Author(s): SANTIN, F., CUNHA, M.G., MELLO, D., Institution: FACULDADE VP, Country: BRAZIL, Abstract-ID: 286

INTRODUCTION:
Ultramarathons impose extreme and prolonged physiological stress, increasing the risk of dehydration and exercise-associated hyponatremia. Adequate hydration balance is therefore essential for performance and safety. Therefore, this study aimed to analyze the hydration status of an ultramarathon athlete during a 320-km race.
METHODS:
Case study of a 44-year-old female amatour athlete during a 320-km ultramarathon completed over three days (total race time: 70h 20min) in Nova Trento, Santa Catarina, southern Brazil. The event was the Mons Ultra Trail®, part of the Ultra Trail World Championship®, and was held on mixed terrain, including dirt roads, open and closed forest trails, and historical paths, with a total positive elevation gain of 10,700 m. Real-time monitoring of total fluid loss, electrolyte loss, and sodium loss was performed using a Nix Biosensor®, worn on the athlete’s forearm via a disposable patch transmitting data by Bluetooth to a smartphone application. Total water intake and electrolyte consumption were recorded, including the ingestion of a sports drink (Liquidz®) provided in 6-g stick containing 374mg of sodium, 64mg of potassium, and 216mg of magnesium. Laboratory biochemical analyses were conducted to assess electrolyte status one week before the race (pre), two days after completion (post), and 30 days after the event (post-30). All food intake was controlled, quantified, and calculated in terms of total energy (kcal) and carbohydrate intake. Energy expenditure during the race was monitored using a Garmin® device.
RESULTS:
Data collected by the biosensor showed a total fluid loss of 19,180mL, electrolyte loss of 15,719mg, and sodium loss of 7,451mg. Total water intake was 19,250mL. In addition, the athlete consumed 58 sticks of Liquidz®, resulting in a total electrolyte replacement of 20,126mg of sodium, 3,712mg of potassium, and 12,528mg of magnesium. Biochemical analyses revealed: sodium concentration of 136 mEq/L pre-race, 140 mEq/L post-race, and 140 mEq/L at 30 days post-race; potassium concentration of 4.6 mEq/L pre-race, 3.5 mEq/L post-race, and 4.2 mEq/L at 30 days post-race; and magnesium concentration of 1.84 mg/dL pre-race, 1.69 mg/dL post-race, and 1.57 mg/dL at 30 days post-race. Total caloric intake during the race was 14,185kcal, with a carbohydrate consumption of 3,111g. Total energy expenditure was estimated at 18,000kcal, resulting in a net caloric deficit of 3,815 kcal at the end of the race.
CONCLUSION:
Individualized diet and real-time monitoring fluids and electrolyte balance can effectively maintain sodium homeostasis and prevent exercise-associated hyponatremia during extreme ultramarathon events, even under substantial fluid loss and energy deficit. These findings highlight the practical value of combining wearable biosensors with planned electrolyte replacement strategies to guide hydration decisions, enhance safety, and support performance in ultraendurance competitions.
Supported by LIQUIDZ®.