Changes in Cortisol and Testosterone During Acclimatization and the Relationship to Energetic Outcomes

When in energetically demanding environments (e.g., high altitude, backcountry expeditions), humans acclimatize to compounded intensive stressors. Acclimatization is possible in part by using the dynamically responsive neuroendocrine system, with changes to hormones like cortisol (CORT) and testosterone (T), which both play important metabolic roles. We sought to examine how these hormones change during acclimatization and what their relationship was to energetic outcomes (i.e., physical activity intensity and average energy expenditure (AEE)).

Data were collected from 70 healthy individuals (age range: 18-53 years; female = 39) throughout a 3-month long expedition in the American Rockies. Repeated measures of pre-activity salivary baseline and acute change (i.e., reactivity) samples of CORT and T were taken throughout the 3-month period. Physical activity intensity and energy expenditure were also assessed in a subset of participants using the wGT3X-BT Actigraph monitor.

Over the 3-month period, we found that time on the course moderated the relationship between CORT reactivity and physical activity intensity (%MVPA) and AEE. Compared to the start of the expedition, female baseline T was significantly higher in the middle and end, and male baseline T was significantly higher at the end. Additionally, female T acutely declined significantly more at the end of the expedition compared to the beginning. We also found that time on course and sex moderated the relationship between T reactivity and activity intensity.

These findings suggest a dynamic relationship between neuroendocrine and energetic outcomes during acclimatization, which may further differ between sexes.