Total Energy Expenditure and ad Libitum Fluid/Nutrient Intake During a 24-Hour Mountain-Bike Event: A Case Study

Previous studies have used the doubly labeled water method to evaluate the total energy expenditure (TEE) during Ironman, ultramarathon trail runs, and competitive road cycling. However, the technique has not been applied to a 24-hour cross-country mountain-bike event. Purpose: This case study aimed to measure the TEE, cycling metrics, and ad libitum nutrient/fluid intake during a 24-hour cross-country mountain-bike race. Methods: A trained male cyclist (41 y, 74.1 kg, 172.4 cm) received an oral dose of doubly labeled water prior to the 24-hour event for the calculations of TEE and water turnover. Nude body weight and urine samples were collected prerace, during the race, and postrace. Total nutrient intake and total fluid intake in addition to cycling metrics (speed, power output, cadence, and heart rate) were continuously recorded during the event. Results: The rider completed 383 km coupled with a vertical gain of 7737 m during the 24-hour event. Average speed, power, and heart rate were 16.3 (2) km·h^-1, 122 (29) W, and 134 (18) beats·min^-1, respectively. TEE and total nutrient intake were 41 and 23.5 MJ, respectively. Total carbohydrate intake was 1192 g with an average hourly intake of 58 (22) g·h^-1. Total body weight was 75.3 and 72.3 kg prerace and postrace, respectively, with a measured ad libitum total fluid intake of 13.3 L and a water turnover of 17.2 L. Conclusions: These data provide novel insights for measures of TEE, total energy intake, and total fluid intake during an ultraendurance cross-country mountain-biking event and provide a foundation for future race/training needs.