1Anthropology, University of Notre Dame, 2Rocky Mountain, National Outdoor Leadership School
April 16, 2020 , Platinum Ballroom
Under ecological stressors like high altitude and cold stress, humans experience rapid physiological changes as they acclimatize to the surrounding conditions. This often results in relatively swift negative outcomes (e.g. extreme weight loss) within the acclimatization period (~2-3 weeks). However, bodies can rebound from stressors and return to baseline once acclimatized, though it is unknown how individual factors such as sex or age may affect acclimatization success. Working with the National Outdoor Leadership School, we looked at healthy individuals (n = 71) on ~90-day expeditions through the Rocky Mountains where prior work demonstrated that ecological demands lead to negative energy balance. Assessing within-individual changes, we tested how sex and age predicted body composition changes in high altitude and cold environments. Individuals’ body fat declined from the beginning to the end of the expedition, on average, as did their body weight in the early expedition stages (ps< 0.05) but the effect sizes were small. Notably, they had typically returned to their baseline body weight by the expedition’s end. Finally, for the first three quarters of the expedition, both men and women gained significant lean muscle mass (p<0.05). Neither sex nor age were significantly linked to body composition changes. Under these metabolically demanding conditions, it is unexpected that participants experienced relatively minimal overall declines in body fat, rebounds in body mass, and upticks in muscle mass. This suggests future work should explore the possibility that individuals may use behavioral strategies or alternative physiological mechanisms to metabolically acclimatize alongside expending of energy stores.
This project is supported by the NSF GRFP, the Institute for Scholarship in the Liberal Arts, the NSF DDRIG, PEO Scholar Award, and AAUW Women American Fellowship.