Hyponatremia and weight changes in an ultra-distance triathlon

Speedy DB, Faris JG, Hamlin M, Gallagher PG, Campbell RGD Clinical Journal of Sports Medicine 1997;7:180-184

Abstract:

Objective:

To
describe the weight changes and the incidence of hyponatremia during an
ultradistance triathlon in the athletes who attend medical care after
the race.

Design:

Descriptive research.

Setting:

The 1996 New Zealand Ironman Triathlon in which each athlete swam 3.8 km, cycled 180 km, and ran 42 km.

Participants:

Ninety-five
athletes attending for medical care after the race were studied. One
hundred sixty-nine athletes who did not attend for medical care were
also weighed before and after the race.

Main Outcome Measures:

Weights
were measured at race registration and on finishing the race.
Whole-blood sodium concentration was measured in those athletes with
clinical evidence of fluid or electrolyte disturbances.

Results:

Weights
were significantly decreased at the end of the race in the athletes
seeking medical care (n = 48, mean % delta wt = -2.5%, p < 0.001)
and also in the athletes who did not seek medical care (n = 169, mean %
delta wt = -2.9%, p < 0.001). Seventeen percent of race starters
sought medical attention. Dehydration accounted for 26% of primary
diagnoses and hyponatremia for 9%. One athlete with hyponatremia (Na
130 mEq/L) is described who drank 16 L over the course of the race,
with a weight gain of 2.5 kg. This is consistent with the hypothesis of
fluid overload as the cause of his hyponatremia. Hyponatremia accounted
for four of five admissions to the hospital after the race. An inverse
relationship between postrace sodium concentrations and percentage
change in body weight was observed (r = -0.63).

Conclusions:

Hyponatremia
is an important risk to the health of athletes competing in an
ultradistance triathlon, with fluid overload the likely aetiology.