Figure 10. Exercise associated hyponatremia in triathletes. 1089 triathletes were studied. The mean plasma sodium level at the finish was 140.5±4.2 mmol/L (range 111-152). Among athletes completing the study events, 10.6% had documented hyponatremia: 8.7% mild; 1.6% severe; and 0.3% critical (3 athletes in total with plasma sodium levels 120, 119, and 111 mmol/L respectively). Multivariate analysis showed a significant association between development of hyponatremia and the following factors: female gender; longer times to complete a race. Critical hyponatremia occurred in participants who finished in the 12th and 14th hours of the race (145).