HYPONATREMIA AND ADVENTURE RACING

Abstract

PURPOSE To determine hydration status, serum sodium concentration and the incidence of hyponatremia in athletes competing in the sport of adventure racing. METHODS Six male and five female endurance-trained athletes participating in a 48-hour adventure race served as subjects. Race components included trail running, orienteering, mountain biking and kayaking. Environmental conditions during the race were relatively mild, with a high temperature of 34°C and a low of 9°C, corresponding humidity measurements were 43% and 70%, respectively. Food and fluid intake was measured and recorded for each subject throughout the race to determine total and hourly intakes. RESULTS The mean and range of times for participation were 23.86±5.54 hr and 17.5–30.8 hr; none of the 11 subjects were able to complete the race due to injuries or perceptions of cold, fatigue, and/or malaise. Data analysis revealed a mean body weight loss of 1.53±1.20 kg, which was 1.98% of prerace body weight. The group mean post-race serum sodium was 134.7±7.3 mEq/L, and 6 of the 11 subjects had post-race serum sodium levels within the classification of hyponatremia (< 135 mEq/L). Mean hourly fluid and sodium intakes were 309±100 ml and 295±126 mg, respectively. CONCLUSION Data indicated that fluid consumption was less than that recommended by the ACSM. Considering that over half of the subjects became mildly hyponatremic, it is recommended that adventure race directors alert participants and race volunteers to the potential hazards imposed by these ultraendurance events in order to prevent medical emergencies related to hydration and electrolyte imbalances.