Human cold adaptation: An unfinished agenda v2.0.

BACKGROUND: Research on human extreme cold climate adaptations has benefitted from a recent resurgence since Ted Steegmann laid out his Human Cold Adaptation Agenda in 2007. Human biologists have drastically expanded our knowledge in this area during the last 15 years, but we still have a great deal more work to do to fulfill the cold climate adaptation agenda. METHODS: Here, I follow Steegmann's example by providing a review of cold climate adaptations and setting forth a new, expanded agenda. RESULTS: I review the foundational work on cold climate adaptations including classic Bergmann, Allen, and Thomson rules as well as early work assessing metabolic differences among Indigenous cold climate populations. From there, I discuss some of the groundbreaking work currently taking place on cold climate adaptations such as brown adipose tissue (a heat generating organ), physical activity levels, metabolic rates, and behavioral/cultural mechanisms. Finally, I present a path forward for future research with a focus on some of the basic extreme cold adaptations as well as how human biologists should approach the effects of climate change on human health and well-being, particularly within a cold climate context. CONCLUSION: The Arctic has felt the dramatic effects of climate change sooner and more acutely than other parts of the world, making it an ideal location for studying both cold climate adaptations and climate change resilience. Human biologists have a great deal to contribute to the conversation on not only adaptations to extreme cold, but also the ways in which climate change is being embodied by cold climate populations.

The value of publicly engaged podcasting in human biology.

Podcasting about science may be popular, but does it motivate engagement? The Human Biology Association and American Journal of Human Biology (AJHB) cosponsor a podcast that highlights recent articles. We hypothesized that AJHB articles discussed on the podcast (n = 42) receive more online views than other articles from the same issues. We used Student's t-tests to compare mean article views and found podcasted articles received more views, but the difference was not significant. When extreme outliers were removed, podcasted articles had over twice the views of control articles (p = .04), indicating that journal-affiliated podcasting can increase science engagement.

Indication of mixed glucose and fatty acid use by inferred brown adipose tissue activity in Samoans.

OBJECTIVES: Despite the growing rates of global obesity and the known positive associations between brown adipose tissue (BAT) and cardiovascular health, little is known about the metabolic effects of BAT activity in Samoans, a population at high risk of obesity and type II diabetes. Here we assessed the potential effects of inferred BAT activity on metabolic health markers in Samoan adults exposed to mild cold. METHODS: Using point-of-care finger prick technology we measured fasting glucose, total cholesterol, high-density lipoprotein (HDL), and low-density lipoprotein (LDL) levels before and after 30 min of cold exposure among 61 individuals (38 females, 23 males, ages 31-54) from 'Upolu Island, Samoa. Respiratory quotient was measured by indirect calorimetry to determine substrate metabolism at room temperature and cold exposure. RESULTS: Fasting glucose levels decreased significantly (p < .001) after cold exposure while neither total cholesterol (p = .88), HDL (p = .312), nor LDL (p = .089) changed. Respiratory quotient decreased significantly (p = .009) between exposures, suggesting an increased preference for lipid metabolism as a response to cold. CONCLUSIONS: The observed effects of inferred BAT activity on biomarkers suggest BAT activity utilizes both glucose and lipid-derived fatty acids as fuel for thermogenesis. Our work provides evidence for the beneficial metabolic effects of BAT and emphasizes the need for the population-specific development of metabolic treatments involving BAT to ensure the successful and equitable minimization of extreme consequences of obesity and metabolic health.

The impact of winter warming and more frequent icing events on reindeer herder occupational safety, health, and wellbeing.

