| Summary: | Objective The objective of this study was to determine the potential roles of follistatin and myostatin on body composition under conditions of prolonged physical activity, chronic cold exposure and remote isolation. Methods Participants traveling on foot in the 2017 Yukon Arctic Ultra 692‐km (430‐mile) were recruited for the study. Measurements and samples were obtained at pre‐event, mile 173 at Carmacks checkpoint 1 (C1), mile 239 at Pelly Crossing (C2) and post‐event. Body composition measurements were obtained using bioelectrical impedance analysis. Wrist worn accelerometer devices were utilized to provide an estimation of caloric expenditure and dietary recall provided an assessment of caloric intake. Blood serum samples were collected, centrifuged on‐site, frozen and later analyzed using enzyme linked immunosorbent assays to determine myostatin and follistatin concentrations. Results were analyzed using one‐way ANOVA, presented as means±SEM and considered significant at P<0.05 . Results Ten participants (37±10 yr, body mass index: 24.4±2.6 kg/m 2 8 males, 2 females) were recruited, and five male participants completed the entire event in 260±9 hours. Caloric intake/expenditure was 4,244±471 kcal/day and 6,669±427 kcal/day, respectively, indicating a caloric deficit of 2,425±653 kcal/day. Total mass, body mass index and fat mass were reduced at each time point of the event. Fat free mass was unchanged throughout the event (Pre‐event: 60±3 kg, C1: 60±3 kg, C2: 60±3 kg, Post‐event: 59±1 kg). Follistatin was increased at C1 (1,715±310 pg/mL) in comparison to all other time points. Myostatin trended towards an increased level at C1 (20,494±5,531 pg/mL). Conclusions Despite a remarkable caloric deficit and extreme cold conditions, fat free mass was preserved in participants traveling on foot in the event. Transient alterations in follistatin and myostatin may occur during chronic exercise and may potentially influence the regulation of lean tissue retention under these conditions. Future studies will be ...
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