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Oral Salt Supplementation During Ultradistance Exercise
Abstract
The objective of this study was to determine whether sodium supplementation 1) influences changes in body weight, serum sodium [Na], and plasma volume (PV), and 2) prevents hyponatremia in Ironman triathletes.
The study was carried out at the South African Ironman triathlon.
Thirty-eight athletes competing in the triathlon were given salt tablets to ingest during the race. Data collected from these athletes [salt intake group (SI)] were compared with data from athletes not given salt [no salt group (NS)].
Salt tablets were given to the SI group to provide approximately 700 mg/h of sodium.
Serum sodium, hemoglobin, and hematocrit were measured at race registration and after the race. Weights were measured before and after the race. Members of SI were retrospectively matched to subjects in NS for 1) weight change and 2) pre-race [Na].
The SI group developed a 3.3-kg weight loss (p < 0.0001) and significantly increased their [Na] (delta[Na] 1.52 mmol/L; p = 0.005). When matched for weight change during the race, SI increased their [Na] compared with NS (mean 1.52 versus 0.04 mmol/L), but this did not reach statistical significance (p = 0.08). When matched for pre-race [Na], SI had a significantly smaller percent body weight loss than NS (-4.3% versus -5.1%; p = 0.04). There was no significant difference in the increase of [Na] in both groups (1.57 versus 0.84 mmol/L). PV increased equally in both groups. None of the subjects finished the race with [Na] < 135 mmol/L.
Sodium ingestion was associated with a decrease in the extent of weight loss during the race. There was no evidence that sodium ingestion significantly influenced changes in [Na] or PV more than fluid replacement alone in the Ironman triathletes in this study. Sodium supplementation was not necessary to prevent the development of hyponatremia in these athletes who lost weight, indicating that they had only partially replaced their fluid and other losses during the Ironman triathlon.
... To our knowledge, only three investigations have determined the effectiveness of salt or sodium supplementation during field endurance protocols (Speedy et al., 2002; Hew-Butler et al., 2006; Cosgrove & Black, 2013). These investigations included ad libitum fluid intake regimes instead of matching fluid and sweat volumes. ...
... Several investigations have been devoted to determining the effects of salt ingestion on endurance performance (Vrijens & Rehrer, 1999; Sanders et al., 2001; Speedy et al., 2002; Twerenbold et al., 2003; Hew-Butler et al., 2006; Coso et al., 2008; Anastasiou et al., 2009; Cosgrove & Black, 2013). Briefly, most laboratorybased investigations have found benefits of salt supplementation during endurance activities such as improved physical performance, attenuated decrease of serum sodium concentration and expanded plasma volume. ...
... However, laboratory investigations have always accompanied the salt supplementation during exercise with a fluid ingestion regime that matched sweat losses, which probably facilitated the occurrence of these benefits. Field investigations regarding the effects of salt supplementation during endurance events (Speedy et al., 2002; Hew-Butler et al., 2006; Cosgrove & Black, 2013) have increased the applicability of the experimental setting by using ad libitum fluid intake regimes, as is the case during real competitions. ...
The aim of this study was to investigate the effectiveness of oral salt supplementation to improve exercise performance during a half-ironman triathlon. Twenty-six experienced triathletes were matched for age, anthropometric data, and training status, and randomly placed into the salt group (113 mmol Na(+) and 112 mmol Cl(-) ) or the control group (cellulose). The experimental treatments were ingested before and during a real half-ironman triathlon competition. Pre- and post-race body mass, maximal force during a whole-body isometric strength test, maximal height during a countermovement jump, were measured, and blood samples were obtained. Sweat samples were obtained during the running section. Total race time was lower in the salt group than in the control group (P = 0.04). After the race, whole-body isometric strength (P = 0.17) and jump height (P = 0.49) were similarly reduced in both groups. Sweat loss (P = 0.98) and sweat Na(+) concentration (P = 0.72) were similar between groups. However, body mass tended to be less reduced in the salt group than in the control group (P = 0.09) while post-race serum Na(+) (P = 0.03) and Cl(-) (P = 0.03) concentrations were higher in the salt group than in the control group. Oral salt supplementation was effective to lessen body mass loss and increase serum electrolyte concentration during a real half-ironman.
© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.
... This disagrees with some laboratory controlled studies [4,5], and the research on pre-exercise sodium loading protocols [20,21] which have shown that volumes of sodium similar to the amounts ingested in this study improve performance. However, the results of this study are consistent with the more recent research using a time-trial or racing situation to assess performance in the field [6,10,11]. The time-trial exercise prescription used in this study was of a similar duration to marathons, triathlons, and many cycling road races; events with reported cases of hyponatremia and targeted guidelines for sodium and fluid intakes [9]. ...
... Two studies have investigated sodium supplementation during ironman races [10,11] both reported no performance differences between those taking sodium supplements and those without sodium during ironman triathlons. However, the controls on the sodium intake of the control group were minimal and the design of the study meant that the numerous factors other than sodium which are known to influence performance were not controlled i.e. training load, carbohydrate intake, genetic physiology. ...
... Cyclists were given a coded, clear zip-lock bag each containing 15 clear capsules with either 233 mg sodium chloride, or an identical corn flour placebo. Participants were instructed to consume three capsules for every hour, which equated to 700 mg NaCl.h-1, consistent with doses used in previous trials [2,11], and recommended by Zapf et al. [16]. Water and ‘Jet Plane’ lollies (Pascall, Auckland, New Zealand) could be consumed ad libitum during the trial but the weights consumed were recorded to the nearest 0.1 g (Salter Vista Electronic Scales, England). ...
Background
Sodium ingestion during exercise may exert beneficial effects on endurance performance by either its ability to attenuate the decrease in plasma volume or reduce the risk of Exercise Associated Hyponatremia (EAH). This study aimed to investigate the effect of sodium supplements on endurance performance during a 72 km road cycling time-trial in cool conditions (13.8 ± 2.0°C).
Methods
Nine well-trained cyclists (5 male, 4 female) participated in this randomized, double-blinded cross-over study, receiving either a 700 mg.h-1 salt capsule, or a corn flour placebo during the time trial. Water was ingested ad-libitum throughout the time trial. Measurements were taken pre, post, and 40 min following time-trials, analysing blood, sweat, and urinary hydration and sodium concentration.
Results
Sodium supplements had no effect on time-trial performance (overall time = 171 min sodium vs. 172 min placebo; p = 0.46). There was also no effect on the change in plasma sodium concentration from pre to post time trial between trials (relative plasma [Na+] change (pre-post): sodium = 0.56%, placebo = 0.47%; p = 0.60). The greatest difference observed was a significantly change in plasma volume from pre to post exercise between the salt and the placebo trial (p = 0.02), which corresponded with an increased thirst with sodium supplementation.
Conclusion
Sodium supplements therefore do not improving performance during exercise of approximately 3 h duration in cool conditions.
... It has however recently been proposed that sodium supplementation in fluids is not required during endurance exercise in the heat, since sodium losses (e.g. sweat, urine, and faeces) appear to be attenuated during periods of sodium restriction or deprivation [14,22,23]. However, a comprehensive assessment of sodium ingestion and status of ultra-runners during MSUM conducted in a hot ambient environment has not previously been conducted to confirm appropriate sodium ingestion advice to this population. ...
... These results are in accordance with previous studies suggesting that sodium supplementation may not be required during exercise in certain UER, since adaptations to increase sodium bioavailability and prevent losses (e.g. sweat, urine, and faeces) take place in response to periods of sodium deprivation or restriction [14,23,24]. ...
Abstract Background Anecdotal evidence suggests ultra-runners may not be consuming sufficient water through foods and fluids to maintenance euhydration, and present sub-optimal sodium intakes, throughout multi-stage ultra-marathon (MSUM) competitions in the heat. Subsequently, the aims were primarily to assess water and sodium intake habits of recreational ultra-runners during a five stage 225 km semi self-sufficient MSUM conducted in a hot ambient environment (Tmax range: 32°C to 40°C); simultaneously to monitor serum sodium concentration, and hydration status using multiple hydration assessment techniques. Methods Total daily, pre-stage, during running, and post-stage water and sodium ingestion of ultra-endurance runners (UER, n = 74) and control (CON, n = 12) through foods and fluids were recorded on Stages 1 to 4 by trained dietetic researchers using dietary recall interview technique, and analysed through dietary analysis software. Body mass (BM), hydration status, and serum sodium concentration were determined pre- and post-Stages 1 to 5. Results Water (overall mean (SD): total daily 7.7 (1.5) L/day, during running 732 (183) ml/h) and sodium (total daily 3.9 (1.3) g/day, during running 270 (151) mg/L) ingestion did not differ between stages in UER (p
... In the sport section, sodium helps to maintain serum electrolyte concentrations resulting in a balance of intravascular osmotic pressure and plasma volume [18]. It increases the thirst stimulus and reduces the amount of urine produced [19], effects that ultimately reduce physical fatigue and medical problems associated with these homeostatic imbalances in endurance sports [20]. However, attention should be paid to excess sodium, which contributes to high blood pressure and damage to certain organs such as the heart, kidneys and bones [21]. ...
The majority of reviews on sports nutrition issues focus on macronutrients, often omitting or paying less attention to substances such as sodium. Through the literature, it is clear that there are no reviews that focus entirely on the effects of sodium and in particular on endurance sports. Sodium intake, both at high and low doses, has been found to be associated with health and performance issues in athletes. Besides, there have been theories that an electrolyte imbalance, specifically sodium, contributes to the development of muscle cramps (EAMC) and hyponatremia (EAH). For this reason, it is necessary to create this systematic review, in order to report extensively on the role of sodium consumption in the population and more specifically in endurance and ultra-endurance athletes, the relationship between the amount consumed and the occurrence of pathological disorders, the usefulness of simultaneous hydration and whether a disturbance of this substance leads to EAH and EAMC. As a method of data collection, this study focused on exploring literature from 2000–2021. The search was conducted through the research engines PubMed and Scopus. In order to reduce the health and performance effects in endurance athletes, simultaneous emphasis should be placed on both sodium and fluid intake.
... Therefore, sodium consumption did not prevent EHN from occurring in cyclists LC and AM, and low sodium intake by other cyclists was not associated with EHN. Similar conclusions have been published regarding ultramarathon competitors by Speedy et al. [85], Hew-Butler et al. [86], Hoffman and Stuempfle [80], and Hoffman and Myers [87]. ...
During endurance exercise, two problems arise from disturbed fluid–electrolyte balance: dehydration and overhydration. The former involves water and sodium losses in sweat and urine that are incompletely replaced, whereas the latter involves excessive consumption and retention of dilute fluids. When experienced at low levels, both dehydration and overhydration have minor or no performance effects and symptoms of illness, but when experienced at moderate-to-severe levels they degrade exercise performance and/or may lead to hydration-related illnesses including hyponatremia (low serum sodium concentration). Therefore, the present review article presents (a) relevant research observations and consensus statements of professional organizations, (b) 5 rehydration methods in which pre-race planning ranges from no advanced action to determination of sweat rate during a field simulation, and (c) 9 rehydration recommendations that are relevant to endurance activities. With this information, each athlete can select the rehydration method that best allows her/him to achieve a hydration middle ground between dehydration and overhydration, to optimize physical performance, and reduce the risk of illness.
... It is important to replace fluid deficits after a preceding bout of activity since it is accepted that any deficit incurred prior to the next bout of exercise could lead to impairment in endurance performance [49,50]. In the present study, no differences in endurance performance were found among the test drinks which is consistent with the studies conducted in field settings where the efficacy of sodium supplementation was evaluated [51,52]. It is noteworthy that a standardised breakfast was provided in the present investigation, to ensure that the participants did not commence the trials with any caloric deficit from overnight fasting. ...
