Hyponatremia in ultradistance triathletes

Alterações hidroeletrolíticas agudas ocorridas no Triatlon Ironman Brasil

O Triatlon Ironman caracteriza-se por ser uma atividade de resistência constituída por 3,8km de natação, 180km de ciclismo e 42,2km de corrida, no qual o atleta exercita-se, em média, por cerca de 13 horas. Neste contexto, o atleta exposto a tal carga de esforço e adversidades ambientais, experimenta alterações orgânicas agudas em seus sistemas biológicos, incluindo os distúrbios hidroeletrolíticos. O objetivo deste estudo é descrever as alterações hídricas e eletrolíticas encontradas em atletas de triatlon Ironman. De 2002 a 2005 foram avaliados 109 atletas voluntários antes e imediatamente após as provas realizadas em Florianópolis-SC Brasil, com análise sanguínea dos eletrólitos sódio, e potássio, e medida de massa corporal. Os dados do sódio sérico de 89 atletas foram correlacionados com o grau de desidratação e modificações percentuais de peso corporal. Dados de 77 atletas, quanto ao potássio sérico, foram avaliados isoladamente de forma descritiva. Seis atletas (6,7%) apresentaram-se euhidratados ou superhidratados ao final da prova, 50 atletas desidrataram de 0 a 3% (56,2%), 29 de 3 a 6% (32,6%) e 4 atletas (4,5%) desidrataram mais que 6%. Houve uma tendência a ocorrer hiponatremia entre aqueles que desidrataram menos ou ganharam peso. O potássio teve um comportamento dentro dos limites da normalidade em toda amostra. Conclui-se que os distúrbios hidroeletrolíticos (hiponatremia e desidratação) são incidentes nesta modalidade esportiva, sendo a superhidratação a etiologia provável da hiponatremia denotada pelo ganho ou perdas discretas de peso.

Hyponatremia treatment guidelines 2007: expert panel recommendations

Although hyponatremia is a common, usually mild, and relatively asymptomatic disorder of electrolytes, acute severe hyponatremia can cause substantial morbidity and mortality, particularly in patients with concomitant disease. In addition, overly rapid correction of chronic hyponatremia can cause severe neurologic deficits and death, and optimal treatment strategies for such cases are not established. An expert panel assessed the potential contributions of aquaretic nonpeptide small-molecule arginine vasopressin receptor (AVPR) antagonists to hyponatremia therapies. This review presents their conclusions, including identification of appropriate treatment populations and possible future indications for aquaretic AVPR antagonists.

Maximising performance in triathlon: applied physiological and nutritional aspects of elite and non-elite competitions

Triathlon is a sport consisting of sequential swimming, cycling and running. The main diversity within the sport of triathlon resides in the varying event distances, which creates specific technical, physiological and nutritional considerations for athlete and practitioner alike. The purpose of this article is to review physiological as well as nutritional aspects of triathlon and to make recommendations on ways to enhance performance. Aside from progressive conditioning and training, areas that have shown potential to improve triathlon performance include drafting when possible during both the swim and cycle phase, wearing a wetsuit, and selecting a lower cadence (60-80 rpm) in the final stages of the cycle phase. Adoption of a more even racing pace during cycling may optimise cycling performance and induce a "metabolic reserve" necessary for elevated running performance in longer distance triathlon events. In contrast, drafting in swimming and cycling may result a better tactical approach to increase overall performance in elite Olympic distance triathlons. Daily energy intake should be modified to reflect daily training demands to assist triathletes in achieving body weight and body composition targets. Carbohydrate loading strategies and within exercise carbohydrate intake should reflect the specific requirements of the triathlon event contested. Development of an individualised fluid plan based on previous fluid balance observations may assist to avoid both dehydration and hyponatremia during prolonged triathlon racing.

Serum biochemistry and morbidity among runners presenting for medical care after an Australian mountain ultramarathon

OBJECTIVE

To determine if exercise-associated hyponatremia (EAH) was a cause of morbidity among runners requiring medical care at an Australian mountain ultramarathon.

DESIGN

Case series.

SETTING

Six Foot Track mountain ultramarathon, New South Wales, Australia, March 2006.

PATIENTS

Runners presenting to the medical facility.

ASSESSMENT

Serum biochemistry.

RESULTS

No cases of exercise-associated hyponatremia were identified among 9 athletes (from 775 starters) who were treated with intravenous fluid therapy. Unwell runners had a mean serum (Na) of 143 mmol/L (range 138-147 mmol/L). All runners tested had elevated serum urea and creatinine concentrations.

CONCLUSION

In this setting, EAH was not a significant cause of morbidity.

Serum chemistry alterations in Alaskan sled dogs during five successive days of prolonged endurance exercise

OBJECTIVE

To determine the impact of successive days of endurance exercise on select serum chemistry values in conditioned Alaskan sled dogs.

DESIGN

Prospective cohort study.

ANIMALS

10 conditioned Alaskan sled dogs.

PROCEDURES

All dogs ran 160 km/d for 5 consecutive days. Serum was obtained prior to exercise and immediately after each exercise run; all samples were obtained before dogs were fed. Serum electrolyte, mineral, protein, total bilirubin, urea nitrogen, creatinine, and cardiac troponin-I concentrations and serum alkaline phosphatase, alanine aminotransferase, creatine kinase, and aspartate aminotransferase activities were measured. Data were analyzed by means of analysis of covariance for a randomized complete block design with dog as a blocking variable, time as a covariate, and distance run as the treatment of interest. Least square mean values were compared with values obtained prior to exercise, and linear and quadratic contrasts were examined.

RESULTS

Serum globulin concentration was low prior to exercise (mean +/- SD, 2.2 +/- 0.3g/dL) and progressively decreased as exercise continued. Exercise was associated with increases in serum chloride, urea nitrogen, and cardiac troponin-I concentrations and serum alanine aminotransferase, creatine kinase, and aspartate aminotransferase activities and with progressive decreases in serum potassium, total protein, and albumin concentrations.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that multiple successive days of endurance exercise resulted in mild aberrations in serum chemistry variables in conditioned sled dogs. Changes likely reflected the metabolic stresses of prolonged endurance exercise as well as dietary composition. Hypoglobulinemia in resting, conditioned sled dogs may reflect the immunosuppressive or catabolic effects of intense endurance training.

An ultracyclist with pulmonary edema during the Bicycle Race Across America

Ultraendurance athletic events tax the limits of physiological homeostasis. Maintenance of sodium and water balance is a particularly difficult challenge in such events. We present the case of a 38-yr-old participant in the Bicycle Race Across America who developed severe pulmonary edema while cycling at an altitude of 2380 m on the fourth day of the race. With hospitalization and standard support for pulmonary edema, he made a quick, full recovery. A post-race work-up revealed no evidence of underlying cardiopulmonary disease or susceptibility to high-altitude pulmonary edema. His weight on the day of hospitalization was 2.7 kg greater than his pre-race weight. We hypothesize that his excessive daily sodium intake (23-25 g, or 1000-1100 mEq) during the course of the race likely led to an expanded extracellular volume, increased hydrostatic pressure, and decreased oncotic pressure. These factors, in combination with ambient hypoxia, elevated cardiac output, and reduced renal perfusion expected with sustained, high-level exercise, may have led to the development of acute pulmonary edema. This case highlights the pitfalls of overly aggressive sodium intake in endurance races, particularly when such races are conducted at high altitude, where the hypoxia-induced rise in pulmonary artery pressures may amplify the effects of changes in hydrostatic and oncotic pressure that occur with extracellular volume expansion.

