Prevalence of exercise-associated hyponatremia in male ultraendurance athletes

Ultra-Cycling- Past, Present, Future: A Narrative Review

BACKGROUND

Ultra-endurance events are gaining popularity in multiple exercise disciplines, including cycling. With increasing numbers of ultra-cycling events, aspects influencing participation and performance are of interest to the cycling community.

MAIN BODY

The aim of this narrative review was, therefore, to assess the types of races offered, the characteristics of the cyclists, the fluid and energy balance during the race, the body mass changes after the race, and the parameters that may enhance performance based on existing literature. A literature search was conducted in PubMed, Scopus, and Google Scholar using the search terms 'ultracycling', 'ultra cycling', 'ultra-cycling', 'ultra-endurance biking', 'ultra-bikers' and 'prolonged cycling'. The search yielded 948 results, of which 111 were relevant for this review. The studies were classified according to their research focus and the results were summarized. The results demonstrated changes in physiological parameters, immunological and oxidative processes, as well as in fluid and energy balance. While the individual race with the most published studies was the Race Across America, most races were conducted in Europe, and a trend for an increase in European participants in international races was observed. Performance seems to be affected by characteristics such as age and sex but not by anthropometric parameters such as skin fold thickness. The optimum age for the top performance was around 40 years. Most participants in ultra-cycling events were male, but the number of female athletes has been increasing over the past years. Female athletes are understudied due to their later entry and less prominent participation in ultra-cycling races. A post-race energy deficit after ultra-cycling events was observed.

CONCLUSION

Future studies need to investigate the causes for the observed optimum race age around 40 years of age as well as the optimum nutritional supply to close the observed energy gap under consideration of the individual race lengths and conditions. Another research gap to be filled by future studies is the development of strategies to tackle inflammatory processes during the race that may persist in the post-race period.

Acute Kidney Injury and Hyponatremia in Ultra-Trail Racing: A Systematic Review

Background and objectives: Ultra-trail races can cause episodes of acute kidney injury (AKI) and exercise-associated hyponatremia (EAH) in healthy subjects without previous renal pathology. This systematic review aims to review the incidence of these two syndromes together and separately taking into account the length and elevation of the ultra-trail race examined. Materials and Methods: A systematic review was conducted through electronic search in four electronic databases (PubMed, EBSCO, Web of Science and Alcorze). Results: A total of 1127 articles published between January 2006 and December 31, 2021 were included, 28 of which met the inclusion criteria. The studies were categorized according to the length and stages of the race in four categories: medium (42 to 69 km), long (70 to 99 km), extra (>100 km) and multi-stage if they included various stages. A total of 2950 runners (666 females and 2284 males) were extracted from 28 publications. The AKI incidence found was 42.04% (468 cases of 1113), and 195 of 2065 were diagnosed with EAH, accounting for 9.11%. The concurrence of both pathologies together reached 11.84% (27 individuals) from a total of 228 runners with AKI and EAH simultaneously analyzed. Sorted by race category, the AKI+EAH cases were distributed as follows: 18 of 27 in the extra (13.63% and n = 132), 4 in the large (5.79% and n = 69) and 5 in the medium category (18.15% and n = 27). Conclusions: According to these results, extra and medium races showed a similar incidence of AKI+EAH. These findings underline the importance of the duration and intensity of the race and may make them responsible for the etiology of these medical conditions. Due to their variable incidence, EAH and AKI are often underdiagnosed, leading to poorer prognosis, increased condition seriousness and hindered treatment. The results of this review urge participants, coaches and race organizers to take measures to improve the early diagnosis and urgent treatment of possible EAH and AKI cases.

Extreme Ultra-Trail Race Induces Muscular Damage, Risk for Acute Kidney Injury and Hyponatremia: A Case Report

A case study involving a healthy trained male athlete who completed a 786 km multi-stage ultra-trail race. Several markers were analyzed in blood and urine samples: creatinine (SCR) for kidney damage, sodium ([Na⁺]) for hyponatremia, creatine kinase (CK) for exertional rhabdomyolysis, as well as other hematological values. Samples were taken before and after the race and during the recovery period (days 2 and 9 after the race). Results showed: SCR = 1.13 mg/dl, [Na⁺] =139 mmol/l and CK = 1.099 UI/l. Criteria for the determination of acute kidney damage were not met, and [Na+] concentration was above 135 mEq/L, indicating the absence of hyponatremia. Exertional rhabdomyolysis was suffered by the athlete (baseline CK increased fivefold), though this situation was reverted after 9 days of recovery. Ultra-trail races cause biochemical changes in athletes, which should be known about by healthcare professionals.

