake during exercise.

Does salt increase thirst?

Our diet is believed to be overly rich in sodium, and it is commonly believed that sodium intake increases drinking. Hence the concern of a possible contribution of dietary sodium to beverage intake which in turn may contribute to obesity and ill health. Here we examine whether voluntary, acute intake of a sodium load, as occurs in routine eating and snacking, increases thirst and drinking. We find that after ingesting 3.5 or 4.4 g NaCl (men) and 1.9 or 3.7 g (women) on nuts during 15 minutes, there is no increase in thirst or drinking of freely available water in the following 2 h compared with eating similar amounts of sugared or unflavored nuts. This suggests that routine ingestion of boluses of salt (~30-40% of daily intake for men, ~ 20-40% for women) does not increase drinking. Methodological concerns such as about nuts as vehicle for sodium suggest further research to establish the generalizability of this unexpected result.

Optimal composition of fluid-replacement beverages

The objective of this article is to provide a review of the fundamental aspects of body fluid balance and the physiological consequences of water imbalances, as well as discuss considerations for the optimal composition of a fluid replacement beverage across a broad range of applications. Early pioneering research involving fluid replacement in persons suffering from diarrheal disease and in military, occupational, and athlete populations incurring exercise- and/or heat-induced sweat losses has provided much of the insight regarding basic principles on beverage palatability, voluntary fluid intake, fluid absorption, and fluid retention. We review this work and also discuss more recent advances in the understanding of fluid replacement as it applies to various populations (military, athletes, occupational, men, women, children, and older adults) and situations (pathophysiological factors, spaceflight, bed rest, long plane flights, heat stress, altitude/cold exposure, and recreational exercise). We discuss how beverage carbohydrate and electrolytes impact fluid replacement. We also discuss nutrients and compounds that are often included in fluid-replacement beverages to augment physiological functions unrelated to hydration, such as the provision of energy. The optimal composition of a fluid-replacement beverage depends upon the source of the fluid loss, whether from sweat, urine, respiration, or diarrhea/vomiting. It is also apparent that the optimal fluid-replacement beverage is one that is customized according to specific physiological needs, environmental conditions, desired benefits, and individual characteristics and taste preferences.

Salt appetite in the elderly

The present study investigated whether salt appetite in the elderly is impaired similar to thirst because of the commonality of their physiological substrates and whether alterations in salt appetite are related to mood. Elderly (65–85 years, n 30) and middle-aged (45–58 years, n 30) men and women were compared in two test sessions. Thirst, psychophysical ratings of taste solutions, dietary Na and energy intakes, seasoning with salt and sugar, number of salty and sweet snacks consumed, preferred amounts of salt in soup and sugar in tea, and an overall measure of salt appetite and its relationship with mood, nocturia and sleep were measured. Elderly participants were found to be less thirsty and respond less to thirst. In contrast, no impairment of salt appetite was found in them, and although they had a reduced dietary Na intake, it dissipated when corrected for their reduced dietary energy intake. Diet composition and Na intake were found to be similar in middle-aged and elderly participants, despite the lesser intake in elderly participants. There were no age-related differences in the intensity of taste or hedonic profile of Na, in salting habits, in tests of salting soup, or number of salty snacks consumed. No relationship of any measure of salt appetite with mood measured by the Positive and Negative Affect Schedule, frequency of nocturia, or sleep duration was observed. The age-related impairment of the physiology of mineralofluid regulation, while compromising thirst and fluid intake, spares salt appetite, suggesting that salt appetite in humans is not regulated physiologically. Intact salt appetite in the elderly might be utilised judiciously to prevent hyponatraemia, increase thirst and improve appetite.

Effects of active drinking practices on fluid consumption and sweat rate while exercising in a hot environment

PURPOSE

To examine the effects of active drinking practices on fluid consumption and sweat rate while exercising in a hot environment.

METHODS

Nine men completed two experiments. Each consisted of 3 phases: pre-testing (pre), training period, and post-testing (post). During testing, the subjects ran on a treadmill at a moderate intensity for 90 min at 39 ± 1℃ followed by a 3-h recovery. They drank ad libitum. During training, they ran for 90 min for 7 days while either drinking actively (AH, 150% of weight loss) or passively (PH, 50% of weight loss).