This study investigated the efficacy of ingesting an oral rehydration solution (DD) that has a high electrolyte concentration after exercise on fluid balance and cycling performance in comparison with a sports drink (SD) and water (WA). Nine healthy males aged 24 ± 2 years (mean ± SD), with peak oxygen uptake (VO2 peak) 55 ± 6 mL·kg−1·min−1 completed three experimental trials in a randomised manner ingesting WA, SD (carbohydrates: 62 g·L−1, sodium: 31 ± 3 mmol·L−1) or DD (carbohydrates: 33 g·L−1, sodium: 60 ± 3 mmol·L−1). On all trials, fluid was ingested during 75 min cycling at 65% VO2 peak (temperature: 30.4 ± 0.3 °C, relative humidity: 76 ± 1%, simulated wind speed: 8.0 ± 0.6 m·s−1) and during 2 h of recovery (temperature: 23.0 ± 1.0 °C, relative humidity: 67 ± 2%), with the total volume equivalent to 150% of sweat loss during the ride. A 45 min pre-load cycling time trial at a 65% VO2 peak followed by a 20 km time trial was conducted after a further 3 h of recovery. Fluid retention was higher with DD (30 ± 15%) than WA (−4 ± 19%; p < 0.001) and SD (10 ± 15%; p = 0.002). Mean ratings of palatability were similar among drinks (WA: 4.25 ± 2.60; SD: 5.61 ± 1.79; DD: 5.40 ± 1.58; p = 0.33). Although time trial performance was similar across all three trials (WA: 2365 ± 321 s; SD: 2252 ± 174 s; DD: 2268 ± 184 s; p = 0.65), the completion time was faster in eight participants with SD and seven participants with DD than with WA. Comparing SD with DD, completion time was reduced in five participants and increased in four participants. DD was more effective at restoring the fluid deficit during recovery from exercise than SD and WA without compromising the drink’s palatability with increased sodium concentration. Most individuals demonstrated better endurance exercise time trial performance with DD and SD than with WA.
... Dehydration causes fatigue due to hyperthermia, lowers the uptake of FFAs in turn results in overutilisation of muscle glycogen (Gonz alez-Alonso et al. 1999). As some of the studies have found that sodium supplementation beyond that is present in the food, tend to have an adverse effect and no added benefits to the hydration (Speedy et al. 2002, Luks et al. 2007). The best way that is recommended to maintain hydration is to 'drink to thirst' without using sodium supplementation beyond that taken in food and fluids even when exercising in high ambient temperatures (Hoffman & Stuempfle 2014). ...
Endurance refers to the ability of skeletal muscles to perform continuously withstanding the hardships of exercise. Endurance exercises have three phases: pre-, during-, and post-workout phase. The nutritional requirements that drive these phases vary on intensity, type of workout, individual’s body composition, training, weather conditions, etc. Generally, the pre-workout phase requires glycogen synthesis and spare glycogen breakdown. While workout phase, requires rapid absorption of exogenous glucose, insulin release to transport glucose into muscle cells, replenish the loss of electrolytes, promote fluid retention, etc. However, post-workout phase requires quick amino acid absorption, muscle protein synthesis, repair of damaged muscle fibres and tendon, ameliorate inflammation, oxidative stress, etc. Therefore, nutritional sources that can help these metabolic requirements is recommended. In this review, various dietary interventions including timing and amount of nutrient consumption that can promote the above metabolic requirements that in turn support in improving the endurance potential in athletes are discussed.
• HIGHLIGHTS
• Review article describes nutritional requirements of endurance exercises.
• It also describes nutritional interventions to enhance the endurance potential in athletes.
... This supports the findings of several studies that found that sodium supplementation was not required to maintain [Na + ] during endurance events. 22,26,31 We found the prevalence of postrace hyponatremia during this race to be surprisingly low, which may reflect the more temperate conditions (0-28°C at nearby locations, mean 24.5°C) during the 2011 event when compared with usual temperatures at this race. 8 Compared with previous studies completed at this event 6,8 and a nearby 161-km mountain-trail race, 7 the low prevalence of EAH (5.8%) was unusual and likely increased the difficulty of establishing the relationships that this study investigated. ...
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.
... However, the effectiveness of sodium supplementation for prevention of EAH is more controversial. Prior work suggests that serum sodium concentrations are not affected by sodium supplementation during exercise (Hew-Butler et al., 2006;Speedy et al., 2002;Winger et al., 2013). It has also been demonstrated that sodium supplementation is not necessary during exercise up to 30 hr in hot conditions . ...
Symptomatic exercise-associated hyponatremia (EAH) is known to be a potential complication from over hydration during exercise, but there remains a general belief that sodium supplementation will prevent EAH. We present a case in which a runner with prior history of EAH consulted a sports nutritionist who advised him to consume considerable supplemental sodium which did not prevent him from developing symptomatic EAH during a subsequent long run. Emergency medical services were requested for this runner shortly after he finished a 17-hour, 72-km run and hike in Grand Canyon National Park during which he reported having consumed 9.2-10.6Lof water and >6500mg of sodium. First responders determined his serum sodium concentration with point-of-care testingwas122 mEq/L. His hyponatremia was documented to have improved from field treatment with an oral hypertonic solution of 800 mg of sodium in 200 ml of water, and improved further after significant aquaresis despite in hospital treatment with isotonic fluids (lactated Ringer's). He was discharged about 5 hours after admission in good condition. This case demonstrates that while oral sodium supplementation does not necessarily prevent symptomatic EAH associated with over hydration, early recognition and field management with oral hypertonic saline in combination with fluid restriction can be effective treatment for mild EAH. There continues to be a lack of universal understanding of the underlying pathophysiology and appropriate hospital management of EAH.
... One could even theorize that the sodium supplementation, due to transient hyperosmolality, contribut- ed to the overhydration and subsequent hyponatremia by increasing thirst drive in the present runner. Regardless, the presence of hyponatremia in this runner, despite sodium supplementation, supports previous work suggesting that sodium supplementation during exercise does not affect post-race blood sodium concentration [33,34,35], and does not prevent hyponatremia when the athlete is overhydrating [36]. ...
Background:
Proper acute management of exercise-associated hyponatremia (EAH) has been known for decades, yet this information has not been uniformly implemented. Since treatment of EAH with isotonic fluids can result in delayed recovery and death, it is important that proper acute management in the field and hospital be utilized.
Case report:
We describe a participant of the 161-km Western States Endurance Run (WSER) who presented with seizure after dropping out at 145 km. He had gained 2.2% of his initial weight by 126 km from using sodium supplements and drinking copious volumes of fluids. He was treated promptly in the field for presumed EAH with two intravenous boluses of 100 mL of 3% hypertonic saline and showed rapid improvement in neurologic status. His recovery was then delayed with the use of high volumes of intravenous isotonic fluids, apparently for concern over his mild exertional rhabdomyolysis.
Conclusions:
Symptomatic EAH should be acutely managed with hypertonic saline, whereas treatment with high volumes of isotonic fluids may delay recovery and has even resulted in deaths from cerebral edema. Concern over central pontine myelinolysis from rapid correction of hyponatremia in EAH is unsupported. Furthermore, the exertional rhabdomyolysis often associated with EAH, and the concern over progression to acute kidney failure, should not dictate initial treatment.
... This supports the findings of several studies that found that sodium supplementation was not required to maintain [Na + ] during endurance events. 22,26,31 We found the prevalence of postrace hyponatremia during this race to be surprisingly low, which may reflect the more temperate conditions (0-28°C at nearby locations, mean 24.5°C) during the 2011 event when compared with usual temperatures at this race. 8 Compared with previous studies completed at this event 6,8 and a nearby 161-km mountain-trail race, 7 the low prevalence of EAH (5.8%) was unusual and likely increased the difficulty of establishing the relationships that this study investigated. ...
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.
... Regarding the ‘Position Statement’ of the ‘International Marathon Medical Directors Association’ [43] which recommends drinking ad libitium between 0.4 and 0.8 L/h during a race the present Ironman triathletes behaved correctly by drinking only in response to their thirst. Like in the reports of Hew-Butler et al.[44], Speedy et al.[45], and Noakes [46] describing no correlation between sodium intake, post-race serum [Na+ and the change in serum [Na+, we also found no correlation between these parameters and therefore can confirm their findings. Kavouras [47] and Shireffs [48] described that in case of dehydration body mass decreases while urine specific gravity increases. ...
An association between fluid intake and limb swelling has been described for 100-km ultra-marathoners. We investigated a potential development of peripheral oedemata in Ironman triathletes competing over 3.8 km swimming, 180 km cycling and 42.2 km running.
In 15 male Ironman triathletes, fluid intake, changes in body mass, fat mass, skeletal muscle mass, limb volumes and skinfold thickness were measured. Changes in renal function, parameters of skeletal muscle damage, hematologic parameters and osmolality in both serum and urine were determined. Skinfold thicknesses at hands and feet were measured using LIPOMETER® and changes of limb volumes were measured using plethysmography.
The athletes consumed a total of 8.6 ± 4.4 L of fluids, equal to 0.79 ± 0.43 L/h. Body mass, skeletal muscle mass and the volume of the lower leg decreased (p <0.05), fat mass, skinfold thicknesses and the volume of the arm remained unchanged (p >0.05). The decrease in skeletal muscle mass was associated with the decrease in body mass (p <0.05). The decrease in the lower leg volume was unrelated to fluid intake (p >0.05). Haemoglobin, haematocrit and serum sodium remained unchanged (p >0.05). Osmolality in serum and urine increased (p <0.05). The change in body mass was related to post-race serum sodium concentration ([Na+]) (r = −0.52, p <0.05) and post-race serum osmolality (r = −0.60, p <0.05).
In these Ironman triathletes, ad libitum fluid intake maintained plasma [Na+] and plasma osmolality and led to no peripheral oedemata. The volume of the lower leg decreased and the decrease was unrelated to fluid intake. Future studies may investigate ultra-triathletes competing in a Triple Iron triathlon over 11.4 km swimming, 540 km cycling and 126.6 km running to find an association between fluid intake and the development of peripheral oedemata.
... For example,Hiller et al. (1987)showed that 27% (17/64) of studied athletes requiring medical care in the 1982-1985 Hawaii Ironman triathlons were hyponatremic following the race. Initial attempts to lower the occurrence of hyponatremia were to supplement with sodium tablets during the race, but these studies showed no effect of salt supplementation (Speedy et al., 2002;Hew-Butler et al., 2006). While fluid overload appears to be the main cause of hyponatremia (Speedy et al., 1997Speedy et al., , 2001Noakes, 2010), it can still occur when athletes lose body mass. ...
Laursen PB. Long distance triathlon: demands, preparation and performance. J. Hum. Sport Exerc. Vol. 6, No. 2, pp. 247-263, 2011. The rise in worldwide popularity of long distance triathlon racing comes with it an increased interest into how to train and prepare optimally for such an event. This paper examines the physiologic and bioenergetic demands of long distance triathlon racing, including energy requirements, muscle damage consequences, thermoregulatory demands and water turnover rates. In response to these physiological challenges, the second part of the paper describes the training goals and race practices that may assist to minimize these disturbances, in turn, optimizing performance and health for the long distance triathlete. Some of these race strategies include appropriate pacing, ensuring adequate fluid and carbohydrate consumption, acclimating to the heat, and consuming caffeine in appropriate quantities.
Exercise-associated hyponatremia (EAH) was first described as water intoxication by Noakes et al. in 1985 and has become an important topic linked to several pathological conditions. However, despite progressive research, neurological disorders and even deaths due to hyponatremic encephalopathy continue to occur. Therefore, and due to the growing popularity of exercise-associated hyponatremia, this topic is of great importance for marathon runners and all professionals involved in runners’ training (e.g., coaches, medical staff, nutritionists, and trainers). The present narrative review sought to evaluate the prevalence of EAH among marathon runners and to identify associated etiological and risk factors. Furthermore, the aim was to derive preventive and therapeutic action plans for marathon runners based on current evidence. The search was conducted on PubMed, Scopus and Google Scholar using a predefined search algorithm by aggregating multiple terms (marathon run; exercise; sport; EAH; electrolyte disorder; fluid balance; dehydration; sodium concentration; hyponatremia). By this criterion, 135 articles were considered for the present study. Our results revealed that a complex interaction of different factors could cause EAH, which can be differentiated into event-related (high temperatures) and person-related (female sex) risk factors. There is variation in the reported prevalence of EAH, and two major studies indicated an incidence ranging from 7 to 15% for symptomatic and asymptomatic EAH. Athletes and coaches must be aware of EAH and its related problems and take appropriate measures for both training and competition. Coaches need to educate their athletes about the early symptoms of EAH to intervene at the earliest possible stage. In addition, individual hydration strategies need to be developed for the daily training routine, ideally in regard to sweat rate and salt losses via sweat. Future studies need to investigate the correlation between the risk factors of EAH and specific subgroups of marathon runners.
