Explore the vast range of titles available.

The acute effects of exercise on metabolic energy expenditure and inflammation are well studied, but the long-term effects of regular daily physical activity on metabolic and endocrine effects are less clear. Further, prior studies investigating the impact of daily physical activity in large cohorts have generally relied on self-reported activity. Here, we used the U.S. National Health and Nutrition Examination Survey (NHANES) to investigate the relationship between daily physical activity and both thyroid and immune activity. Daily physical activity was assessed through accelerometry or accelerometry-validated survey responses. Thyroid activity was assessed from circulating levels of thyroid stimulating hormone (TSH) and thyroxine (T4). Immune function was assessed from circulating cytokines (C-reactive protein [CRP], immunoglobulin E [IgE], fibrinogen) and blood cell counts. In general linear models including body mass index, age, gender, activity and TSH as factors, active adults had a lower levels of T4 and reduced slope of the TSH:T4 relationship. Similarly, greater physical activity was associated with lower CRP and fibrinogen levels (but not IgE) and lower white blood cell, basophil, monocyte, neutrophil, and eosinophil (but not lymphocyte) counts. Daily physical activity was also associated with lower prevalence of clinically elevated CRP, WBC, and lymphocytes in a dose-response manner. These results underscore the long-term impact of daily physical activity on both systemic metabolic activity (thyroid) and on specific physiological tasks (immune). The regulatory effects of physical activity on other bodily systems are clinically relevant and should be incorporated into public health strategies promoting exercise.

Human reproduction is energetically costly, even more so than other primates. In this review, we consider how the energy cost of physical activity impacts reproductive tasks. Daily energy expenditure appears to be constrained, leading to trade-offs between activity and reproduction expenditures in physically active populations. High workloads can lead to suppression of basal metabolic rate and low gestational weight gain during pregnancy and longer interbirth intervals. These responses lead to variation in fertility, including age at first reproduction and interbirth interval. The influence of energetics is evident even in industrialized populations, where cultural and economic factors predominate. With the decoupling of skills acquisition from food procurement, extrasomatic resources and investment in individual offspring becomes very costly. The result is greater investment in fewer offspring. We present a summary of age at first reproduction and interbirth interval trends across a diverse, global sample representing 44 countries and two natural fertility populations. While economic factors impact fertility, women in energy-rich, industrialized populations are capable of greater reproductive output than women in energy-stressed populations. Thus, energetic factors can be disentangled from cultural and economic impacts on fertility. Future research should focus on objective measurements of energy intake, energy expenditure, and physical activity in a broader sample of populations to elucidate the role of energetics in shaping reproductive outcomes and health.

Energy expenditure (EE) during treadmill walking under normal conditions (normobaric normoxia, 21% O 2 ) and moderate hypoxia (13% O 2 ) was measured. Ten healthy young men and ten healthy young women walked on a level (0°) gradient a range of speeds (0.67–1.67 m s −1 ). During walking, there were no significant differences in reductions in arterial oxygen saturation (SpO 2 ) between the sexes. The hypoxia-induced increase in EE, heart rate (HR [bpm]) and ventilation ( V ̇ E [L min −1 ]) were calculated. Using a multivariate model that combined EE, V ̇ E , and HR to predict ΔSpO 2 (hypoxia-induced reduction), a very strong fit model both for men (r 2  = 0.900, P  < 0.001) and for women was obtained (r 2  = 0.957, P  < 0.001). The contributions of EE, VE, and HR to ΔSpO 2 were markedly different between men and women. V ̇ E and EE had a stronger effect on ΔSpO 2 in women ( V ̇ E : 4.1% in women vs. 1.7% in men; EE: 28.1% in women vs. 15.8% in men), while HR had a greater effect in men (82.5% in men and 67.9% in women). These findings suggested that high-altitude adaptation in response to hypoxemia has different underlying mechanisms between men and women. These results can help to explain how to adapt high-altitude for men and women, respectively.