Heat Acclimatization, Cooling Strategies, and Hydration during an Ultra-Trail in Warm and Humid Conditions

The aim of this study was to assess the history of exertional heat illness (EHI), heat preparation, cooling strategies, heat related symptoms, and hydration during an ultra-endurance running event in a warm and humid environment. This survey-based study was open to all people who participated in one of the three ultra-endurance races of the Grand Raid de la Réunion. Ambient temperature and relative humidity were 18.6 ± 5.7 °C (max = 29.7 °C) and 74 ± 17%, respectively. A total of 3317 runners (56% of the total eligible population) participated in the study. Overall, 78% of the runners declared a history of heat-related symptoms while training or competing, and 1.9% reported a previous diagnosis of EHI. Only 24.3% of study participants living in temperate climates declared having trained in the heat before the races, and 45.1% of all respondents reported a cooling strategy during the races. Three quarter of all participants declared a hydration strategy. The planned hydration volume was 663 ± 240 mL/h. Fifty-nine percent of the runners had enriched their food or drink with sodium during the race. The present study shows that ultra-endurance runners have a wide variability of hydration and heat preparation strategies. Understandings of heat stress repercussions in ultra-endurance running need to be improved by specific field research.

Nutrition-Related Adverse Outcomes in Endurance Sports Competitions: A Review of Incidence and Practical Recommendations

During the last few years, the numbers of competitors in endurance and ultra-endurance sports modalities have increased significantly. This type of competition is an extreme challenge for athletes. Therefore, they have an increased the risk of developing medical and nutritional problems. The aim of the work is to estimate the incidence of nutrition-related adverse outcomes in endurance and ultra-endurance sports, considering the variables that influence them. A critical review was carried out based on the PubMed database, by means of a search strategy based on keywords separated by Boolean connectors. For all the results obtained in a period from 2008 to 2019, a series of inclusion/exclusion criteria was applied to select only the studies that fitted the objective of the present study. Results and discussion: Of the 871 publications identified, 33 met the inclusion criteria. The adverse outcomes found included exercise-associated hyponatremia (EAH), heat stroke by exertion (EHS), gastrointestinal (GI) problems, dehydration, and hypothermia; the provision of misinformation to athletes about nutrient intake and hydration during competition was identified as the main cause. Conclusions: The main adverse outcomes in endurance and ultra-endurance sports modalities are EAH, GI inconveniences, and EHS. These problems can affect the performance and health status of the athlete during and post-competition. Several nutritional guidelines have been suggested that can prevent these adverse outcomes, and it is essential to individualize and adjust the nutritional intake and hydration status according to the characteristics of each competition.

What are the Limiting Factors During an Ultra-Marathon? A Systematic Review of the Scientific Literature

This review aimed to analyse factors that limited performance in ultra-marathons and mountain ultra-marathons. A literature search in one database (PubMed) was conducted in February 2019. Quality of information of the articles was evaluated using the Oxford´s level of evidence and the Physiotherapy Evidence Database (PEDro) scale. The search strategy yielded 111 total citations from which 23 met the inclusion criteria. Twenty one of the 23 included studies had a level of evidence 2b (individual cohort study), while the 2 remaining studies had a level of evidence of 5 (expert opinion). Also, the mean score in the PEDro scale was 3.65 ± 1.61, with values ranging from 0 to 7. Participants were characterised as experienced or well-trained athletes in all of the studies. The total number of participants was 1002 (893 men, 86 women and 23 unknown). The findings of this review suggest that fatigue in ultra-endurance events is a multifactorial phenomenon that includes physiological, neuromuscular, biomechanical and cognitive factors. Improved exercise performance during ultra-endurance events seems to be related to higher VO_2max values and maximal aerobic speed (especially during submaximal efforts sustained over a long time), lower oxygen cost of transport and greater running experience.