Background
Sodium supplements are ubiquitous in endurance running, but their impact on performance has been subjected to much debate. The objective of the study was to assess the effect of sodium supplementation as a weight-based predictor of race performance in ultramarathon runners.
Methods
Prospective observational study during an 80 km (50 mi) stage of a 6-stage 250 km (155 mi) ultramarathon in Chile, Patagonia, Namibia, and Mongolia. Finish line hydration status as measured by weight change, point-of-care serum sodium, and questionnaire provided sodium ingestion categories at 33rd percentile and 66th percentile both for weight-adjusted rate and total sodium consumption, then analyzed for significant relationships to race performance, dysnatremia, and hydration.
Results
Two hundred sixty-six participants were enrolled, with 217 (82%) with complete sodium supplement rate data, 174 (80%) with finish line sodium, and 161 (74%) with both pre-race weights and total sodium ingestion allowing weight-based analysis. Sodium intake ranged from 131–533 mg/h/kg (2–7.2 gm), with no statistically significant impact on pace, race time, or quintile rank. These outcomes did not change when sodium intake was analyzed as a continuous variable or by sub-group analysis of the 109 (68%) normonatremic runners. When controlled for weight-adjusted sodium intake, performance was poorly correlated with hydration (r = − 0.152, 95% CI − 0.348–0.057). Dehydrated runners outperformed those overhydrated, with 11% of top 25th percentile finishers dehydrated (versus 2.8% overhydrated), with 3.6 min/km faster pace and time 4.6 h faster finishing time.
Conclusions
No association was found between sodium supplement intake and ultramarathon performance. Dehydrated runners were found to have the best performance. This reinforces the message to avoid overhydration.
Cold water immersion (CWI) purportedly reduces inflammation and improves muscle recovery after exercise, yet its effectiveness in specific contexts (ultraendurance) remains unclear. Thus, our aim was to study hematological profiles, systemic inflammation, and muscle damage responses to a specific post-race CWI (vs. control) during recovery after the Ironman World Championship, a culmination of ∼100 000 athletes competing in global qualifying Ironman events each year. Twenty-nine competitors were randomized into either a CWI or control (CON) group. Physiological parameters and blood samples were taken at pre-race, after intervention (POST), and 24 (+1DAY) and 48 hours (+2DAY) following the race. Muscle damage markers (plasma myoglobin, serum creatine kinase) were elevated at POST, +1DAY, and +2DAY, while inflammatory cytokines interleukin (IL)-6, IL-8, and IL-10 and total leukocyte counts were increased only at POST. CWI had no effect on these markers. Numbers of the most abundant circulating cell type, neutrophils, were elevated at POST more so in CWI (p < 0.05, vs. CON). Despite that neutrophil counts may be a sensitive marker to detect subtle effects, CWI does not affect recovery markers 24- and 48-hours post-race (vs. CON). Overall, we determined that our short CWI protocol was not sufficient to improve recovery.
Novelty: Ironman World Championship event increased circulating muscle damage markers, inflammatory markers, and hematological parameters, including circulating immune cell sub-populations that recover 24–48 hours after the race. 12-min CWI post-ultraendurance event affects the absolute numbers of neutrophils acutely, post-race (vs. CON), but does not impact recovery 24- and 48-hours post-race.
Objective:
Analyze the effect of sodium supplementation, hydration, and climate on dysnatremia in ultramarathon runners.
Design:
Prospective observational study.
Setting:
The 2017 80 km (50 mile) stage of the 250 km (150 mile) 6-stage RacingThePlanet ultramarathon in 2017 Chilean, Patagonian, and 2018 Namibian, Mongolian, and Chilean deserts.
Participants:
All race entrants who could understand English were invited to participate, with 266 runners enrolled, mean age of 43 years (± 9), 61 (36%) females, average weight 74 kg (± 12.5), and average race time 14.5 (± 4.1) hours. Post-race sodium collected on 174 (74%) and 164 (62%) participants with both the blood sample and post-race questionnaire.
Intervention:
Weight change and finish line serum sodium levels were gathered.
Main outcome measures:
Incidence of exercise-associated hyponatremia (EAH; <135 mmol·L) and hypernatremia (>145 mmol·L) by sodium ingestion and climate.
Results:
Eleven (6.3%) runners developed EAH, and 30 (17.2%) developed hypernatremia. Those with EAH were 14 kg heavier at baseline, had significantly less training distances, and averaged 5 to 6 hours longer to cover 50 miles (80 km) than the other participants. Neither rate nor total ingested supplemental sodium was correlated with dysnatremia, without significant differences in drinking behaviors or type of supplement compared with normonatremic runners. Hypernatremic runners were more often dehydrated [8 (28%), -4.7 kg (± 9.8)] than EAH [4 (14%), -1.1 kg (± 3.8)] (P < 0.01), and EAH runners were more frequently overhydrated (6, 67%) than hypernatremia (1, 11%) (P < 0.01). In the 98 (56%) runners from hot races, there was EAH OR = 3.5 [95% confidence interval (CI), 0.9-25.9] and hypernatremia OR = 8.8 (95% CI, 2.9-39.5) compared with cold races.
Conclusions:
This was the first study to show that hot race climates are an independent risk factor for EAH and hypernatremia. Sodium supplementation did not prevent EAH nor cause hypernatremia. Longer training distances, lower body mass, and avoidance of overhydration were shown to be the most important factors to prevent EAH and avoidance of dehydration to prevent hypernatremia.
Minerals and trace elements (MTEs) are micronutrients involved in hundreds of biological processes. Deficiency in MTEs can negatively affect athletic performance. Approximately 50% of athletes have reported consuming some form of micronutrient supplement; however, there is limited data confirming their efficacy for improving performance. The aim of this study was to systematically review the role of MTEs in exercise and athletic performance. Six electronic databases and grey literature sources (MEDLINE; EMBASE; CINAHL and SportDISCUS; Web of Science and clinicaltrials.gov) were searched, in accordance with PRISMA guidelines. Results: 17,433 articles were identified and 130 experiments from 128 studies were included. Retrieved articles included Iron (n = 29), Calcium (n = 11), Magnesium, (n = 22), Phosphate (n = 17), Zinc (n = 9), Sodium (n = 15), Boron (n = 4), Selenium (n = 5), Chromium (n = 12) and multi-mineral articles (n = 5). No relevant articles were identified for Copper, Manganese, Iodine, Nickel, Fluoride or Cobalt. Only Iron and Magnesium included articles of sufficient quality to be assigned as 'strong'. Currently, there is little evidence to support the use of MTE supplementation to improve physiological markers of athletic performance, with the possible exception of Iron (in particular, biological situations) and Magnesium as these currently have the strongest quality evidence. Regardless, some MTEs may possess the potential to improve athletic performance, but more high quality research is required before support for these MTEs can be given. PROSPERO preregistered (CRD42018090502).
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.
Keywords: Sex, ultramarathon, swimming, cycling, running
Objective:
To present evidence-based recommendations that promote optimized fluid-maintenance practices for physically active individuals.
Background:
Both a lack of adequate fluid replacement (hypohydration) and excessive intake (hyperhydration) can compromise athletic performance and increase health risks. Athletes need access to water to prevent hypohydration during physical activity but must be aware of the risks of overdrinking and hyponatremia. Drinking behavior can be modified by education, accessibility, experience, and palatability. This statement updates practical recommendations regarding fluid-replacement strategies for physically active individuals.
Recommendations:
Educate physically active people regarding the benefits of fluid replacement to promote performance and safety and the potential risks of both hypohydration and hyperhydration on health and physical performance. Quantify sweat rates for physically active individuals during exercise in various environments. Work with individuals to develop fluid-replacement practices that promote sufficient but not excessive hydration before, during, and after physical activity.
Ultra-endurance competition is defined as events that exceed than 6 hours in duration. The longer events rely on long-term preparation, sufficient nutrition, accommodation of environmental stressors, and psychologic toughness. Successful ultra-endurance performance is characterized by the ability to sustain a higher absolute speed for a given distance than other competitors. This can be achieved through a periodized training plan and by following key principles of training. Periodization is an organization of training into large, medium and small training blocks which are referred to as macro-, meso-, and microcycles, respectively. When the sequencing of training is correctly applied, athletes can achieve a high state of competition readiness and during the months of hard training, avoid the overtraining syndrome. A plan is executed in accordance with the following principles of training: all-around development, overload, specificity, individualization, consistent training, and structural tolerance. Training relies heavily on the athlete’s tolerance to repetitive strain. Today’s ultra-endurance athlete must also follow appropriate nutritional practices in order to recover and prepare for daily training and remain injury free and healthy. Rehydration after exercise, together with the timing and method of increased food intake to cope with heavy training, are essential for optimal performance. Furthermore, the treatment of soft tissue after training or racing is necessary to control inflammation.
Cellulite is the result of complex physiological changes of the subcutaneous fat layer and of microcirculation, clinically manifesting as orange peel skin especially in women and involving thighs, buttocks, and abdomen. An adequate water intake has been suggested to be helpful in controlling the development and worsening of the disease. An open randomized controlled study has been performed to evaluate modification induced by an adequate diet associated to low-sodium or high-sodium water intake on some clinical features of patients affected with mild to moderate cellulite.
Non-invasive instrumental investigations (Bioelectrical Impedance Analysis (BIA), thermography and skin echography) were used before and after dietary treatment. A significant improvement of the disease, in terms of weight loss, cutaneous microcirculation and reduction of subcutaneous fat layer, was observed in the group of patients who underwent low-sodium water intake. An adequate dietary treatment associated to a low-sodium water intake is able to efficiently controll some biological and clinical parameters of mild to moderate cellulite.
This paper examines the various nutritional challenges which athletes encounter in preparing for and participating in ultra-endurance walking and running events. Special attention is paid to energy level, performance, and recovery within the context of athletes’ intake of carbohydrate, protein, fat, and various vitamins and minerals. It outlines, by way of a review of literature, those factors which promote optimal performance for the ultra-endurance athlete and provides recommendations from multiple researchers concerned with the nutrition and performance of ultra-endurance athletes. Despite the availability of some research about the subject, there is a paucity of longitudinal material which examines athletes by nature and type of ultra-endurance event, gender, age, race, and unique physiological characteristics. Optimal nutrition results in a decreased risk of energy depletion, better performance, and quicker full-recovery.
Exercise associated hyponatraemia (EAH) is a serious and life threatening complication of extreme endurance sports, and is due to excessive consumption of hypotonic fluids together with non-osmotic stimulation of arginine vasopressin (AVP) causing dilutional hyponatraemia. Loss of sodium in sweat, reduced renal capacity to eliminate free water, and water released form metabolism are other contributing factors. In severe cases hyponatraemic encephalopathy may develop. These severe cases can be effectively treated with infusion of 3% hypertonic saline. Prevention of EAH depends on education of participants to take moderate amounts of fluids according to thirst, taking into account weather conditions on race day.
Introduction: The triathlon is an endurance sport in which 3 consecutive events are performed: swimming, cycling and running. It has been found that the loss of muscle strength is related to the blood markers'concentration of muscle damage during a half-ironman triathlon. It has also been observed that an electrolyte imbalance is produced in triathletes during long distance triathlons. Purpose: The aim of this study was to analyze blood parameters to determine dehydration (body mass and osmolality), elec trolyte loss (chlorine, potassium, sodium and calcium) and muscle damage (myoglobin, CK and LDH) in a half-ironman triathlon. Methods: Before and after the race body weight was measured and blood samples were extracted to 34 triathletes aged 35.7 ± 6.5 years whose average finish time was 5:12:20 ± 00:34:59 hours. Standard biochemical analyzers were used to measure the samples. Results: Significant increases (P<0.05) were found from pre-to-post race in myoglobin (from 32.8 ± 13 to 654.8 ±451.3 μg • L-1); in CK (from 169.3 ± 86.2 to 564.5±428.9 U • L-1); and in LDH (318.4 ± 56.2 to 479.0 ± 78.6 U • L-1). It was also found a significant increase (P<0.05) from pre-to-post race in the calcium (from 9.5 ± 0.4 to 10.3 ± 0.4 mmol • L-1), sodium (140.6 ± 1.4 vs. 143.0 ± 2.0 mmol • L1) and the osmolality (from 293.9 ± 7.3 vs. 301 ± 7.0 μg L-1). Body mass decreased significantly (from 72.8 ± 6.4 to 69.5±6.4kg;P<0.05). Conclusions: Significant increases in blood markers of muscle damage occur in a half-ironman triathlon. Dehydration markers, as well as calcium and sodium values, are also affected in a significant way.
