Metabolic scaling: a many-splendoured thing

Animals at rest and during exercise display rates of aerobic metabolism, VO2, that represent mainly the sum of mitochondrial respiration rates in various organs. The relative contributions of these organs change with physiological state such that internal organs such as liver, kidney and brain account for most of the whole-body VO2 at rest, while locomotory muscles account for >90% of the maximum rate, VO2max, during maximal aerobic exercise. Mechanisms that regulate VO2 are complex and the relative importance of each step in a series, estimated by metabolic control analysis, depends upon the level of biological organization under consideration as well as physiological state. Despite this complexity, prominent single-cause models propose that metabolic rates are supply-limited and that the scaling of supply systems provides a sufficient explanation for the allometric scaling of metabolism. We argue that some assumptions, as well as current interpretations of the meaning (or consequences) of these constraints are flawed, i.e., elephants do not have lower mass-specific basal or maximal rates of aerobic metabolism because their mitochondria are more supply-limited than those of shrews. Animals do not violate the laws of physics, and the allometric scaling of supply systems would be expected, to some extent, to be matched by capacities for (and rates of) energy expenditure. But life is not so simple. Animals are so diverse that to do justice to metabolic scaling, it is also necessary to consider the scaling of energy expenditure. It is by doing so that models of metabolic scaling can be consistent with current paradigms in metabolic regulation and accommodate the range of inter- and intraspecific exponents found in nature. The "allometric cascade," a first attempt at such an accounting, was a source of great satisfaction to Peter Hochachka. It was the last door that he helped open to comparative physiologists before he said goodbye.     

Lifestyle-Based Approaches Provide Insights into Body Size Variation Across Environmental Gradients in Anurans

Body size of organisms as a fitness-related phenotype has evolved in response to local conditions, often through the size-dependent thermoregulatory mechanisms. The direction and degree of this response should depend on animals’ lifestyle in terms of the preference for terrestrial or aquatic conditions, especially so for adult anurans that differ in lifestyle among species but all must maintain certain body temperatures for metabolism. It may be expected that anuran species frequently exposed to terrestrial environments characterized by fluctuant thermal conditions are more plastic in body size along thermal gradients than those highly relaying on aquatic environments where thermal conditions are relatively stable. We test this prediction using both interspecific and intraspecific data. With anurans in China as the model organisms, we show that across terrestrial species but not aquatic species, body size decreases with increasing ambient temperature. From the published literature worldwide, we summarized that more terrestrial versus fewer aquatic species follow the predicted ecogeographical size patterns. In addition, both interspecific and intraspecific data reveal that arboreal anurans do not exhibit the size cline, probably because relatively warm climates experienced by these species impose weak selective pressures on heat conservation or adaptation to tree-climbing constrains the variation in body size. Our finding highlights the importance of taking lifestyle into account when assessing macroevolutionary trends in body size for anurans in particular and ectothermic taxa in general.     

A Review for Life-history Traits Variation in Frogs Especially for Anurans in China

Environmental variation can promote differentiation in life-history traits in species of anurans. Increased environmental stress usually results in larger age at sexual maturity, older mean age, longer longevity, slower growth, larger body size, and a shift in reproductive allocation from offspring quantity to quality, and a stronger trade-off between offspring size and number. However, previous studies have suggested that there are inconsistent geographical variations in life-history traits among anuran species in China. Hence, we here review the intraspecific patterns and differences in life-history traits(i.e., egg size, clutch size, testes size, sperm length, age at sexual maturity, longevity, body size and sexual size dimorphism) among different populations within species along geographical gradients for anurans in China in recent years. We also provide future directions for studying difference in sperm performance between longer and shorter sperm within a species through transplant experiments and the relationships between metabolic rate and brain size and life-history.     

Broad-scale spatial patterns of canopy cover and pond morphology affect the structure of a Neotropical amphibian metacommunity

Spatial and environmental processes influence species composition at distinct scales. Previous studies suggested that the distribution of larval anurans at the landscape-scale is influenced by environmental gradients related to adult breeding site selection, such as pond canopy cover, but not by water chemistry. However, the combined effects of spatial, pond morphology, and water chemistry variables on metacommunity structure of larval anurans have not been analyzed yet. We used a partial redundancy analysis with variation partitioning to analyze the relative influence of pond morphology (e.g., depth, area, and aquatic vegetation), water chemistry, and spatial variables on a tadpole metacommunity from southeastern Brazil. We predict that pond morphology and canopy cover will influence the metacommunity at broad spatial scales, while water chemistry would play a larger role at finer scales. We found that broad-scale spatial patterns of pond canopy cover and pond morphology strongly influenced metacommunity structure, with water chemistry being not significant. Additionally, species composition was spatially autocorrelated at short distances. We suggest that the reproductive behavior of adult anurans is driving tadpole metacommunity dynamics, since pond morphology, but not water chemistry affects breeding site selection by adults. Our results contribute to the understanding of amphibian species diversity in tropical wetlands.     

