Alaska Mountain Wilderness Ski Classic: Alterations in Caloric Expenditure and Body Composition

Introduction: The Alaska Mountain Wilderness Ski Classic is a self-supported ultramarathon cross-country skiing event that traverses one of the mountain ranges of Alaska each winter. Unique aspects of this event challenge athletes with a significant amount of physical and mental stress while in the chronically cold conditions of the Arctic. Assessment of energy requirements or body composition has never been performed during this event. The objective of the study was to evaluate the influence of the 2016 Alaska Mountain Wilderness Ski Classic on caloric expenditure and body composition. Methods: Caloric expenditure was estimated using GT3x+ Actigraph accelerometers and ActiLife software. Lean tissue mass, total fat mass, visceral fat mass, and bone mineral density were measured using a General Electric iDXA before and after the event. Data are presented as mean±SD. Differences were analyzed using paired t tests with significance at P<0.05. Results: Fifteen participants (age=32.7±6.6 years, body mass index=23.7±2.3 kg·m²) completed the study, 8 males and 7 females. Caloric expenditure was 6238±1390 kcal·day^-1, and 37,163±8425 kcal for the entire event. Fat mass was reduced from pre-event (∆1.3±0.7 kg, P=0.00003). There was an increase in lean tissue mass (∆1.7±1.3 kg, P=0.0003) and relative skeletal muscle index (∆0.2±0.2 kg·m² P=0.001). There was no change in bone mineral density (∆0±0 g·cm³, P=0.4). Conclusions: Despite the metabolic demands, fat mass was reduced and lean tissue mass was preserved. Future studies of this event should be directed toward assessment of the nutritional provisions utilized and the mechanisms responsible for the preservation of lean tissue mass.