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PURPOSE: The Alaska Mountain Wilderness Ski Classic (AMWSC) is considered to be one of the most challenging ultra-endurance events in the world. The event has endured for more than 2 decades and various courses have traversed the Wrangell St. Elias, Chugach, Brooks and Alaska mountain ranges. There are no food drops, rest stations, or marked trails as skiers are free to pick the best route (ie., 100-150 miles) through the mountainous and remote Alaskan backcountry. Given the combined challenges of chronic activity, mental stress and cold exposure on physiological resilience, the purpose of this study was to evaluate the influence of the 2016 AMWSC that was staged in the Brooks Range (northernmost mountain range in North America) on energy expenditure and body composition. A two-tailed paired t-test was used to compare pre- and post-event alterations in lean body mass, fat mass and bone mineral density. METHODS: Fifteen male and female participants (mean±SEM; Age = 31.4±0.7, BMI = 23.7±0.6) were recruited for the study. Lean body mass, total fat mass, visceral fat mass and bone mineral density were measured using a General Electric iDXA pre- and post-event. In order to estimate total and daily energy expenditure, all participants wore a Actigraph wGT3X-BT monitor throughout the event. RESULTS: The first finishing group completed the event in 100 hours and 25 min, and the last individual completed the event at 121 hours and 7 min setting a course record for the closest time range within the finishing groups. Lean body mass and the relative skeletal muscle index (RSMI) increased by 1.7±0.3 kg and 0.22±0.05 kg/m2, respectively. While there was a significant reduction (-1.3±0.2 kg) in total fat mass, there was no change in bone mineral density (0.0044±0.0085 g/cm3). Including a correction for pack weight, daily energy expenditure was 5084±244, 7314±332, 7492±422, 7505±307, 6538±376, 3843±592, 5889±859 kcal, respectively over the course of the event. Total energy expenditure was 37,162±2174 kcal. CONCLUSION: Lean body mass and RSMI increased in all athletes. Previous work using isotopic methodologies during acute exercise have demonstrated that urea reincorporation into protein increased during exercise. Future studies are planned with this cohort that will utilize isotopic methodology to measure changes in protein synthesis and skeletal muscle using minimally invasive isotopic approaches. This work will gain even more relevance with increased access to the Arctic, including the potential deployment of military personnel to maintain the interests of nations within the regions. Therefore, we must understand the influence of cold exposure and sustained levels of physical activity on physiological resilience.

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