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.

Cardiac Risk of Extreme Exercise

Habitual moderate intensity exercise is a vital component of a healthy lifestyle. For most of the population, increasing exercise duration and intensity beyond current recommendations appears to impart additional cardiovascular benefits; however, recent data has raised the possibility of an inflection point after which additional exercise no longer imparts benefit and may even result in negative cardiovascular outcomes. Exercise at the extremes of human endurance places a large hemodynamic stress on the heart and results in occasionally profound cardiac remodeling in order to accommodate the huge increases in cardiac output demanded by such endeavors. These changes have the potential to become maladaptive and heighten the risk of various arrhythmias, influence the rate of coronary atherosclerosis, and alter the risk of sudden cardiac death. Herein, we will discuss the potential negative impact of extreme exercise on cardiovascular risk.

Nutrition in Ultra-Endurance: State of the Art

Athletes competing in ultra-endurance sports should manage nutritional issues, especially with regards to energy and fluid balance. An ultra-endurance race, considered a duration of at least 6 h, might induce the energy balance (i.e., energy deficit) in levels that could reach up to ~7000 kcal per day. Such a negative energy balance is a major health and performance concern as it leads to a decrease of both fat and skeletal muscle mass in events such as 24-h swimming, 6-day cycling or 17-day running. Sport anemia caused by heavy exercise and gastrointestinal discomfort, under hot or cold environmental conditions also needs to be considered as a major factor for health and performance in ultra-endurance sports. In addition, fluid losses from sweat can reach up to 2 L/h due to increased metabolic work during prolonged exercise and exercise under hot environments that might result in hypohydration. Athletes are at an increased risk for exercise-associated hyponatremia (EAH) and limb swelling when intake of fluids is greater than the volume lost. Optimal pre-race nutritional strategies should aim to increase fat utilization during exercise, and the consumption of fat-rich foods may be considered during the race, as well as carbohydrates, electrolytes, and fluid. Moreover, to reduce the risk of EAH, fluid intake should include sodium in the amounts of 10–25 mmol to reduce the risk of EAH and should be limited to 300–600 mL per hour of the race.

Fluid Metabolism in Athletes Running Seven Marathons in Seven Consecutive Days

Purpose: Hypohydration and hyperhydration are significant disorders of fluid metabolism in endurance performance; however, little relevant data exist regarding multi-stage endurance activities. The aim of the present study was to examine the effect of running seven marathons in 7 consecutive days on selected anthropometric, hematological and biochemical characteristics with an emphasis on hydration status.

Methods: Participants included 6 women and 20 men (age 42.6 ± 6.2 years). Data was collected before day 1 (B₁) and after day 1 (A₁), 4 (A₄), and 7 (A₇).

Results: The average marathon race time was 4:44 h:min (ranging from 3:09 – 6:19 h:min). Plasma sodium, plasma potassium and urine sodium were maintained during the race. Body mass (p < 0.001, η² = 0.501), body fat (p < 0.001, η² = 0.572) and hematocrit (p < 0.001, η² = 0.358) decreased. Plasma osmolality (Posm) (p < 0.001, η² = 0.416), urine osmolality (Uosm) (p < 0.001, η² = 0.465), urine potassium (p < 0.001, η² = 0.507), urine specific gravity (Usg) (p < 0.001, η² = 0.540), plasma urea (PUN) (p < 0.001, η² = 0.586), urine urea (UUN) (p < 0.001, η² = 0.532) and transtubular potassium gradient (p < 0.001, η² = 0.560) increased at A₁, A₄, and A₇ vs. B₁. Posm correlated with PUN at A₁ (r = 0.59, p = 0.001) and A₄ (r = 0.58, p = 0.002). The reported post-race fluid intake was 0.5 ± 0.2 L/h and it correlated negatively with plasma [Na⁺] (r = −0.42, p = 0.007) at A₄ and (r = −0.50, p = 0.009) at A₇. Uosm was associated with UUN at A₁ (r = 0.80, p < 0.001), at A₄ (r = 0.81, p < 0.001) and at A₇ (r = 0.86, p < 0.001) and with Usg (r = 0.71, p < 0.001) at A₁, (r = 0.52, p = 0.006) at A₄ and (r = 0.46, p = 0.02) at A₇.