The classic anthropological hypothesis known as the “obstetrical dilemma” is a well-known explanation for human altriciality, a condition that has significant implications for human social and behavioral evolution. The hypothesis holds that antagonistic selection for a large neonatal brain and a narrow, bipedal-adapted birth canal poses a problem for childbirth; the hominin “solution” is to truncate gestation, resulting in an altricial neonate. This explanation for human altriciality based on pelvic constraints persists despite data linking human life history to that of other species. Here, we present evidence that challenges the importance of pelvic morphology and mechanics in the evolution of human gestation and altriciality. Instead, our analyses suggest that limits to maternal metabolism are the primary constraints on human gestation length and fetal growth. Although pelvic remodeling and encephalization during hominin evolution contributed to the present parturitional difficulty, there is little evidence that pelvic constraints have altered the timing of birth.

The purpose of this study was to examine the influence of body mass index (BMI), physical activity (PA) level, dietary inflammatory index (DII), and oral contractive (OC) use on C-reactive protein (CRP) levels, and to determine if elevated CRP values reflect systemic inflammation in OC users. Data were obtained from four cycles (1999-2006) of the U.S. National Health and Nutrition Examination Survey (NHANES) study, yielding a sample of 496 current OC users and a comparator group of 1,583 regularly menstruating women. A general linear model was used to test for interaction effects among BMI, PA level, and OC use, after adjusting for age and smoking status, with log-transformed CRP (lnCRP) identified as the outcome variable. Sequential general linear models with no interaction terms were then constructed to examine the impact of BMI, PA level, and OC use on circulating lnCRP after adjusting for age and smoking status. Follow-up analyses used general linear models to assess the relationship between lnCRP and other indices of systemic inflammation among OC users and nonusers, and to examine the predictors of lnCRP within each subgroup. The omnibus model including smoking status, age, PA level, OC use, and BMI did not identify any statistically significant two-way or three-way interaction effects (all p ≥ .259). The adjusted r 2 value of the model modestly increased from 0.3789 to 0.3801 when all interaction terms were removed. After adjusting for smoking status and age, a sequentially built model indicated that PA level was inversely related to lnCRP values ( p = .0019). When OC use was added to the model, it was positively associated with lnCRP values ( p < .0001), with statistically and clinically significant lnCRP differences between OC users and nonusers. BMI was the last variable entered into the model, which was positively associated with lnCRP ( p < .0001). Among OC nonusers, PA level ( p = .0008) and BMI ( p <  .0001) were significantly predictive of lnCRP levels after adjusting for smoking status and age. In contrast, PA level was not significantly predictive of lnCRP values ( p = .718) among OC users. All alternative indices of inflammation were positively correlated with lnCRP values (all p < .0001), but correlations were significantly stronger among OC users than nonusers (all p < .05). In a subset of OC nonusers with complete nutrition data, PA level ( p =  .021), BMI ( p <  .0001), and DII ( p =  .007) were significantly predictive of lnCRP after adjusting for smoking status and age. In contrast, PA level ( p =  .709) and DII ( p =  .690) were not significantly predictive of lnCRP values among OC users. In conclusion, OC-induced elevations in CRP appear to be reflective of a chronic, systemic inflammatory response. PA and low DII are associated with lower CRP among OC nonusers, but do not mitigate CRP elevations among OC users.

The shape of the human female pelvis is thought to reflect an evolutionary trade-off between two competing demands: a pelvis wide enough to permit the birth of large-brained infants, and narrow enough for efficient bipedal locomotion. This trade-off, known as the obstetrical dilemma, is invoked to explain the relative difficulty of human childbirth and differences in locomotor performance between men and women. The basis for the obstetrical dilemma is a standard static biomechanical model that predicts wider pelves in females increase the metabolic cost of locomotion by decreasing the effective mechanical advantage of the hip abductor muscles for pelvic stabilization during the single-leg support phase of walking and running, requiring these muscles to produce more force. Here we experimentally test this model against a more accurate dynamic model of hip abductor mechanics in men and women. The results show that pelvic width does not predict hip abductor mechanics or locomotor cost in either women or men, and that women and men are equally efficient at both walking and running. Since a wider birth canal does not increase a woman's locomotor cost, and because selection for successful birthing must be strong, other factors affecting maternal pelvic and fetal size should be investigated in order to help explain the prevalence of birth complications caused by a neonate too large to fit through the birth canal.