RESULTS

The actual volume consumed in training was three times greater during AH than during PH. In post during AH, the volume of drinking was two times greater than pre (1592 ± 953 and 855 ± 551 mL, respectively; p < 0.05). No difference in volume consumption during PH between pre and post was found. The sweat loss during exercise was greater in post (1377 ± 956 mL) than in pre (558 ± 642 mL) during AH (p < 0.05), but not during PH. Rectal temperature and heart rate decreased after training. Serum osmolality following exercise were not different than the baseline or between the conditions.

CONCLUSION

Active drinking practices while exercising in a hot environment induced greater voluntary fluid intake and sweat loss.

Exercise-associated hyponatremia in an ultra-endurance mountain biker: a case report

Symptomatic exercise-associated hyponatremia (EAH), which is relatively common among marathon runners, is an uncommon event among ultra-endurance athletes. A 44-year-old man presented to the emergency department with increased thirst after successfully completing a 100-mile mountain bike race in Leadville, Colorado. Initial laboratory tests revealed a blood sodium level of 116 mEq/L. The primary etiologic factor in EAH is fluid consumption in excess of fluid losses in prolonged exertion. Early diagnosis and management is crucial to prevent cerebral and pulmonary edema.

Hydration in female drivers in a 1044 km dog sled race in Finnmark

OBJECTIVE

Drinking strategies during long dog sled competitions are important to avoid dehydration. Most of the studies involving dog sled racers (mushers) refer to male subjects. The purpose of this study was to study female mushers participating in a dog sled race of 1044 km, with a focus on hydration and drinking behavior.

METHODS

Two female mushers (aged 50 and 23 years), of the 6 who signed up for participation in the dog sled 1044 km race, volunteered for the study. Before the race, maximum oxygen uptake and maximum heart rate (HR) were determined. Body compositions was measured before and shortly after the race. Heart rate was continuously measured by a HR monitor in the first 2 legs of the race, and urine samples were collected during the race. Urine osmolality and urine specific gravity were determined using freezing point depression and handheld refractometer. Values of urine osmolality greater than 900 mOsm · L(-1) and specific gravity greater than 1.030 were used as signs of dehydration.

RESULTS

The older musher had a mean HR of 65%, and the younger musher had a mean HR of 57% of the predicted maximum HR. The mushers reached a peak HR of 91% of their predicted maximum; they worked at an average HR of 55% (average of all legs). The younger woman had urine osmolality values above the dehydration limits in most of the samples. Only small changes in the before and after race anthropometric measurements were found.

CONCLUSIONS

Dog sled racing is a strenuous activity and drinking strategies are important to avoid dehydration. It seems that the drinking strategy of our subjects was adequate to supplement the hydration loss; yet, emotional arousals occurring during the race may affect drinking behavior. The attentive assistance of the mushers' handlers is therefore important.

24-h fluid kinetics and perception of sweat losses following a 1-h run in a temperate environment

This study examined 24-h post-run hydration status and sweat loss estimation accuracy in college age runners (men=12, women=8) after completing a 1-h self-paced outdoor run (wet bulb globe temperature=19.9±3.0 °C). Sweat losses (1353±422 mL; 1.9%±0.5% of body mass) were significantly greater (p<0.001) than perceived losses (686±586 mL). Cumulative fluid consumption equaled 3876±1133 mL (218±178 mL during) with 37% of fluid ingested lost through urine voids (1450±678 mL). Fluid balance based on intake and urine production equaled +554±669 mL at 12 h and +1186±735 mL at 24 h. Most runners reported euhydrated (pre-run urine specific gravity (USG)=1.018±0.008) with no changes (p=0.33) at hours 12 or 24 when both genders were included. However, USG was higher (p=0.004) at 12 h post-run for men (1.025±0.0070 vs. 1.014±0.007), who consumed 171%±40% of sweat losses at 12 h vs. 268%±88% for women. Most runners do not need intervention concerning between bout hydration needs in temperate environments. However, repeated USG measurements were able to identify runners who greatly under or over consumed fluid during recovery. Practitioners can use multiple USG assessments as cheap method to detect runners who need to modify their hydration strategies and should promote assessment of sweat losses by change in body mass, as runners had poor perception of sweat losses.