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.
In ultra-endurance races, athletes face limits in nutrition regarding energy and fluid metabolism. An ultra-endurance performance lasting for 24 hours or longer leads to a mean daily energy deficit of ~7,000 kcal. This energy deficit leads to a decrease in body mass, covered by a decrease in both fat mass and skeletal muscle mass. The energy deficit cannot be prevented by adequate energy intake. To avoid dehydration during an ultra-endurance performance, adequate fluid intake is required. In case of fluid overload, both exercise-associated hyponatremia and swelling of limbs may occur. Adequate ad libitum fluid intake of ~300-400 ml per hour may prevent both exercise-associated hyponatremia and swelling of limbs. To summarize, in ultra-endurance races, an energy deficit seems to be unavoidable. Potential strategies might be to increase pre-race body mass by a diet to increase fat mass and/or strength training to augment skeletal muscle mass. Another possibility could be increasing energy intake during racing by consuming a fat-rich diet. However, future studies are required to investigate these aspects.
Objective:
This narrative review summarizes findings for Ironman triathlon performance and intends to determine potential predictor variables for Ironman race performance in female and male triathletes.
Methods:
A literature search was performed in PubMed using the terms "Ironman", "triathlon", and "performance". All resulting articles were searched for related citations.
Results:
Age, previous experience, sex, training, origin, anthropometric and physiological characteristics, pacing, and performance in split disciplines were predictive. Differences exist between the sexes for anthropometric characteristics. The most important predictive variables for a fast Ironman race time were age of 30-35 years (women and men), a fast personal best time in Olympic distance triathlon (women and men), a fast personal best time in marathon (women and men), high volume and high speed in training where high volume was more important than high speed (women and men), low body fat, low skin-fold thicknesses and low circumference of upper arm (only men), and origin from the United States of America (women and men).
Conclusion:
These findings may help athletes and coaches to plan an Ironman triathlon career. Age and previous experience are important to find the right point in the life of a triathlete to switch from the shorter triathlon distances to the Ironman distance. Future studies need to correlate physiological characteristics such as maximum oxygen uptake with Ironman race time to investigate their potential predictive value and to investigate socio-economic aspects in Ironman triathlon.
Exercise-associated hyponatremia (EAH) is the development of a low serum sodium in association with endurance exercise of any type. The pathogenesis includes excessive water intake, inappropriate vasopressin release, impairment in urinary dilution, as well as other mechanisms. Prompt recognition of the signs and symptoms of EAH can be life saving. The rapid use of hypertonic (3%) saline in athletes with EAH leads to rapid resolution of symptoms. In the absence of appropriate therapy, EAH has lead to tragic consequences in otherwise healthy adults.
From the advent of competitive sport until 1969, athletes were advised to avoid drinking any fluids during exercise since it was believed that fluid ingestion would impair exercise performance. Athletes in those years actively followed that advice, priding themselves on their ability to run even 26-mile (42-km) marathon races without drinking. The ignorance extends to those emergency ambulance personnel and emergency care physicians who believe that “dehydration” can cause an altered level of consciousness including the development of coma and who, as a result, have treated overhydrated athletes suffering from exercise-associated hyponatremia (EAH) or exercise associated hyponatremic encephalopathy (EAHE), with the rapid infusion of large volumes of iso- or hypotonic NaCl solutions. The only effect of such treatment is to acutely increase intracerebral pressure, with the production of cerebellar coning, respiratory arrest, and brain death.
This narrative review summarizes recent intentions to find potential predictor variables for ultra-triathlon race performance (ie, triathlon races longer than the Ironman distance covering 3.8 km swimming, 180 km cycling, and 42.195 km running). Results from studies on ultra-triathletes were compared to results on studies on Ironman triathletes.
A literature search was performed in PubMed using the terms "ultra", "triathlon", and "performance" for the aspects of "ultra-triathlon", and "Ironman", "triathlon", and "performance" for the aspects of "Ironman triathlon". All resulting papers were searched for related citations. Results for ultra-triathlons were compared to results for Ironman-distance triathlons to find potential differences.
Athletes competing in Ironman and ultra-triathlon differed in anthropometric and training characteristics, where both Ironmen and ultra-triathletes profited from low body fat, but ultra-triathletes relied more on training volume, whereas speed during training was related to Ironman race time. The most important predictive variables for a fast race time in an ultra-triathlon from Double Iron (ie, 7.6 km swimming, 360 km cycling, and 84.4 km running) and longer were male sex, low body fat, age of 35-40 years, extensive previous experience, a fast time in cycling and running but not in swimming, and origins in Central Europe.
Any athlete intending to compete in an ultra-triathlon should be aware that low body fat and high training volumes are highly predictive for overall race time. Little is known about the physiological characteristics of these athletes and about female ultra-triathletes. Future studies need to investigate anthropometric and training characteristics of female ultra-triathletes and what motivates women to compete in these races. Future studies need to correlate physiological characteristics such as maximum oxygen uptake (VO2max) with ultra-triathlon race performance in order to investigate whether these characteristics are also predictive for ultra-triathlon race performance.
We present 3 cases of severe hyponatremia occurring on a commercially guided river rafting trip on the Colorado River in Grand Canyon National Park. All 3 women appeared to have been overhydrating because of concern about dehydration and required evacuation within 24 hours of each other after the staggered onset of symptoms, which included fatigue and emesis progressing to disorientation or seizure. Each was initially transferred to the nearest hospital and ultimately required intensive care. Imaging and laboratory data indicated all 3 patients had hypervolemic hyponatremia. Unlike the well-documented exercise-associated hyponatremia cases commonly occurring in prolonged endurance athletic events, these 3 unique cases of acute hyponatremia were not associated with significant exercise. The cases illustrate the diagnostic and treatment challenges related to acute hyponatremia in an austere setting, and underscore the importance of preventive measures focused on avoidance of overhydration out of concern for dehydration.
Published by Elsevier Inc.
This study examined the incidence, severity, and timing of gastrointestinal (GI) symptoms in finishers and non-finishers of the 161-km Western States Endurance Run. A total of 272 runners (71.0% of starters) completed a post-race questionnaire that assessed the incidence and severity (none = 0, mild = 1, moderate = 2, severe = 3, very severe = 4) of 12 upper (reflux/heartburn, belching, stomach bloating, stomach cramps/pain, nausea, vomiting) and lower (intestinal cramps/pain, flatulence, side ache/stitch, urge to defecate, loose stool/diarrhoea, intestinal bleeding/bloody faeces) GI symptoms experienced during each of four race segments. GI symptoms were experienced by most runners (96.0%). Flatulence (65.9% frequency, mean value 1.0, s = 0.6 severity), belching (61.3% frequency, mean value 1.0, s = 0.6 severity), and nausea (60.3% frequency, mean value 1.0, s = 0.7 severity) were the most common symptoms. Among race finishers, 43.9% reported that GI symptoms affected their race performance, with nausea being the most common symptom (86.0%). Among race non-finishers, 35.6% reported that GI symptoms were a reason for dropping out of the race, with nausea being the most common symptom (90.5%). For both finishers and non-finishers, nausea was greatest during the most challenging and hottest part of the race. GI symptoms are very common during ultramarathon running, and in particular, nausea is the most common complaint for finishers and non-finishers.
This work examines whether sodium supplementation is important in prevention of hyponatremia during continuous exercise up to 30 hours, and if any distinguishing characteristics of those developing hyponatremia could be identified.
Participants of the 161-km Western States Endurance Run underwent body weight measurements before, during and after the race, completed a post-race questionnaire about drinking strategies and use of sodium supplementation during four race segments, and underwent analysis of post-race serum sodium concentration.
The post-race questionnaire was completed by 74.5% of the 376 starters, a post-race blood sample was provided by 61.1% of the 296 finishers, and 53.0% of finishers completed the post-race survey and also provided a post-race blood sample. Among this population, the incidence of hyponatremia among finishers was 6.6%, and sodium supplements were used by 93.9% of the runners. Post-race serum sodium concentration was found to be directly related to the rate of sodium intake in supplements (r=0.24, p=0.0027) and indirectly related to the percentage change in body weight from immediately before the race start (r=-0.19, p=0.10). There was no difference in rate of sodium intake in supplements between the hyponatremic and normonatremic finishers, and none of the hyponatremic finishers lost >4.3% body weight. Hyponatremic finishers were not distinguished from normonatremic or hypernatremic finishers by other runner characteristics considered, drinking strategies or gastrointestinal symptoms of nausea and vomiting.
We conclude that a low sodium intake in supplements has minimal responsibility for development of hyponatremia during continuous exercise up to 30 hours, whereas overhydration is the primary characteristic of those developing hyponatremia. Therefore, avoiding overhydration appears to be the most important means for preventing hyponatremia under these conditions.
Abstract Probiotic supplementation has traditionally focused on gut health. However, in recent years, the clinical applications of probiotics have broadened to allergic, metabolic, inflammatory, gastrointestinal and respiratory conditions. Gastrointestinal health is important for regulating adaptation to exercise and physical activity. Symptoms such as nausea, bloating, cramping, pain, diarrhoea and bleeding occur in some athletes, particularly during prolonged exhaustive events. Several studies conducted since 2006 examining probiotic supplementation in athletes or highly active individuals indicate modest clinical benefits in terms of reduced frequency, severity and/or duration of respiratory and gastrointestinal illness. The likely mechanisms of action for probiotics include direct interaction with the gut microbiota, interaction with the mucosal immune system and immune signalling to a variety of organs and systems. Practical issues to consider include medical and dietary screening of athletes, sourcing of recommended probiotics and formulations, dose-response requirements for different probiotic strains, storage, handling and transport of supplements and timing of supplementation in relation to travel and competition.
Participation in ultramarathon races and our knowledge of these athletes continues to grow as the sport becomes more popular. With such growth, it is apparent that both 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 medial issues. The goal of this article is to review the evaluation and treatment of common musculoskeletal injuries and medical illnesses in ultramarathon runners.
To examine controversies about hydration strategies, participants (383 starters) of a 161 km ultramarathon (maximum temperature 39.0°C) underwent body weight measurements before, during and after the race; and completed a post-race questionnaire on drinking strategies and sodium supplementation use during 4 race segments. Drinking to thirst was the most common (p < 0.01) drinking strategy (used by 67.0% during at least one segment) and most runners (95.6%) used sodium supplementation during at least one segment. There was no difference in the extent of weight loss (mean 2.0-3.1%) or the weight change pattern when comparing groups using different hydration strategies. Among top-10 finishers, half had lost more than 2% of starting body weight by 90 km. We conclude that weight loss greater than 2% does not necessarily have adverse consequences on performance, and use of sodium supplements or drinking beyond thirst is not required to maintain hydration during ultra-endurance events with high thermal stress.
Blood samples were drawn from 6 National Football League players for baseline measures and then prior to morning prac- tice on days 3, 5, and 9. Mean blood sodium level was lower on days 3 (136.9±0.6 mmol·L -1 ) and day 5 (138.1±0.6 mmol·L -1 ) compared to baseline (140.4±0.4 mmol·L -1 ) and day 9 (140.3±0.4 mmol·L -1 ). Mean blood potassium level was higher on day 5 (4.16±0.13 mmol·L -1 ) and day 9 (4.36±0.08 mmol·L -1 ) compared to baseline (3.77±0.15 mmol·L -1 ). Mean plasma volume was low- er on day 3 (-4.9%±2.4%) compared to day 5 (4.5%±1.9%), and mean mass (days 2 through 9) was below baseline before and af- ter practices. Blood sodium level declined by day 3 of preseason and was maintained at low normal levels at the expense of con- tracted plasma volume. Increased resting blood potassium levels on days 5 and 9 indicated rhabdomyolysis. Increased consump- tion of sodium is important for professional football players to maintain plasma volume during the first week of preseason.
