Fluid and electrolyte replacement in the ultramarathon runner

We studied three male runners during three separate ultramarathon races. Serial blood samples were tested for electrolytes, renal function, albumin, calcium, phosphorus, and magnesium. Two runners had aldosterone levels measured during the race and one runner had blood lactate levels measured. All runners ingested an isotonic fluid and electrolyte solution during the race. The runners consumed the solution without medical complications and maintained prerace body weights and hydration levels. Each runner maintained normal endocrine/metabolic parameters. We concluded that it is possible to maintain normal hydration and electrolyte states during a prolonged race, provided that sufficient fluid and electrolyte solutions are ingested.