Maintenance of plasma volume and serum sodium concentration despite body weight loss in ironman triathletes

OBJECTIVE

To examine the relationship between body weight, plasma volume, and serum sodium concentration ([Na]) during prolonged endurance exercise.

DESIGN

Observational field study.

SETTINGS

2000 South African Ironman Triathlon.

PARTICIPANTS

181 male triathletes competing in an Ironman triathlon.

MAIN OUTCOME MEASURES

Body weight, plasma volume, and serum ([Na]) change from pre- to postrace.

RESULTS

Significant body weight loss occurred (-4.9 +/- 1.7%; P < 0.0001), while both plasma volume (1.0 +/- 11.2%; P = 0.4: NS) and serum [Na] (0.6 +/- 2.4%; P < 0.001) increased from pre- to postrace. Blood volume (-0.6 +/- 6.6%) and red cell volume (-2.6 +/- 5.5%; P < 0.001) decreased in conjunction with the body weight loss. There was a strong correlation between blood and plasma volume change, both as a percentage, and absolute change in fluid volume (r = 0.9; P < 0.001). Body weight change was positively correlated with plasma volume change (r = -0.4; P < 0.001), but inversely correlated with serum [Na] change (r = -0.4; P < 0.001). Plasma volume change was not significantly correlated with serum [Na] change (r = 0.0; NS). Serum [Na] change was inversely correlated with both percentage of red cell volume change (r = -0.2; P < 0.05) and percentage body weight change (r = -0.4; P < 0.001).

CONCLUSION

Plasma volume and serum [Na] were maintained in male Ironman triathletes, despite significant (5%) body weight loss during the course of the race. Body weight was not an accurate "absolute" surrogate of fluid balance homeostasis during prolonged endurance exercise. Clinicians should be warned against viewing these three regulatory parameters as interchangeable during an Ironman triathlon.

Ibuprofen does not affect serum electrolyte concentrations after an ultradistance run

OBJECTIVE

To determine the effects of ibuprofen on serum electrolyte concentrations after a 160 km running race.

METHODS

Twenty nine subjects (mean (SD) age 47.9 (7.4) years) ingested 600 mg ibuprofen the day before, and 1200 mg ibuprofen during, a 160 km competitive trail running race (approximately every 4 h in 200 mg doses). Twenty five control subjects (mean (SD) age 46.8 (10.3) years) avoided ingestion of ibuprofen before or during the race. Blood was drawn on the day before the race and immediately after the race. Serum biochemical profiles were analysed by a clinical laboratory. Significant effects of treatment and time were determined with a general linear model with repeated measures.

RESULTS

Subjects in the two groups did not differ by age, training volume, race experience, body mass index, body fat, or finishing time (25.8 (3.3) vs 25.6 (3.9) h). Body weight did not change significantly over the race (measured before, mid-race (90 km), and after). Ibuprofen ingestion did not significantly affect any of the serum markers including creatine kinase (p = 0.16). A significant decrease in serum sodium (p = 0.006), potassium (p = 0.001), chloride (p<0.001), calcium (p<0.001), albumin (p<0.001) and globulin (p<0.001) was observed after the race. Increases were seen in creatine kinase (p<0.001), creatinine (p<0.001), blood urea nitrogen (p<0.001), uric acid (p<0.001) and glucose (p<0.001) as the result of the race.

CONCLUSIONS

These data suggest that the non-specific cyclo-oxygenase inhibitor, ibuprofen, does not alter serum electrolyte concentrations during ultradistance running. However, the stress of ultradistance running appears to be related to significant changes in certain serum markers.

Exercise-associated hyponatremia, renal function, and nonsteroidal antiinflammatory drug use in an ultraendurance mountain run

OBJECTIVE

To study biochemical parameters and renal function in runners completing a 60 km mountain run and to investigate the incidence of exercise-associated hyponatremia (EAH). To assess the effects of nonselective nonsteroidal antiinflammatory medication (NSAIDs) and cyclooxygenase-2 (COX-2) selective nonsteroidal antiinflammatory medication (COXIBs) on these parameters.

DESIGN

Observational cohort study.

SETTING

Kepler Challenge 60 km mountain run, Te Anau, New Zealand, December 2003.

PARTICIPANTS

One hundred thirty-one of the 360 runners entered in the race were prospectively enrolled as volunteers on the day before the race.

MAIN OUTCOME MEASURES

Subjects were weighed at race registration the day before the race and at the finish line. Blood was taken within 5 minutes of finishing and was analyzed for serum sodium, creatinine, urea, and potassium concentrations, and hematocrit. Participants were questioned about medication use in the 24 hours before and during the race (NSAIDs, COXIBs, other medications).

RESULTS

Complete data sets were obtained on 123 runners. Five athletes were biochemically hyponatremic [(Na) 130-134 mM] and four were hypernatremic [(Na) 146-148 mM]. Hyponatremia was associated with a mean weight gain of 1.32 kg (range, -1.5 to 1.6 kg). Serum [Na] varied inversely with weight change. Estimated creatinine clearance did not vary with percent weight loss. Estimated creatinine clearance declined with increasing runner age. Sixty-five percent of runners did not use any medication, whereas 20% had used NSAIDs and 15% had taken COXIBs. There were no statistically significant differences between NSAID and COXIB users in any measured parameters or between all NSAID and COXIB users when compared with nonusers.

CONCLUSIONS

Mild asymptomatic EAH was found to occur in 4% of the volunteer ultraendurance mountain runner study group and was associated with a mean weight gain of 1.32 kg (range, -1.5 to 1.6 kg) during the race. Seven percent gained weight but remained normonatremic, suggesting other compensatory mechanisms. Hypernatremia was found in 3% and was associated with a mean weight loss. Postrace serum sodium concentration varied inversely with percent weight change. Runners using any NSAID were more likely to become hyponatremic. Estimated creatinine clearance increased with increasing age. Elevated serum creatinine concentration at the end of the race returned to normal when remeasured the week after the race. Thirty-five percent of runners were found to use NSAIDs or COXIBs. The measures of weight change and of serum sodium, potassium, urea, and creatine concentration did not differ between NSAID and COXIB users or between all nonsteroidal antiinflammatory users and nonusers.

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.

