WEIGHT CHANGES AND SERUM SODIUM CONCENTRATIONS AFTER AN ULTRADISTANCEMULTISPORT TRIATHLON

Objective: This study describes the incidence of hyponatremia and the weight changes during an ultradistance multisport triathlon. Design: D escriptive research. Setting: A 1-day triathlon in which each athlete kayaks 67 km, cycles 148 km, and runs 23.8 km. Participants: Forty-eig ht athletes competing in the race were studied. Interventions: None. M ain outcome measures: All subjects were weighed before the race and on completion of the race. A blood sample for serum sodium was taken at the finish of the race. Results: The mean weight change over the cours e of the race was a loss of 2.5 kg (SD +/- 1.7, n = 48), or a mean per centage loss of body weight of 3.1% (SD +/- 2.07). This was highly sta tistically significant (p < 0.0001) using the Student paired t test. N o athletes gained weight, and six athletes maintained their same weigh t. Only one athlete was hyponatremic (Na = 134 mEq/L). This athlete ma intained his weight over the course of the race and he did not seek me dical attention. The mean serum sodium concentration at the end of the race was 139.3 mEq/L (SD = 2.28, n = 47). There was a significant cor relation (r = 0.30, p = 0.04) between sodium levels and weight change during the race: the greater the weight loss, the higher the serum sod ium concentration. There was no significant correlation between the de gree of weight loss and athletes' finishing times (r = 0.11, p = 0.45) . Conclusions: Symptomatic hyponatremia did not occur in the 1996 Coas t to Coast multisport triathlon, although one athlete had borderline h yponatremia. Athletes lose significant amounts of weight over the cour se of this multisport event, but nevertheless manage to complete the r ace.