Both carbohydrate depletion and dehydration have been shown to decrease performance whilst severe dehydration can also cause adverse health effects. Therefore carbohydrate and fluid requirements are increased with exercise. Ingestion of 200–300 g of CHO 3–4 h prior to exercise is an effective strategy in order to meet daily CHO demands and increase CHO availability during the subsequent exercise period. There is little evidence that CHO during the hour immediately prior to exercise has adverse effects such as rebound hypoglycaemia. CHO ingestion during exercise has been shown to improve performance as measured by enhanced work output or decreased exercise time to complete a fixed amount of work. Recent studies have demonstrated that exogenous CHO oxidation rates can be increased by ingesting combinations of CHO that use different intestinal CHO transporters. After exercise maximal muscle glycogen re-synthesis rates can be achieved by ingesting CHO at a rate of ∼1.2 g/kg/h, in relatively frequent (e.g., 15–30 min) intervals for up to 5 h following exercise. Protein amino acid mixtures may increase glycogen synthesis further but only if relatively small amounts of CHO are ingested.Hypohydration and hyperthermia alone have negative effects on performance but their combination is particularly serious, both in terms of performance and health. Dehydration can be prevented by fluid ingestion pre exercise and during exercise. Because of large individual differences it is difficult to individualise the advice. Perhaps the best guidance for athletes is to weigh themselves to assess fluid losses during training and racing and limit weight losses to 1% during exercise lasting longer than 1.5 h. Excessive fluid intake has been associated with hyponatremia. Post exercise the volume of fluid ingested and sodium intake are important determinants of rehydration.
Exercise-associated hyponatremia (EAH) typically occurs during or up to 24 hours after prolonged physical activity, and is defined by a serum or plasma sodium concentration below the normal reference range of 135 mEq/L. It is also reported to occur in individual physical activities or during organized endurance events conducted in austere environments in which medical care is limited or often not available, and patient evacuation to definitive care is often greatly delayed. Rapid recognition and appropriate treatment are essential in the severe form to ensure a positive outcome. Failure in this regard is a recognized cause of event-related fatality. In an effort to produce best practice guidelines for EAH in the austere environment, the Wilderness Medical Society convened an expert panel. The panel was charged with the development of evidence-based guidelines for management of EAH. Recommendations are made regarding the situations when sodium concentration can be assessed in the field and when these values are not known. These recommendations are graded based on the quality of supporting evidence and balance between the benefits and risks/burdens for each parameter according to the methodology stipulated by the American College of Chest Physicians.
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Exercise-associated hyponatremia (EAH) has mainly been investigated in runners and triathletes. In mountain bikers, EAH was studied in two multi-stage races, but not in a single stage race. The aim of this study was to investigate the prevalence of EAH in a single-stage mountain bike ultra-marathon. In the 'Swiss Bike Masters' over 120 km with a climb of ~ 5,000 m in altitude, we determined pre and post race body mass, hematocrit, plasma sodium concentration ([Na⁺]), and urinary specific gravity in 37 cyclists. Athletes recorded their fluid intake while racing. No athlete developed EAH. The cyclists drank on average (means ± SD) 0.7 ± 0.2 l/h. Fluid intake was significantly and negatively related to race time (r = -0.41, P < 0.05), but showed no association with post race plasma [Na⁺], the change in plasma [Na⁺], post race body mass, or the change in body mass. The athletes lost 1.4 kg body mass (P < 0.05), plasma [Na⁺] decreased by 0.7% (P < 0.05), plasma volume increased by 1.4% and urinary specific gravity increased by 0.4% (P < 0.05). The change in body mass was neither related to post race plasma [Na⁺] nor to the change in plasma [Na⁺]. The decrease in plasma [Na⁺] was not related to fluid intake. The change in plasma [Na⁺] was related to post race plasma [Na⁺] (r = 0.40, P < 0.01). Ad libitum fluid intake showed no case of EAH in a single-stage mountain bike ultra-marathon. In contrast to previous findings, the faster athletes drank more than the slower ones.
Participation in ultraendurance events has been increasing. Appropriate nutrition in training and fueling while racing within the confines of gastrointestinal tolerability is essential for optimal performance. Unfortunately, there has been a paucity of studies looking at this special population of athletes. Recent field studies have helped to clarify appropriate fluid intake and dispel the myth that moderate dehydration while racing is detrimental. Additional current nutrition research has looked at the role of carbohydrate manipulation during training and its effect on macronutrient metabolism, as well as of the benefits of the coingestion of multiple types of carbohydrates for race fueling. The use of caffeine and sodium ingestion while racing is common with ultraendurance athletes, but more research is needed on their effect on performance. This article will provide the clinician and the athlete with the latest nutritional information for the ultraendurance athlete.
It is the position of the American College of Sports Medicine that adequate fluid replacement helps maintain hydration and, therefore, promotes the health, safety, and optimal physical performance of individuals participating in regular physical activity. This position statement is based on a comprehensive review and interpretation of scientific literature concerning the influence of fluid replacement on exercise performance and the risk of thermal injury associated with dehydration and hyperthermia. Based on available evidence, the American College of Sports Medicine makes the following general recommendations on the amount and composition of fluid that should be ingested in preparation for, during, and after exercise or athletic competition:
1. It is recommended that individuals consume a nutritionally balanced diet and drink adequate fluids during the 24-h period before an event, especially during the period that includes the meal prior to exercise, to promote proper hydration before exercise or competition.
2. It is recommended that individuals drink about 500 ml (about 17 ounces) of fluid about 2 h before exercise to promote adequate hydration and allow time for excretion of excess ingested water.
3. During exercise, athletes should start drinking early and at regular intervals in an attempt to consume fluids at a rate sufficient to replace all the water lost through sweating (i.e., body weight loss), or consume the maximal amount that can be tolerated.
4. It is recommended that ingested fluids be cooler than ambient temperature[between 15° and 22°C (59° and 72°F)] and flavored to enhance palatability and promote fluid replacement. Fluids should be readily available and served in containers that allow adequate volumes to be ingested with ease and with minimal interruption of exercise.
5. Addition of proper amounts of carbohydrates and/or electrolytes to a fluid replacement solution is recommended for exercise events of duration greater than 1 h since it does not significantly impair water delivery to the body and may enhance performance. During exercise lasting less than 1 h, there is little evidence of physiological or physical performance differences between consuming a carbohydrate-electrolyte drink and plain water.
6. During intense exercise lasting longer than 1 h, it is recommended that carbohydrates be ingested at a rate of 30-60 g · h-1 to maintain oxidation of carbohydrates and delay fatigue. This rate of carbohydrate intake can be achieved without compromising fluid delivery by drinking 600-1200 ml· h-1 of solutions containing 4%-8% carbohydrates (g · 100 ml-1). The carbohydrates can be sugars (glucose or sucrose) or starch (e.g., maltodextrin).
7. Inclusion of sodium (0.5-0.7 g · 1-1 of water) in the rehydration solution ingested during exercise lasting longer than 1 h is recommended since it may be advantageous in enhancing palatability, promoting fluid retention, and possibly preventing hyponatremia in certain individuals who drink excessive quantities of fluid. There is little physiological basis for the presence of sodium in an oral rehydration solution for enhancing intestinal water absorption as long as sodium is sufficiently available from the previous meal.
Objective: To record weight changes, fluid intake and changes in serum sodium concentration in ultradistance triathletes.
Design: Descriptive research.
Setting: Ironman triathlon (3.8 km swim, 180 km cycle, 42.2 km run). Air temperature at 1200 h was 21°C, (relative humidity 91%). Water temperature was 20.7°C.
Participants: 18 triathletes.
Interventions: None.
Main Outcome Measures: Subjects were weighed and had blood drawn for serum sodium concentration [Na], hemoglobin, and hematocrit, pre-race, post-race, and at 0800 h on the morning following the race (recovery); subjects were also weighed at transitions. Fluid intake during the race was estimated by athlete recall.
Results: Median weight change during the race = -2.5 kg (p < 0.0006). Subjects lost weight during recovery (median = -1.0 kg) (p < 0.03). Median hourly fluid intake = 716 ml/h (range 421-970). Fluid intakes were higher on the bike than on the run (median 889 versus 632 ml/h, p = 0.03). Median calculated fluid losses cycling were 808 ml/h and running were 1,021 ml/h. No significant difference existed between pre-race and post-race [Na] (median 140 versus 138 mmol/L) or between post-race and recovery [Na] (median 138 versus 137 mmol/L). Plasma volume increased during the race, median + 10.8% (p = 0.0005). There was an inverse relationship between change in [Na] pre-race to post-race and relative weight change (r = -0.68, p = 0.0029). Five subjects developed hyponatremia ([Na] 128-133 mmol/L).
Conclusions: Athletes lose 2.5 kg of weight during an ultra-distance triathlon, most likely from sources other than fluid loss. Fluid intakes during this event are more modest than that recommended for shorter duration exercise. Plasma volume increases during the ultradistance triathlon. Subjects who developed hyponatremia had evidence of fluid overload despite modest fluid intakes.
Symptomatic hyponatremia has been reported in athletes participating in marathon and ultra-marathon events. We report four cases of symptomatic hyponatremia in hikers in the Grand Canyon. These are the first cases reported in recreational hikers in a wilderness setting. The overall fluid status of these patients is not well defined. In most instances this probably represents dilutional hyponatremia from sweat loss replaced with plain water. Recreational wilderness participants may require electrolyte replacement similar to endurance athletes.
It is the position of the American College of Sports Medicine that adequate fluid replacement helps maintain hydration and, therefore, promotes the health, safety, and optimal physical performance of individuals participating in regular physical activity. This position statement is based on a comprehensive review and interpretation of scientific literature concerning the influence of fluid replacement on exercise performance and the risk of thermal injury associated with dehydration and hyperthermia. Based on available evidence, the American College of Sports Medicine makes the following general recommendations on the amount and composition of fluid that should be ingested in preparation for, during, and after exercise or athletic competition: 1) It is recommended that individuals consume a nutritionally balanced diet and drink adequate fluids during the 24-hr period before an event, especially during the period that includes the meal prior to exercise, to promote proper hydration before exercise or competition. 2) It is recommended that individuals drink about 500 ml (about 17 ounces) of fluid about 2 h before exercise to promote adequate hydration and allow time for excretion of excess ingested water. 3) During exercise, athletes should start drinking early and at regular intervals in an attempt to consume fluids at a rate sufficient to replace all the water lost through sweating (i.e., body weight loss), or consume the maximal amount that can be tolerated. 4) It is recommended that ingested fluids be cooler than ambient temperature [between 15 degrees and 22 degrees C (59 degrees and 72 degrees F])] and flavored to enhance palatability and promote fluid replacement. Fluids should be readily available and served in containers that allow adequate volumes to be ingested with ease and with minimal interruption of exercise. 5) Addition of proper amounts of carbohydrates and/or electrolytes to a fluid replacement solution is recommended for exercise events of duration greater than 1 h since it does not significantly impair water delivery to the body and may enhance performance. During exercise lasting less than 1 h, there is little evidence of physiological or physical performance differences between consuming a carbohydrate-electrolyte drink and plain water. 6) During intense exercise lasting longer than 1 h, it is recommended that carbohydrates be ingested at a rate of 30-60 g.h(-1) to maintain oxidation of carbohydrates and delay fatigue. This rate of carbohydrate intake can be achieved without compromising fluid delivery by drinking 600-1200 ml.h(-1) of solutions containing 4%-8% carbohydrates (g.100 ml(-1)). The carbohydrates can be sugars (glucose or sucrose) or starch (e.g., maltodextrin). 7) Inclusion of sodium (0.5-0.7 g.1(-1) of water) in the rehydration solution ingested during exercise lasting longer than 1 h is recommended since it may be advantageous in enhancing palatability, promoting fluid retention, and possibly preventing hyponatremia in certain individuals who drink excessive quantities of fluid. There is little physiological basis for the presence of sodium in n oral rehydration solution for enhancing intestinal water absorption as long as sodium is sufficiently available from the previous meal.
Objective of this study was to get more insight in hematology, biochemistry, and endocrinology of ultra-endurance exercise, to improve knowledge in this field, supplementation, and medical care of affected athletes.
A large body of individual hematological, biochemical, and endocrinological parameters was analyzed in the blood taken from ultra-athletes before and after completing the 1993 Colmar ultra triathlon covering 7.5 km swimming, 360 km cycling, and approximately 85 km running.
Nine experienced ultra-athletes participated in the study. A follow-up was not possible since the athletes left Colmar within 24 hrs after the contest.