Renal Function and Vasopressin During Marathon Running

Over the past 2 decades, exercise-associated hyponatraemia (EAH) has emerged as an important complication of prolonged endurance physical activities. Data collected since the first reports of EAH have strongly implicated a dilutional hyponatraemia from inappropriate retention of body water as the primary cause of EAH. Although high rates of fluid consumption clearly contribute to the pathogenesis of EAH, a review of the available data does not support the view that EAH can be ascribed solely to excess drinking. Because the kidney is exquisitely sensitive to low plasma levels of the antidiuretic hormone arginine vasopressin (AVP) and because many non-osmotic stimuli to AVP secretion normally occur during prolonged endurance exercise activity, it is more likely that a combination of higher than normal fluid intakes in the setting of modest elevations of plasma AVP levels from a variety of potential stimuli during prolonged physical activity accounts for the majority of cases of EAH. In any individual, the degree to which AVP secretion is stimulated and whether it can be suppressed with sufficient fluid ingestion, will determine their susceptibility to EAH as a result of fluid ingestion both before and after physical activity, accounting for the high degree of individual variability in the occurrence of this potentially life-threatening metabolic disorder.

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.

[Volume and electrolyte disturbances in endurance sport]

Long-lasting endurance exercise is associated with significant losses of fluid and sodium chloride, mainly due to sweat loss. To maintain endurance capacity and to avoid negative health consequences, endurance athletes should, therefore, drink fluids containing electrolytes during and after training or competition. In long-lasting endurance exercise it is recommended that athletes drink about 600-800 ml/h of fluid including adequate substitution of sodium. The excessive ingestion of fluid, however, brings about a danger of hyponatremia, which can be avoided by suitable measures. Body weight control is one of the parameters that should be carefully monitored before and after intensive endurance exercise.

Incidence and prevalence of hyponatremia

Hyponatremia is the most common electrolyte abnormality encountered in clinical practice. The reported frequency of the disorder is determined by a number of factors, including the definition of hyponatremia, the frequency of testing, the healthcare setting, and the patient population. This review focuses on the incidence and prevalence of hyponatremia. In acute hospital care, particular attention is given to admission versus hospital-acquired hyponatremia. Although less well studied, the epidemiology of hyponatremia in the ambulatory-based setting and the geriatric/nursing home population is also summarized. Finally, the frequency of hyponatremia occurring in special clinical conditions--including congestive heart failure, cirrhosis, pneumonia, and acquired immunodeficiency syndrome--as well as in marathon runners will be reviewed. Substantial additional work is still required to determine the true occurrence of hyponatremia in the various clinical settings. Beyond the phenomenologic value, advances in the epidemiology of hyponatremia should also provide insights in the prognostic implications as well as the preventive and management strategies of the disorder in various clinical settings.

Role of Sodium in Fluid Homeostasis with Exercise

This paper provides a review of recent literature concerning the interactive effects of sodium and fluid ingestion in maintaining fluid homeostasis during and following exposure to heat and exercise. Heavy sweating during exercise combined with heat exposure commonly produces fluid deficits corresponding to 1-8% loss in body mass. Thus, a great deal of attention has been focused on developing fluid replacement guidelines and products for active people. Recently, there have been reports of more frequent cases of hyponatremia among individuals who tend to over-ingest water during exercise lasting more than four hours, and inclusion of sodium chloride in the fluid replacement beverage is often suggested as a potential means of reducing risk of hyponatremia. Although hyponatremia is not likely to be a major risk factor for the general population, ultra-endurance athletes and people with occupational physical activity and heat exposure may benefit from these recommendations. Replacement of fluid deficits after exercise and heat exposure is another area that has received considerable attention. Studies in this area suggest that if water is consumed, the volume ingested needs to exceed the fluid deficit by approximately 150% to compensate for the urinary losses that will occur with water ingestion. Inclusion of sodium chloride and other solutes in the rehydration beverage reduces urinary water loss, leading to more rapid recovery of the fluid balance. Data are presented in this paper that suggest a quantifiable interactive relationship between sodium content and fluid volume in promoting rapid recovery of fluid balance after exercise and thermal-induced dehydration.

Sudden collapse of a young female cross country runner

The case is reported of a young previously healthy female cross country runner who collapsed on completion of a cross country run. The cause of the collapse was non-cardiogenic pulmonary oedema as a manifestation of hyponatraemic encephalopathy. The concurrent occurrence of non-cardiogenic pulmonary oedema and encephalopathy due to hyponatraemia is unusual.

Environmental illness in athletes

This article examines environmental illness in athletes. Causes, symptoms, and treatment of heat-related illness, cold-related illness, and altitude-related illness are discussed.

NSAID Use Increases the Risk of Developing Hyponatremia during an Ironman Triathlon

PURPOSE

Exertional hyponatremia ((Na) < 135 mmol x L(-1)) is a potentially serious condition associated with endurance sports. It has been postulated that nonsteroidal antiinflammatory drug (NSAID) use may be a risk factor. This observational cohort study aimed to determine whether NSAID use is a risk factor for exertional hyponatremia and altered renal function during endurance exercise.

METHODS

A total of 330 athletes in the 2004 New Zealand Ironman triathlon (3.8-km swim, 180-km cycle, and 42.2-km run) were weighed before and after the race. A blood sample was drawn for measurement of plasma sodium (Na), potassium (K), urea (urea), and creatinine (creatinine) concentrations postrace.

RESULTS

The incidence of NSAID use was 30%, whereas the overall incidence of hyponatremia was 1.8%. NSAID use was related to the incidence of hyponatremia (P = 0.0002). The NSAID group had lower plasma Na (P = 0.02) and higher plasma K (P = 0.002), urea (P = 0.05), and creatinine (P = 0.01). Lower Na was also significantly related to female gender, lower prerace body weight, younger age and a smaller weight loss during the race. Race times were not associated with plasma Na; however, faster triathletes lost more weight. Estimated fluid intake was not different in the NSAID group, but heavier triathletes reported greater fluid intakes.

CONCLUSIONS

NSAIDs are commonly used by athletes competing in endurance events and are a risk factor for hyponatremia and altered renal function. Notwithstanding high rates of NSAID use, the incidence of hyponatremia was low. We attribute this to changes in fluid replacement guidelines and drink station availability that reduce the risk of overdrinking, the principal cause of this condition.

Exercise associated hyponatraemia: quantitative analysis to understand the aetiology

BACKGROUND

The development of symptomatic hyponatraemia consequent on participation in marathon and ultraendurance races has led to questions about its aetiology and prevention.

OBJECTIVES

To evaluate: (a) the assertion that sweat sodium losses cannot contribute to the development of hyponatraemia during endurance exercise; (b) the adequacy of fluid replacement recommendations issued by the International Marathon Medical Directors Association (IMMDA) for races of 42 km or longer; (c) the effectiveness of commercial sports drinks, compared with water, for attenuating plasma sodium reductions.

METHODS

A mathematical model was used to predict the effects of different drinking behaviours on hydration status and plasma sodium concentration when body mass, body composition, running speed, weather conditions, and sweat sodium concentration were systematically varied.

RESULTS

Fluid intake at rates that exceed sweating rate is predicted to be the primary cause of hyponatraemia. However, the model predicts that runners secreting relatively salty sweat can finish ultraendurance exercise both dehydrated and hyponatraemic. Electrolyte-containing beverages are predicted to delay the development of hyponatraemia. The predictions suggest that the IMMDA fluid intake recommendations adequately sustain hydration over the 42 km distance if qualifiers-for example, running pace, body size-are followed.

