Acclimating to the Extreme: Energy Expenditure, Neuroendocrine Systems, and Social Dynamics in Novel and Challenging Environments

This dissertation evaluated how individuals’ biology and behavior acclimatize to energetically-demanding environment over 3-month long expeditions through the American Rockies as a part of the National Outdoor Leadership School (NOLS). Specifically, this project assessed how body composition, hormones, and energetic physiology (n = 71) changed over the 3-month period as well as the relationship between changes in hormones and how people spent energy. Additionally, this project assessed how processes related to social dynamics, such as perceptions of stress and resilience, relate to individual physiology, particularly hormone and energetic systems. I examined how processes related to social and interpersonal dynamics influence individual hormonal and energetic physiology under challenging ecological conditions. These are theoretically important processes that are germane to contemporary human experience, including everyday functioning in an extreme environment, and that are potentially relevant to periodic demands placed on past human populations. In addition, this project brings innovative and integrative perspectives measuring different and interrelated physiological and behavioral systems repeatedly over time, which can inform our understanding of the timescale over which these complex changes occur as humans accommodate the pertinent environmental and social stressors. Our findings demonstrated that body weight and lean muscle decline when first beginning an expedition but are able to rebound by the end of the three-month period. In addition, I found that cortisol response attenuated by the middle of the course but is elevated at the beginning and the end of the course. I also found that in a highly demanding yet tightly controlled setting like the NOLS course, individual perceptions of lower stress and greater resilience during the expeditions predicted lower cortisol production, which may have had downstream impacts on health and performance. Further, we found that greater resilience predicted greater energy expenditure, on average, suggesting that resilient individuals worked harder and spent more energy. These findings have important implications for positive-perception building in small teams engaged in challenging environments can provide critical insights into how individuals successfully cope with the high-energy demands of new and difficult environments.