Conclusions: Despite the decrease in body mass, fluid and electrolyte balance was maintained with no decrease in plasma volume after running seven marathons in seven consecutive days. Current findings support the hypothesis that body mass changes do not reflect changes in the hydration status during prolonged exercise.

Exercise-Associated Hyponatremia: 2017 Update

Exercise-associated hyponatremia (EAH) was initially described in the 1980s in endurance athletes, and work done since then has conclusively identified that overdrinking beyond thirst and non-osmotic arginine vasopressin release are the most common etiologic factors. In recent years, EAH has been described in a broader variety of athletic events and also has been linked to the development of rhabdomyolysis. The potential role of volume and sodium depletion in a subset of athletes has also been described. This review focuses on the most recent literature in the field of EAH and summarizes key new findings in the epidemiology, pathophysiology, treatment, and prevention of this condition.

Exercise-Associated Collapse: Is Hyponatremia in Our Head?

Exercise-associated hyponatremia (EAH) is one of the most common causes of exercise-associated collapse. The primary pathogenesis of EAH is largely the result of excessive fluid intake but is influenced by other factors, including hormonal abnormalities (ie, inappropriate arginine vasopressin secretion), renal abnormalities, and mobilization of sodium stores. Early recognition of EAH is crucial to appropriate treatment, because symptoms are varied and may be confused with other causes of exercise-associated collapse. Onsite testing of [Na+] will confirm the diagnosis but is not always available. Rapid treatment of EAH will depend upon the type and severity of symptoms. Treatment protocols range from fluid restriction or oral hypertonic fluids for mild symptoms to intravenous hypertonic fluids for more severe symptoms. Preventative strategies should emphasize fluid consumption based on thirst and athlete/coach/staff education regarding proper hydration practices.

Medical Clearance for Desert and Land Sports, Adventure, and Endurance Events

Endurance events are increasing in popularity in wilderness and remote settings, and participants face a unique set of potential risks for participation. The purpose of this article is to outline these risks and allow the practitioner to better guide the wilderness adventurer who is anticipating traveling to a remote or desert environment.

Medical Clearance for Desert and Land Sports, Adventure, and Endurance Events

Endurance events are increasing in popularity in wilderness and remote settings, and participants face a unique set of potential risks for participation. The purpose of this article is to outline these risks and allow the practitioner to better guide the wilderness adventurer who is anticipating traveling to a remote or desert environment.

Physiopathological, Epidemiological, Clinical and Therapeutic Aspects of Exercise-Associated Hyponatremia

Exercise-associated hyponatremia (EAH) is dilutional hyponatremia, a variant of inappropriate antidiuretic hormone secretion (SIADH), characterized by a plasma concentration of sodium lower than 135 mEq/L. The prevalence of EAH is common in endurance (<6 hours) and ultra-endurance events (>6 hours in duration), in which both athletes and medical providers need to be aware of risk factors, symptom presentation, and management. The development of EAH is a combination of excessive water intake, inadequate suppression of the secretion of the antidiuretic hormone (ADH) (due to non osmotic stimuli), long race duration, and very high or very low ambient temperatures. Additional risk factors include female gender, slower race times, and use of nonsteroidal anti-inflammatory drugs. Signs and symptoms of EAH include nausea, vomiting, confusion, headache and seizures; it may result in severe clinical conditions associated with pulmonary and cerebral edema, respiratory failure and death. A rapid diagnosis and appropriate treatment with a hypertonic saline solution is essential in the severe form to ensure a positive outcome.

Evaluation and treatment of injury and illness in the ultramarathon athlete

Participation in ultramarathon races and knowledge of these athletes continues to increase as the sport becomes more popular. Physicians and athletes need to better understand the impact of the unique aspects of ultramarathon races, such as race environment (temperature, humidity, and altitude), race distance, race stages, nutritional requirements and equipment, on athlete injuries and illness. Proper treatment of injuries and illnesses during an ultramarathon race is important for avoiding long-term medical issues. In this article, the evaluation and treatment of common musculoskeletal injuries and medical illnesses in ultramarathon runners are reviewed.