CONCLUSIONS

Actions to prevent hyponatraemia should focus on minimising overdrinking relative to sweating rate and attenuating salt depletion in those who excrete salty sweat. This simulation demonstrates the complexity of defining fluid and electrolyte consumption rates during athletic competition.

Three independent biological mechanisms cause exercise-associated hyponatremia: evidence from 2,135 weighed competitive athletic performances

To evaluate the role of fluid and Na+ balance in the development of exercise-associated hyponatremia (EAH), changes in serum Na+ concentrations ([Na+]) and in body weight were analyzed in 2,135 athletes in endurance events. Eighty-nine percent of athletes completed these events either euhydrated (39%) or with weight loss (50%) and with normal (80%) or elevated (13%) serum [Na+]. Of 231 (11%) athletes who gained weight during exercise, 70% were normonatremic or hypernatremic, 19% had a serum [Na+] between 129-135 mmol/liter, and 11% a serum [Na+] of <129 mmol/liter. Serum [Na+] after racing was a linear function with a negative slope of the body weight change during exercise. The final serum [Na+] in a subset of 18 subjects was predicted from the amount of Na+ that remained osmotically inactive at the completion of the trial. Weight gain consequent to excessive fluid consumption was the principal cause of a reduced serum [Na+] after exercise, yet most (70%) subjects who gained weight maintained or increased serum [Na+], requiring the addition of significant amounts of Na+ (>500 mmol) into an expanded volume of total body water. This Na+ likely originated from osmotically inactive, exchangeable stores. Thus, EAH occurs in athletes who (i) drink to excess during exercise, (ii) retain excess fluid because of inadequate suppression of antidiuretic hormone secretion, and (iii) osmotically inactivate circulating Na+ or fail to mobilize osmotically inactive sodium from internal stores. EAH can be prevented by insuring that athletes do not drink to excess during exercise, which has been known since 1985.

The downed runner

Race coverage can be a rewarding experience for the sports medicine clinician. Several conditions are likely to present to the medical tent, and accurate diagnosis is critical to proper treatment. An algorithm approach as outlined in this article can provide a starting point for the assessment of the downed runner. Recognition of the primary causes for collapse can help to instigate the correct treatment approach. A proper history and physical examination often can help to differentiate significant cardiac events from the more innocuous EAC. Furthermore, avoiding immediate i.v. fluids in the downed runner is prudent, at least until an appropriate diagnosis is made. This will help to prevent iatrogenic hyponatremia. In sum, proper preparation and knowledge of the ailments that affect long distance runners will help to maintain an effective medical tent on race day.

Medical considerations in triathlon competition: recommendations for triathlon organisers, competitors and coaches

Competitors in triathlons experience a range of environmental conditions and physiological demands in excess of that found in individual sport events of comparable duration. Consequently, there is a broad range of possible medical problems and complications that must be taken into account when preparing for such races. For most competitors, an Olympic-distance triathlon typically takes between 2-4 hours to complete. This race begins with a swimming segment of 1500 m. Given the wide variety of race venues found around the world, these swims occur in an assortment of water temperatures (from warm to cold) and conditions (from ocean surf to lake calm). Swimmers often exit the water in a state of moderate dehydration and hypothermia and then immediately start the 40 km cycling leg. Many do so in their swimming attire. A wide variety of road surfaces, technically challenging topography, variable environmental conditions and dramatically changing velocities can be encountered on the cycle course. The race concludes with a 10 km running leg. Since it is the final leg, it is often completed in higher ambient temperatures than those encountered at the start, with the athlete possibly running in a significant state of dehydration and fatigue. Other medical problems commonly encountered in triathlon include: muscle cramping, heat illness, postural hypotension, excessive exposure to ultraviolet radiation, musculoskeletal injuries and trauma, gastrointestinal problems as well as post-race bacterial infection, immunosuppression, sympathetic nervous system and psychological exhaustion, and haemolysis. The rate of occurrence of such events and the severity of their potentially negative outcomes is a function of the methods used by both the race organisers and the competitors to prevent or respond to the conditions imposed by the race. Triathletes also commonly compete in both shorter 'sprint distance' events (in the range of a 0.75 km swim, 20 km cycle and 5 km run) and longer events including both one-half and full Ironman distances (2.5 and 3.8 km swim, 80 and 180 km cycle, 20 and 42 km run, respectively), as well as ultra-distance events that exceed the Ironman distance. In the longer events, the previously mentioned medical considerations are further magnified and additional considerations such as hyponatraemia can also occur. Reducing risk associated with these concerns is accomplished by: taking into account weather and water temperature/conditions data prior to event scheduling; effective swim, cycle and run course organisation and management; environmental monitoring prior to and during the event; the implementation of a water safety plan; provision of appropriate fluid replacement throughout the course; implementation of helmet use and non-drafting regulations in the cycling leg; and competitor knowledge regarding fluid replacement, biomechanical technique, physical preparation, safe equipment and course familiarity. Despite these concerns, triathlon participation appears to relatively safe for persons of all ages, assuming that high-risk adults undertake health screening.

Nutritional considerations in triathlon

Triathlon combines three disciplines (swimming, cycling and running) and competitions last between 1 hour 50 minutes (Olympic distance) and 14 hours (Ironman distance). Independent of the distance, dehydration and carbohydrate (CHO) depletion are the most likely causes of fatigue in triathlon, whereas gastrointestinal (GI) problems, hyperthermia and hyponatraemia are potentially health threatening, especially in longer events. Although glycogen supercompensation may be beneficial for triathlon performance (even Olympic distance), this does not necessarily have to be achieved by the traditional supercompensation protocol. More recently, studies have revealed ways to increase muscle glycogen concentrations to very high levels with minimal modifications in diet and training. During competition, cycling provides the best opportunity to ingest fluids. The optimum CHO concentration seems to be in the range of 5-8% and triathletes should aim to achieve a CHO intake of 60-70 g/hour. Triathletes should attempt to limit body mass losses to 1% of body mass. In all cases, a drink should contain sodium (30-50 mmol/L) for optimal absorption and prevention of hyponatraemia.Post-exercise rehydration is best achieved by consuming beverages that have a high sodium content (>60 mmol/L) in a volume equivalent to 150% of body mass loss. GI problems occur frequently, especially in long-distance triathlon. Problems seem related to the intake of highly concentrated carbohydrate solutions, or hyperosmotic drinks, and the intake of fibre, fat and protein. Endotoxaemia has been suggested as an explanation for some of the GI problems, but this has not been confirmed by recent research. Although mild endotoxaemia may occur after an Ironman-distance triathlon, this does not seem to be related to the incidence of GI problems. Hyponatraemia has occasionally been reported, especially among slow competitors in triathlons and probably arises due to loss of sodium in sweat coupled with very high intakes (8-10 L) of water or other low-sodium drinks.

Serum Electrolytes in Ironman Triathletes with Exercise-Associated Muscle Cramping

PURPOSE

To compare serum electrolyte concentrations of cramping and control Ironman triathletes.