Body mass change and ultraendurance performance: a decrease in body mass is associated with an increased running speed in male 100-km ultramarathoners

We investigated, in 50 recreational male ultrarunners, the changes in body mass, selected hematological and urine parameters, and fluid intake during a 100-km ultramarathon. The athletes lost (mean and SD) 2.6 (1.8) % in body mass (p < 0.0001). Running speed was significantly and negatively related to the change in body mass (p < 0.05). Serum sodium concentration ([Na⁺]) and the concentration of aldosterone increased with increasing loss in body mass (p < 0.05). Urine-specific gravity increased (p < 0.0001). The change in body mass was significantly and negatively related to postrace serum [Na⁺] (p < 0.05). Fluid intake was significantly and positively related to both running speed (r = 0.33, p = 0.0182) and the change in body mass (r = 0.44, p = 0.0014) and significantly and negatively to both postrace serum [Na⁺] (r = -0.42, p = 0.0022) and the change in serum [Na⁺] (r = -0.38, p = 0.0072). This field study showed that recreational, male, 100-km ultramarathoners dehydrated as evidenced by the decrease in >2 % body mass and the increase in urine-specific gravity. Race performance, however, was not impaired because of the loss in body mass. In contrast, faster athletes lost more body mass compared with slower athletes while also drinking more. The concept that a loss of >2% in body mass leads to dehydration and consequently impairs endurance performance must be questioned for ultraendurance athletes competing in the field. For practical applications, a loss in body mass during a 100-km ultramarathon was associated with a faster running speed.

Impact of a carbohydrate-electrolyte drink on ingestive behaviour, affect and self-selected intensity during recreational exercise after 24-h fluid restriction

This study examined the effects of a carbohydrate-electrolyte drink on voluntary fluid intake, affect and self-selected intensity during recreational exercise after fluid restriction. In a randomised counterbalanced design, ten physically active adults were dehydrated via a 24-h period of fluid restriction before completing two 20-min bouts of cardiovascular exercise, 20-min of resistance exercise and 20 min on a cycle ergometer at a self-selected intensity with ad libitum access to water (W) or a carbohydrate-electrolyte solution (CES). Fluid restriction induced hypohydration of ∼1.2% initial body mass. Fluid intake during exercise was greater with CES (2105 ± 363 vs. 1470 ± 429 mL; P<0.01) and resulted in more adequate hydration (-0.03 ± 0.65 vs. -1.26 ± 0.80%; P<0.01). Plasma glucose concentrations (4.48 ± 0.40 vs. 4.28 ± 0.32 mmol L(-1); P<0.01) and pleasure ratings (2.63 ± 1.17 vs. 1.81 ± 1.37; P<0.01) were greater with CES than W. Mean power output during exercise performed at a self-selected intensity was 5.6% greater with CES (171 ± 63 vs. 162 ± 60 W; P<0.05). In physically active adults performing a 'real-life' recreational exercise simulation, CES resulted in more adequate hydration and an enhanced affective experience that corresponded with an increase in self-selected exercise intensity.

Hydration profile and influence of beverage contents on fluid intake by women during outdoor recreational walking

