Assessment of Energy Expenditure using Doubly Labelled Water during an Altitude Training Camp in Elite Alpine Skiers

The doubly labelled water (DLW) method is considered as the gold standard for assessment of energy expenditure. Without interfering with everyday life or training schedules, it may also serve as an accurate field technique in elite sport settings. Alpine Skiing is characterized by a complex movement profile and phases of demanding on-snow glacier training in extreme environments, where maintaining energy balance and body composition is crucial for performance and may aid injury prevention. The present study investigated the impact of a short-term training camp at altitude on energy balance in world-class alpine skiers, using DLW as a reference method.

In a prospective observational study, active male (n=9, 27±2.9 yrs) and female (n=10, 25±3.0 yrs) international skiers completed a 7 to 15-day training camp at altitude (base: 1800m, glacier: 3500m). All athletes received a single oral dose of 0.5 g/kg H₂¹⁸O (10% enriched) and 0.3 g/kg D₂O (99,8% enriched). After calculating initial isotope enrichment from urine samples obtained prior to and following total body water equilibrium, athletes provided daily urine samples for a minimum of 6 days to determine elimination rates of both isotopes via the multipoint method. Body composition was assessed directly before and after the camp and body mass was monitored continuously. Food intake in altitude was assessed via observation by trained staff, and capillary blood was used for markers of energy balance, namely leptin and triiodothyronine.