METHODS

Triathletes suffering from acute exercise-associated muscle cramping (EAMC) after the 2000 South African Ironman Triathlon formed the cramping group (CR, N = 11). Non-cramping triathletes matched for race finishing time and body mass formed the control group (CON, N = 9). All subjects were weighed at race start and immediately post-race. Blood samples were drawn from both groups during recovery for the analysis of serum magnesium, glucose, sodium, potassium and chloride concentrations. Hemoglobin concentration and hematocrit were also measured. Surface electromyography (EMG) (mV) was recorded from a non-cramping control muscle (triceps) and the most severely cramping lower limb muscle of the CR group. EMG was recorded at the beginning of every minute for a 10-min period during recovery.

RESULTS

There were no significant differences between the groups for body mass or percent body mass loss during the race. Post-race sodium concentration was significantly lower (P = 0.01) in the CR group than the CON group (140 +/- 2 vs 143 +/- 3 mmol.L) but was within the normal clinical range of post-race serum sodium concentrations. There were no significant differences between the two groups for post-race serum electrolytes, glucose, hemoglobin concentrations or hematocrit. Surface EMG (mV) was significantly higher (P < 0.05) in the cramping muscles than the control muscle of the CR group at 0, 3, 4, and 5 min of the 10-min recording period.

CONCLUSION

Acute EAMC in ironman triathletes is not associated with a greater percent body mass loss or clinically significant differences in serum electrolyte concentrations. The increased EMG activity of cramping muscles may reflect increased neuromuscular activity.

Medical Concerns of Marathons

One must remember that the first marathon runner, Phidippides, collapsed and died at the finish of his race. Fortunately, death has been an infrequent occurrence in modern day marathons. However, the physical exertion required to complete a marathon coupled with exposure to often harsh environmental conditions and an increase in the number of novice participants makes injuries inevitable. The medical team's main goal is to implement strategies to prevent serious injury and illness through pre-event planning, race day preparedness, and postevent evaluations. The three general categories of injuries encountered with marathon participation include medical conditions, musculoskeletal injuries, and dermatologic complaints. The focus of this article is on the evaluation and management of the varied medical concerns encountered on race day along with the essentials in prerace planning and preparedness.

Sex Differences in Voluntary Fluid Intake by Older Adults during Exercise

PURPOSE

This study compared the voluntary fluid intake behavior of older men and women (54-70 yr) when provided cold, palatable beverages and ample opportunity to drink between repeated bouts of exercise in the heat.

METHODS

Thirteen men and 14 women performed four bouts of 15-min cycling at 65% VO2peak followed by 15 min of rest at 30 degrees C and 50% relative humidity. In separate trials, subjects drank either a carbohydrate-electrolyte solution (CES) or water ad libitum during the rest periods and were unaware that their fluid intake was being measured.

RESULTS

Fluid intake behavior was repeatable (intraclass correlation coefficient = 0.75), and subjects drank enough of either beverage to match sweating rates and maintain their body mass (BM). Fluid intake per kilogram of BM was greater with CES (18.7 +/- 2.2 vs 15.1 +/- 2.1 mL x kg(-1); P < 0.05), and plasma volume (PV) was better maintained during the CES trials (-1.3 +/- 1.1 vs -4.2 +/- 1.1% during the second half of the session). Women drank significantly more water than the men on a per kilogram basis (17.2 +/- 2.9 vs 12.8 +/- 1.7 mL x kg(-1) BM), and one woman (BM = 45.7 kg) became hyponatremic (S(NA) = 126 mmol x L(-1)) with symptoms during the water trial.

CONCLUSION

Older adults drank enough to maintain fluid balance when palatable fluid was readily available; however, CES promoted greater voluntary fluid intake and restored PV losses faster than water. In addition, older women drank more water than men during interval exercise in the heat, which may put smaller women at an increased risk for developing hyponatremia.

Women hydrate more than men during a marathon race: hyponatremia in the Houston marathon: a report on 60 cases

OBJECTIVE

To examine the relationship between gender and the development of hyponatremia in marathon runners.

DESIGN

A retrospective analysis of prerace and postrace data collected on 117 runners completing the Houston Marathon from 2000 to 2003.

SETTING

The Houston Marathon.

PARTICIPANTS

A total of 117 marathon runners (63 male and 54 female) who consented to participate in hyponatremia research.

MAIN OUTCOME MEASURES

Prerace and postrace body weight and serum sodium ([Na+]) concentrations were measured. Total fluid intake was self-reported immediately following the race.

RESULTS

: Of the runners tested, 28% developed hyponatremia ([Na+] < or = 135 mmol/L). Hyponatremic runners (n = 33) drank significantly more fluid (31.70 versus 18.90 cups; P < 0.001), lost the least weight (-0.14 versus -1.61 kg; P < 0.001), and dropped serum [Na+] levels further (-7.48 versus -1.92; P < 0.001) compared with nonhyponatremic runners. Female runners (n = 54) were significantly lighter (62.46 versus 80.73 kg; P < 0.001), ran slower (303.02 versus 269.06 minutes; P < 0.001), lost the least weight (-0.62 versus -1.68 kg; P < 0.001), dropped serum [Na+] levels further (-4.44 versus -2.67; P < 0.01), and had lower postrace serum [Na+] values (136.87 versus 138.50; P < 0.01) compared with male runners while consuming the same total amount of fluid during the race (22.87 versus 22.30 cups; P = 0.83, NS). There were significant inverse relationships between serum [Na+] change versus body weight change (r = -0.65; P < 0.001) and between postrace [Na+] versus body weight change (r = -0.60; P < 0.001), with significant sex differences noted only between nonhyponatremic female and male runners (-0.91 versus -0.2.05 kg; P < 0.001) and between hyponatremic and nonhyponatremic male runners (-0.11 versus -2.05 kg; P < 0.001).

CONCLUSIONS

Female marathon runners drink more fluid than male runners in proportion to body size. A loss of 3 kg body weight corresponds to a 0 change in serum [Na+] from prerace to postrace, suggesting that a loss of 3 kg during a marathon represents euhydration and not dehydration. All cases of hyponatremia reported in this study are a result of overhydration based on this convention.

Hyponatremia among runners in the Boston Marathon

BACKGROUND

Hyponatremia has emerged as an important cause of race-related death and life-threatening illness among marathon runners. We studied a cohort of marathon runners to estimate the incidence of hyponatremia and to identify the principal risk factors.

METHODS

Participants in the 2002 Boston Marathon were recruited one or two days before the race. Subjects completed a survey describing demographic information and training history. After the race, runners provided a blood sample and completed a questionnaire detailing their fluid consumption and urine output during the race. Prerace and postrace weights were recorded. Multivariate regression analyses were performed to identify risk factors associated with hyponatremia.