This study examined hydration status, sweat losses, and the effects of flavoring and electrolytes on fluid intake for women (n = 27, age = 24 ± 4 years) walking at a self-selected pace for ~1 h on a 1 km outdoor path during summer mornings or evenings. Over five consecutive days, participants consumed ad libitum one non-caloric beverage containing: (1) water (W), (2) acidified water (AW), (3) acidified water with electrolytes (AWE), (4) acidified water with flavor (AWF), and (5) acidified water with flavor and electrolytes (AWFE) in a counter-balanced order during walks and a 1-h recovery period. Walk Wet bulb globe temperature (26.2 ± 1.8 °C) and pace (6.0 ± 0.5 km/h) did not differ among beverages (P > 0.05). Thirty-four percent of pre-walk urine specific gravity samples exceeded 1.020. Flavoring (AWF 700 ± 393 mL; AWFE 719 ± 405 mL) did not result in greater consumption (P > 0.05) over W (560 ± 315 mL), with all three beverages exceeding grand mean sweat losses (528 ± 208 mL). Addition of electrolytes did not influence (P > 0.05) the intake between AW versus AWE or AWF versus AWFE. The results of this study indicate that the majority of women will consume fluids in excess of their sweat losses within 1 h post-walk. Over half of consumption took place during walks, highlighting the importance of fluid availability during exercise. Great among-subjects variability in sweat losses and fluid intake support the need for promoting individualized hydration strategies based on the changes in body mass for athletic populations.

Sex difference in fluid balance responses during prolonged exercise

Maintaining a proper fluid balance is important during exercise as athletes are prone to develop dehydration during exercise. Although several factors may regulate the fluid balance, little is known about the role of sex during prolonged moderate-intensity exercise. Therefore, we compared body mass changes and fluid balance parameters in men vs women in a large heterogeneous group of participants during prolonged exercise. Ninety-eight volunteers walked 30-50 km at a self-selected pace. Exercise duration (8 h, 32 min) and intensity (69% HRmax) were comparable between groups. Men demonstrated a significantly larger change in body mass than women (-1.6% vs -0.9%, respectively, P < 0.001) and a higher incidence of dehydration (defined as ≥ 2% body mass loss) compared with women (34% vs 12%, respectively, odds ratio = 4.2, 95% CI = 1.1-16.7). Changes in blood sodium levels were significantly different between men (+1.5 mmol/L) and women (-0.4 mmol/L), while 27% of the men vs 0% of the women showed postexercise hypernatremia (sodium levels ≥ 145 mmol/L). Moreover, men demonstrated a significantly lower fluid intake (2.9 mL/kg/h) and higher fluid loss (5.0 mL/kg/h) compared with women (3.7 and 4.8 mL/kg/h, respectively). Taken together, our data suggest that men and women demonstrate different changes in fluid balance in response to a similar bout of exercise.

Higher prevalence of exercise-associated hyponatremia in female than in male open-water ultra-endurance swimmers: the 'Marathon-Swim' in Lake Zurich

We investigated the prevalence of exercise-associated hyponatremia (EAH) in 25 male and 11 female open-water ultra-endurance swimmers participating in the 'Marathon-Swim' in Lake Zurich, Switzerland, covering a distance of 26.4 km. Changes in body mass, fat mass, skeletal muscle mass, total body water, urine specific gravity, plasma sodium concentration [Na(+)] and haematocrit were determined. Two males (8%) and four females (36%) developed EAH where one female was symptomatic with plasma sodium [Na(+)] of 127 mmol/L. Body mass and plasma [Na(+)] decreased (p < 0.05). The changes in body mass correlated in both male and female swimmers to post-race plasma [Na(+)] (r = -0.67, p = 0.0002 and r = -0.80, p = 0.0034, respectively) and changes in plasma [Na(+)] (r = -0.68, p = 0.0002 and r = -0.79, p = 0.0039, respectively). Fluid intake was neither associated with changes in body mass, post-race plasma [Na(+)] or the change in plasma [Na(+)]. Sodium intake showed no association with either the changes in plasma [Na(+)] or post-race plasma [Na(+)]. We concluded that the prevalence of EAH was greater in female than in male open-water ultra-endurance swimmers.

Fluid consumption and sweating in National Football League and collegiate football players with different access to fluids during practice

CONTEXT

Considerable controversy regarding fluid replacement during exercise currently exists.

OBJECTIVE

To compare fluid turnover between National Football League (NFL) players who have constant fluid access and collegiate football players who replace fluids during water breaks in practices.

DESIGN

Observational study.

SETTING

Respective preseason training camps of 1 National Collegiate Athletic Association Division II (DII) football team and 1 NFL football team. Both morning and afternoon practices for DII players were 2.25 hours in length, and NFL players practiced for 2.25 hours in the morning and 1 hour in the afternoon. Environmental conditions did not differ.

