OBJECTIVE

To study biochemical parameters and renal function in runners completing a 60 km mountain run and to investigate the incidence of exercise-associated hyponatremia (EAH). To assess the effects of nonselective nonsteroidal antiinflammatory medication (NSAIDs) and cyclooxygenase-2 (COX-2) selective nonsteroidal antiinflammatory medication (COXIBs) on these parameters.

DESIGN

Observational cohort study.

SETTING

Kepler Challenge 60 km mountain run, Te Anau, New Zealand, December 2003.

PARTICIPANTS

One hundred thirty-one of the 360 runners entered in the race were prospectively enrolled as volunteers on the day before the race.

MAIN OUTCOME MEASURES

Subjects were weighed at race registration the day before the race and at the finish line. Blood was taken within 5 minutes of finishing and was analyzed for serum sodium, creatinine, urea, and potassium concentrations, and hematocrit. Participants were questioned about medication use in the 24 hours before and during the race (NSAIDs, COXIBs, other medications).

RESULTS

Complete data sets were obtained on 123 runners. Five athletes were biochemically hyponatremic [(Na) 130-134 mM] and four were hypernatremic [(Na) 146-148 mM]. Hyponatremia was associated with a mean weight gain of 1.32 kg (range, -1.5 to 1.6 kg). Serum [Na] varied inversely with weight change. Estimated creatinine clearance did not vary with percent weight loss. Estimated creatinine clearance declined with increasing runner age. Sixty-five percent of runners did not use any medication, whereas 20% had used NSAIDs and 15% had taken COXIBs. There were no statistically significant differences between NSAID and COXIB users in any measured parameters or between all NSAID and COXIB users when compared with nonusers.

CONCLUSIONS

Mild asymptomatic EAH was found to occur in 4% of the volunteer ultraendurance mountain runner study group and was associated with a mean weight gain of 1.32 kg (range, -1.5 to 1.6 kg) during the race. Seven percent gained weight but remained normonatremic, suggesting other compensatory mechanisms. Hypernatremia was found in 3% and was associated with a mean weight loss. Postrace serum sodium concentration varied inversely with percent weight change. Runners using any NSAID were more likely to become hyponatremic. Estimated creatinine clearance increased with increasing age. Elevated serum creatinine concentration at the end of the race returned to normal when remeasured the week after the race. Thirty-five percent of runners were found to use NSAIDs or COXIBs. The measures of weight change and of serum sodium, potassium, urea, and creatine concentration did not differ between NSAID and COXIB users or between all nonsteroidal antiinflammatory users and nonusers.