134 can ensue [35]. Athletes at greatest risk are those with the saltiest sweat ([60 mmol Na/L) as they will lose the greatest amount of sodium per liter of sweat [36]. Although an athlete who is acclimatized to warm weather will reduce their sweat sodium losses, a typical person (40 mmol Na/L) will lose almost 1 gm of sodium per hour given a modest sweat loss of 1 l/h [37]. In the absence of other interven- tions there is a signiﬁcant time and sweat rate factor in determining hyponatremia risk. A second common cause of exercise-related hypona- tremia occurs with the dilution effect of ﬂuid consumption. In the 1980s and 1990s it was common to hear race organizers and even the US military recommend that ath- letes and recruits consume ﬂuids in excess of rated thirst to prevent dehydration [38]. Even though these organizers were well meaning, these recommendations and guidelines failed to account for physiologic limitations. The kidneys have a water ﬁltration limit of approximately 1 l/h, how- ever these athletes and recruits were consuming greater than 1.5 l/h [39]. This is the theorized reasoning for the increased incidence of hyponatremia during this time per- iod. The subsequent release of the ACSM position stand on exercise and ﬂuid replacement in 1996 (subsequently revised in 2007) partially addressed the risks and helped to reduce the incidence of hyponatremia associated with excess ﬂuid consumption [40]. Despite these changes, Noakes and Speedy [38] reported that there is considerable risk of hyponatremia in groups exercising greater than 4 h. The theory is that in a sport such as a typical marathon, these slower runners will consume more ﬂuid than they sweat out and suffer from dilution hyponatremia. These concerns were directly addressed in the most recent International Marathon Medical Directors Association Position Statement 2006, which gives recommendations of ﬂuid intake that is directly proportional to running speed [41, 42]. Although slower runners should not restrict ﬂuid intake during competition, it is important that they do not drink excessively. In addition to monitoring ﬂuid intake to prevent hypo- natremia, data suggest that salt supplementation may be beneﬁcial [6]. However, there is also conﬂicting research that suggests that the changes associated with this type of supplementation are insigniﬁcant [43]. Therefore, the direct etiology for this practice and its efﬁcacy are not completely clear. Anecdotally, the practice continues to be recommended as it increases thirst and subsequently improves hydration status throughout the competition. Moreover, popular sports drinks do not contain sufﬁcient concentrations of sodium to replace sweat losses [44]. As greater numbers compete in endurance events, there have also been reports of increasing numbers of medica- tion-associated causes of hyponatremia. Non-steroidal anti- Curr Rev Musculoskelet Med (2008) 1:131–136 inﬂammatory medications (NSAID) and even the cyclo- oxygenase-2 inhibitors have been shown to signiﬁcantly inhibit free water clearance by the kidneys in athletes during endurance competition [45]. This effect has been associated with serum dilution, weight gain, and hypona- tremia [46]. Though the incidence of NSAID use has been found to be greater than the incidence of hyponatremia, there are positive correlations [47]. Despite previous ﬁnd- ings and the theoretical physiologic reasoning for the association between NSAID and hyponatremia, Dumke et al. [48] refutes the signiﬁcance of ibuprofen and hypo- natremia in elite athletes when dose of medication is controlled. Overall, prudence would indicate instructing endurance athletes at risk for hyponatremia to avoid NSAIDs around competitions until further research is completed. In spite of limited data, women are considered to be at a signiﬁcantly greater risk to develop hyponatremia than men. The anecdotal reasoning has many sources, ranging from slower running speeds, to women being more acutely aware of maintaining adequate hydration, resulting in inadvertent over consumption of ﬂuids [49]. In reality, there is a real theoretical physiologic reason for women to be at a greater risk. The increased estrogen level in women of childbearing age has been cited. Physiologically estro- gen has been found to inhibit the sodium potassium ATPase enzyme, thus hindering the removal of potassium from brain cells, resulting in increased risk of cerebral edema associated with episodes hyponatremia [50]. Thus, though the etiologic reason for increased hyponatremia rates in women compared to men is unclear, there is an increased physiologic risk for poorer outcomes once these women have symptomatic hyponatremia. Overall, the best treatment of hyponatremia is to prevent it from occurring through education of the athletes, coa- ches, and medical staff. Once a competitor is experiencing symptoms of hyponatremia such as cramps or mild changes in sensorium, giving salty foods is one of the safest treat- ments. Hypertonic 3% saline is only warranted in severe symptoms of hyponatremia [51]. The use of isotonic ﬂuid replacement is contraindicated as this may further com- plicate ﬂuid overload and hyponatremia. Typically, patients will have spontaneous diuresis with resolution of symptoms and should be monitored until this time if ﬂuid overload is suspected [52]. Later in the race, less-condi- tioned slower runners are at increased risk of hyperhydration and hyponatremia. Competition The effects of altered hydration can inﬂuence athletes cognitively in addition to physically. This can even occur