Chorley, J. N., Cianca, J. C., Divine, J. G., & Hew, T. (2003). Sodium and fluid balance in hyponatremic marathon runners and controls. Medicine and Science in Sports and Exercise, 35(5), Supplement abstract 1372.

Hyponatremia is sometimes known as "water intoxication" and stems from drinking too much water, usually before long endurance events or events in the heat. The excess water dilutes salt (sodium chloride) concentrations. Salt is an electrolyte that is vitally involved in maintenance of "water balance" in the body.

Volunteers (N = 111) from the Houston (200, 2001, 2002) and Boston (2001) marathons completed pre- and post-event questionnaires and submitted to blood analyses.

Ss who were hyponatremic had greater sodium loss, greater sweat sodium concentrations, and consumed more fluids than nonhyponatremics. Sweat rates were similar and there were no gender differences.

Implication. Excessive fluid intake before and during an extended period of sweating and exercise can lead to excessive loss of electrolytes, particularly salt. This is likely to have a detrimental effect on performance.

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