PATIENTS OR OTHER PARTICIPANTS

Eight NFL players (4 linemen, 4 backs) and 8 physically matched DII players (4 linemen, 4 backs) participated.

INTERVENTION(S)

All players drank fluids only from their predetermined individual containers. The NFL players could consume both water and sports drinks, and the DII players could only consume water.

MAIN OUTCOME MEASURE(S)

We measured fluid consumption, sweat rate, total sweat loss, and percentage of sweat loss replaced. Sweat rate was calculated as change in mass adjusted for fluids consumed and urine produced.

RESULTS

Mean sweat rate was not different between NFL (2.1 +/- 0.25 L/h) and DII (1.8 +/- 0.15 L/h) players (F(1,12) = 2, P = .18) but was different between linemen (2.3 +/- 0.2 L/h) and backs (1.6 +/- 0.2 L/h) (t(14) = 3.14, P = .007). We found no differences between NFL and DII players in terms of percentage of weight loss (t(7) = -0.03, P = .98) or rate of fluid consumption (t(7) = -0.76, P = .47). Daily sweat loss was greater in DII (8.0 +/- 2.0 L) than in NFL (6.4 +/- 2.1 L) players (t(7) = -3, P = .02), and fluid consumed was also greater in DII (5.0 +/- 1.5 L) than in NFL (4.0 +/- 1.1 L) players (t(7) = -2.8, P = .026). We found a correlation between sweat loss and fluids consumed (r = 0.79, P < .001).

CONCLUSIONS

During preseason practices, the DII players drinking water at water breaks replaced the same volume of fluid (66% of weight lost) as NFL players with constant access to both water and sports drinks.

Exercise-associated hyponatremia during winter sports

Exercise-associated hyponatremia (EAH) is hyponatremia that occurs <or= 24 hours after prolonged physical activity. It is a potentially serious complication of marathons, triathlons, and ultradistance events, and can occur in hot and cold environments. Clear evidence indicates that EAH is a dilutional hyponatremia caused by excessive fluid consumption and the inappropriate release of arginine vasopressin. Cerebral and pulmonary edema can cause serious signs and symptoms, including altered mental status, respiratory distress, seizures, coma, and death. Rapid diagnosis and urgent treatment with hypertonic saline is necessary to prevent severe complications or death. Prevention is based on educating athletes to avoid excessive drinking before, during, and after exercise.

Pregame urine specific gravity and fluid intake by National Basketball Association players during competition

CONTEXT

Urine specific gravity (USG) has been used to estimate hydration status in athletes on the field, with increasing levels of hypohydration indicated by higher USG measurements (eg, greater than 1.020). Whether initial hydration status based on a urine measure is related to subsequent drinking response during exercise or athletic competition is unclear.

OBJECTIVE

To determine the relationship between pregame USG and the volume of fluid consumed by players in a professional basketball game.

DESIGN

Cross-sectional study.

SETTING

Basketball players were monitored during Summer League competition.

PATIENTS OR OTHER PARTICIPANTS

Players (n = 29) from 5 teams of the National Basketball Association agreed to participate.

MAIN OUTCOME MEASURE(S)

Pregame USG was measured for each player on 2 occasions. Athletes were given ad libitum access to fluid during each game and were unaware of the purpose of the study. Volume of fluid intake was measured for each player. To assess sweat loss, athletes were weighed in shorts before and after each game.

RESULTS

Sweat loss ranged from 1.0 to 4.6 L, with a mean sweat loss of 2.2 +/- 0.8 L. Fluid intake ranged from 0.1 to 2.9 L, with a mean fluid intake of 1.0 +/- 0.6 L. Pregame USG was greater than 1.020 in 52% of the urine samples collected and was not correlated with fluid volume consumed during either of the games (r = 0.15, P = .48, and r = 0.15, P = .52, respectively).

CONCLUSIONS

Approximately half of the players began the games in a hypohydrated state, as indicated by USG. Fluid intake during the game did not compensate for poor hydration status before competition. Furthermore, sweat losses in these players during games were substantial (greater than 2 L in approximately 20 minutes of playing time). Therefore, both pregame and during-game hydration strategies, such as beverage availability and player education, should be emphasized.