The athletes finished the ultra-contest at rankings 4, 5, 7, 8, 9, 11, 18, 22, 23 in a total time between 23:38:53 and 27:54:30 hr:min:sec. Their final body mass (68.6 +/- 1 kg) was significantly lower than at baseline (71.9 +/- 4.2 kg). Non of the athletes made use of medical care. Data after this contest reflect mild hyponatremia, intravascular hemolysis, increased triglyceride turnover, acute-phase reaction, hyperaldosteronemia 2061 +/- 1013 pmol.L-1), hypercortisolemia 971 +/- 486 nmol.L-1), hyper-growth-hormonemia (median 6.8 ng.ml-1), hypoinsulinemia, hypo-free-testosteronemia (42 +/- 17 pmol.L-1), protein catabolism, depressed testicular function, oliguria, and muscle cell leakage.
In our opinion, data presented do not reflect any acute health risks in healthy athletes who are well prepared and carefully supplied during such a contest.
In this study, we examined whether athletes, who typically replace only approximately 50% of their fluid losses during moderate-duration endurance exercise, should attempt to replace their Na+ losses to maintain extracellular fluid volume. Six male cyclists performed three 90-min rides at 65% of peak O2 uptake in a 32 degrees C environment and ingested either no fluid (NF), 1.21 of water (W), or saline (S) containing 100 mmol of NaCl x l(-1) to replace their electrolyte losses. Both W and S conditions decreased final heart rates by approximately 10 betas min(-1) (P<0.005) and reduced falls in plasma volume (PV) by approximately 4% (P<0.05). Maintenance of PV after 10 min in the W trial prevented further rises in plasma concentrations of Na+ [Na+], Cl- and protein but in the S and NF trials, plasma [Na+] continued to increase by approximately 4 mEq x l(-1). Differences in plasma [Na+] had little effect on the approximately 2.4 l fluid, approximately 120 mEq Na+ and approximately 50 mEq K+ losses in sweat and urine in the three trials. The main effects of W and S were on body fluid shifts. During the NF trial, PV and interstitial fluid (ISF) and intracellular fluid (ICF) volumes decreased by approximately 0.1, 1.2 and 1.0 l, respectively. In the W trial, the approximately 1.2 l fluid and approximately 120 mEq Na+ losses contracted the ISF volume, and in the S trial, ISF volume was maintained by the movement of water from the ICF. Since the W and S trials were equally effective in maintaining PV, Na+ ingestion may not be of much advantage to athletes who typically replace only approximately 50% of their fluid losses during competitive endurance exercise.
This Position Stand provides guidance on fluid replacement to sustain appropriate hydration of individuals performing physical activity. The goal of prehydrating is to start the activity euhydrated and with normal plasma electrolyte levels. Prehydrating with beverages, in addition to normal meals and fluid intake, should be initiated when needed at least several hours before the activity to enable fluid absorption and allow urine output to return to normal levels. The goal of drinking during exercise is to prevent excessive (>2% body weight loss from water deficit) dehydration and excessive changes in electrolyte balance to avert compromised performance. Because there is considerable variability in sweating rates and sweat electrolyte content between individuals, customized fluid replacement programs are recommended. Individual sweat rates can be estimated by measuring body weight before and after exercise. During exercise, consuming beverages containing electrolytes and carbohydrates can provide benefits over water alone under certain circumstances. After exercise, the goal is to replace any fluid electrolyte deficit. The speed with which rehydration is needed and the magnitude of fluid electrolyte deficits will determine if an aggressive replacement program is merited.
This study assessed whether replacing sweat losses with sodium-free fluid can lower the plasma sodium concentration and thereby precipitate the development of hyponatremia. Ten male endurance athletes participated in one 1-h exercise pretrial to estimate fluid needs and two 3-h experimental trials on a cycle ergometer at 55% of maximum O 2 consumption at 34°C and 65% relative humidity. In the experimental trials, fluid loss was replaced by distilled water (W) or a sodium-containing (18 mmol/l) sports drink, Gatorade (G). Six subjects did not complete 3 h in trial W, and four did not complete 3 h in trial G. The rate of change in plasma sodium concentration in all subjects, regardless of exercise time completed, was greater with W than with G (−2.48 ± 2.25 vs. −0.86 ± 1.61 mmol ⋅ l ⁻¹ ⋅ h ⁻¹ , P = 0.0198). One subject developed hyponatremia (plasma sodium 128 mmol/l) at exhaustion (2.5 h) in the W trial. A decrease in sodium concentration was correlated with decreased exercise time ( R = 0.674; P = 0.022). A lower rate of urine production correlated with a greater rate of sodium decrease ( R = −0.478; P = 0.0447). Sweat production was not significantly correlated with plasma sodium reduction. The results show that decreased plasma sodium concentration can result from replacement of sweat losses with plain W, when sweat losses are large, and can precipitate the development of hyponatremia, particularly in individuals who have a decreased urine production during exercise. Exercise performance is also reduced with a decrease in plasma sodium concentration. We, therefore, recommend consumption of a sodium-containing beverage to compensate for large sweat losses incurred during exercise.
The hyponatremia of exercise may exist in symptomatic and asymptomatic forms. Symptomatic hyponatremia is usually characterized by severe alterations in cerebral function including coma and grand ma1 seizures; it develops especially in less competitive athletes who have maintained high rates of fluid intake during endurance events lasting at least 5 hours. The hyponatremia becomes symptomatic when the volume of excess fluid retained exceeds 2 to 3 liters. The etiology of the condition is unknown. Possibly as many as three or more pathologies (abnormal fluid retention possibly due to inappropriate ADH secretion, abnormal regulation of the extracellular fluid volume, translocation of sodium into a "third space") must be present for symptomatic hyponatremia to develop. The avoidance of overhydration would appear to be the only certain way that susceptible individuals can prevent symptomatic hyponatremia. Sodium chloride containing solutions ingested in physiologically significant concentrations would likely ...
To the Editor.—
Marathon running is gaining increasing popularity. An understanding of the pathophysiology of exertion is important so that runners can be advised on how to minimize the medical hazards of their sport. We therefore read with great interest the report by Frizzell et al1 describing severe acute hyponatremia in marathon runners. The authors attribute the hyponatremia detected in their patients to an excessive loss of sodium in sweat and to drinking hypotonic fluids. Undoubtedly these are important etiologic factors.The recent discovery of a putative natriuretic hormone,2 atrial natriuretic peptide (ANP), is causing a major revision in the understanding of salt and water homeostasis. Increasing the circulating concentration of ANP has been shown to cause a salt-losing state in man.3 There are to date no published data on the effects of exertion on circulating concentrations of ANP. We have therefore performed a pilot study to
Plasma volume expansion usually occurs with acute endurance exercise and endurance training both in humans and in animals. In most cases, the increase in plasma volume is associated with lower haematocrit without red cell mass change or an actual reduction in red cell mass, causing relative or true anaemia, respectively. The combination of exercise and heat acclimation (which produces also hypervolaemia, but at a lesser degree than exercise) enhances hypervolaemia induced by exercise training alone. The onset of the phenomenon is extremely rapid: hypervolaemia is observed within minutes or hours of the cessation of exercise. However, 2 days are necessary to reach peak plasma volume expansion after a marathon run or longer race. The magnitude of this natural expansion ranges from 9 to 25%, corresponding to an additional 300 to 700ml of plasma. The magnitude of this alteration depends on preceding exercise: ambient conditions, intensity and duration of exercise, body posture and frequency of the exercise bouts. The larger the reduction in plasma volume during exercise, the greater the subsequent hypervolaemia. The hydration status of the subjects before and during exercise might modify also plasma volume changes: sufficient fluid ingestion can lead to plasma volume expansion even during prolonged exercise.
Fluid-regulating hormones (aldosterone, arginine vasopressin and atrial natriuretic factor) in conjunction with an elevation in plasma protein content promote hypervolaemia. However, the role and the mechanism of the increase in protein mass remain unclear and the hormonal role in the induction of chronic hypervolaemia is still an open question.
Hypervolaemia can improve performance by inducing better muscle perfusion, and by increasing stroke volume and maximal cardiac output. By increasing skin blood flow, plasma volume expansion also enhances thermoregulatory responses to exercise. This leads to the important concept of optimal plasma volume and haematocrit, and performance.
To assess the relationship between self-selected fluid intake patterns and changes in plasma volume and serum electrolytes during prolonged exercise, five men completed ultramarathon runs ranging from 50 to 100 km. There was a significant relationship between fluid intake and plasma volume changes but no changes occurred in either serum sodium or potassium. Subjects who ingested the most fluid during the race had a modest hemodilution without any changes in serum or potassium. This response may have been influenced by the consumption of beverages containing osmotically active solutes such as sodium and glucose.
In our previous studies on the relationship between prolonged physical stress and muscle enzyme activities, a number of individuals suffered a hyponatremic state. The present study was conducted to evaluate the effect of prolonged physical stress on the development of hyponatremia. Seventeen physically fit male subjects were studied during a 24-hour endurance march. Serum sodium, that averaged 142 +/- 2 before the march, decreased during the march to 135 +/- 2 mEq/l (p less than 0.01 versus before the march). Blood and plasma volumes increased by 8 and 16% (p less than 0.05), respectively. Creatinine clearance before the march declined from 118 +/- 24 to 74 +/- 19 ml/min (p less than 0.005) during the march and correlated negatively with serum sodium (p less than 0.002; r = 0.59). Urinary sodium excretion before the march was 132 +/- 55 and during the march was 123 +/- 62 mEq/24 h. Free water clearance rose during the march and correlated negatively with serum sodium (p less than 0.001), suggesting an appropriate renal diluting response. However, the fall in serum sodium correlated positively with water intake (p less than 0.01; r = 0.59). These results show that hyponatremia develops during endurance marching in normal subjects on an unrestricted high water intake. The renal response to water intake is appropriate; however, the subjects fall to produce maximally diluted urine. Therefore, we suggest that water intake should follow physiological needs and not forced to cause hyponatremia during prolonged physical stress.
Renal function including fluid and electrolyte balance was studied during recovery in eight subjects who developed symptomatic hyponatremia (HN; plasma sodium concentration less than 130 mM) during an 88-km ultramarathon footrace and compared with results for normonatremic runners [NN; n = 18, mean postrace plasma sodium concentration, 138.2 +/- 1.2 (SE) mM]. Estimated fluid intake during the race for HN was 12.5 +/- 1.6 (SE) liters over 9 h 41 min (+/- 28 min). HN excreted a net fluid excess of 2.95 +/- 0.56 (range 1.2-5.9) liters compared with a fluid deficit of 2.7 +/- 0.3% body weight in NN. The sodium deficit was 153 +/- 35 mmol in HN and 187 +/- 37 mmol in NN. Despite the fluid overload, plasma volume was decreased by 24.1 +/- 5.0% in HN compared with 8.2 +/- 2.6% in NN. Serum renin activity (5.1 +/- 2.0 ng.ml-1.h-1), aldosterone concentrations (410 +/- 34 ng/l), creatinine clearances (174.8 +/- 28.2 ml/min), and urine output (6.4 +/- 1.0 ml/min) were markedly elevated in HN during recovery. Thus the hyponatremia of exercise results from fluid retention in subjects who ingest abnormally large fluid volumes during prolonged exercise.
Recent studies have shown that potentially fatal hyponatremia can develop during prolonged exercise. To determine the incidence of hyponatremia in athletes competing in ultradistance events, we measured serum sodium levels in 315 of 626 (50%) runners who were treated for collapse after two 90 km ultramarathon footraces (total starters 20,335; total finishers 18,031) and in 101 of 147 (69%) finishers in a 186 km ultratriathlon. In both races the athletes drank fluids with low sodium chloride content (less than 6.8 mmol.l-1). Hyponatremia (serum sodium level less than 130 mmol.l-1) was identified in 27 of 315 (9%) collapsed runners in the 90 km races and in none of the triathletes. In response to diuretic therapy, the runner with the most severe hyponatremia (serum sodium level = 112 mmol.l-1) excreted in excess of 7.5 l dilute urine during the first 17 h of hospitalization. These data suggest that, although symptomatic hyponatremia occurs in less than 0.3% of competitors during prolonged exercise even when they ingest little sodium chloride, it is found in a significant proportion (9%) of collapsed runners. A regulated contraction of the extracellular fluid volume would explain why the majority of athletes maintain normal serum sodium levels even though they develop a significant sodium chloride deficit during prolonged exercise. Alternatively, sodium chloride losses during prolonged exercise may be substantially less than are currently believed. Physicians treating collapsed ultradistance athletes need to be aware that as many as 10% or more of such patients may be hyponatremic.
