Integrated neuromuscular training intervention applied in schools induces a higher increase in salivary high molecular weight adiponectin and a more favorable body mass index, cardiorespiratory fitness and muscle strength in children as compared to the traditional physical education classes

Background

High-molecular-weight adiponectin (HMW-adiponectin) is a cardio-metabolic health protector. Objectives: (1) to compare body mass index (BMI), cardiorespiratory fitness (CRF) and muscle strength (MS) in healthy school-children depending on their baseline salivary-HMW-adiponectin concentration; and (2) to apply a 3-month integrated neuromuscular training (INT) and evaluate its effects on salivary-HMW-adiponectin concentration, BMI, CRF and MS in the same children. Additional goal: to identify if any potential changes during the 3-month period may be related to a potential change in salivary-HMW-adiponectin concentration.

Methods

Ninety children (7.4 ± 0.3 years) were recruited in primary schools and randomly allocated into control or intervention group. The intervention consisted of a 3-month INT applied during physical education (PE) classes, twice-weekly, while the control group had traditional PE classes. Body mass and height were measured, BMI was calculated and HMW-adiponectin was quantified in saliva. To assess CRF and MS, 800 m-run and hand-dynamometry were applied, respectively. All measurements were performed twice, at baseline and after 3 months.

Results

Children with higher baseline salivary-HMW-adiponectin have more favorable BMI (p = 0.006) and slightly higher CRF (p = 0.017) in comparison to the children with lower baseline salivary-HMW-adiponectin. There were no big changes after the 3-month-period neither in the control, nor the INT group. However, it is worthy to note that the INT induced slightly higher increase in salivary-HMW-adiponectin (p = 0.007), and a slightly higher improvement in BMI (p = 0.028), CRF (p = 0.043) and MS (p = 0.003), as compared to the traditional PE classes. Finally, the INT-induced improvement in CRF was associated with the increased post-salivary-HMW-adiponectin concentration (p = 0.022).

Conclusion

Main findings may suggest the potential utility of an INT as a cost-effective strategy that can be applied in schools to induce cardio-protective effects in school-children.

Does Behavior Evolve First? Correlated Responses to Selection for Voluntary Wheel-Running Behavior in House Mice

AbstractHow traits at multiple levels of biological organization evolve in a correlated fashion in response to directional selection is poorly understood, but two popular models are the very general "behavior evolves first" (BEF) hypothesis and the more specific "morphology-performance-behavior-fitness" (MPBF) paradigm. Both acknowledge that selection often acts relatively directly on behavior and that when behavior evolves, other traits will as well but most with some lag. However, this proposition is exceedingly difficult to test in nature. Therefore, we studied correlated responses in the high-runner (HR) mouse selection experiment, in which four replicate lines have been bred for voluntary wheel-running behavior and compared with four nonselected control (C) lines. We analyzed a wide range of traits measured at generations 20-24 (with a focus on new data from generation 22), coinciding with the point at which all HR lines were reaching selection limits (plateaus). Significance levels (226 P values) were compared across trait types by ANOVA, and we used the positive false discovery rate to control for multiple comparisons. This meta-analysis showed that, surprisingly, the measures of performance (including maximal oxygen consumption during forced exercise) showed no evidence of having diverged between the HR and C lines, nor did any of the life history traits (e.g., litter size), whereas body mass had responded (decreased) at least as strongly as wheel running. Overall, results suggest that the HR lines of mice had evolved primarily by changes in motivation rather than performance ability at the time they were reaching selection limits. In addition, neither the BEF model nor the MPBF model of hierarchical evolution provides a particularly good fit to the HR mouse selection experiment.

Selective breeding for high voluntary exercise in mice increases maximal (V̇O2,max) but not basal metabolic rate

In general, sustained high rates of physical activity require a high maximal aerobic capacity (V̇O2,max), which may also necessitate a high basal aerobic metabolism (BMR), given that the two metabolic states are linked via shared organ systems, cellular properties and metabolic pathways. We tested the hypotheses that (a) selective breeding for high voluntary exercise in mice would elevate both V̇O2,max and BMR, and (b) these increases are accompanied by increases in the size of some internal organs (ventricle, triceps surae muscle, liver, kidney, spleen, lung, brain). We measured 72 females from generations 88 and 96 of an ongoing artificial selection experiment comprising four replicate High Runner (HR) lines bred for voluntary daily wheel-running distance and four non-selected control lines. With body mass as a covariate, HR lines as a group had significantly higher V̇O2,max (+13.6%, P<0.0001), consistent with previous studies, but BMR did not significantly differ between HR and control lines (+6.5%, P=0.181). Additionally, HR mice did not statistically differ from control mice for whole-body lean or fat mass, or for the mass of any organ collected (with body mass as a covariate). Finally, mass-independent V̇O2,max and BMR were uncorrelated (r=0.073, P=0.552) and the only statistically significant correlation with an organ mass was for V̇O2,max and ventricle mass (r=0.285, P=0.015). Overall, our results indicate that selection for a behavioral trait can yield large changes in behavior without proportional modifications to underlying morphological or physiological traits.

Lower-level predictors and behavioral correlates of maximal aerobic capacity and sprint speed among individual lizards

The standard paradigm of organismal biology views lower-level traits (e.g. aspects of physiology) as determining organismal performance ability (e.g. maximal sprint speed), which in turn constrains behavior (e.g. social interactions). However, few studies have simultaneously examined all three levels of organization. We used focal observations to record movement behaviors and push-up displays in the field for adult male Sceloporus occidentalis lizards during the breeding season. We then captured animals, measured aspects of their physiology, morphology and performance, and counted ectoparasites and endoparasites as potential predictors of sprint speed and maximal oxygen consumption (V̇O2,max). Field behaviors were statistically repeatable, but not strongly so. Sprint speed and V̇O2,max were repeatable using residuals from regressions on body mass (speed: r=0.70; V̇O2,max: r=0.88). Both calf [standardized partial regression (path) coefficient B=0.53] and thigh [B=-0.37] muscle mass (as residuals from regressions on body mass) were significant predictors of sprint speed; hemoglobin concentration (B=0.42) was a predictor of V̇O2,max. In turn, V̇O2,max predicted the maximum number of four-legged push-ups per bout (B=0.39). In path analysis, log likelihood ratio tests indicated no direct paths from lower-level traits to behavior, supporting the idea that morphology, in the broad sense, only affects behavior indirectly through measures of performance. Our results show that inter-individual variation in field behaviors can be related to performance ability, which in turn reflect differences in morphology and physiology, although not parasite load. Given the low repeatability of field behaviors, some of the relationships between behavior and performance may be stronger than suggested by our results.