BACKGROUND: Northern Finland, like the rest of the Arctic, has experienced increases in mean annual temperature, the number of winter rains, the number of thaw-freeze days, the number of extremely warm weather events, and a shortened snow season. These changes have produced numerous problems for reindeer herders whose livelihoods rely on a healthy ecosystem with predictable weather patterns. METHODS: We performed a scoping literature review to assess how climate change induced extreme weather has negatively impacted reindeer herding as well as the health and wellbeing of reindeer herders. RESULTS: Late snow cover negatively impacts reindeer herding through a more widely dispersed herd that increases the work to gather reindeer, leads to reduced calf weight, and results in less meat for sale. This increased labor, especially in extreme cold conditions, can also negatively impact reindeer herder health. Icing due to thaw-freeze and rain-on-snow events makes it impossible for reindeer to dig through the snow to access lichens, increasing the need for reindeer herders to keep the herd in winter enclosures and provide supplemental feed. CONCLUSION: Climate change induced weather events such as late snow cover and icing increase reindeer herder efforts and expenses, put their livelihood at risk, and put their health at risk.

To the extreme! How biological anthropology can inform exercise physiology in extreme environments.

The fields of biological anthropology and exercise physiology are closely related and can provide mutually beneficial insights into human performance. These fields often use similar methods and are both interested in how humans function, perform, and respond in extreme environments. However, these two fields have different perspectives, ask different questions, and work within different theoretical frameworks and timescales. Biological anthropologists and exercise physiologists can greatly benefit from working together when examining human adaptation, acclimatization, and athletic performance in the extremes of heat, cold, and high-altitude. Here we review the adaptations and acclimatizations in these three different extreme environments. We then examine how this work has informed and built upon exercise physiology research on human performance. Finally, we present an agenda for moving forward, hopefully, with these two fields working more closely together to produce innovative research that improves our holistic understanding of human performance capacities informed by evolutionary theory, modern human acclimatization, and the desire to produce immediate and direct benefits.

Total Energy Expenditure and Nutritional Intake in Continuous Multiday Ultramarathon Events.

Continuous multiday ultramarathon competitions are increasingly popular and impose extreme energetic and nutritional demands on competitors. However, few data have been published on energy expenditure during these events. Here, we report doubly labeled water-derived measures of total energy expenditure (in kilocalories per day) and estimated physical activity level (PAL: total energy expenditure/basal metabolic rate) collected from five elite and subelite finishers (four males and one female, age 34.6 ± 4.9 years)-and nutritional intake data from the winner-of the Cocodona 250, a ∼402-km race in Arizona, and from a fastest-known-time record (one male, age 30 years) on the ∼1,315-km Arizona Trail. PAL during these events exceeded four times basal metabolic rate (Cocodona range: 4.34-6.94; Arizona Trail: 5.63). Combining the results with other doubly labeled water-derived total energy expenditure data from ultraendurance events show a strong inverse relationship between event duration and PAL (r2 = .68, p < .0001). Cocodona race duration was inversely, though not significantly, associated with PAL (r2 = .70, p = .08). Water turnover varied widely between athletes and was not explained by PAL or body mass. The Cocodona race winner met ∼53% of energy demand via dietary intake, 85.6% of which was carbohydrate, while ∼47% of energy demand was met via catabolism of body energy stores. Together, these results illustrate the energetic deficits incurred during competitive continuous multiday ultramarathon efforts and implicate macronutrient absorption and/or storage as key factors in ultramarathon performance.

Weather permitting: Increased seasonal efficiency of nonshivering thermogenesis through brown adipose tissue activation in the winter.

OBJECTIVES: We investigated seasonal changes in brown adipose tissue (BAT) activation and metabolism in a temperate-climate Albany, NY population. METHODS: Data were collected among 58 participants (21 males, 37 females, ages: 18-51) in the summer and 59 participants (23 males, 36 females, ages: 18-63) in the winter in Albany, New York. BAT activity was inferred by comparing metabolic rate, heat dissipation in the supraclavicular area, and respiratory quotient at room temperature and cold exposure. Seasonal variation in BAT was determined by comparing these measurements from summer and winter. RESULTS: At mild cold exposure, heat dissipation of the supraclavicular area was significantly greater in the winter compared to summer (p < .001); however, no significant differences were found between seasons in metabolic rate measurements. This suggests BAT activation may be metabolically more efficient in the winter, due to prolonged lower seasonal temperatures relative to summer. Respiratory quotient significantly increased upon mild cold exposure in the winter compared to summer (p < .001). While carbohydrate utilization increased in the winter, fat remained the primary metabolic substrate for BAT activity across both seasons. CONCLUSION: The seasonal variations in the effects of nonshivering thermogenesis on metabolic rate and substrate metabolism suggest a buffering of energy expenditure and an increased use of glucose as fuel by BAT as a result of acclimatization to cold in the winter. These findings point towards a potential role of BAT in human whole-body mediated glucose disposal and cold adaptation.

