Regulation of Electrolyte and Fluid Metabolism in Multi-stage Ultra-Marathoners. We have studied at ‘Swiss Jura Marathon’ if the prevalence of the stress-associated hyponatremia is higher than in a simple ultra-based.The prevalence of hyponatremia was not higher than other ultra-rural. The course of sodium excretion in the urine could indicate that the stress-associated hyponatremia could come about by a hormonal dysregulation as a fluid overload. The abstract to the study can be found under https://pubmed.ncbi.nlm.nih.gov/22638835/