Metabolic rate, sleep duration, and body temperature in evolution of mammals and birds: the influence of geological time of principal groups divergence

This study contains an analysis of basal metabolic rate (BMR) in 1817 endothermic species. The aim was to establish how metabolic scaling varies between the main groups of endotherms during evolution. The data for all the considered groups were combined and the common exponent in the allometric relationship between the BMR and body weight was established as b = 0.7248. Reduced to the common slope, the relative metabolic rate forms the following series: Neognathae – Passeriformes – 1.00, Neognathae – Non-Passeriformes – 0.75, Palaeognathae – 0.53, Eutheria – 0.57, Marsupialia – 0.44, and Monotremata – 0.26. The main finding is that the metabolic rate in the six main groups of mammals and birds consistently increases as the geological time of the group’s divergence approaches the present. In parallel, the average body temperature in the group rises, the duration of sleep decreases and the duration of activity increases. BMR in a taxon correlates with its evolutionary age: the later a clade diverged, the higher is its metabolic rate and the longer is its activity period; group exponents decrease as group divergence nears present times while with increase metabolic rate during activity, they not only do not decrease but can increase. Sleep duration in mammals was on average 40% longer than in birds while BMR, in contrast, was 40% higher in birds. The evolution of metabolic scaling, body temperature, sleep duration, and activity during the development of endothermic life forms is demonstrated, allowing for a better understanding of the underlying principles of endothermy formation.

Individual (Co)variation in Resting and Maximal Metabolic Rates in Wild Mice

AbstractBasal metabolic rate (BMR) represents the lowest level of aerobic metabolism in a resting, postabsorptive endotherm as measured within the thermoneutral zone. By contrast, maximal metabolic rate ([Formula: see text]max) reflects the upper limit of aerobic metabolism achieved during intensive exercise. As BMR and [Formula: see text]max define the boundaries of the possible levels of aerobic metabolism expressed by a normothermic individual, a key question is whether BMR and [Formula: see text]max are correlated. In the present study, we took repeated paired measurements of thermoneutral resting metabolic rate (RMR_t) and [Formula: see text]max on 165 white-footed mice (Peromyscus leucopus). Over a single summer (May-October), repeatability (R ± SE) was low but statistically significant ([Formula: see text]) for both RMR_t and [Formula: see text]max ([Formula: see text] for RMR_t; [Formula: see text] for [Formula: see text]max). Willingness to run during the forced-exercise trials was also significantly repeatable ([Formula: see text]). At the residual level (within individual), RMR_t and [Formula: see text]max tended to be positively correlated ([Formula: see text], [Formula: see text]), suggesting the presence of correlated phenotypic plasticity. By contrast, RMR_t and [Formula: see text]max were significantly negatively correlated at the among-individual level ([Formula: see text]). To the extent that variation in RMR_t reflects variation in BMR, the negative among-individual correlation does not corroborate the idea that a costly metabolic machinery is needed to support a high [Formula: see text]max. Future research should investigate the (genetic) relationship between RMR_t (and BMR) and other energetically expensive behaviors and activities to better understand how energy is allocated within individuals.

Exercise in Treatment of Migraine Including Chronic Migraine

PURPOSE OF REVIEW

With this review, we aimed to investigate the effect of exercise on migraine and explored the possibility of exercise as a treatment option for migraine.

RECENT FINDINGS

A close association of physical activity and exercise with migraine has been reported in clinical and population-based studies. Recent randomized controlled trials investigating the effect of aerobic exercise as a migraine-preventive treatment have revealed a notable improvement in migraine symptoms. Data on the effect of anaerobic exercise and exercise for flexibility, coordination, and relaxation on migraine are currently insufficient to make any recommendations. Possible pathways for the attenuation of migraine by exercise include the endogenous opioid and cannabinoid systems, brain-derived neurotrophic factor, inflammation, and behavioral/psychological factors. Regarding efficacy, side effects, and health benefits, aerobic exercise is a potentially beneficial strategy in the preventive treatment of migraine. Further studies are needed to delineate an evidence-based exercise program for migraine treatment.

Allometric relations of respiratory variables in Amniota: Effects of phylogeny, form, and function

Biological variables are frequently described by analyzing scaling relationships of the variable against body mass (M_B). Respiratory variables are no exception and allometric relations for oxygen consumption, pulmonary ventilation, tidal volume, breathing frequency, and lung volume have been described in the literature. While the allometric relations of respiratory variables given for mammals and birds are very consistent among different studies, scaling relationships for non-avian reptiles have only been scarcely described and show considerable variation between studies. Since no comprehensive study of allometric relations of respiratory variables has been carried out comparing the different groups of non-avian reptiles, we analyzed morphological and physiological variables of the respiratory system of crocodilians, chelonians, lizards, snakes, birds, and mammals, regarding the allometric relations of each variable from a phylogenetic perspective as well as related to lung morphology. Our results indicated that few respiratory variables possess significant phylogenetic signals and that tidal volume, breathing frequency (except mammals), and air convection requirement were independent of phylogeny. Contrary to the literature, lung volume of amniotes scaled isometrically to M_B, with the exception of lizards (M_B^0.78). Air convection requirement scaled isometrically in mammals and birds, but was more variable among non-avian reptiles, from a taxonomic perspective and in regard to different lung structures. In conclusion, respiratory variables among non-avian reptiles scaled more variably than previously expected, both according to phylogeny and to lung type, warranting future studies to explore structure-function relations of the reptilian respiratory system, especially regarding snakes and crocodilians, since these groups had very few data available for analysis.

Temperature effects on metabolic scaling of a keystone freshwater crustacean depend on fish-predation regime

According to the metabolic theory of ecology, metabolic rate, an important indicator of the pace of life, varies with body mass and temperature as a result of internal physical constraints. However, various ecological factors may also affect metabolic rate and its scaling with body mass. Although reports of such effects on metabolic scaling usually focus on single factors, the possibility of significant interactive effects between multiple factors requires further study. In this study, we show that the effect of temperature on the ontogenetic scaling of resting metabolic rate of the freshwater amphipod Gammarus minus depends critically on habitat differences in predation regime. Increasing temperature tends to cause decreases in the metabolic scaling exponent (slope) in population samples from springs with fish predators, but increases in population samples from springs without fish. Accordingly, the temperature sensitivity of metabolic rate is not only size-specific, but also its relationship to body size shifts dramatically in response to fish predators. We hypothesize that the dampened effect of temperature on the metabolic rate of large adults in springs with fish, and of small juveniles in springs without fish are adaptive evolutionary responses to differences in the relative mortality risk of adults and juveniles in springs with versus without fish predators. Our results demonstrate a complex interaction among metabolic rate, body mass, temperature and predation regime. The intraspecific scaling of metabolic rate with body mass and temperature is not merely the result of physical constraints related to internal body design and biochemical kinetics, but rather is ecologically sensitive and evolutionarily malleable.