Changes in foot volume, body composition, and hydration status in male and female 24-hour ultra-mountain bikers

BACKGROUND

The effects of running and cycling on changes in hydration status and body composition during a 24-hour race have been described previously, but data for 24-hour ultra-mountain bikers are missing. The present study investigated changes in foot volume, body composition, and hydration status in male and female 24-hour ultra-mountain bikers.

METHODS

We compared in 49 (37 men and 12 women) 24-hour ultra-mountain bikers (ultra-MTBers) changes (Δ) in body mass (BM). Fat mass (FM), percent body fat (%BF) and skeletal muscle mass (SM) were estimated using anthropometric methods. Changes in total body water (TBW), extracellular fluid (ECF) and intracellular fluid (ICF) were determined using bioelectrical impedance and changes in foot volume using plethysmography. Haematocrit, plasma [Na+], plasma urea, plasma osmolality, urine urea, urine specific gravity and urine osmolality were measured in a subgroup of 25 ultra-MTBers (16 men and 9 women).

RESULTS

In male 24-hour ultra-MTBers, BM (P < 0.001), FM (P < 0.001), %BF (P < 0.001) and ECF (P < 0.05) decreased whereas SM and TBW did not change (P > 0.05). A significant correlation was found between post-race BM and post-race FM (r = 0.63, P < 0.001). In female ultra-MTBers, BM (P < 0.05), %BF (P < 0.05) and FM (P < 0.001) decreased, whereas SM, ECF and TBW remained stable (P > 0.05). Absolute ranking in the race was related to Δ%BM (P < 0.001) and Δ%FM in men (P < 0.001) and to Δ%BM (P < 0.05) in women. In male ultra-MTBers, increased post-race plasma urea (P < 0.001) was negatively related to absolute ranking in the race, Δ%BM, post-race FM and Δ%ECF (P < 0.05). Foot volume remained stable in both sexes (P > 0.05).

CONCLUSIONS

Male and female 24-hour ultra-MTBers experienced a significant loss in BM and FM, whereas SM remained stable. Body weight changes and increases in plasma urea do not reflect a change in body hydration status. No oedema of the lower limbs occurred.

Electrolyte disorders and in-hospital mortality during prolonged heat periods: a cross-sectional analysis

Background

Heat periods during recent years were associated with excess hospitalization and mortality rates, especially in the elderly. We intended to study whether prolonged warmth/heat periods are associated with an increased prevalence of disorders of serum sodium and potassium and an increased hospital mortality.

Methods

In this cross-sectional analysis all patients admitted to the Department of Emergency Medicine of a large tertiary care facility between January 2009 and December 2010 with measurements of serum sodium were included. Demographic data along with detailed data on diuretic medication, length of hospital stay and hospital mortality were obtained for all patients. Data on daily temperatures (maximum, mean, minimum) and humidity were retrieved by Meteo Swiss.

Results

A total of 22.239 patients were included in the study. 5 periods with a temperature exceeding 25°C for 3 to 5 days were noticed and 2 periods with temperatures exceeding 25°C for more than 5 days were noted. Additionally, 2 periods with 3 to 5 days with daily temperatures exceeding 30°C were noted during the study period. We found a significantly increased prevalence of hyponatremia during heat periods. However, in the Cox regression analysis, prolonged heat was not associated with the prevalence of disorders of serum sodium or potassium. Admission during a heat period was an independent predictor for hospital mortality.

Conclusions

Although we found an increased prevalence of hyponatremia during heat periods, no convincing connection could be found for hypernatremia or disorders of serum potassium.

The prevalence of exercise-associated hyponatremia in 24-hour ultra-mountain bikers, 24-hour ultra-runners and multi-stage ultra-mountain bikers in the Czech Republic

BACKGROUND

To assess the prevalence of exercise-associated hyponatremia (EAH) in two 24-hour mountain bike (MTB) (R1,R2), one 24-hour running (R3) and one multi-stage MTB (R4) races held in the Czech Republic in a cluster of four cross-sectional studies.

METHODS

In 27 ultra-mountain bikers (ultra-MTBers), 12 ultra-runners, and 14 multi-stage MTBers, fluid intake, changes (Δ) in body mass, hematocrit, plasma volume, plasma [Na+], plasma [K+], plasma osmolality, urine [Na+], urine [K+], urine specific gravity, urine osmolality, K+/Na+ ratio in urine, transtubular potassium gradient and glomerular filtration rate were measured and calculated. The use of non-steroidal anti-inflammatory drugs and symptoms of EAH were recorded using post-race questionnaires.