Core temperature and metabolic responses after carbohydrate intake during exercise at 30 degrees C

CONTEXT

Carbohydrate ingestion has recently been associated with elevated core temperature during exercise in the heat when testing for ergogenic effects. Whether the association holds when metabolic rate is controlled is unclear. Such an effect would have undesirable consequences for the safety of the athlete.

OBJECTIVE

To examine whether ingesting fluids containing carbohydrate contributed to an accelerated rise in core temperature and greater overall body heat production during 1 hour of exercise at 30 degrees C when the effort was maintained at steady state.

DESIGN

Crossover design (repeated measures) in randomized order of treatments of drinking fluids with carbohydrate and electrolytes (CHO) or flavored-water placebo with electrolytes (PLA). The beverages were identical except for the carbohydrate content: CHO = 93.7 +/- 11.2 g, PLA = 0 g.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Nine physically fit, endurance-trained adult males.

INTERVENTION(S)

Using rectal temperature sensors, we measured core temperature during 30 minutes of rest and 60 minutes of exercise at 65% of maximal oxygen uptake (Vo(2) max) in the heat (30.6 degrees C, 51.8% relative humidity). Participants drank equal volumes (1.6 L) of 2 beverages in aliquots 30 minutes before and every 15 minutes during exercise. Volumes were fixed to approximate sweat rates and minimize dehydration.

MAIN OUTCOME MEASURE(S)

Rectal temperature and metabolic response (Vo(2), heart rate).

RESULTS

Peak temperature, rate of temperature increase, and metabolic responses did not differ between beverage treatments. Initial hydration status, sweat rate, and fluid replacement were also not different between trials, as planned.

CONCLUSIONS

Ingestion of carbohydrate in fluid volumes that minimized dehydration during 1 hour of steady-state exercise at 30 degrees C did not elicit an increase in metabolic rate or core temperature.

Acute effects of sodium ingestion on thirst and cardiovascular function

Sweating during exercise, especially during exercise in the heat, leads to sodium and water losses, and the quantity of these losses depends upon the intensity and duration of the activity, genetic predisposition and conditioning of the individual, and environmental factors. In athletes, adequate sodium intake is necessary to maintain fluid balance during training and competition. To ensure the precise regulation of volume and osmolality of body fluids, a number of integrated neural and hormonal systems have evolved to control thirst and sodium appetite. These systems respond to stimuli that arise from a deficit of fluid arising in both the intracellular and extracellular fluid compartments or to systemic hypertonicity. Thirst is highly sensitive to increases in plasma sodium concentration and osmolality, requiring only a 2%-3% increase to induce feelings of thirst. A larger change in plasma volume (10%) is required to induce thirst if there is no concomitant change in plasma sodium concentration. If plain water is used to replenish body water, plasma volume is preferentially restored over the interstitial and intracellular fluid space, suppressing plasma sodium concentration and removing the dipsogenic drive long before total body fluid has been restored. During or after dehydrating exercise, sodium ingestion helps to maintain and restore plasma volume and osmolality by continuing thirst sensation (thus drinking) and also by increasing body fluid retention. A high sodium meal or intravascular hypertonic saline infusion may cause transient osmotically mediated blood pressure increases, but in healthy people, acute sodium ingestion does not cause sustained hypertension. The purpose of this review is to provide evidence that acute increases in sodium are an intrinsic part of the thirst response during and after exercise, and that blood pressure increases associated with hypertonicity appear to be short lived.