Translating Preclinical Research for Exercise Oncology: Take It to the VO2max

Several observational studies have found that the risk for breast cancer is significantly reduced in persons who engage in greater amounts of physical activity. Additional observational studies of breast cancer survivors indicate that greater physical activity before or after diagnosis associates with reduced disease-specific mortality. However, no large randomized controlled trials have examined the effect of structured exercise training on disease outcomes in breast cancer. Among the many hurdles in designing such trials lies the challenge of determining how a given regimen of exercise from efficacious preclinical studies can be extrapolated to an equivalent “dose” in humans to guide decisions around treatment regimen in early-phase studies. We argue that preclinical researchers in exercise oncology could better facilitate this endeavor by routinely measuring changes in exercise capacity in the subjects of their breast cancer models. VO_2max, the maximal rate of whole-organism oxygen consumption during a progressive exercise test, is emphasized here because it has become a standard measure of cardiorespiratory fitness, is well-integrated in clinical settings, and scales allometrically among nonhuman animals in preclinical research and breast cancer patients/survivors in the clinic. We also conduct secondary analyses of existing whole-transcriptome datasets to highlight how greater uptake and delivery of oxygen during exercise may reverse the typically hypoxic microenvironment of breast tumors, which often associates with more aggressive disease and worse prognosis.

A comparative study of cardio-metabolic responses to exercise between untrained non-athletic young Nigerian adults and trained soccer players

We aimed at evaluating the cardiovascular and metabolic responses to sub-maximal exercise tests in untrained non-athletic young adults and comparing them with those of trained and more active soccer players. Forty healthy young adult males (20 untrained non-athletic undergraduates and 20 trained soccer players) aged 20-35 years participated in the study. The participants performed the exercise tests using a mechanically braked magnetic ergometer bicycle. Blood pressure and heart rate (HR) of participants were measured at rest and during the exercise test. The steady-state oxygen uptake (VO2SS) of subjects was estimated from a standardised sub-maximal VO2 equation. Data indicated significantly (P<0.05) higher absolute VO2SS, relative VO2SS, work rate, exercise oxygen pulse and cardiac output, but lower steady-state HR and %HRmax among the soccer players compared with the untrained individuals. No significant differences were observed in exercise systolic blood pressure, rate pressure product, resting HR reserve and %HR reserve between the two groups. Pearson’s partial correlation test indicted independent relationships between VO2SS (relative and absolute) and oxygen pulse, steady-state HR, percentage of HRmax, percentage of HR reserve, resting HR and working HR reserve respectively. The present study indicated greater cardio-metabolic responses to sub-maximal exercise and higher aerobic fitness in trained soccer players compared with the untrained non-athletic individuals.

The Effect of Glutamine Supplementation on Oxidative Stress and Matrix Metalloproteinase 2 and 9 After Exhaustive Exercise

Background

Glutamine is the most abundant amino acid in plasma and skeletal muscles and an important fuel for immune system cells. It has beneficial anti-inflammatory and antioxidant properties which may be considered as a potentially useful supplement for athletes. The present study was conducted to investigate the effect of glutamine supplementation on oxidative stress and matrix metalloproteinase 2 and 9 after exhaustive exercise in young healthy males.

Materials and methods

In this study, 30 healthy males (supplement =15 and control=15) were randomly assigned into two groups. The supplement group received 0.3 g/kg BW of glutamine along with 25 gr of sugar dissolved in 250 cc water per day. The control group received 25 gr of sugar in 250 cc water per day. Fasting blood samples were taken at baseline and at the end of 14 days of intervention. The participants underwent exercise until experiencing full-body exhaustive fatigue for 16 ± 2.84 mins, and then fasting blood samples were taken. Serum levels of TAC, MDA, MMP2, MMP9, glutathione, and hs-CRP were measured.

Results

Serum levels of MDA and hs-CRP significantly decreased in the supplement group (p< 0.05). The serum level of TAC significantly increased in the supplement group (p< 0.05). Glutathione serum levels significantly increased after exhaustive exercise (p< 0.05). Serum levels of MMP2 and MMP9 remained unchanged.

Conclusion

Results of this study showed that, some biochemical factors are time-dependent and can increase or decrease over time, as well as, serum levels of hs-CRP and MDA decreased with glutamine supplementation along with the increase in the TAC serum levels, but this supplementation had no effect on serum levels of MMP2 and MMP9 in exhaustive exercise.

Effect of high-intensity exercise on cardiorespiratory fitness in stroke survivors: A systematic review and meta-analysis

BACKGROUND

Knowledge of the optimal protocol and safety of particularly high-intensity exercise applied to individuals with stroke is lacking.

OBJECTIVE

This systematic review and meta-analysis aimed to investigate the effect of high-intensity exercise on cardiorespiratory fitness in stroke survivors.

METHODS

We performed a systematic electronic search for articles in MedLine via PubMed, EMBASE, Web of Science, Cochrane Central Register of Controlled Trials, CINAHL, and SPORTSDiscus up to April 1, 2019. Peak oxygen consumption (VO₂peak), 6-min walk test (6MWT), fastest 10-m walk test (10MWT), and adverse events were assessed. The standardized mean difference (SMD), weighted mean difference (WMD), and odds ratios (ORs) were used to compute the effect size, and subgroup analysis was conducted to test the consistency of results as well as sensitivity analysis to assess the robustness of the results. The quality of evidence was assessed with the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system.

