Metabolic Responses to the Yukon Arctic Ultra: Longest and Coldest in the World.

PURPOSE: The Yukon Arctic Ultra is considered the longest and coldest ultraendurance event in the world. Cold exposure and exercise has been reported to influence circulating levels of myo-, adipo- and hepato-kines that may influence considerable alterations in the regulation of metabolism. The purpose of the study was to evaluate the influence of the Yukon Arctic Ultra (430 mile event) on potential activators of brown fat, metabolites and body composition in healthy individuals. METHODS: Eight male and female participants (mean+/-SEM; age = 44+/-3 yr; BMI = 23.4+/-0.9) were recruited for participation. Blood samples were collected at pre-event, mid event and post-event checkpoints. RESULTS: The temperature during the event ranged from -45[degrees]C to -8[degrees]C. Due to these extremely challenging conditions, 50% of the participants withdrew from competition by the 300 mile mark, and those that surpassed 300 miles lost a significant (p=0.002; p=0.01) amount of body weight (76+/-5 kg to 73+/-4 kg) and fat mass (13+/-1 kg to 12+/-3 kg), respectively. With respect to serum irisin, there was a trend (p=0.06) towards significance from pre-event (1033+/-88 ng/ml), mid-event (1265+/-23 ng/ml) to post-event (1289+/-24 ng/ml). Serum meteorin and fibroblast growth factor-21 remained stable throughout the event. There were no changes in creatinine, acetoacetate, acetate, and valine. Serum lactate decreased (p=0.04) during the event. CONCLUSION: The influence of cold exposure and extreme physical exertion may promote substantial increases in serum irisin, and specific alterations in substrate metabolism that largely preserve skeletal muscle and physiological resilience. (C) 2016 American College of Sports Medicine

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