Compared to other apes, humans live longer, reproduce faster and have larger brains; here, total energy expenditure is studied in humans and all species of great ape, and is shown to be significantly higher in humans, demonstrating that the human lineage has experienced an energy-boosting acceleration in metabolic rate. Metabolic factors in human evolution Humans live longer than other apes, reproduce faster and have larger brains. This uniquely human portfolio of metabolically costly traits suggests that at some point in the hominin lineage there was a relaxation of energetic constraints, but the underlying mechanisms involved remain largely unknown. Here Herman Pontzer et al . study total energy expenditure in humans and all known species of great ape. They also revisit the archival data that seemed to have confused the issue somewhat. The authors conclude that total energy expenditure is significantly higher in humans, and that this is related to fat mass and particularly to brain mass. Thus human evolution owes much to an increased metabolic rate, along with changes in energy allocation, one result being our predisposition to deposit fat, whilst other hominoids remain relatively lean. Humans are distinguished from the other living apes in having larger brains and an unusual life history that combines high reproductive output with slow childhood growth and exceptional longevity 1 . This suite of derived traits suggests major changes in energy expenditure and allocation in the human lineage, but direct measures of human and ape metabolism are needed to compare evolved energy strategies among hominoids. Here we used doubly labelled water measurements of total energy expenditure (TEE; kcal day −1 ) in humans, chimpanzees, bonobos, gorillas and orangutans to test the hypothesis that the human lineage has experienced an acceleration in metabolic rate, providing energy for larger brains and faster reproduction without sacrificing maintenance and longevity. In multivariate regressions including body size and physical activity, human TEE exceeded that of chimpanzees and bonobos, gorillas and orangutans by approximately 400, 635 and 820 kcal day −1 , respectively, readily accommodating the cost of humans’ greater brain size and reproductive output. Much of the increase in TEE is attributable to humans’ greater basal metabolic rate (kcal day −1 ), indicating increased organ metabolic activity. Humans also had the greatest body fat percentage. An increased metabolic rate, along with changes in energy allocation, was crucial in the evolution of human brain size and life history.

Recent work suggests human physiology is not well adapted to prolonged periods of inactivity, with time spent sitting increasing cardiovascular disease and mortality risk. Health risks from sitting are generally linked with reduced levels of muscle contractions in chair-sitting postures and associated reductions in muscle metabolism. These inactivity-associated health risks are somewhat paradoxical, since evolutionary pressures tend to favor energy-minimizing strategies, including rest. Here, we examined inactivity in a huntergatherer population (the Hadza of Tanzania) to understand how sedentary behaviors occur in a nonindustrial economic context more typical of humans’ evolutionary history. We tested the hypothesis that nonambulatory rest in hunter-gatherers involves increased muscle activity that is different from chair-sitting sedentary postures used in industrialized populations. Using a combination of objectively measured inactivity from thigh-worn accelerometers, observational data, and electromygraphic data, we show that huntergatherers have high levels of total nonambulatory time (mean ± SD = 9.90 ± 2.36 h/d), similar to those found in industrialized populations. However, nonambulatory time in Hadza adults often occurs in postures like squatting, and we show that these “active rest” postures require higher levels of lower limbmuscle activity than chair sitting. Based on our results, we introduce the Inactivity Mismatch Hypothesis and propose that human physiology is likely adapted to more consistently active muscles derived from both physical activity and from nonambulatory postures with higher levels of muscle contraction. Interventions built on this model may help reduce the negative health impacts of inactivity in industrialized populations.

When searching for food, many organisms adopt a superdiffusive, scale-free movement pattern called a Lévy walk, which is considered optimal when foraging for heterogeneously located resources with little prior knowledge of distribution patterns [Viswanathan GM, da Luz MGE, Raposo EP, Stanley HE (2011) The Physics of Foraging: An Introduction to Random Searches and Biological Encounters ]. Although memory of food locations and higher cognition may limit the benefits of random walk strategies, no studies to date have fully explored search patterns in human foraging. Here, we show that human hunter–gatherers, the Hadza of northern Tanzania, perform Lévy walks in nearly one-half of all foraging bouts. Lévy walks occur when searching for a wide variety of foods from animal prey to underground tubers, suggesting that, even in the most cognitively complex forager on Earth, such patterns are essential to understanding elementary foraging mechanisms. This movement pattern may be fundamental to how humans experience and interact with the world across a wide range of ecological contexts, and it may be adaptive to food distribution patterns on the landscape, which previous studies suggested for organisms with more limited cognition. Additionally, Lévy walks may have become common early in our genus when hunting and gathering arose as a major foraging strategy, playing an important role in the evolution of human mobility.