RESULTS

We included 17 studies (PEDro score≥4) in the meta-analysis. Post-intervention, high-intensity exercise had a significant effect on peak oxygen uptake (VO₂peak; SMD=0.56, P<0.01, I²=8%; WMD=2.53mL/kg/min; high quality of evidence) and 6MWT (SMD=0.26, P<0.01, I²=40%; WMD=17.08m; moderate quality of evidence) but not fastest 10MWT (SMD=0.33, P=0.27, I²=77%; WMD=0.05m/s; low quality of evidence). Subgroup analysis showed better effects of higher-intensity treadmill training (≥70% heart rate reserve/VO₂peak) for a longer duration (≥12 weeks) on VO₂peak and 6MWT in sub-acute or chronic stroke survivors. The high-intensity exercise and control groups did not differ in adverse events including falls [odds ratio (OR) 1.40, P=0.35, I²=11%; low quality of evidence], pain (OR 3.34, P=0.09, I²=0%; moderate quality of evidence), or skin injuries (OR 1.08, P=0.90, I²=0%; low quality of evidence).

CONCLUSIONS

Our meta-analysis suggests that high-intensity exercise is beneficial for cardiorespiratory fitness in stroke survivors and might be safe as a novel intervention in cardiopulmonary rehabilitation after stroke.

Finding the peak of dynamic oxygen uptake during fatiguing exercise in fish

As fish approach fatigue at high water velocities in a critical swimming speed (U _crit) test, their swimming mode and oxygen cascade typically move to an unsteady state because they adopt an unsteady, burst-and-glide swimming mode despite a constant, imposed workload. However, conventional rate of oxygen uptake (Ṁ _O2 ) sampling intervals (5-20 min) tend to smooth any dynamic fluctuations in active Ṁ _O2  (Ṁ _O2active) and thus likely underestimate the peak Ṁ _O2active Here, we used rainbow trout (Oncorhynchus mykiss) to explore the dynamic nature of Ṁ _O2active near U _crit using various sampling windows and an iterative algorithm. Compared with a conventional interval regression analysis of Ṁ _O2active over a 10-min period, our new analytical approach generated a 23% higher peak Ṁ _O2active Therefore, we suggest that accounting for such dynamics in Ṁ _O2active with this new analytical approach may lead to more accurate estimates of maximum Ṁ _O2  in fishes.

Data quality and the comparative method: the case of pregnancy failure in rodents

In mammalian species where infanticide by males is likely, females exhibit counterstrategies to prevent or mitigate the costs of infanticide. One putative mitigation strategy is the “Bruce effect,” in which pregnant or inseminated females exposed to an unfamiliar male experience pregnancy block or failure. Females then mate with the new male, thus shifting investment from a “doomed” pregnancy to a more fruitful one. However, the Bruce effect may be an adaptive response to other factors besides infanticide. For example, if paternal care is necessary for offspring survival, and an unfamiliar male replacing the original mate is unlikely to provide such care to offspring of a litter it did not sire, then a female may terminate a pregnancy to initiate a new one. The infanticide and paternal care hypotheses have not been rigorously tested because comparative data on the Bruce effect across mammals are scarce. We compiled data on the Bruce effect, infanticide, and paternal care from one particularly rich source of information, rodents, but found the data set to be less rich than expected. The Bruce effect, infanticide, and paternal care were common among rodent species, but we found no clear relationship among the traits. However, this was likely due to 1) a bias toward positive results, 2) missing data, and 3) a reliance on studies of captive animals. These are common problems in comparative research, and we outline standards that should be implemented to successfully answer questions of importance in the field.

Efficacy and Safety of Whey Protein Supplements on Vital Sign and Physical Performance Among Athletes: A Network Meta-Analysis

Introduction: Athletes train physically to reach beyond their potential maximum aerobic threshold. Whey protein supplements (WPS) are often used in conjunction with physiotherapy and psychotherapy to regain better vital sign and physical performances. This review aimed to explore the clinical evidence on the efficacy and safety of WPS in sports performance and recovery among athletes.

Methodology: A comprehensive literature search was performed to identify relevant randomized control trials (RCTs) that investigated the efficacy and safety of WPS on the vital sign and physical performance among athletes. The Cochrane Risk of Bias (ROB) Assessment tools were used to assess the quality of the studies. Meta-analysis was conducted using the frequentist model with STATA version 14.2®.

Results: A total of 333,257 research articles were identified out of which 20 RCTs were included for qualitative synthesis and network meta-analysis with 351 participants. Among the studies, 7 had low ROB and 3 RCTs had high ROB. Of these 20 trials, 16 trials were randomized clinical trials which compared whey protein supplements (WPS) with various comparators i.e., L-alanine, bovine colostrum, carbohydrate, casein, leucine, maltodextrin, rice, protein + caffeine were compared with placebo. Analysis from the pairwise meta-analysis revealed that for respiratory exchange ratio (RER) WPS was found to be significantly improving compared to maltodextrin (WMD = 0.012; 95%CI = 0.001, 0.023). Similarity to RPE (Rate Perceived Exertion), slight difference between WPS and the comparators, however, when the estimation was favorable to the comparators, there was moderate-high heterogeneity. For VO_2max, high heterogeneity appeared when WPS compared to maltodextrin with the I² = 97.8% (WMD = 4.064; 95% CI = −4.230, 12.359), meanwhile bovine colostrum (WMD = −2.658; 95%CI = −6.180, 0.865) only comparator that was better than WPS. According to the estimated effect of the supplements on physical performance outcome results, maximum power (8 studies, 185 athletes), highest ranked was bovine colostrum (SUCRA = 70.7%) and the lowest ranked was placebo (SUCRA = 17.9%), yet all insignificant. Then again, on average power (nine studies, 187 athletes), WPS was the highest ranked (SUCRA = 75.4 %) about −112.00 watt (−187.91, −36.08) and most of the estimations were significant. Body mass was reported in 10 studies (171 athletes), carbohydrate may be at the highest ranked (SUCRA = 66.9%) but it is insignificant. Thought the second highest ranked was WPS (SUCRA = 64.7%) and it is significant (WMD = −6.89 kg; CI = −8.24, −5.54).

Conclusion: The findings of this review support the efficacy and safety of WPS as an ergogenic aid on athletes' sports performance and recovery. The overall quality of clinical evidence was found to be valid and reliable from the comprehensive search strategy and ROB assessment.

