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

No abstract

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.

Athletes lose 2.5 kg of weight during an ultradistance 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.

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

No abstract

(AVP)(p) was markedly elevated after the ultramarathon despite unchanged plasma [Na(+)](.) Therefore, an inability to maximally suppress (AVP)(P) during exercise as a result of nonosmotic stimulation of AVP secretion may contribute to the pathogenesis of exercise-associated hyponatremia if voluntary fluid intake were to exceed fluid output.

Energy balance of 10 male and 8 female triathletes participating in an Ironman event (3.8-km swim, 180-km cycle, 42.2-km run) was investigated. Energy intake (EI) was monitored at 7 designated points by dietary recall of food and fluid consumption. Energy expenditure (EE) during cycling and running was calculated using heart rate-VO, regression equations and during swimming by the multiple regression equation: Y = 3.65v+ 0.02W- 2.545 where Yis VO,in L x min(-1), v is the velocity in m s(-1), Wis the body weight in kilograms. Total EE (10,036 +/- 931 and 8,570 +/- 1,014 kcal) was significantly greater than total EI (3,940 +/- 868 and 3,115 +/- 914 kcal, p <.001) for males and females, respectively, although energy balance was not different between genders. Finishing time was inversely related to carbohydrate (CHO) intake (g x kg(-1) x h(-1)) during the marathon run for males (r = -.75,p <.05), and not females, suggesting that increasing CHO ingestion during the run may have been a useful strategy for improving Ironman performance in male triathletes.