RESULTS

Of the 53 finishers, three (5.7%) developed post-race EAH, thereof one (3.7%) ultra-MTBer, one (8.3%) ultra-runner and one (7.1%) multi-stage MTBer. Plasma [Na+] decreased significantly (p < 0.001) only in R4. Urine osmolality (R1, R3, R4 p < 0.001; R2 p < 0.05) and glomerular filtration rate (p < 0.001) increased, and body mass decreased in all races (p < 0.05). Δ body mass was inversely related to the number of kilometers achieved (p < 0.001) in R2 where better ultra-MTBers tended to lose more weight. Δ body mass (p < 0.001) and %Δ body mass (p = 0.05) were positively related to lower post-race plasma [Na+] in R3 that was associated with increased loss in body mass. Fluid intake was positively related to race performance in R1 and R2 (R1: p = 0.04; R2: p = 0.01) where ultra-MTBers in R1 and R2 who drank more finished ahead of those who drank less. Post-race plasma [Na+] was negatively associated with race performance in ultra-MTBers in R2 (p < 0.05), similarly ultra-runners in R3 (p < 0.05) where finishers with more kilometres had lower post-race plasma [Na+].

CONCLUSIONS

The prevalence of EAH in the Czech Republic was no higher compared to existing reports on ultra-endurance athletes in other countries. Lower plasma [Na+] and development of EAH may be attributed to overdrinking, a pituitary secretion of vasopressin, an impaired mobilization of osmotically inactive sodium stores, and/or an inappropriate inactivation of osmotically active sodium.

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.

The effect of physiology and hydration beliefs on race behavior and postrace sodium in 161-km ultramarathon finishers

PURPOSE

To determine if beliefs about physiology and rehydration affect ultramarathon runners' hydration behaviors or if these beliefs increase the risk for exercise-associated hyponatremia (EAH).

METHODS

Participants of the 2011 161-km Western States Endurance Run completed a prerace questionnaire, prerace and postrace body-mass measurements, and postrace assessment of serum sodium ([Na⁺]).

RESULTS

Of 310 finishers, 309 (99.7%) completed the prerace questionnaire and 207 (67%) underwent postrace blood studies. Twelve (5.8%) finishers had asymptomatic EAH ([Na⁺] range 131-134 mmol/L). The most common hydration plan (43.1%) was drinking according to schedule, and these runners did so to replace fluid lost when sweating (100%) and to avoid dehydration (81.2%). Prerace drinking plan was not associated with postrace [Na⁺] or the development of postrace hyponatremia. There also were no group differences between those with and those without EAH for any other variables including planned energy intake or knowledge of fluid balance. Runners not planning to drink to thirst trended toward more influence from advertisements (P = .056) and were significantly more influenced by scientific organizations (P = .043) than runners with other drinking plans. Finally, runners who believe that EAH is caused by excessive drinking adopted a lower-volume drinking plan (P = .005), while runners who believe that EAH is caused by sodium loss via sweating reported more common use of sodium supplementation during the race (P = .017).

CONCLUSIONS

Beliefs regarding the causes of EAH alter race behaviors including drinking plan and sodium supplementation but do not appear to affect the likelihood of developing EAH during a 161-km ultramarathon.

Hyponatremia is associated with higher NT-proBNP than normonatremia after prolonged exercise

OBJECTIVE

To determine the incidence of and risk factors for exercise-associated hyponatremia (EAH) in cyclists completing a long-distance bike ride and to assess whether postexercise serum NT-proBNP concentration (brain natriuretic protein precursor) differed between riders with and without EAH.

DESIGN

Observational study.

SETTING

"Around the Bay in a Day" cycle event, October 2010.

PARTICIPANTS

One hundred thirty-nine cyclists prospectively enrolled, with 90 completing 210 or 250 km.

MAIN OUTCOME MEASURES

Body weight change and fluid intake during the event, and postevent serum sodium concentration ([Na+]) and NT-proBNP concentration ([NT-proBNP]).