Terrestrial locomotion energy costs vary considerably between species: no evidence that this is explained by rate of leg force production or ecology

Inter-specifically, relative energy costs of terrestrial transport vary several-fold. Many pair-wise differences of locomotor costs between similarly-sized species are considerable, and are yet to be explained by morphology or gait kinematics. Foot contact time, a proxy for rate of force production, is a strong predictor of locomotor energy costs across species of different size and might predict variability between similarly sized species. We tested for a relationship between foot contact time and metabolic rate during locomotion from published data. We investigated the phylogenetic correlation between energy expenditure rate and foot contact time, conditioned on fixed effects of mass and speed. Foot contact time does not explain variance in rate of energy expenditure during locomotion, once speed and body size are accounted for. Thus, perhaps surprisingly, inter-specific differences in the mass-independent net cost of terrestrial transport (NCOT) are not explained by rates of force production. We also tested for relationships between locomotor energy costs and eco-physiological variables. NCOT did not relate to any of the tested eco-physiological variables; we thus conclude either that interspecific differences in transport cost have no influence on macroecological and macrophysiological patterns, or that NCOT is a poor indicator of animal energy expenditure beyond the treadmill.

Hypoxia exposure alleviates impaired muscular metabolism, glucose tolerance, and aerobic capacity in apelin-knockout mice

High altitude hypoxia adaptation can improve glucose tolerance in people with metabolic syndrome and type 2 diabetes (T2D). Apelin is an endogenous ligand of the G protein-coupled receptor APJ and has possible roles in energy metabolism. Apelin-null mice have been reported to exhibit impaired insulin sensitivity, which can be reversed by supplementation of exogenous apelin. Here, we examined the effects of 4 weeks' intermittent hypoxia exposure on physiological and biochemical variables in apelin knockout (KO) mice. Apelin KO mice exhibited decreased expression of substrate metabolism-associated genes/proteins, impaired glucose tolerance, and reduced exercise capacity compared to wild-type mice, and all of these effects were rescued by hypoxia. These findings suggest that hypoxia intervention may possibly be able to alleviate metabolic conditions caused by genetic defects.

Flight energetics, caste dimorphism and scaling properties in the bumblebee, Bombus impatiens

Animal size affects the energetics of locomotion. Using female caste dimorphism in bumblebees, we assessed how body mass impacts morphological and physiological traits linked with flight. The allometric relationships obtained for wing surface area, wingbeat frequency, and flight and resting metabolic rates of workers could predict the trait values of queens that were more than fourfold larger. Flight success of queens decreased over time in part because of a large increase in body mass and a decrease in traits linked with flight, namely wingbeat frequency and metabolic rate, and the activity of metabolic enzymes tended to decrease. After taking into account temporal changes, body mass, flight wingbeat frequency and metabolic rate were repeatable. Finally, we found significant family resemblance for all traits measured, indicating that shared genes and/or environmental effects impact phenotypic variation. Together, our results show that the functional association between body morphology and flight physiology is robust, providing further insights into the mechanistic basis of metabolic rate scaling patterns during locomotion in animals.

Approaches for testing hypotheses for the hypometric scaling of aerobic metabolic rate in animals

Hypometric scaling of aerobic metabolism [larger organisms have lower mass-specific metabolic rates (MR/g)] is nearly universal for interspecific comparisons among animals, yet we lack an agreed upon explanation for this pattern. If physiological constraints on the function of larger animals occur and limit MR/g, these should be observable as direct constraints on animals of extant species and/or as evolved responses to compensate for the proposed constraint. There is evidence for direct constraints and compensatory responses to O2 supply constraint in skin-breathing animals, but not in vertebrates with gas-exchange organs. The duration of food retention in the gut is longer for larger birds and mammals, consistent with a direct constraint on nutrient uptake across the gut wall, but there is little evidence for evolving compensatory responses to gut transport constraints in larger animals. Larger placental mammals (but not marsupials or birds) show evidence of greater challenges with heat dissipation, but there is little evidence for compensatory adaptations to enhance heat loss in larger endotherms, suggesting that metabolic rate (MR) more generally balances heat loss for thermoregulation in endotherms. Size-dependent patterns in many molecular, physiological, and morphological properties are consistent with size-dependent natural selection, such as stronger selection for neurolocomotor performance and growth rate in smaller animals and stronger selection for safety and longevity in larger animals. Hypometric scaling of MR very likely arises from different mechanisms in different taxa and conditions, consistent with the diversity of scaling slopes for MR.

Long-Term Trait Consistency in Mice Selected for Swim-Induced High Aerobic Capacity

The majority of studies show that metabolic rates are usually repeatable at the individual level, although their repeatabilities tend to decline with time and to be strongly affected by physiological changes. Changes in individual repeatabilities may therefore affect putative differences between experimental groups or populations. This problem is particularly relevant to artificial selection experiments that apply the selection protocol at early life stages, running the risk of a poor correlation of the trait with itself throughout the life cycle of individuals. Moreover, significant physiological changes (e.g., induced by reproduction) may affect traits under selection and therefore their postreproductive differentiation between selected lines. Here, using a unique animal model-mice from four lines selected for [Formula: see text] during swimming in 25°C water and four random-bred control (reference) lines-we analyzed the long-term consistency of aerobic capacity as well as postswim hypothermia in primiparous and nonreproducing females at 12, 25, and 29 wk of age. Our results show that significant between-line type divergence in [Formula: see text] and hypothermia persists over time and is only weakly affected by past reproduction. Furthermore, both traits are also repeatable within lines at the individual level. More generally, our results suggest that past reproduction events are unlikely to significantly affect between-population and between-individual differences in [Formula: see text] and related traits.

Locomotion, Energetics, Performance, and Behavior: A Mammalian Perspective on Lizards, and Vice Versa

SYNOPSIS

Animals are constrained by their abilities and by interactions with environmental factors, such as low ambient temperatures. These constraints range from physical impossibilities to energetic inefficiencies, and may entail trade-offs. Some of the constraints related to locomotion and activity metabolism can be illustrated through allometric comparisons of mammals and lizards, as representative terrestrial vertebrate endotherms and ectotherms, respectively, because these lineages differ greatly in aerobic metabolic capacities, resting energetic costs, and thermoregulatory patterns. Allometric comparisons are both useful and unavoidable, but "outlier" species (unusual for their clade) can also inform evolutionary scenarios, as they help indicate extremes of possible adaptation within mammalian and saurian levels of organization. We compared mammals and lizards for standard metabolic rate (SMR), maximal oxygen consumption during forced exercise (VO2max), net (incremental) cost of transport (NCT), maximal aerobic speed (MAS), daily movement distance (DMD), daily energy expenditure (DEE) during the active season, and the ecological cost of transport (ECT = percentage of DEE attributable to locomotion). (Snakes were excluded because their limbless locomotion has no counterpart in terrestrial mammals.) We only considered lizard SMR, VO2max, NCT, MAS, and sprint speed data if measured at 35-40 °C. On average, MAS is ∼7.4-fold higher in mammals, whereas SMR and VO2max are ∼6-fold greater, but values for all three of these traits overlap (or almost overlap) between mammals and lizards, a fact that has not previously been appreciated. Previous studies show that sprint speeds are similar for smaller mammals and lizards, but at larger sizes lizards are not as fast as some mammals. Mammals move ∼6-fold further each day than lizards, and DMD is by far the most variable trait considered here, but their NCT is similar. Mammals exceed lizards by ∼11.4-fold for DEE. On average for both lineages, the ECT is surprisingly low, somewhat higher for lizards, and positively allometric. If a lizard and mammal of 100 g body mass were both to move their entire DMD at their MAS, they could do so in ∼21 and 17 min, respectively, thus de-emphasizing the possible importance of time constraints. We conclude that ecological-energetic constraints related to locomotion are relatively more likely to occur in large, carnivorous lizards. Overall, our comparisons support the idea that the (gradual) evolution of mammalian endothermy did not necessarily require major changes in locomotor energetics, performance, or associated behaviors. Instead, we speculate that the evolution of thermoregulatory responses to low temperatures (e.g., shivering) may have been a key and "difficult" step in this transition.