Practical management of exercise-associated hyponatremic encephalopathy: the sodium paradox of non-osmotic vasopressin secretion

Exercise-associated hyponatremia (EAH) is a potentially fatal fluid imbalance largely resulting from sustained fluid intake beyond the capacity for fluid excretion during endurance exercise. Common symptoms include vomiting, confusion, altered mental status, and seizures; however, these symptoms can also be seen with hypernatremic encephalopathy, making measurement of plasma sodium concentration imperative when athletes present with these symptoms. Recent evidence supports the inappropriate secretion of the antidiuretic hormone, arginine vasopressin (AVP), as the primary pathophysiological mechanism underlying the development of dilutional EAH. It appears that AVP is stimulated normally during prolonged endurance running by non-osmotic factors such as an exercise-induced plasma volume decrease; therefore, any excess fluid intake will likely be retained, and sodium will likely be excreted. The capacity for a small concentrated bolus of a hypertonic saline solution to rapidly reverse cerebral edema and remove any decreased plasma volume stimulus to AVP secretion is the most efficacious treatment for acute EAH encephalopathy to date. The prompt administration of an intravenous (IV) bolus of hypertonic saline in the field or hospital setting can be lifesaving once EAH is documented. Conversely, oral sodium supplementation will not prevent the development of EAH encephalopathy if exuberant fluid intake combined with non-osmotic secretion of AVP occurs during prolonged physical activity. As a result, the seemingly paradoxical use of sodium supplementation as the most effective practical management therapy (IV bolus) and ineffective preventive strategy can be reconciled through a more complete understanding of the pathophysiological mechanisms underlying EAH.

Voluntary drinking and hydration in trained, heat-acclimatized girls exercising in a hot and humid climate

This study examined the effects of beverage composition on the voluntary drinking pattern, body fluid balance and body temperature responses of heat-acclimatized trained girls exercising intermittently in outdoor conditions (WBGT = 30.9 +/- 0.2 degrees C). Twelve trained, heat-acclimatized girls (age = 10.6 +/- 0.2 years) performed three 3-h sessions, each consisting of four 20-min cycling bouts at 60% VO2max, alternating with 25-min rest. One of three beverages was assigned: unflavored water (W), flavored water (FW) or flavored water plus 6% carbohydrate and 18 mmol/l NaCl (CNa). Drinking was ad libitum. Total intake was similar among conditions (W = 953.3 +/- 107.8 ; FW = 1026.5 +/- 138.1; CNa = 906.4 +/- 107.5 g). A mild hypohydration occurred during the three conditions (W = -1.12%; FW = -0.95%; CNa = -0.74% BW, P > 0.05). Sweat loss, higher than previously reported for sedentary girls, was not different among conditions (W = 1,051.5 +/- 90.8; FW = 979.9 +/- 72.8; CNa = 1,052.7 +/- 52.6 g). The average amount of urine produced (W = 269.8 +/- 85.9; FW = 320.8 +/- 87.2; CNa = 85.6 +/- 9.3 g) was 73 and 68% lower [corrected] during CNa compared to [corrected] FW and W, respectively, [corrected] (CNa vs. FW, P < 0.05), CNa vs W, P = 0.06) [corrected] The increase in rectal temperature, heart rate and all perceptual variables did not differ among conditions. In conclusion, flavoring of the water and addition of 6% carbohydrate plus 18 mmol/l NaCl do not prevent mild hypohydration in trained, heat-acclimatized girls with high sweating rates. However, there is a tendency towards a greater fluid retention with the CNa beverage.

Voluntary drinking and hydration in non-acclimatized girls exercising in the heat

The intent of this study was to assess the influence of drink flavor and composition on voluntary drinking and hydration status in girls exercising intermittently in the heat (35 +/- 1 degrees C, 45-50% relative humidity). Twelve physically active, nonacclimatized girls (9-12 years) performed three 3 h identical sessions, each consisting of four 20 min cycling bouts at 50% (VO(2max)), separated by 25 min of rest. One of the three beverages (chilled to 8-10 degrees C) was assigned to each session: unflavored water (W), grape-flavored water (FW) and grape-flavored water plus 6% carbohydrate and 18 mmol l(-1) NaCl (CNa). Drinking was ad libitum. Body weight (BW), drink intake (DI), heart rate, rectal and skin temperatures, and perceptions of thirst and stomach fullness were monitored periodically. Total DI was 759, 940, 1,045 g in W, FW and CNa, respectively (P < 0.05 for CNa-W and FW-W). BW changes were -0.15, 0.16, and 0.45% in W, FW and CNa, respectively, but only the difference between CNa and W was significant (P < 0.05). Other physiological and perceptual variables were not different between trials. In conclusion, beverage flavoring regardless if its combination with carbohydrate and NaCl, mildly enhanced voluntary drinking in young non-acclimatized girls. In contrast to previous research in young boys, euhydration was maintained in the girls by an adequate intake of unflavored water.

