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Clin J Sport Med. 2010 May;20(3):193-9. doi: 10.1097/JSM.0b013e3181da53ea.

Can changes in body mass and total body water accurately predict hyponatremia after a 161-km running race?

Author information

  • 1Sports Medicine Program, University of California Davis Medical Center, Sacramento, California, USA. dklebus@gmail.com

Abstract

OBJECTIVE:

To relate changes in body mass, total body water (TBW), extracellular fluid (ECF), and serum sodium concentration ([Na]) from a 161-km ultramarathon to finish time and incidence of hyponatremia.

DESIGN:

Observational.

SETTING:

: The 2008 Rio Del Lago 100-Mile (161-km) Endurance Run in Granite Bay, California.

PARTICIPANTS:

Forty-five runners.

MAIN OUTCOME MEASUREMENTS:

Pre-race and post-race body mass, TBW, ECF, and serum [Na].

RESULTS:

Body mass and serum [Na] significantly decreased 2% to 3% (P < 0.001) from pre-race to post-race, but TBW and ECF were unchanged. Significant relationships were observed between finish time and percentage change in body mass (r = 0.36; P = 0.01), TBW (r = 0.50; P = 0.007), and ECF (r = 0.61; P = 0.003). No associations were found between post-race serum [Na] and percentage change in body mass (r = -0.04; P = 0.94) or finish time (r = 0.5; P = 0.77). Hyponatremia (serum [Na] < 135 mmol/L) was present among 51.2% of finishers. Logistic regression prediction equation including pre-race TBW and percentage changes in TBW and ECF had an 87.5% concordance with the classification of hyponatremia.

CONCLUSIONS:

Hyponatremia occurred in over half of the 161-km ultramarathon finishers but was not predicted by change in body mass. The combination of pre-race TBW and percentage changes in TBW and ECF explained 87.5% of the variation in the incidence of hyponatremia.

CLINICAL SIGNIFICANCE:

Exercise-associated hyponatremia can occur simultaneously with dehydration and cannot be predicted by weight checks at races.

PMID:
20445360
[PubMed - indexed for MEDLINE]
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