Demystifying mentorship: Tips for successfully navigating the mentor-mentee journey.

BACKGROUND: Quality mentorship is crucial for long-term success in academia and overall job satisfaction. Unfortunately, formal mentorship training is lacking, and there is little recourse for failed mentor-mentee relationships. METHODS: We performed a literature review to understand the current state of mentorship research with a focus on: (1) what mentorship is and why it is important for success; (2) establishing mentor-mentee relationships; and (3) the role of diversity, equity, and inclusion. RESULTS: From the literature review, we compiled a number of mentorship recommendations for individuals, departments, institutions, and professional associations. These recommendations focus on building a mentorship network, establishing formalized mentorship training, how to build a productive and mutually beneficial mentor-mentee relationship, and instituting a system of mentorship accountability. CONCLUSION: We hope that by centralizing this information and providing a list of resources and actionable recommendations we inspire and encourage others to make meaningful changes in their approach to mentorship to create a more kind, caring, and equitable environment in which to conduct our work.

#Hackademics: Hacks toward success in academia.

OBJECTIVE: The Sausage of Science is a podcast for the Human Biology Association and the American Journal of Human Biology through which we introduced a special series called #Hackademics. The podcast was initially used to highlight the scholarship and humanity of fellow human biologists through interviews about "how the sausage is made" in research-that is, the nuts and bolts that go into our publications. However, we soon realized there is much more a weekly podcast can do to help colleagues in our interrelated fields. METHODS: Here we introduce the different contributions to this #Hackdemics special issue. Through #Hackademics, we address under-discussed topics in academia such as work-life integration, hostile academic environments, decolonization of research and teaching, and science communication, among others. RESULTS: The feedback received from listeners for the #Hackademics series reinforced a need for more tools for navigating the academic side of our disciplines. Furthermore, there was a need to decentralize what is often termed "institutional knowledge" by sharing it in a more authoritative medium-a special issue of peer-reviewed articles in our Association's esteemed journal. This special issue's contributions also elevate diverse voices with multiple authors at different career stages. CONCLUSIONS: Using the institutional credibility of peer-review to legitimize these topics, this issue's articles can be a resource for those looking to initiate conversations or change within their departments or institutions with the hope of creating a kinder, more respectful, collaborative, equitable, and accessible academic environment.

Reindeer herders from subarctic Finland exhibit high total energy expenditure and low energy intake during the autumn herd roundup.

OBJECTIVE: High levels of total energy expenditure (TEE, kcal/day) have been documented among numerous human populations such as tropical climate horticulturalists and high-altitude agriculturalists. However, less work has been conducted among highly physically active cold climate populations. METHODS: In October 2018, TEE was measured using the doubly labeled water (TEEDLW , N = 10) and flex-heart rate methods (TEEHR , N = 24) for 6-14 days among reindeer herders (20-62 years) in northern Finland during an especially physically demanding, but not seasonally representative, period of the year for herders-the annual reindeer herd roundup. Self-reported dietary intake was also collected during TEE measurement periods. TEE was then compared to that of hunter gatherer, farming, and market economies. RESULTS: During the herd roundup, herders expended a mean of 4183 ± 949 kcal/day as measured by the DLW method, which was not significantly different from TEEHR . Mean caloric intake was 1718 ± 709 kcal/day, and was significantly lower than TEEDLW and TEEHR (p < .001). Herder TEEDLW was significantly higher than that of hunter gatherer (p = .0014) and market (p < .0014) economy populations; however, herder TEEDLW was not different from that of farming populations (p = .91). CONCLUSION: High TEE and low caloric intake among herders reflect the extreme demands placed on herders during the annual herd round up. Although TEEDLW was similar between cold climate herders and hot climate farming populations, there are likely differences in how that TEE is comprised, reflecting the local ecologies of these populations.