A broad-scale comparison of aerobic activity levels in vertebrates: endotherms versus ectotherms

Differences in the limits and range of aerobic activity levels between endotherms and ectotherms remain poorly understood, though such differences help explain basic differences in species' lifestyles (e.g. movement patterns, feeding modes, and interaction rates). We compare the limits and range of aerobic activity in endotherms (birds and mammals) and ectotherms (fishes, reptiles, and amphibians) by evaluating the body mass-dependence of VO₂ max, aerobic scope, and heart mass in a phylogenetic context based on a newly constructed vertebrate supertree. Contrary to previous work, results show no significant differences in the body mass scaling of minimum and maximum oxygen consumption rates with body mass within endotherms or ectotherms. For a given body mass, resting rates and maximum rates were 24-fold and 30-fold lower, respectively, in ectotherms than endotherms. Factorial aerobic scope ranged from five to eight in both groups, with scope in endotherms showing a modest body mass-dependence. Finally, maximum consumption rates and aerobic scope were positively correlated with residual heart mass. Together, these results quantify similarities and differences in the potential for aerobic activity among ectotherms and endotherms from diverse environments. They provide insights into the models and mechanisms that may underlie the body mass-dependence of oxygen consumption.

Aerobic power and flight capacity in birds: a phylogenetic test of the heart-size hypothesis

Flight capacity is one of the most important innovations in animal evolution; it only evolved in insects, birds, mammals and the extinct pterodactyls. Given that powered flight represents a demanding aerobic activity, an efficient cardiovascular system is essential for the continuous delivery of oxygen to the pectoral muscles during flight. It is well known that the limiting step in the circulation is stroke volume (the volume of blood pumped from the ventricle to the body during each beat), which is determined by the size of the ventricle. Thus, the fresh mass of the heart represents a simple and repeatable anatomical measure of the aerobic power of an animal. Although several authors have compared heart masses across bird species, a phylogenetic comparative analysis is still lacking. By compiling heart sizes for 915 species and applying several statistical procedures controlling for body size and/or testing for adaptive trends in the dataset (e.g. model selection approaches, phylogenetic generalized linear models), we found that (residuals of) heart size is consistently associated with four categories of flight capacity. In general, our results indicate that species exhibiting continuous hovering flight (i.e. hummingbirds) have substantially larger hearts than other groups, species that use flapping flight and gliding show intermediate values, and that species categorized as poor flyers show the smallest values. Our study reveals that on a broad scale, routine flight modes seem to have shaped the energetic requirements of birds sufficiently to be anatomically detected at the comparative level.

Comparison of Canadian firefighters and healthy controls based on submaximal fitness testing and strength considering age and gender

INTRODUCTION

Few studies have addressed whether firefighters are fitter than the general population and possess sufficient levels of aerobic capacity and muscle strength to perform on-duty tasks in a safe and efficient manner, considering age and gender. We aimed to evaluate the fitness levels of Hamilton firefighters, and to determine the effects of age and gender.

METHODS

In total, 89 participants were recruited. The modified Canadian aerobic fitness test was used to determine participants' estimated maximal oxygen consumption (V_O2max) levels. For upper and lower body strength levels, a calibrated J-Tech hand-held dynamometer and a National Institute for Occupational Safety and Health (NIOSH) lifting device was used respectively.

RESULTS

Firefighters' mean (SD) V_O2max level was 40.30 ± 6.25 ml·kg^-1·min^-1. Age proved to have a statistically significant impact on V_O2max (p < 0.001). Gender displayed statistically significant effects on strength levels. Firefighters' age was the only statistically significant independent variable, and accounted for 61.00% of the variance in firefighters' aerobic capacity levels.

CONCLUSIONS

Firefighters possessed somewhat similar aerobic capacities but much higher levels of body strength when compared with the general population. With age, firefighters' aerobic capacities decreased; however, their upper and lower body strength levels remained the same.

Ecological and phylogenetic variability in the spinalis muscle of snakes

Understanding the origin and maintenance of functionally important subordinate traits is a major goal of evolutionary physiologists and ecomorphologists. Within the confines of a limbless body plan, snakes are diverse in terms of body size and ecology, but we know little about the functional traits that underlie this diversity. We used a phylogenetically diverse group of 131 snake species to examine associations between habitat use, sidewinding locomotion and constriction behaviour with the number of body vertebrae spanned by a single segment of the spinalis muscle, with total numbers of body vertebrae used as a covariate in statistical analyses. We compared models with combinations of these predictors to determine which best fit the data among all species and for the advanced snakes only (N = 114). We used both ordinary least-squares models and phylogenetic models in which the residuals were modelled as evolving by the Ornstein-Uhlenbeck process. Snakes with greater numbers of vertebrae tended to have spinalis muscles that spanned more vertebrae. Habitat effects dominated models for analyses of all species and advanced snakes only, with the spinalis length spanning more vertebrae in arboreal species and fewer vertebrae in aquatic and burrowing species. Sidewinding specialists had shorter muscle lengths than nonspecialists. The relationship between prey constriction and spinalis length was less clear. Differences among clades were also strong when considering all species, but not for advanced snakes alone. Overall, these results suggest that muscle morphology may have played a key role in the adaptive radiation of snakes.