With the increasing participation in triathlons of all distances has come a corresponding increase in the need for competent medical information relating to the care of these triathletes. Although medical organization at triathlons involves certain principles which should be applied regardless of race specifics, there are certain other arrangements that will vary with the size and length of the event. For example, the longer races require a reliable communication system, fully equipped mobile response teams, and a larger number of medical staff. Medical communication needs can be served by having priority medical transmissions via UHF radio from mobile vans to a main medical station. An average of 2.5 physicians and 7.5 nurses and other paramedical volunteers for each group of 100 competitors has been found to be sufficient to meet the medical needs of triathletes. The swim, although having the greatest potential for catastrophe, accounts for only 1-3% of medical visits at the Hawaii Ironman Triathlon. Ten percent of injuries requiring medical evaluation at the Hawaii Ironman occur during the bike portion of the race. The rest occur either during the run or after finishing. Seventy-one percent of the total medical visits come directly from the finish line. Dehydration and exhaustion account for the majority of primary medical diagnoses. Appropriate medical care at triathlon races is necessary to aid athletes in safely experiencing their physical potentials.
In ultraendurance triathlons, dehydration and electrolyte balance are important factors in race completion and level of performance. Dehydration is the most common reason for a triathlete in the Hawaii Ironman Triathlon to need medical assistance. Hyponatremia is the predominant electrolyte disturbance. We have previously described exercise-induced hyponatremia and documented its incidence as a function of race length and state of hydration. This syndrome, dehydration plus hyponatremia, is extremely rare in races lasting less than 4 h but becomes common in races lasting longer than 8 h. Recommendations are made to help ultraendurance athletes understand and maintain proper fluid and electrolyte balance.
Triathlons (races involving consecutive swimming, bi cycling, and running) have become commonplace in the United States. These races may involve from 30 min utes to 36 hours of continuous exercise, usually in warm or hot environments. Little has been published regarding the medical and physiological aspects of these events. This paper represents the first large study to date on the subject, including both an analysis of medical complications at six triathlons as well as a prospective electrolyte study conducted at two of these races.
Medical records were kept and examined for all ath letes requiring treatment during a typical United States Triathlon Series (USTS) race in 1986 (1,000 starters; finish times, 2 to 4 hours), a typical Ironman Qualifier (IQ) race in 1986 (622 starters; finish times, 4 to 8 hours), and the 1982 through 1985 Hawaii lronman World Championships (4,583 starters; finish times, 9 to 17 hours). At the USTS race, fewer than 2% (17/1,000) of the starters required aid, at the IQ, approximately 10% (61 /622) of the starters were treated, and at the Ironman, an average of 17% (794/4,583) received med ical attention. The most common diagnoses at the USTS and IQ were dehydration and heat exhaustion. At the lronman, dehydration and heat problems were complicated by hyponatremia.
Because hyponatremia has been reported as a com plication of ultraendurance events, a prospective study was performed on 36 athletes during a USTS race and 64 athletes at the 1984 lronman race. Prerace and postrace blood samples showed that no athletes were hyponatremic following the shorter USTS race, but 27% (17/64) of the athletes studied were hyponatremic fol lowing the lronman race.
Medical personnel should be prepared to treat a minimum of 2% and up to 10% of the athletes in races lasting up to 4 hours, 10% to 20% of those in races lasting 4 to 8 hours, and at least 20% of starters in races lasting between 9 and 17 hours. For races less than 4 hours, the IV fluid of choice should be D5 1/2 NSS (normal saline solution). For races longer than 4 hours, D5NSS should be used for IV resuscitation.
Five young unacclimatised subjects were exposed for 4 h at 34‡ C (10‡ C dew-point temperature and 0.6 m · s−1 air velocity), while exercising on a bicycle ergometer: 25 min work — 5 min rest cycles for 2 hours followed by 20 min work — 10 min rest cycles for two further hours. 5 experimental sessions were carried out: one without rehydration (NO FLUID) resulting in 3.1% mean loss of body weight (δ Mb), and four sessions with 20‡ C fluid ingestion of spring water (WATER), hypotonic (HYPO), isotonic (ISO) and hypertonic (HYPER) solutions to study the effects of fluid osmolarity on rehydration. Mean final rehydration (±SE) after fluid intake was 82.2% (±1.2). Heart rate was higher in NO FLUID while no difference among conditions was found in either δ Mb or hourly sweat rates. Sweating sensitivity was lowest in the dehydration condition, and highest in the WATER one. Modifications in plasma volume and osmolarity demonstrated that NO FLUID induced hyperosmotic hypovolemia, ISO rehydration rapidly led to plasma isoosmotic hypervolemia, while WATER led to slightly hypoosmotic normovolemia.
It is concluded that adequate rehydration through ingestion of isotonic electrolyte-sucrose solution, although in quantities much smaller than evaporative heat loss, rapidly restored and expanded plasma volume. While osmolarity influenced sweating sensitivity, the plasma volume changes (δ PV) within the range −6%⩽δ PV⩽+4% had little effect on temperature adjustments in our conditions.
Two ultramarathon runners were hospitalized with hyponatremic encephalopathy after completing 80 and 100 km (50 and 62 miles), respectively, of the 1983 American Medical Joggers Association ultramarathon race in Chicago. The two runners consumed such large quantities of free water during the race that apparent water intoxication developed. Both recovered satisfactorily after treatment with intravenous saline. The hyponatremia was caused primarily by increased intake and retention of dilute fluids and contributed to by excessive sweat sodium loss. A possible explanation for the postrace onset of symptoms might be the sudden absorption of fluid in the gastrointestinal tract after exercise ceased, with subsequent further dilution of the plasma sodium. Hyponatremia, which has not been commonly associated with exercise, should be considered as a possible consequence of ultraendurance events.
Four athletes developed water intoxication (hyponatremia) during endurance events lasting more than 7 h. The etiology of the condition appears to be voluntary hyperhydration with hypotonic solutions combined with moderate sweat sodium chloride losses. The reason why the fluid excess in these runners was not corrected by increased urinary losses is unknown. When advised to drink less during prolonged exercise, three of the athletes have subsequently completed prolonged endurance events uneventfully.
Observations on hematocrit (Hct) and hemoglobin (Hb) were made in 6 men before and after running long enough to cause a 4% decrease in body weight. Subscripts B and A were used to denote before dehydration and after dehydration, respectively. Relations were derived between BV(b), BV(a), HB(b), Hb(a), Hct(b), and Hct(a) with which the percentage decreases in BV, CV, and PV can be calculated, as well as the concentration of hemoglobin in red cells, g/100 ml-1 (MCHC). When subjects reach the same level of dehydration the water loss from the various body compartments may vary reflecting the difference in salt losses in sweat. Changes in PV calculated from the increase in plasma protein concentration averaged -7.5% compared with -12.2% calculated from changes in Hb and Hct. The difference could be accounted for by a loss of 6% plasma protein from the circulation.
Plasma volume (PV) changes to 15 min quiet standing were analysed (Hb/Hct-alterations) in two studies (nine and 11 healthy males). Data confirmed and extended our findings that blood, arterial or venous, sampled on standing fails to reveal the induced overall haemoconcentration (PV loss). First, standing led to markedly incomplete mixing of blood between circulatory compartments. Secondly, with sampling of antecubital venous blood, haemoconcentration was strongly affected by regional plasma loss and, apparently equally important, by regional blood flow. These difficulties were circumvented, however, by the finding that the PV restitution (haemoconcentration) in the recumbent subject after standing fitted invariably a monoexponential function with striking precision. It allowed, by extrapolation, a seemingly superior definition of the PV reduction at the very end of standing as supported by the fact that PV changes from Hb/Hct and from IgM protein concentration changes were similar, refuting that Fcell-changes contributed to the pronounced Hb/Hct changes. The described novel approach revealed a nicely reproducible PV loss of no less than 692 +/- 46 mL (18.1 +/- 0.6%, Study I; 18.4 +/- 0.5%, Study II), or approximately 11% reduction of blood volume, showing that quiet standing leads to a much more rapid and haemodynamically important decrease in PV than reported previously. Yet, PV was virtually restored within 20 min of recumbency after standing, with 50% recovery within 6 min and regain of as much as 70 mL in the very first min. The latter data indicate that the body possesses a surprising capacity for rapid fluid transfer from the extra- to the intravascular space.
Thirty competitors in the Hawaii Ironman Triathlon were prospectively studied to determine whether fluid and electrolyte disturbances were causes for seeking race-day medical care. Athlete weights were significantly (p < 0.0001) decreased during the race, but decreases were not different in treated (n = 11; % delta wt -2.3 +/- 2.9) versus not treated (n = 19; % delta wt - 2.0 +/- 1.9) athletes. Hyponatremia occurred in nine athletes (30%), and hypomagnesemia in six (20%), but only half of athletes were either electrolyte imbalance sought care. Although athletes receiving medical care may have fluid and electrolyte problems, these abnormalities may also occur in healthy athletes.
Although hyponatremia (HN) has been reported among endurance athletes, its etiology often remains uncertain and of great interest to clinicians and physiologists. This case report presents physiologic evidence regarding the etiology and development of HN during exercise in the heat. A 21-yr-old male volunteer (K.G.) unexpectedly experienced symptomatic HN during a research investigation that involved controlled sodium (Na+) intake (137 mEq Na+.d-1 for 7d) and exercise-heat acclimation (41 degrees C; 30 min.h-1, 8 h.d-1 for 10 d). Fluid balance, physiologic variables, and hematologic/hormone data were measured before and after the HN episode, with similar measurements recorded for nine unaffected volunteers. The results indicated: 1) HN was verified in K.G. (plasma Na+ < 130 mEq.l-1) after only 4 h of mild, intermittent exercise in heat; 2) K.G.'s heart rate, rectal temperature, blood pressure, and Na+ losses in sweat and urine were < or = control subjects at all times; 3) between hours 4-7, an inappropriately large release of vasopressin coincided with a decrease of urine volume to 0 ml.h-1. It was concluded that a large intake (10.3 l.7h-1) and retention (2.77 l.7h-1) of water and a "low normal" initial plasma Na+ (134 mEq.l-1) were primary factors in the development of HN in K.G., whereas Na+ losses in sweat and urine were normal and served only to exacerbate HN.
Exercise-induced hyponatremia is commonly believed to be associated only with extraordinary physical efforts, or particularly strenuous exercise. Hyponatremia complicating moderate exercise has not been described previously. The authors describe the characteristics of seven patients with life-threatening hyponatremia associated with mild to moderate exercise. All patients suffered from nausea, vomiting, agitation, and confusion, appearing during or after moderate physical activity. Grand mal convulsions occurred in five of the patients. In laboratory results, hyponatremia was as low as 115 mEq/L, with a relatively high sodium concentration in the urine. High serum creatine kinase activity levels were found in most of the patients. All patients were discharged in good condition, without neurologic sequela. The authors conclude that hyponatremia is a possible complication of moderate exercise, and not only of endurance sports, and that exercise-induced hyponatremia can produce severe neurologic manifestations. The mechanism of the hyponatremia is unclear, but may be due to a hemodynamically inappropriate stimulus for antidiuretic hormone secretion.
This study describes the incidence of hyponatremia and the weight changes during an ultradistance multisport triathlon.
Descriptive research.
A 1-day triathlon in which each athlete kayaks 67 km, cycles 148 km, and runs 23.8 km.
Forty-eight athletes competing in the race were studied.
None.
All subjects were weighed before the race and on completion of the race. A blood sample for serum sodium was taken at the finish of the race.
The mean weight change over the course of the race was a loss of 2.5 kg (SD +/- 1.7, n = 48), or a mean percentage loss of body weight of 3.1% (SD +/- 2.07). This was highly statistically significant (p < 0.0001) using the Student paired t test. No athletes gained weight, and six athletes maintained their same weight. Only one athlete was hyponatremic (Na = 134 mEq/L). This athlete maintained his weight over the course of the race and he did not seek medical attention. The mean serum sodium concentration at the end of the race was 139.3 mEq/L (SD = 2.28, n = 47). There was a significant correlation (r = 0.30, p = 0.04) between sodium levels and weight change during the race: the greater the weight loss, the higher the serum sodium concentration. There was no significant correlation between the degree of weight loss and athletes' finishing times (r = 0.11, p = 0.45).
