A The incidence of exercise-associated hyponatremia (EAH) is higher in women than in men. We present three cases of a very mild post-race EAH in female winners of three 24-h ultra races in various weather conditions and disciplines with post-race plasma sodium [Na⁺] levels of 134 mM (Case 1), 133 mM (Case 2) and 134 mM (Case 3). Moreover, Case 1 and Case 2 showed elevated creatine kinase concentrations of >10,000 U/l with an absence of renal function abnormality. The common characteristics were female sex, veteran recreational category, long race experience in the particular sports discipline, excellent race performance, similar total weekly training hours and the presence of luteal phase of the menstrual cycle during the race. Hematocrit and hemoglobin decreased and post-race K⁺/Na⁺ ratio in urine increased in all three cases. In addition, an increased body mass and a decreased urine specific gravity and urine osmolality suggested over-drinking in Case 1. A decrease in the glomerular filtration rate and creatine clearance accompanied by an increase in urine [Na⁺] may contribute to fluid overload in Cases 2 and 3. Furthermore, urine osmolality reached a level indicating antidiuretic hormone secretion in all the present cases. Therefore, we recommend that race medical personnel should not forget to look for EAH even in fast and experienced female athletes and during races in different environmental conditions.

Centre of Sports Activities Brno University of Technology Brno 64300 Czech Republic

Exercise Physiology Laboratory Nikaia 18450 Greece

Institute of Experimental Biology Masaryk University Brno 61137 Czech Republic

Institute of Primary Care University of Zurich Zurich 8091 Switzerland

The Private University of the Principality of Liechenstein 9495 Liechenstein

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