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

Area of Science:

• Exercise Physiology
• Sports Science
• Ultraendurance Sports

Background:

• The doubly labeled water (DLW) method is established for measuring total energy expenditure (TEE) in endurance athletes.
• Previous DLW studies have focused on Ironman triathlons, ultramarathon trail runs, and road cycling.
• Application of DLW to 24-hour cross-country mountain biking events was previously uninvestigated.

Purpose of the Study:

• To quantify TEE in a 24-hour cross-country mountain-bike race.
• To assess cycling performance metrics during the event.
• To measure ad libitum nutrient and fluid consumption throughout the race.

Main Methods:

• A trained male cyclist participated in a 24-hour cross-country mountain-bike race.
• Doubly labeled water was administered to calculate TEE and water turnover.
• Body weight, urine samples, nutrient intake, fluid intake, speed, power output, cadence, and heart rate were monitored.

Main Results:

• The cyclist completed 383 km with 7737 m vertical gain.
• Average speed was 16.3 km/h, power output 122 W, and heart rate 134 bpm.
• Total TEE was 41 MJ, total nutrient intake 23.5 MJ, with 1192 g carbohydrates consumed. Fluid intake was 13.3 L.

Conclusions:

• This study provides novel data on TEE, energy intake, and fluid intake during ultraendurance mountain biking.
• The findings establish a baseline for understanding physiological demands in this sport.
• This research supports future recommendations for race and training nutritional and hydration strategies.