PURPOSE: Given the new reclassification options for women serving in the military and new tensions related to arctic shipping routes, the purpose of this study was to evaluate sex differences in energy expenditure and body composition data collected during the Alaska Mountain Wilderness Ski Classic. METHODS: Fifteen race participants (8 males and 7 females, aged 31-54) were recruited for the study. Participants completed pre- and post-race body composition scans via dual energy x-ray absorptiometry (DEXA). Participants wore activity monitors around their wrists for the entire duration of their participation in the race. Pack weights were measured prior to the race. RESULTS: There was no difference in time to completion between men and women (ie.,125±20.1 hours and 119.3±18.0 hours, respectively, p=0.6). Pack weights relative to body mass were significantly lower in men (20.7±2.0%) compared to women (25.9±5.4%). Pre- and Post-percent fat mass was significantly lower in men (14.8±4.0 and 12.8±3.5) compared to women (19.8±2.7 and 18.0±2.5), respectively. Calculated total energy expenditure for the duration of the race was higher in men (42,679 and 30,861 kcal, men and women, respectively, p=0.002). Energy expended in order to complete the race was proportionate to total weight (body and pack) regardless of gender (R2 =0.84). CONCLUSION: Despite the challenge of carrying a heavier pack weight relative to their body mass, the women were able to complete the race in the same amount of time as the men. Previous studies suggest that at extreme distances women may possess a metabolic advantage over men. Further research is warranted to better understand the unique physiological advantages women in the military may offer under similar conditions.

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