Drinking guidelines for exercise: what evidence is there that athletes should drink "as much as tolerable", "to replace the weight lost during exercise" or "ad libitum"?

The most recent (1996) drinking guidelines of the American College of Sports Medicine (ACSM) propose that athletes should drink "as much as tolerable" during exercise. Since some individuals can tolerate rates of free water ingestion that exceed their rates of free water loss during exercise, this advice has caused some to overdrink leading to water retention, weight gain and, in a few, death from exercise-associated hyponatraemic encephalopathy. The new drinking guidelines of the International Olympic Committee (IOC), recently re-published in this Journal, continue to argue that athletes must drink enough to replace all their weight lost during exercise and to ingest sodium chloride since sodium is "the electrolyte most critical to performance and health". In this rebuttal to that Consensus Document, I argue that these new guidelines, like their predecessors, lack an adequate, scientifically proven evidence base. Nor have they been properly evaluated in appropriately controlled, randomized, prospective clinical trials. In particular, these new guidelines provide erroneous recommendations on five topics. If novel universal guidelines for fluid ingestion during exercise are to be promulgated by important international bodies including the IOC, they should first be properly evaluated in appropriately controlled, randomized, prospective clinical trials conducted under environmental and other conditions that match those found in "out-of-doors" exercise. This, and the potential influence of commercial interests on scientific independence and objectivity, are the two most important lessons to be learned from the premature adoption of those 1996 ACSM drinking guidelines that are not evidence-based. These concerns need to be addressed before the novel IOC guidelines are accepted uncritically. Otherwise the predictable consequences of the premature adoption of the 1996 ACSM guidelines will be repeated.

Exercise and Fluid Replacement

This Position Stand provides guidance on fluid replacement to sustain appropriate hydration of individuals performing physical activity. The goal of prehydrating is to start the activity euhydrated and with normal plasma electrolyte levels. Prehydrating with beverages, in addition to normal meals and fluid intake, should be initiated when needed at least several hours before the activity to enable fluid absorption and allow urine output to return to normal levels. The goal of drinking during exercise is to prevent excessive (>2% body weight loss from water deficit) dehydration and excessive changes in electrolyte balance to avert compromised performance. Because there is considerable variability in sweating rates and sweat electrolyte content between individuals, customized fluid replacement programs are recommended. Individual sweat rates can be estimated by measuring body weight before and after exercise. During exercise, consuming beverages containing electrolytes and carbohydrates can provide benefits over water alone under certain circumstances. After exercise, the goal is to replace any fluid electrolyte deficit. The speed with which rehydration is needed and the magnitude of fluid electrolyte deficits will determine if an aggressive replacement program is merited.

Evidence-Based Approach to Lingering Hydration Questions

Studies related to fundamental hydration issues have required clinicians to re-examine certain practices and concepts. The ingestion of substances such as creatine, caffeine, and glycerol has been questioned in regards to safety and hydration status. Reports of overdrinking (hyponatremia) also have brought into question the practices of drinking appropriate fluid amounts and the role that fluid-electrolyte balance has in the etiology of heat illnesses such as heat cramps. This article offers a fresh perspective on timely topics related to hydration, fluid balance, and exercise in the heat.

Exercise-associated hyponatremia

Exercise-associated hyponatremia has been described after sustained physical exertion during marathons, triathlons, and other endurance athletic events. As these events have become more popular, the incidence of serious hyponatremia has increased and associated fatalities have occurred. The pathogenesis of this condition remains incompletely understood but largely depends on excessive water intake. Furthermore, hormonal (especially abnormalities in arginine vasopressin secretion) and renal abnormalities in water handling that predispose individuals to the development of severe, life-threatening hyponatremia may be present. This review focuses on the epidemiology, pathogenesis, and therapy of exercise-associated hyponatremia.