Sex differences and shifts in body composition, physical activity, and total energy expenditure across a 3-month expedition.

OBJECTIVES: An energetically demanding environment like a wilderness expedition can lead to potent stressors on human physiology and homeostatic balance causing shifts in energy expenditure and body composition. These shifts likely have consequences on overall health and performance and may potentially differ by sex. It is therefore critical to understand the potential differential body composition and energy expenditure changes in response to a novel and challenging environment in both males and female bodies. METHODS: Data were collected from 75 healthy individuals (female = 41; ages 18-53) throughout a 3-month long expedition in the American Rockies. Body mass, body fat, and lean muscle mass were measured before, during, and after the course. Physical activity intensity and energy expenditure were also measured in a subset of participants using the wGT3X-BT Actigraph wrist monitor and an accompanying Bluetooth heart rate monitor. RESULTS: Over the 3-month period, individuals initially experienced declines in body mass, body fat percentage, and lean muscle mass. Participants partially rebounded from these deficits to maintain overall body mass with a slight recomposition of body fat and lean muscle mass. Our data also demonstrated that sex moderated total energy expenditure, where females experienced a modest decline whereas males experienced an increase in energy expenditure from the beginning to the end of the course. CONCLUSIONS: Understanding changes in energy storage in the body and variation in energy expenditure between sexes during a 3-month expedition has critical implications for maintaining health and performance in an energetically demanding environment where resources may be scarce.

"I feel terrible and need to exercise to find any sort of joy": What COVID stay-at-home orders tell us about exercise as vitality politics and entertainment in the United States.

During COVID-19 stay-at-home orders (SaHOs), people faced drastic shifts in their work and home lives. These shifts, in combination with the temporary closure of gyms and fitness centers, led to exercise-routine disruption. We conducted a survey to assess how people were affected by SaHOs in terms of exercise-routine change, feelings about exercise, perceived physical and mental health, as well as exercise-routine plans once SaHOs were lifted. In this article, we examine why affluent white American women exercised before and during COVID-19 SaHOs. The article focuses on the role of pleasure and entertainment as key components of exercise practices for these women. We found that changes in motivation reveal that exercise regimens are part of contemporary vitality politics, or current cultural and subjective desires and abilities to manipulate and optimize biological human processes, that include both health and entertainment. Therefore, we argue that exercise is a meaningful cultural, entertainment, and biopolitical activity.

Between a rock and a cold place: Neanderthal biocultural cold adaptations.

A large body of work focuses on the unique aspects of Neanderthal anatomy, inferred physiology, and behavior to test the assumption that Neanderthals were hyper-adapted to living in cold environments. This research has expanded over the years to include previously unexplored and potentially adaptive features such as brown adipose tissue and fire-usage. Here we review the current state of knowledge of Neanderthal cold adaptations along morphological, physiological, and behavioral lines. While highlighting foundational as well as recent work, we also emphasize key areas for future research. Despite thriving in a variety of climates, it is well-accepted that Neanderthals appear to be the most cold-adapted of known fossil hominin groups; however, there are still many unknowns. There is a great deal yet to be uncovered about the nature and manifestation of Neanderthal adaptation and how the synergy of biology and culture helped buffer them against extreme and variable environments.

Feasibility of using infrared thermal imaging to examine brown adipose tissue in infants aged 18 to 25 months.