RESULTS

Of 766 runners enrolled, 488 runners (64 percent) provided a usable blood sample at the finish line. Thirteen percent had hyponatremia (a serum sodium concentration of 135 mmol per liter or less); 0.6 percent had critical hyponatremia (120 mmol per liter or less). On univariate analyses, hyponatremia was associated with substantial weight gain, consumption of more than 3 liters of fluids during the race, consumption of fluids every mile, a racing time of >4:00 hours, female sex, and low body-mass index. On multivariate analysis, hyponatremia was associated with weight gain (odds ratio, 4.2; 95 percent confidence interval, 2.2 to 8.2), a racing time of >4:00 hours (odds ratio for the comparison with a time of <3:30 hours, 7.4; 95 percent confidence interval, 2.9 to 23.1), and body-mass-index extremes.

CONCLUSIONS

Hyponatremia occurs in a substantial fraction of nonelite marathon runners and can be severe. Considerable weight gain while running, a long racing time, and body-mass-index extremes were associated with hyponatremia, whereas female sex, composition of fluids ingested, and use of nonsteroidal antiinflammatory drugs were not.

Serum electrolyte concentrations and hydration status are not associated with exercise associated muscle cramping (EAMC) in distance runners

OBJECTIVES

To determine whether acute exercise associated muscle cramping (EAMC) in distance runners is related to changes in serum electrolyte concentrations and hydration status.

METHODS

A cohort of 72 runners participating in an ultra-distance road race was followed up for the development of EAMC. All subjects were weighed before and immediately after the race. Blood samples were taken before the race, immediately after the race, and 60 minutes after the race. Blood samples were analysed for glucose, protein, sodium, potassium, calcium, and magnesium concentrations, as well as serum osmolality, haemoglobin, and packed cell volume. Runners who suffered from acute EAMC during the race formed the cramp group (cramp, n = 21), while runners with no history of EAMC during the race formed the control group (control, n = 22).

RESULTS

There were no significant differences between the two groups for pre-race or post-race body weight, per cent change in body weight, blood volume, plasma volume, or red cell volume. The immediate post-race serum sodium concentration was significantly lower (p = 0.004) in the cramp group (mean (SD), 139.8 (3.1) mmol/l) than in the control group (142.3 (2.1) mmol/l). The immediate post-race serum magnesium concentration was significantly higher (p = 0.03) in the cramp group (0.73 (0.06) mmol/l) than in the control group (0.67 (0.08) mmol/l).

CONCLUSIONS

There are no clinically significant alterations in serum electrolyte concentrations and there is no alteration in hydration status in runners with EAMC participating in an ultra-distance race.

Nutrient intake and performance during a mountain marathon: an observational study

In order to study nutrient intake of amateur runners during a mountain marathon, compliance with recommendations, and association with performance, an intake of 42 participants in a Swiss mountain marathon was assessed by direct observation. Data on demographics, dietary preparation and race experience were obtained by questionnaires. Anthropometrical measures were performed before and after the race. Mean hourly intakes (SD) of fluid, carbohydrate, energy and sodium were 545 (158) ml, 31 (14) g, 141 (63) kcal [or 590 (264) kJ], and 150 (203) mg respectively. A third of the runners drank 600 ml h(-1) or more, 52% consumed less than 30 g h(-1 )carbohydrates, 95% consumed less than 500 mg h(-1) sodium. Mean weight loss was 4 (1.5) kg; 30 runners (71%) lost over 3% body mass. Mean running time was 7 h 3 min (1 h 17 min). Most participants failed to meet nutritional recommendations. None were at risk of overhydration. Body composition and race experience were correlated with performance, but not nutrient intake. Because experienced runners are well trained, fitter, and know better their personal needs during such a race, it is difficult to disentangle these associations. As causal relationship cannot be proven with this cross-sectional design, non-compliance with intake recommendations requires additional experimental research on the impact of nutrient intake on field performance.

Weight changes, medical complications, and performance during an Ironman triathlon

BACKGROUND

Subjects exercising without fluid ingestion in desert heat terminated exercise when the total loss in body weight exceeded 7%. It is not known if athletes competing in cooler conditions with free access to fluid terminate exercise at similar levels of weight loss.

OBJECTIVES

To determine any associations between percentage weight losses during a 224 km Ironman triathlon, serum sodium concentrations and rectal temperatures after the race, and prevalence of medical diagnoses.

METHODS

Athletes competing in the 2000 and 2001 South African Ironman triathlon were weighed on the day of registration and again immediately before and immediately after the race. Blood pressure and serum sodium concentrations were measured at registration and immediately after the race. Rectal temperatures were also measured after the race, at which time all athletes were medically examined. Athletes were assigned to one of three groups according to percentage weight loss during the race.

RESULTS

Body weight was significantly (p<0.0001) reduced after the race in all three groups. Serum sodium concentrations were significantly (p<0.001) higher in athletes with the greatest percentage weight loss. Rectal temperatures were the same in all groups, with only a weak inverse association between temperature and percentage weight loss. There were no significant differences in diagnostic indices of high weight loss or incidence of medical diagnoses between groups.

CONCLUSIONS

Large changes in body weight during a triathlon were not associated with a greater prevalence of medical complications or higher rectal temperatures but were associated with higher serum sodium concentrations.

Sodium Status of Collapsed Marathon Runners

Context.—Recommendations for prevention and treatment of medical emergencies in participants in marathon races center on maintenance of adequate hydration status and administration of fluids. Recently, new recommendations for fluid replacement for marathon runners were promulgated by medical and athletic societies. These new guidelines encourage runners to drink ad libitum between 400 and 800 mL/h as opposed to the previous “as much as possible” advice.

Objective.—To assess the sodium and hydration (plasma osmolality) status of collapsed marathon runners after the promulgation of new hydration guidelines.

Design.—Plasma sodium and osmolality values of runners who presented to the medical tent at the finish line of the 2003 Boston Marathon were measured.

Results.—Using reference ranges derived from the general population, of 140 collapsed runners, 35 (25%) were hypernatremic (sodium, &gt;146 mEq/L) and 6 (12%) were hyperosmolar (osmolality, &gt;296 mOsm/kg H2O), whereas 9 (6%) were hyponatremic (sodium, &lt;135 mEq/L) and 8 (16%) were hypo-osmolar (osmolality, &lt;280 mOsm/kg H2O). Compared with a population of marathon runners who had experienced no medical difficulties, 9% of the runners were hypernatremic, 5% were hyponatremic, 8% were hypo-osmolar, and none were hyperosmolar.

Conclusions.—Our findings indicate a significant incidence of hypernatremia with hyperosmolality and hyponatremia with hypo-osmolality among collapsed runners despite the new fluid intake recommendations, suggesting that either further educational measures are required or that the new guidelines are not entirely adequate to prevent abnormalities in fluid balance. Furthermore, the immediate medical management of hypernatremia and hyponatremia is different. Administration of fluids to severely hyponatremic patients may result in fatal cerebral edema. Our findings caution against institution of treatment until laboratory tests determine the patient's sodium status.