Caffeine stimulates voluntary wheel running in mice without increasing aerobic capacity

The "energy drink" Red Bull and the "sports drink" Gatorade are often marketed to athletes, with claims that they cause performance gains. However, both are high in sugars, and also consumed by non-athletes. Few studies have addressed the effects of these drinks or their biologically active components in rodent exercise models. We used three experiments to test effects on both voluntary exercise behavior and maximal aerobic capacity in lines of mice known to differ in "athletic" traits. Mice from four replicate High Runner (HR) lines have been selectively bred for voluntary running on wheels, and run approximately three times as many revolutions per day as do mice from four non-selected Control (C) lines. HR mice also have higher endurance and maximal oxygen consumption (VO₂max) during forced treadmill exercise. In Experiment 1, we tested the hypothesis that Gatorade or Red Bull might cause or allow mice to increase their voluntary wheel running. On days 5 and 6 of 6days of wheel access, as is used to select breeders, HR mice ran 3.3-fold more than C, and females ran 1.2-fold more than males, with no linetype by sex interaction. On day 7, mice were administered Gatorade, Red Bull or tap water. During the subsequent 19-hour period, Gatorade had no statistical effect on running, but Red Bull significantly increased distance run by both sexes and in both HR and C lines. The increase in distance run caused by Red Bull was attributable to time spent running, not an increase in mean (or maximum) speed. As previous studies have found that sucrose alone does not generally increase wheel running, we tested two other active ingredients in Red Bull, caffeine and taurine, in Experiment 2. With a similar testing protocol, caffeine alone and caffeine+taurine increased running by about half the magnitude of Red Bull. In Experiment 3, we tested the hypothesis that Red Bull or caffeine alone can increase physiological performance ability during aerobic exercise, measured as VO₂max. In a repeated-measures design spanning 6days, females were housed with water bottles containing Red Bull, caffeine or water in a randomized order, and tested for VO₂max twice while receiving each fluid (6 total trials). Neither Red Bull nor caffeine significantly affected either VO₂max or a measure of trial cooperativity (rated on a scale of 1-5), but both treatments significantly reduced tiredness (rated on a scale of 1-3) scored at the end of trials for both HR and C lines. Taken together, our results suggest that caffeine increases voluntary exercise levels of mice by delaying fatigue, rather than increasing aerobic capacity.

Is Maximum Food Intake in Endotherms Constrained by Net or Factorial Aerobic Scope? Lessons from the Leaf-Eared Mouse

Food availability varies substantially throughout animals' lifespans, thus the ability to profit from high food levels may directly influence animal fitness. Studies exploring the link between basal metabolic rate (BMR), growth, reproduction, and other fitness traits have shown varying relationships in terms of both magnitude and direction. The diversity of results has led to the hypothesis that these relationships are modulated by environmental conditions (e.g., food availability), suggesting that the fitness consequences of a given BMR may be context-dependent. In turn, there is indirect evidence that individuals with an increased capacity for aerobic work also have a high capacity for acquiring energy from food. Surprisingly, very few studies have explored the correlation between maximum rates of energy acquisition and BMR in endotherms, and to the best of our knowledge, none have attempted to elucidate relationships between the former and aerobic capacity [e.g., maximum metabolic rate (MMR), aerobic scope (Factorial aerobic scope, FAS; Net aerobic scope, NAS)]. In this study, we measured BMR, MMR, maximum food intake (recorded under low ambient temperature and ad libitum food conditions; MFI), and estimated aerobic scope in the leaf-eared mouse (Phyllotis darwini). We, then, examined correlations among these variables to determine whether metabolic rates and aerobic scope are functionally correlated, and whether an increased aerobic capacity is related to a higher MFI. We found that aerobic capacity measured as NAS is positively correlated with MFI in endotherms, but with neither FAS nor BMR. Therefore, it appears plausible that the capacity for assimilating energy under conditions of abundant resources is determined adaptively by NAS, as animals with higher NAS would be promoted by selection. In theory, FAS is an invariant measurement of the extreme capacity for energy turnover in relation to resting expenditure, whereas NAS represents the maximum capacity for simultaneous aerobic processes above maintenance levels. Accordingly, in our study, FAS and NAS represent different biological variables; FAS, in contrast to NAS, may not constrain food intake. The explanations for these differences are discussed in biological and mathematical terms; further, we encourage the use of NAS rather than FAS when analyzing the aerobic capacity of animals.

Studying the evolutionary significance of thermal adaptation in ectotherms: The diversification of amphibians' energetics

A fundamental problem in evolutionary biology is the understanding of the factors that promote or constrain adaptive evolution, and assessing the role of natural selection in this process. Here, comparative phylogenetics, that is, using phylogenetic information and traits to infer evolutionary processes has been a major paradigm . In this study, we discuss Ornstein-Uhlenbeck models (OU) in the context of thermal adaptation in ectotherms. We specifically applied this approach to study amphibians's evolution and energy metabolism. It has been hypothesized that amphibians exploit adaptive zones characterized by low energy expenditure, which generate specific predictions in terms of the patterns of diversification in standard metabolic rate (SMR). We complied whole-animal metabolic rates for 122 species of amphibians, and adjusted several models of diversification. According to the adaptive zone hypothesis, we expected: (1) to find "accelerated evolution" in SMR (i.e., diversification above Brownian Motion expectations, BM), (2) that a model assuming evolutionary optima (i.e., an OU model) fits better than a white-noise model and (3) that a model assuming multiple optima (according to the three amphibians's orders) fits better than a model assuming a single optimum. As predicted, we found that the diversification of SMR occurred most of the time, above BM expectations. Also, we found that a model assuming an optimum explained the data in a better way than a white-noise model. However, we did not find evidence that an OU model with multiple optima fits the data better, suggesting a single optimum in SMR for Anura, Caudata and Gymnophiona. These results show how comparative phylogenetics could be applied for testing adaptive hypotheses regarding history and physiological performance in ectotherms.