BACKGROUND: Recent studies in adults indicate that cold-induced temperature change of supraclavicular skin corresponds with brown adipose tissue (BAT) thermogenesis. AIM: This study examined the feasibility of using thermography to assess temperature changes in infants aged 18-25 months after mild cooling. Further, this study sought to evaluate whether cold exposure induces a thermal response suggestive of BAT activity underlying the supraclavicular region. SUBJECTS AND METHODS: Changes in maximum skin temperature at the supraclavicular and interscapular regions were determined using thermal imaging following a mild 5-minute cooling condition (by removal of clothes in a climate-controlled room) in 67 Samoan infants. Temperature changes of the forehead and hand, known BAT-free regions, served as indicators of cooling efficacy. RESULTS: Infants with increased hand and forehead temperatures after cold exposure were excluded from analysis, reducing the effective sample size to 19 infants. On average, forehead (p < 0.001), hand (p < 0.001) and back (0.029) temperatures dropped significantly while supraclavicular temperatures remained constant. Participants with greater decreases in forehead temperature tended to exhibit greater supraclavicular thermogenesis (p = 0.084), suggesting potential BAT activity in this region. CONCLUSIONS: While further work is necessary to develop a reliable cooling condition, this study provides proof-of-concept for non-invasive assessment of BAT activity in infants.

Elevated resting metabolic rates among female, but not male, reindeer herders from subarctic Finland.

OBJECTIVE: Elevated resting metabolic rates (RMR, kcal/day) are a well-established mechanism for maintaining core body temperature among cold climate populations. A high degree of interindividual variation has recently been noted among circumpolar populations. To further examine RMR variability, we investigated anthropometric and metabolic differences among reindeer herders from subarctic Finland. METHODS: Resting metabolic rates, body mass, body composition, height, age, and sex were measured among 20 reindeer herders (5 females, 15 males, 20-64 years) from seven herding districts surrounding the Arctic Circle of Finland in January of 2019. RESULTS: Females had a mean RMR of 1798 ± 216 kcal/day and males 1753 ± 503 kcal/day. When controlling for body mass and fat-free mass, females had significantly higher RMRs relative to males (P < .01). Contrary to previous cold climate population studies, measured RMR among males was not significantly different from predictive equation estimates (P > .05). However, predictive equations significantly underestimated female RMR by a mean of 25.2% ± 5.9% (P < .01). CONCLUSION: These results mirror earlier findings, though in ways previously unseen. In this population: (a) There is a high degree of RMR interindividual variability, but only among males, and (b) there is evidence for elevated RMR, but only among females. Though the sample size is small, preliminary results suggest the presence of sex-based differences in metabolic adaptations to cold climates within this population subset. Potential reasons for this sex-based difference are discussed including a presentation of a hypothesis about the dual role of thyroid hormone in both reproductive and metabolic processes.

Sustained high levels of physical activity lead to improved performance among "Race Across the USA" athletes.

OBJECTIVE: To investigate physiological and performance adaptations associated with extremely high daily sustained physical activity levels, we followed six runners participating in the 2015 Race Across the USA. Participants completed over 42.2 km a day for 140 days, covering nearly 5,000 km. This analysis examines the improvement in running speed and potential adaptation in mean submaximal heart rate (SHR) throughout the race. METHODS: Data were collected during three 1-week long periods corresponding to the race beginning, middle, and end and included heart rates (HRs), body mass, running distances and speeds. HR data were collected using ActiTrainer HR monitors. Running speeds and distances were also recorded throughout the entire race. RESULTS: Athletes ran significantly faster as the race progressed (p < .001), reducing their mean marathon time by over 63 min. Observed mean SHR during the middle of the race was significantly lower than at the beginning (p = .003); however, there was no significant difference between mean SHR at the middle and end of the race (p = .998). CONCLUSION: These results indicate an early training effect in SHR during the first half of the race, which suggests that other physiological and biomechanical mechanisms were responsible for the continued improvement in running speed and adaptation to the high levels of sustained physical activity.

Body fat attenuates muscle mass catabolism among physically active humans in temperate and cold high altitude environments.