Exercise-Associated Hyponatraemia

In 1958, Edelman and colleagues empirically showed plasma sodium concentration ([Na+]p) to be primarily a function of the sum of exchangeable sodium and potassium (E) divided by total body water (TBW). Based on Edelman's equation, Nguyen and Kurtz derived an equation to show how [Na+]p changes as a function of TBW, change in TBW (DeltaTBW), and change in the sum of exchangeable sodium and potassium (DeltaE). Using the Nguyen-Kurtz equation, the present study examines the sensitivity of [Na+]p to these parameters: [Na+]p is very sensitive to DeltaTBW and moderately sensitive to DeltaE, and is modulated by TBW. For example, for a person with 50 L TBW, a net increase of 1L water lowers [Na+]p by 3.2 mEq/L, but for a person with 25 L TBW it lowers [Na+]p by 6.3 mEq/L (assuming initial [Na+]p is 140 mEq/L). In each case, a loss of 159 mEq of sodium plus potassium (roughly equivalent to 1.5 teaspoons of table salt) would be required to produce the same effect as the net increase of 1 L water. The present review demonstrates why fluid overload predominates over electrolyte loss in the aetiology of exercise-associated hyponatraemia (EAH), and why the excretion of electrolyte-dilute urine is highly effective in correcting EAH (nonetheless, loss of sodium and potassium is significant in long events in warm weather). Sports drinks will, if overconsumed, result in hyponatraemia. Administration of a sports drink to an athlete with fluid overload hyponatraemia further lowers [Na+]p and increases fluid overload. Administration of either a sports drink or normal (0.9%) saline increases fluid overload.

Study of hematological and biochemical parameters in runners completing a standard marathon

OBJECTIVE

To study hematological and biochemical parameters prospectively in runners completing a standard 42.2-km marathon run. To determine the incidence of hyponatremia in runners, and whether consumption of nonsteroidal anti-inflammatory medications (NSAIDs) was associated with alterations in serum biochemical parameters.

DESIGN

Observational cohort study.

SETTING

City of Christchurch (New Zealand) Marathon, June 2002.

PARTICIPANTS

One hundred fifty-five of the 296 athletes entered in the 2002 City of Christchurch Marathon were enrolled in the study.

MAIN OUTCOME MEASURES

Athletes were weighed at race registration and immediately after the race. Blood was drawn postrace for measurement of serum sodium, potassium, creatinine, and urea concentrations and for hematological analysis (hemoglobin concentration, hematocrit, leukocyte distribution).

RESULTS

Complete data sets including prerace and postrace weights, and postrace hematological and biochemical analyses were collected on 134 marathon finishers. Postrace serum sodium concentrations were directly related to changes in body weight (P < 0.0001). There were no cases of biochemical or symptomatic hyponatremia. Thirteen percent of runners had taken an NSAID in the 24 hours prior to the race. Mean values for serum creatinine (P = 0.03) and serum potassium (P = 0.007) concentrations were significantly higher in runners who had taken an NSAID. No athlete who had taken an NSAID had a postrace serum creatinine concentration less than 0.09 mmol/L. Ninety-eight percent of runners had a postrace leukocytosis (mean white cell count, 18.97 b/L), of which the major component was a raised neutrophil count (mean neutrophil count, 15.69 b/L).

CONCLUSIONS

This study found no cases of hyponatremia in runners completing a standard distance marathon. This finding relates to a marathon run under ideal conditions (minimal climatic stress) and in which there were fewer aid stations (every 5 km) than is common in North American marathons (every 1.6 km). Also, aggressive hydration practices were not promoted. Consumption of NSAIDs in the 24 hours prior to distance running was associated with altered renal function.

Event medicine: injury and illness during an expedition-length adventure race

To describe the incidence and type of injury and illness occurring during an expedition-length adventure race and identify those resulting in withdrawal from the event, a prospective cohort study was conducted of the injuries and illness treated during the Subaru Primal Quest Expedition Adventure Race trade mark held in Colorado July 7-16, 2002. All racers, support crewmembers, and race staff were eligible to participate in the study. When a member of the study group received medical care due to an injury or illness, the encounter was recorded on a Medical Encounter Form. If an injury or illness resulted in withdrawal from the race, this was also recorded. Information from the Medical Encounter Forms was used to generate the Medical Log. There were 671 individuals eligible to participate in the study. A total of 243 medical encounters and 302 distinct injuries and illnesses were recorded. There were 179 (59%) injuries and 123 (41%) illnesses. Skin and soft tissue injuries and illness were the most frequent (48%), with blisters on the feet representing the single most common (32.8%). Second was respiratory illness (18.2%), including upper respiratory infection, bronchitis and reactive airway disease-asthma. Respiratory illness was the most common medical reason for withdrawal from the event. Injuries accounted for almost 60% of all injury and illness yet they contributed to less than 15% of the medical withdrawals from the race. Blisters accounted for almost one-third of all conditions treated. Providers of medical support for expedition-length adventure races should be prepared to treat a wide variety of injury and illness.

Recommendations for treatment of hyponatraemia at endurance events

This review focuses on possible pathophysiology of exercise-associated hyponatraemia and its implication on evaluation and treatment of collapsed athletes during endurance events. Rehydration guidelines and field care have traditionally been based on the belief that endurance events create a state of significant fluid deficit in athletes, which must be corrected by liberal hydration. Beliefs in the necessity of liberal hydration may have contributed to cases of hyponatraemia. Assumptions that fluid loss accounts for the entire weight loss during exercise and that fluid ingestion is the only source of water gain during exercise may lead to an overestimation of the degree of volume depletion and the amount of fluid needed for replacement. Increasing evidence suggests that hyponatraemic athletes are fluid overloaded; ingestion of large amount of hypotonic fluid in combination with inappropriate or inadequate physiological responses leads to excessive retention of free fluid. Risk factors include hot weather, female sex, slower finishing time, and possibly the use of nonsteroidal anti-inflammatory medications. Symptoms of hyponatraemia can be subtle and can mimic those of other exercise-related illnesses, thereby complicating its diagnosis and leading to possible inappropriate treatment. Most athletes who collapse at the finish line experience exercise-associated collapse, a benign and transient form of postural hypotension that can be treated simply by continued ambulation after finishing or elevation of legs while in a supine position for those who cannot walk. Care providers should consider the use of intravenous hydration with normal saline carefully since it is not needed by most collapsed athletes and may worsen the condition of patients with unsuspected hyponatraemia. Historic information and clinical signs of volume depletion should be elicited prior to its use. Most hyponatraemic athletes will recover uneventfully with careful observation while awaiting spontaneous diuresis. Use of hypertonic saline should be reserved for patients with severe symptoms. Moderate consumption of carbohydrate-electrolyte solution during exercise may allow the maintenance of adequate hydration and the prevention of hyponatraemia.

Fluid replacement during marathon running

During endurance exercise, about 75% of the energy produced from metabolism is in the form of heat, which cannot accumulate. The remaining 25% of energy available can be used for movement. As running pace increases, the rate of heat production increases. Also, the larger one's body mass, the greater the heat production at a particular pace. Sweat evaporation provides the primary cooling mechanism for the body, and for this reason athletes are encouraged to drink fluids to ensure continued fluid availability for evaporation and circulatory flow to the tissues. Elite level runners could be in danger of heat illness if they race too quickly in hot/humid conditions and may collapse at the end of their event. Most marathon races are scheduled at cooler times of the year or day, however, so that heat loss to the environment is adequate. Typically, this postrace collapse is due simply to postural hypotension from decreased skeletal muscle massage of the venous return circulation to the heart on stopping. Elite athletes manage adequate hydration by ingesting about 200-800 mL/hour, and such collapse is rare. Athletes "back in the pack" are moving at a much slower pace, however, with heat accumulation unlikely and drinking much easier to manage. They are often urged to drink "as much as tolerable," ostensibly to prevent dehydration from their hours out on the race course. Excessive drinking among these participants can lead to hyponatremia severe enough to cause fatalities. A more reasonable approach is to urge these participants not to drink as much as possible but to drink ad libitum (according to the dictates of thirst) no more than 400-800 mL/hour.