Phylogenetic Analysis Supports the Aerobic-Capacity Model for the Evolution of Endothermy

The evolution of endothermy is a controversial topic in evolutionary biology, although several hypotheses have been proposed to explain it. To a great extent, the debate has centered on the aerobic-capacity model (AC model), an adaptive hypothesis involving maximum and resting rates of metabolism (MMR and RMR, respectively; hereafter "metabolic traits"). The AC model posits that MMR, a proxy of aerobic capacity and sustained activity, is the target of directional selection and that RMR is also influenced as a correlated response. Associated with this reasoning are the assumptions that (1) factorial aerobic scope (FAS; MMR/RMR) and net aerobic scope (NAS; MMR - RMR), two commonly used indexes of aerobic capacity, show different evolutionary optima and (2) the functional link between MMR and RMR is a basic design feature of vertebrates. To test these assumptions, we performed a comparative phylogenetic analysis in 176 vertebrate species, ranging from fish and amphibians to birds and mammals. Using disparity-through-time analysis, we also explored trait diversification and fitted different evolutionary models to study the evolution of metabolic traits. As predicted, we found (1) a positive phylogenetic correlation between RMR and MMR, (2) diversification of metabolic traits exceeding that of random-walk expectations, (3) that a model assuming selection fits the data better than alternative models, and (4) that a single evolutionary optimum best fits FAS data, whereas a model involving two optima (one for ectotherms and another for endotherms) is the best explanatory model for NAS. These results support the AC model and give novel information concerning the mode and tempo of physiological evolution of vertebrates.

Body mass scaling of passive oxygen diffusion in endotherms and ectotherms

The area and thickness of respiratory surfaces, and the constraints they impose on passive oxygen diffusion, have been linked to differences in oxygen consumption rates and/or aerobic activity levels in vertebrates. However, it remains unclear how respiratory surfaces and associated diffusion rates vary with body mass across vertebrates, particularly in relation to the body mass scaling of oxygen consumption rates. Here we address these issues by first quantifying the body mass dependence of respiratory surface area and respiratory barrier thickness for a diversity of endotherms (birds and mammals) and ectotherms (fishes, amphibians, and reptiles). Based on these findings, we then use Fick's law to predict the body mass scaling of oxygen diffusion for each group. Finally, we compare the predicted body mass dependence of oxygen diffusion to that of oxygen consumption in endotherms and ectotherms. We find that the slopes and intercepts of the relationships describing the body mass dependence of passive oxygen diffusion in these two groups are statistically indistinguishable from those describing the body mass dependence of oxygen consumption. Thus, the area and thickness of respiratory surfaces combine to match oxygen diffusion capacity to oxygen consumption rates in both air- and water-breathing vertebrates. In particular, the substantially lower oxygen consumption rates of ectotherms of a given body mass relative to those of endotherms correspond to differences in oxygen diffusion capacity. These results provide insights into the long-standing effort to understand the structural attributes of organisms that underlie the body mass scaling of oxygen consumption.

A phylogenetic analysis of macroevolutionary patterns in fermentative yeasts

When novel sources of ecological opportunity are available, physiological innovations can trigger adaptive radiations. This could be the case of yeasts (Saccharomycotina), in which an evolutionary novelty is represented by the capacity to exploit simple sugars from fruits (fermentation). During adaptive radiations, diversification and morphological evolution are predicted to slow‐down after early bursts of diversification. Here, we performed the first comparative phylogenetic analysis in yeasts, testing the “early burst” prediction on species diversification and also on traits of putative ecological relevance (cell‐size and fermentation versatility). We found that speciation rates are constant during the time‐range we considered (ca., 150 millions of years). Phylogenetic signal of both traits was significant (but lower for cell‐size), suggesting that lineages resemble each other in trait‐values. Disparity analysis suggested accelerated evolution (diversification in trait values above Brownian Motion expectations) in cell‐size. We also found a significant phylogenetic regression between cell‐size and fermentation versatility (R² = 0.10), which suggests correlated evolution between both traits. Overall, our results do not support the early burst prediction both in species and traits, but suggest a number of interesting evolutionary patterns, that warrant further exploration. For instance, we show that the Whole Genomic Duplication that affected a whole clade of yeasts, does not seems to have a statistically detectable phenotypic effect at our level of analysis. In this regard, further studies of fermentation under common‐garden conditions combined with comparative analyses are warranted.

Consequences of Fatherhood in the Biparental California Mouse (Peromyscus californicus): Locomotor Performance, Metabolic Rate, and Organ Masses

Although effects of motherhood on mothers have been well documented in mammals, the effects of fatherhood on fathers are not well known. We evaluated effects of being a father on key metabolic and performance measures in the California mouse, Peromyscus californicus. California mice are genetically monogamous in the wild, and fathers show similar parental behavior to mothers, with the exception of lactation. To investigate the impact of fatherhood on fathers, focal males were paired with an intact female (breeding males), a tubally ligated female (nonbreeding males), or another male (virgins). Starting 3-5 d after the birth of each breeding pair's first litter, males were tested for locomotor performance (maximum sprint speed, treadmill endurance), basal metabolic rate (BMR), and maximum oxygen consumption ([Formula: see text]). At the end of the 11-d test period, mice were euthanized, hematocrit was determined, and organs were weighed. Speed, endurance, and [Formula: see text] were significantly repeatable between two replicate measurement days but did not differ among groups, nor did BMR. Breeding males had significantly larger hind limb muscles than did nonbreeding males, whereas virgin males had heavier subcutaneous fat pads than did nonbreeding and breeding males. Several correlations were observed at the level of individual variation (residuals from ANCOVA models), including positive correlations for endurance with [Formula: see text], [Formula: see text] with testes mass, and some of the digestion-related organs with each other. These results indicate that fatherhood may not have pronounced performance, metabolic, or morphological effects on fathers, at least under standard laboratory conditions and across a single breeding cycle.

Metabolic scaling in animals: methods, empirical results, and theoretical explanations

Life on earth spans a size range of around 21 orders of magnitude across species and can span a range of more than 6 orders of magnitude within species of animal. The effect of size on physiology is, therefore, enormous and is typically expressed by how physiological phenomena scale with mass(b). When b ≠ 1 a trait does not vary in direct proportion to mass and is said to scale allometrically. The study of allometric scaling goes back to at least the time of Galileo Galilei, and published scaling relationships are now available for hundreds of traits. Here, the methods of scaling analysis are reviewed, using examples for a range of traits with an emphasis on those related to metabolism in animals. Where necessary, new relationships have been generated from published data using modern phylogenetically informed techniques. During recent decades one of the most controversial scaling relationships has been that between metabolic rate and body mass and a number of explanations have been proposed for the scaling of this trait. Examples of these mechanistic explanations for metabolic scaling are reviewed, and suggestions made for comparing between them. Finally, the conceptual links between metabolic scaling and ecological patterns are examined, emphasizing the distinction between (1) the hypothesis that size- and temperature-dependent variation among species and individuals in metabolic rate influences ecological processes at levels of organization from individuals to the biosphere and (2) mechanistic explanations for metabolic rate that may explain the size- and temperature-dependence of this trait.