Symptomatic hyponatremia did not occur in the 1996 Coast to Coast multisport triathlon, although one athlete had borderline hyponatremia. Athletes lose significant amounts of weight over the course of this multisport event, but nevertheless manage to complete the race.
To describe the weight changes and the incidence of hyponatremia during an ultradistance triathlon in the athletes who attend medical care after the race.
Descriptive research.
The 1996 New Zealand Ironman Triathlon in which each athlete swam 3.8 km, cycled 180 km, and ran 42 km.
Ninety-five athletes attending for medical care after the race were studied. One hundred sixty-nine athletes who did not attend for medical care were also weighed before and after the race.
Weights were measured at race registration and on finishing the race. Whole-blood sodium concentration was measured in those athletes with clinical evidence of fluid or electrolyte disturbances.
Weights were significantly decreased at the end of the race in the athletes seeking medical care (n = 48, mean % delta wt = -2.5%, p < 0.001) and also in the athletes who did not seek medical care (n = 169, mean % delta wt = -2.9%, p < 0.001). Seventeen percent of race starters sought medical attention. Dehydration accounted for 26% of primary diagnoses and hyponatremia for 9%. One athlete with hyponatremia (Na 130 mEq/L) is described who drank 16 L over the course of the race, with a weight gain of 2.5 kg. This is consistent with the hypothesis of fluid overload as the cause of his hyponatremia. Hyponatremia accounted for four of five admissions to the hospital after the race. An inverse relationship between postrace sodium concentrations and percentage change in body weight was observed (r = -0.63).
Hyponatremia is an important risk to the health of athletes competing in an ultradistance triathlon, with fluid overload the likely aetiology.
This study assessed whether replacing sweat losses with sodium-free fluid can lower the plasma sodium concentration and thereby precipitate the development of hyponatremia. Ten male endurance athletes participated in one 1-h exercise pretrial to estimate fluid needs and two 3-h experimental trials on a cycle ergometer at 55% of maximum O2 consumption at 34 degrees C and 65% relative humidity. In the experimental trials, fluid loss was replaced by distilled water (W) or a sodium-containing (18 mmol/l) sports drink, Gatorade (G). Six subjects did not complete 3 h in trial W, and four did not complete 3 h in trial G. The rate of change in plasma sodium concentration in all subjects, regardless of exercise time completed, was greater with W than with G (-2.48 +/- 2.25 vs. -0.86 +/- 1.61 mmol. l-1. h-1, P = 0.0198). One subject developed hyponatremia (plasma sodium 128 mmol/l) at exhaustion (2.5 h) in the W trial. A decrease in sodium concentration was correlated with decreased exercise time (R = 0.674; P = 0.022). A lower rate of urine production correlated with a greater rate of sodium decrease (R = -0. 478; P = 0.0447). Sweat production was not significantly correlated with plasma sodium reduction. The results show that decreased plasma sodium concentration can result from replacement of sweat losses with plain W, when sweat losses are large, and can precipitate the development of hyponatremia, particularly in individuals who have a decreased urine production during exercise. Exercise performance is also reduced with a decrease in plasma sodium concentration. We, therefore, recommend consumption of a sodium-containing beverage to compensate for large sweat losses incurred during exercise.
Hyponatremia ([plasma sodium] <135 mmol x L(-1)) is a potentially serious complication of ultraendurance sports. However, the etiology of this condition is still uncertain. This observational cohort study aimed to determine prospectively the incidence and etiology of hyponatremia in an ultradistance triathlon.
The subjects consisted of 605 of the 660 athletes entered in the New Zealand Ironman triathlon (3.8-km swim, 180-km cycle, and 42.2-km run). Subjects were weighed before and after the race. A blood sample was drawn for measurement of plasma sodium concentration after the race.
Complete data on pre- and postrace weights and plasma sodium concentrations were available in 330 race finishers. Postrace plasma sodium concentrations were inversely related to changes in body weight (P = 0.0001). Women (N = 38) had significantly lower plasma sodium concentrations (133.7 vs 137.4 mmol x L(-1); P = 0.0001) than men (N = 292) and lost significantly less relative weight (-2.7 vs -4.3%; P = 0.0002). Fifty-eight of 330 race finishers (18%) were hyponatremic; of these only 18 (31%) sought medical care for the symptoms of hyponatremia (symptomatic). Eleven of the 58 hyponatremic athletes had severe hyponatremia ([plasma sodium] < 130 mmol x L(-1)); seven of these 11 severely hyponatremic athletes were symptomatic. The relative body weight change of the 11 severely hyponatremic athletes ranged from 2.4% to +5%; eight (73%) of these athletes either maintained or gained weight during the race. In contrast, relative body weight changes in the 47 athletes with mild hyponatremia ([plasma sodium] 130-134 mmol x L(1)) were more variable, ranging from -9.25% to +2.2%.
Hyponatremia is a common biochemical finding in ultradistance triathletes but is usually asymptomatic. Although mild hyponatremia was associated with variable body weight changes, fluid overload was the cause of most (73%) cases of severe, symptomatic hyponatremia.
Hyponatremia is being increasingly recognized as a complication of participation in ultra-endurance sports. Reported is the case of an Ironman triathlete who collapsed at the end of the race, having gained 5% in body weight. His serum sodium concentration at the finish was 116 mmol/L. After an Intensive Care Unit course complicated by recurrent seizures, he eventually made a complete neurologic recovery. The pathogenesis of hyponatremia and its management in such cases is discussed. (C) 2000 Elsevier Science Inc.
To evaluate a method of medical care at an ultradistance triathlon, with the aim of reducing the incidence of hyponatremia.
Descriptive research.
New Zealand Ironman triathlon (3.8 km swim, 180 km cycle, 42.2 km run).
117 of 134 athletes seeking medical care after the triathlon (involving 650 race starters).
A prerace education program on appropriate fluid intake was undertaken. The number of support stations was decreased to reduce the availability of fluid. A body weight measurement before the race was introduced as a compulsory requirement, so that weight change during the race could be included in the triage assessment. An on-site laboratory was established within the race medical tent.
Numbers of athletes and diagnoses, including the incidence of symptomatic hyponatremia (defined as symptoms of hyponatremia in association with a pretreatment plasma sodium concentration [Na] < 135 mmol/L); weight changes; and changes in [Na].
The common diagnoses in the 117 athletes receiving attention were exercise-associated collapse (27%), musculoskeletal complaints (26%), and dehydration (12%). There was a significant reduction in the number of athletes receiving medical care for hyponatremia, from 25 of the 114 athletes who received care in 1997 (3.8% of race starters) to 4 of the 117 athletes who received care in 1998 (0.6% of race starters). Mean weight change among athletes in the 1998 race was -3.1 kg, compared with -2.6 kg in 1997.
A preventive strategy to decrease the incidence of hyponatremia, including education on fluid intake and appropriate placement of support stations, was associated with a decrease in the incidence of symptomatic hyponatremia.
To study fluid and sodium balance in two ultradistance triathletes.
Prospective case study.
An ultradistance triathlon (3.8 km swim, 180 km cycle, 42.2 km run), and during overnight recovery. Ambient air temperature at 12:00 p.m. race day was 21 degrees C, with a relative humidity of 91%. Water temperature was 20.7 degrees C.
Two female ultradistance triathletes, ages 30 and 39 years, who were participating in a larger study investigating weight and electrolyte changes in the Ironman triathlon.
None.
Subjects were weighed and had blood drawn for serum sodium concentration, hemoglobin, hematocrit, arginine vasopressin, and aldosterone concentration prior to and after the race, and at 8:00 a.m. the following morning. Sodium and fluid intake and urinary output were measured during recovery.
Both subjects developed mild hyponatremia (Na 131 and 130 mmol/L) during the race, with a weight gain (0.5 and 1.5 kg). Neither subject had large sodium losses (24 mmol and 20 mmol). Fluid consumption was 733 ml/h and 764 ml/h. Plasma volume increased during the race (25 and 16%). Arginine vasopressin (AVP) levels were not elevated in either subject (1.2 and 1.9 pmol/L). Both subjects demonstrated a water excess during the race (1.5 and 2.5 L), and lost weight during recovery (2.0 and 4.5 kg).
Hyponatremia resulted from fluid retention in the extracellular space, without evidence of large sodium losses or inappropriate AVP secretion.
To study fluid and sodium balance during overnight recovery following an ultradistance triathlon in hyponatremic athletes compared with normonatremic controls. CASE CONTROL STUDY: Prospective descriptive study.
1997 New Zealand Ironman Triathlon (3.8 Km swim, 180 Km cycle, 42.2 Km run).
Seven athletes ("subjects") hospitalized with hyponatremia (median sodium [Na] = 128 mmol L(-1)). Data were compared with measurements from 11 normonatremic race finishers ("controls") (median sodium = 141 mmol L(-1)).
None.
Athletes were weighed prior to, immediately after, and on the morning after, the race. Blood was drawn for sodium, hemoglobin, and hematocrit immediately after the race and the following morning. Plasma concentrations of arginine-vasopressin (AVP) were also measured post race.
Subjects were significantly smaller than controls (62.5 vs. 72.0 Kg) and lost less weight during the race than controls (median -0.5% vs. -3.9%, p = 0.002) but more weight than controls during recovery (-4.4% vs. -0.8%, p 0.002). Subjects excreted a median fluid excess during recovery (1,346 ml): controls had a median fluid deficit (521 ml) (p = 0.009). Estimated median sodium deficit was the same in subjects and controls (88 vs. 38 mmol L(-1), p = 0.25). Median AVP was significantly lower in subjects than in controls. Plasma volume fell during recovery in subjects (-5.9%, p = 0.016) but rose in controls (0.76%, p = NS).
Triathletes with symptomatic hyponatremia following very prolonged exercise have abnormal fluid retention including an increased extracellular volume, but without evidence for large sodium losses. Such fluid retention is not associated with elevated plasma AVP concentrations.
In the study presented here, we examined the affects of a close to complete replacement of sweat water and Na+ losses on fluid shifts during exercise. Six cyclists performed three 4-h rides at 55% of their peak oxygen uptake in a 20 degrees C environment while consuming 3.85 l of an 8% carbohydrate solution containing 5, 50 or 100 mEq.l-1 of Na+. Increases in Na+ intake reduced renal free water clearance from around 40 ml.h-1 to -8 and -121 ml.h-1 and led to a decrease in urine volume from approximately equal to 1.0 to 0.5 l (P < 0.05). In contrast, the 3.5-3.9 l fluid and 150-190 mEq Na+ losses in sweat were similar in each trial, as were the approximately equal to 80 mEq K+ losses in sweat and urine and the 282-288 mosmol.kg-1 plasma osmolalities. During the low-Na+ trial, plasma osmolality was maintained by a approximately equal to 1.3 l contraction of extracellular fluid (ECF) with the loss of approximately equal to 200 mEq Na+. However, in the other trials, approximately equal to 1.3 l of water was lost from the intracellular fluid. During the medium-Na+ trial, a loss of only approximately equal to 40 mEq Na+ maintained ECF volume, and during the high-Na+ trial, a gain of approximately equal to 160 mEq Na+ expanded the ECF by approximately equal to 0.8 l. However, corresponding changes in plasma volumes from -0.20 to 0.15 l had no effect on cardiovascular drift or thermoregulation. These data suggest that during prolonged exercise of moderate intensity under mild environmental conditions when sweat rates are approximately equal to 0.9 l.h-1, complete Na+ replacement maintains plasma volume and reduces dehydration, but when fluid intake matches sweat rate, has little effect on plasma osmolality.
This paper reviews the extensive literature on hyponatremia, a common and potentially serious complication of ultra-distance exercise. Fluid overload is the likely aetiology. Fluid intakes are typically high in athletes who develop hyponatremia, although hyponatremia can occur with relatively modest fluid intakes. The development of fluid overload and hyponatremia in the presence of a modest fluid intake raises the possibility that athletes with this condition may have an impaired renal capacity to excrete a fluid load. The bulk of evidence favours fluid retention in the extracellular space (dilutional hyponatremia) rather than fluid remaining unabsorbed in the intestine. Female gender is an important risk factor for the development of hyponatremia. Management and prevention of exercise-associated hyponatremia are discussed.