Effects of different sodium concentrations in replacement fluids during prolonged exercise in women

OBJECTIVE

To investigate the effect of different sodium concentrations in replacement fluids on haematological variables and endurance performance during prolonged exercise.

METHODS

Thirteen female endurance athletes completed three four hour runs on a 400 m track. Environmental conditions differed between the three trials: 5.3 degrees C and snow (trial 1), 19.0 degrees C and sunny weather (trial 2), 13.9 degrees C and precipitation (trial 3). They consumed 1 litre of fluid an hour during the trials with randomised intake of fluids: one trial (H) with high sodium concentration (680 mg/l), one trial (L) with low sodium concentration (410 mg/l), and one trial with only water (W). Before and after the trials, subjects were weighed and blood samples were taken for analysis of [Na(+)](plasma), packed cell volume, and mean corpuscular volume.

RESULTS

The mean (SD) decrease in [Na(+)](plasma) over the whole trial was significantly (p<0.001) less in trial H (2.5 (2.5) mmol/l) than in trial W (6.2 (2.1) mmol/l). Mild hyponatraemia ([Na(+)](plasma) = 130-135 mmol/l) was observed in only six women (46%) in trial H compared with nine (69%) in trial L, and 12 (92%) in trial W. Two subjects (17%) in trial W developed severe hyponatraemia ([Na(+)](plasma)<130 mmol/l). No significant differences were found in performance or haematological variables with the three different fluids. There was no significant correlation between[Na(+)](plasma) after the run and performance. There was a significant correlation between changes in [Na(+)](plasma) and changes in body weight.

CONCLUSIONS

Exercise induced hyponatraemia in women is likely to develop from fluid overload during prolonged exercise. This can be minimised by the use of replacement fluids of high sodium concentration. Sodium replacement of at least 680 mg/h is recommended for women in a state of fluid overload during endurance exercise of four hours. However, higher [Na(+)](plasma) after the run and smaller decreases in [Na(+)](plasma) during the trials were no indication of better performance over four hours.

Nutritional aspects in ultra-endurance exercise

PURPOSE OF REVIEW

Despite much current debate regarding central and peripheral neural mechanisms which may be responsible for the onset of fatigue during prolonged exercise, maintenance of nutritional and hydration status remains critical for successful participation in ultra-endurance exercise. This review focuses on substrate and fluid homeostasis during ultra-endurance exercise and the use of nutritional supplementation both as ergogenic aid and to attenuate exercise-induced immunosuppression.

RECENT FINDINGS

Current evidence continues to support mandatory high carbohydrate intakes (1). before the event to maximize muscle glycogen stores, (2). during the event to prevent hypoglycaemia and (3). after the event to optimize post-event repletion of endogenous carbohydrate stores. No consistent performance benefit has yet been shown following a high-fat diet. Greater utilization of intrafascicular triglyceride stores appears to account for additional fat utilization in females. Recent trends towards excessive fluid intake have resulted in frequent reports of hyponatraemic hyperhydration in ultra-distance athletes, with greater incidence in women than in men. Carbohydrate supplementation during the event attenuates immunosuppressive hormonal and cytokine responses to ultra-endurance exercise, but may impair vitamin C absorption, while the ergogenic value of caffeine supplementation in ultra-endurance performance is currently being questioned.

SUMMARY

Meeting macronutrient and fluid intake demands remains an important priority for ultra-endurance athletes. Yet these athletes are reported to present with a high incidence of disordered eating patterns during periods of training, and excessive fluid replacement strategies have resulted in an increased incidence of water intoxication with resultant central nervous system dysfunction.

Change in serum sodium concentration during a cold weather ultradistance race

OBJECTIVE

To investigate change in serum sodium concentration and its potential causes during a cold weather ultradistance race.

DESIGN

Descriptive research.

SETTING

A 100-mile (161-km) race over a snow-packed course in the Alaskan wilderness. Athletes competed in 1 of 3 divisions: foot, bike, or ski.

PARTICIPANTS

Twenty athletes (11 runners, 6 cyclists, 3 skiers) volunteered for the study.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Subjects were weighed and had blood drawn for hematocrit, serum sodium, serum aldosterone, and plasma arginine vasopressin concentrations pre- and postrace. Fluid and sodium intake were determined by race dietary analysis.

RESULTS

Serum sodium concentration decreased significantly prerace (140.8 +/- 1.2 mmol/L) to postrace (138.4 +/- 2.2 mmol/L), although no athletes were classified as hyponatremic. Mean weight loss was significant during the race (-1.2 kg), although 1 athlete maintained his weight, and 3 athletes gained small amounts of weight (0.2 kg, 0.2 kg, and 0.5 kg, respectively). Hematocrit decreased significantly prerace (42.2 +/- 3.5) to postrace (40.3 +/- 4.1). Plasma arginine vasopressin and serum aldosterone increased significantly during the race (2.6 +/- 0.7 to 6.0 +/- 4.6 pg/mL and 5.1 +/- 2.6 to 40.8 +/- 25.1 ng/dL, respectively). Fluid consumption was 300 +/- 100 mL/h, and sodium intake was 310 +/- 187 mg/h.

CONCLUSIONS

Decreased serum sodium concentration after a cold weather ultradistance race was due to fluid overload caused by excessive fluid consumption. Current recommendations that ultradistance athletes consume 500 to 1000 mL/h may be too high for athletes competing in the extreme cold.

Heat cramps: fluid and electrolyte challenges during tennis in the heat

Sweat losses during tennis can be considerable. And while most players make a genuine effort to stay well hydrated to maintain performance and reduce the risk of heat illness, regular and copious water intake is often not enough. Besides an extraordinary water loss, extensive sweating can lead to a concomitant large electrolyte deficit too--particularly for sodium. Although a variety of other mineral deficiencies and physiological conditions are purported to cause muscle cramps, evidence suggests that, when a tennis player cramps in warm to hot weather, extensive and repeated sweating during the current and previous matches and a consequent sodium deficit are usually the primary contributing factors. Heat cramps often begin as subtle "twitches" or fasciculations in one or more voluntary muscles and, unless treated, can rapidly progress to widespread debilitating muscle spasms that leave an afflicted player on the court writhing in pain. If sufficient preventive measures are taken well before and during play, such cramping is avoidable in most cases. Appropriate and sufficient salt and fluid intake will enhance rehydration and fluid distribution throughout a player's body, so that heat cramps can be completely averted, even during long matches in the most challenging environments.