RESULTS

Four riders (4.5%) were hyponatremic ([Na+] < 135 mmol/L). The lowest postride [Na+] was 126 mmol/L. Hyponatremia was associated with a mean weight gain of 3.4 kg (3.9% of total body weight). Significant negative correlations were found between postride [Na+] and change in weight (r = -0.34; P < 0.01) and fluid intake when expressed as total volume (r = -0.35; P < 0.01), mL/kg body weight (r = 0.33; P < 0.01), mL·kg·h (r = -0.27; P < 0.01), or mL/h (r = -0.29; P < 0.01). NT-proBNP concentrations levels in 3 of the 4 hyponatremic subjects were markedly elevated compared with eunatremic subjects matched for age, sex, distance ridden, training, and medical history.

CONCLUSIONS

Exercise-associated hyponatremia was found to occur in 4.5% of the study group and was associated with weight gain during a prolonged bike ride. Postride [Na+] varied inversely with weight change and with fluid intake. Three of 4 hyponatremic riders had significant elevations of [NT-proBNP]. These results support the hypothesis that overconsumption of hypotonic fluids in this setting is the most important cause of EAH.

Hydration strategies of runners in the London Marathon

OBJECTIVE

To explore the hydration strategies of marathon runners, their sources of information and knowledge about fluid intake in the marathon, and their understanding of exercise-associated hyponatremia (EAH).

DESIGN

Anonymized questionnaire.

SETTING

London Marathon.

PARTICIPANTS

Marathon race participants.

MAIN OUTCOME MEASURES

Responses regarding planned fluid consumption, volume to be consumed, volume of water and sports drink bottles, and the number of stations from which planning to take a drink. In addition, sources of information about appropriate drinking and understanding of hyponatremia.

RESULTS

In total, 93.1% of the runners had read or been told about drinking fluids on marathon day and 95.8% of competitors had a plan regarding fluid intake. However, 12% planned to drink a volume large enough to put them at higher risk of EAH. Only 21.7% knew the volumes of water and sports drink bottles available on the course; 20.7% were planning to take a drink from all 24 water stations. Only 25.3% planned to drink according to thirst. Although 68.0% of the runners had heard of hyponatremia or low sodium levels, only 35.5% had a basic understanding of its cause and effects.

CONCLUSIONS

Marathon runners lack knowledge about appropriate fluid intake to prevent hyponatremia on race day. Twelve percent reported drinking strategies that put them at risk of EAH. Effective educational interventions are still necessary to prevent overdrinking during marathons.

Physiologic alterations and predictors of performance in a 160-km ultramarathon

OBJECTIVE

To describe physiologic alterations in runners competing in a 160-km endurance event and to evaluate the utility of weight and blood pressure measurements in the assessment of runner performance.

DESIGN

Prospective cohort study.

SETTING

One hundred sixty-km ultramarathon.

PARTICIPANTS

Ninety-one of the 101 participants in the 2010 Tahoe Rim 100 Mile Endurance Run.

ASSESSMENT OF RISK FACTORS

Brachial blood pressure, heart rate, and weight were assessed before competition, at 80 km, and at 160 km.

MAIN OUTCOME MEASURES

Alterations in brachial blood pressure, heart rate, and weight were assessed in finishers. Weight loss, brachial blood pressure, pulse pressure, and heart rate at 80 km were assessed in all participants for their ability to predict failure to finish the race.

RESULTS

Participants who finished 160 km (57%) experienced their fastest heart rates (P < 0.05), lowest systolic pressures (P < 0.05), highest diastolic pressures (P < 0.05), narrowest pulse pressures (P < 0.05), and lowest weights (P < 0.05) at 80 km. High rates of finishing were seen in those who lost >5% of their prerace weight (87%). Categorical weight loss (<3%, 3%-5%, and >5%) was not associated with the ability to finish (P > 0.05) or finishing time (P > 0.05), whereas the presence of a narrow pulse pressure was associated with a high likelihood (likelihood ratio = 9.84; P = 0.002) of failure to finish.

CONCLUSIONS

Greater intracompetition weight loss is not associated with impaired performance but rather may be an aspect of superior performance. Narrow pulse pressure was associated with a high likelihood of failure to finish.

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.