The positive effects of physical activity (PA) on sleep are widely promoted by public health organizations and supported by abundant empirical evidence. Nonetheless, there remains a dearth of studies investigating the association between daytime PA and nighttime sleep among nonurban and nonindustrial populations that habitually engage in PA as part of their subsistence strategy. Here, we examined the bidirectional relationship between PA and sleep. We also looked at age, gender, and occupation-level differences in moderate-to-vigorous PA (MVPA), low, and sedentary activity durations in a rural agropastoral community in South Africa. We collected activity and sleep data from 113 individuals using MotionWatch actigraphy wristwatches across three field seasons (7,111 individual nights). We found that herders spent less time sedentary and had higher activity levels than non-herders. Among non-herders, women had longer MVPA and shorter sedentary activity than men. In general, low to moderate PA decreased total sleep time (TST) and improved sleep quality (increased sleep efficiency (SE), decreased fragmentation, and decreased wake after sleep onset). MVPA and low activity were negatively influenced by TST and positively influenced by SE from the previous night. In summary, low to moderate PA were consistent predictors for higher sleep quality, and higher SE correlated with higher PA the next day. Our findings suggest that sleep quality is more strongly linked to PA than sleep duration.

In backcountry settings, exposure to high altitude and/or cold environments along with rigorous physical activity in a novel environment are physiologically demanding on the human body. The hypothalamic-pituitary-adrenal and hypothalamic-pituitary-gonadal axes, and their outputs cortisol (CORT) and testosterone (T), are key in responding to these demands given their roles in energy allocation and somatic distribution. Here, we worked with National Outdoor Leadership School students (n=71; obs = 291) enrolled in ~90-day expeditions in the American West. We measured longitudinal, within-individual patterns of cortisol, testosterone, physical activity, and energy expenditure (kCal/hr) at multiple time points during the expedition. Using linear mixed models, we found that while CORT stayed consistent across the course while baseline T was significantly higher in the final section of the course (p < 0.05). Further, we found that women (but not men) experienced significantly greater declines in T reactivity in the final section of the course. We also found that for women, the interaction of CORT reactivity and time on the course predicted lower kCal/hr (p < 0.05). Comparatively, the interaction of both baseline T and of T reactivity with time on the course predicted physical activity (p < 0.05) and kCal/hr (p < 0.05), but only in men. These results suggest that when acclimatizing to energetically demanding settings, HPA and HPG axis activation and/or dampening may differ between men and women, reflecting differing energetic and somatic demands on individual bodies. Given the psychobiological role of these axes, there are possible implications on psychosocial dynamics.

It is well-established that indigenous highland populations, such as Andeans and Tibetans, exhibit physiological adaptations to hypobaric hypoxia. However, given the distinct ancestries of these populations, it has been hypothesized that they may have adapted differently to the same selective stress. Further, it has been repeatedly posited in the literature that Tibetans are “better adapted” to high altitudes than Andeans. This work aimed to critically investigate these claims by using a mixed-methods approach, leveraging both physiological and ethnographic data. We recruited two groups of healthy adults (aged 18-35) with highland ancestry who were born and current residents at high altitude. The groups were: Andean Quechuas recruited in Cerro de Pasco, Peru (AND, n = 301) and Tibetan Sherpas recruited in Pheriche, Nepal (SHP, n = 64). Participants were tested in field laboratories using identical equipment and protocols, at nearly identical altitudes (mean barometric pressures of 462.5 and 463.5 mmHg, respectively). We assessed a wide variety of cardiorespiratory variables at rest, submaximal exercise, and maximal exercise. We found that although there were some interesting differences between the groups, particularly with respect to the control of breathing during exercise, their overall exercise performance (VO2max) did not differ significantly (AND = 34.5 vs. SHP = 33.4 mL/kg/min; p = 0.33). Thus, our cardiorespiratory data do not support the notion that one group is “better adapted” than the other. This idea was further challenged by ethnographic data gathered from Sherpa interlocutors, who expressed a distinct discomfort with external narratives of their supposed physical superiority.

Human body size and shape generally adhere to Bergmann’s and Allen’s rules, which describe the relationship between climate and the variation in mass and limb length as metabolic and heat retention adaptations. In this paper, we aim to define the relationship between latitude and body size in an historical high latitude population. Individual death records from the Alaska Health Analytics and Vital Records Section (1914-39) with complete data for height, mass, sex, ethnicity, and latitude aged ≥18 (n=12,725) were used to analyze the relationship between latitude and BMI (kg/m2), mass (kg), and surface area to mass ratio (SA/mass) (cm2/kg). Ordinary least squares (OLS) regression was used to model this relationship. Latitude alone can predict a decrease in BMI and mass and an increase in SA/mass, but with low R2 values. Controlling for sex and ethnicity improved predicted significant decline of BMI per unit latitude (p<0.001). Non-Alaska Native BMI and mass was significantly higher than Alaska Native Peoples (p<0.001) and decreased with latitude, and non-Alaska Native SA/mass was significantly lower (p<0.001) and decreased with latitude. Results of Alaska Native versus non-Alaska Native comparisons of body size and trends with latitude are contradictory to what Bergmann’s and Allen’s rules predict for cold adapted populations. These results suggest that long-term colonialism against Alaska Native Peoples may have contributed to the biosocial inheritance and embodiment of colonial violence, and therefore the observed discrepancies in what would be expected for Arctic-adapted populations.