Fluid and electrolyte balance during a cool weather marathon

Changes in blood, serum, and urine parameters that are usually associated with fluid and electrolyte balance were studied in 45 volunteers who ran the 1987 Pittsburgh Marathon. There were 39 males and 6 females. The mean age was 39.3 years. Their mean fluid intake was 1650 cc and the mean finishing time was 4 hours and 1 minute. The race was run in the rain with a temperature of 46 degrees F. When the prerace and postrace values of the runners were compared, significant increases were noted in the serum sodium, potassium, blood urea nitrogen (BUN), creatinine, uric acid, creatine phosphokinase (CPK), protein, plasma renin, vasopressin, and urinary potassium. Significant decreases were found in weight, blood pressure, and urinary sodium. No significant differences were noted in serum chloride, serum glucose, and hemoglobin/hematocrit. The mean weight loss of 1.9 kg was less than weight losses reported in marathons run under warmer conditions.