OBJECTIVE: Typical diet plans are based on an individual's body mass; however, body composition may be important to consider when an individual is in a negative energy balance. This study examines if high initial body fat and dietary macronutrient content reduce muscle mass catabolism during excursions in temperate and cold high altitude environments. METHODS: Subjects-53 healthy, un-acclimated volunteers (37 males and 16 females)-took part in 12-16 week-long outdoor education courses in moderately high altitude temperate and cold climates in the western United States. Body mass, body fat percentage, fat mass, and muscle mass were measured before and after each excursion. Total energy expenditure and dietary intake were also measured. RESULTS: In temperate and cold environments, both sexes lost significant amounts of body mass. In temperate climates both sexes lost a significant amount of fat mass, but not muscle mass. In cold climates, there was no significant change in fat mass for either sex; however, females gained muscle mass while males lost muscle mass. In both climates subjects with lower initial body fat percentages lost significantly more muscle mass than subjects with higher initial body fat percentages. There was no significant relationship between macronutrient intake and muscle mass loss for either sex. CONCLUSION: These results suggests that during a negative energy balance dietary macronutrient content cannot abate the loss of muscle mass, but body fat may have a protective effect. This information should be used to improve individualized diets based on body composition, not body mass.

Human energy expenditure, allocation, and interactions in natural temperate, hot, and cold environments.

OBJECTIVE: The aim of this research is to analyze how energy is allocated differently in temperate, hot, and cold environments among National Outdoor Leadership School students. METHOD: Basal metabolic rate, physical activity, thermoregulation, and the thermic effect of food were estimated to determine the total energy expenditure and energy allocation differences among a group of healthy, highly active adults (N = 59) participating in National Outdoor Leadership School courses in the western United States. Two of these courses took place in both hot and temperate climates (N = 22) and the other two in both temperate and cold climates (N = 28). Data from a pilot study (N = 6) in a temperate climate were also included. Each climate regime lasted for one month. RESULTS: Total energy expenditure values were statistically equivalent in temperate and hot climates (p = .97). However, subjects experienced significantly higher total energy expenditures in cold climates (p < .0001), expending an additional ∼1550 kcal day-1 . There is a significant interaction between physical activity and thermoregulation, such that physical activity reduces thermoregulatory costs in cold climates, but increases it in hot climates. CONCLUSIONS: Dissection of the energy budget revealed that total energy expenditure is significantly higher in cold climates. This is due to a combination of high levels of physical activity and high thermoregulatory costs. High levels of physical activity may substantially lower the cost of thermoregulation in cold climates, and this interaction should be taken into account when estimating TEE.

The allocation and interaction model: A new model for predicting total energy expenditure of highly active humans in natural environments.

OBJECTIVE: The purpose of this study was to develop a new model, the Allocation and Interaction Model (AIM), to better predict human total energy expenditure (TEE) among a group of highly active humans living in a variety of natural environments. AIM estimates were tested to determine if it produces more accurate TEE predictions than the Factorial Method. METHODS: AIM includes metabolic cost terms for basal metabolic rate, thermoregulation, and the thermic effect of food, as well as more accurate activity cost estimations. AIM was tested using doubly labeled water and Flex-Heart Rate (Flex-HR)-measured TEEs of healthy, highly active adults (N = 59) participating in National Outdoor Leadership School semester-long courses. Data from a month-long pilot study (N = 6) were also included. RESULTS: AIM produced TEE estimates that were not significantly different from measured energy expenditure values. Overall, AIM came within 4.1% of measured values; the Factorial Method underestimated by over 25%. At TEEs greater than 3,000 kcal day(-1) , AIM underestimated TEE by 11% compared to 31.6% by the Factorial Method. Also, at TEEs greater than 3,000 kcal day(-1) , the Flex-HR method overestimated TEE by 17%. CONCLUSIONS: This analysis demonstrated that AIM is more accurate than the Factorial Method for predicting TEE across a range of climates and physical activity levels. This suggests that AIM should be used in place of the Factorial Method for estimating human TEE. Am. J. Hum. Biol. 28:372-380, 2016. © 2015 Wiley Periodicals, Inc.