Oxygen transport during exercise in large mammals. I. Adaptive variation in oxygen demand

This study investigated mechanisms used by horses and steers to increase O2 uptake and delivery (VO2) from resting to maximal rates and identified the mechanisms that enable horses to achieve higher maximal rates of O2 consumption (VO2max) than steers. VO2 and circulatory variables were measured while Standardbred trotting horses and steers (450-kg body mass) stood quietly and ran on a treadmill at speeds up to those eliciting VO2max. As VO2 increased in both species, heart rate and circulating hemoglobin (Hb) concentration increased, thereby increasing O2 delivery by the circulation, while cardiac stroke volume remained unchanged. At VO2max arterial PCO2 increased from its resting value in horses but was unchanged in steers, and arterial PO2 decreased in both species. Although the horses hypoventilated and were hypoxemic at VO2max, no significant decrease in arterial Hb saturation occurred. VO2max of the horses was 2.6 times higher than that of the steers and was associated with a 100% larger cardiac output, 100% larger stroke volume, and 40% higher Hb concentration, whereas heart rates at VO2max were identical in the two species. The higher cardiac output of the horses at VO2max resulted from a 1.2-fold higher mean arterial pressure and 1.6-fold lower peripheral tissue resistance (associated with a larger skeletal muscle capillary bed). Both the magnitude of the difference in VO2max between horses and steers and the mechanisms used to achieve it are the same as observed in smaller pairs of mammalian species with large variation in aerobic capacity.     

Correlational selection and the evolution of genomic architecture

We review and discuss the importance of correlational selection (selection for optimal character combinations) in natural populations. If two or more traits subject to multivariate selection are heritable, correlational selection builds favourable genetic correlations through the formation of linkage disequilibrium at underlying loci governing the traits. However, linkage disequilibria built up by correlational selection are expected to decay rapidly (ie, within a few generations), unless correlational selection is strong and chronic. We argue that frequency-dependent biotic interactions that have 'Red Queen dynamics' (eg, host-parasite interactions, predator-prey relationships or intraspecific arms races) often fuel chronic correlational selection, which is strong enough to maintain adaptive genetic correlations of the kind we describe. We illustrate these processes and phenomena using empirical examples from various plant and animal systems, including our own recent work on the evolutionary dynamics of a heritable throat colour polymorphism in the side-blotched lizard Uta stansburiana. In particular, male and female colour morphs of side-blotched lizards cycle on five- and two-generation (year) timescales under the force of strong frequency-dependent selection. Each morph refines the other morph in a Red Queen dynamic. Strong correlational selection gradients among life history, immunological and morphological traits shape the genetic correlations of the side-blotched lizard polymorphism. We discuss the broader evolutionary consequences of the buildup of co-adapted trait complexes within species, such as the implications for speciation processes.     

Gastric emptying during walking and running: effects of varied exercise intensity

Gastric emptying is increased during running (50%-70% maximal aerobic uptake, VO2max) as compared to rest. Whether this increase varies as a function of mode (i.e. walking vs running) and intensity of treadmill exercise is unknown. To examine the gastric emptying characteristics of water during treadmill exercise performed over a wide range of intensities relative to resting conditions, 10 men ingested 400 ml of water prior to each of six 15 min exercise bouts or 15 min of seated rest. Three bouts of walking exercise (1.57 m.s-1) were performed at increasing grades eliciting approximately 28%, 41% or 56% of VO2max. On a separate day, three bouts of running (2.68 ms-1) exercise were performed at grades eliciting approximately 57%, 65% or 75% of VO2max. Gastric emptying was increased during treadmill exercise at all intensities excluding 75% VO2max as compared to rest. Gastric emptying was similar for all intensities during walking and at 57% and 65% VO2max during running. However, running at 74% VO2max decreased the volume of original drink emptied as compared to all lower exercise intensities. Stomach secretions were markedly less during running as compared to walking and rest. These data demonstrate that gastric emptying is similarly increased during both moderate intensity (approximately 28%-65% VO2max) walking or running exercise as compared to resting conditions. However, gastric emptying decreases during high intensity exercise. Increases in gastric emptying during moderate intensity treadmill exercise may be related to increases in intragastric pressure brought about by contractile activity of the abdominal muscles.     

Specific alterations of physiological parameters in competitive race walkers

Race walking is the technical and athletic expression of fast walking and it can be considered as a type of endurance performance. The purpose of this study was to examine whether 12 weeks of a specially designed training program results in the further training enhancement of endurance performance and the related physiological parameters in already well-trained race walkers competing at the national and international level. The investigation protocol consisted of determining the maximal oxygen uptake (VO2peak) and related gas exchange values using an automated cardiopulmonary exercise system and of determining blood lactate variables (aerobic threshold - LTAer and the maximal lactate steady state - MLSS) during walking with proper technique at 8, 10, 12 and 14 km·h-1 for 4 minutes without rest in between. Thereafter, the speed on the treadmill was increased by 0.5 km·h-1 every two minutes until exhaustion to determine VO2peak. After 12 weeks of a specially designed endurance training, statistically significant increases in VO2peak (61.8±8.5 mL·kg-1·min-1 pre vs. 66.9±9.5 mL·kg-1·min-1 post training; p<0.05) and blood lactate variables (VO2-LTAer and VO2-MLSS; p<0.05) were noted. The obtained results suggest that the applied training program can improve endurance and race performance in previously well trained race walkers.     

Relationship between plasma renin activity and physical fitness in normal subjects

The relationship between plasma renin activity (PRA) at rest and physical fitness was studied in 40 normal young subjects on a liberal sodium intake. Plasma renin activity was measured in arterial blood withdrawn at the end of a 30-min period of rest in recumbency, while physical fitness was expressed by the highest oxygen uptake achieved during an uninterrupted graded exercise test performed in the sitting position on an electromagnetically braked ergometer bicycle (peak VO2). Log PRA correlated significantly and inversely with peak VO2 adjusted for body weight (r = -0.34; P less than 0.05) in single regression analysis. Using multiple regression and adjusted peak VO2, age, urinary sodium excretion and mean intra-arterial pressure as independent variables, no combination of two or more independent variables yielded significant partial correlation coefficients with log PRA. This correlation suggests that PRA at rest is inversely related to the subject's physical fitness.     

Spatial variation in anuran richness,diversity, and abundance across montane wetland habitat in Volcanoes National Park,Rwanda

The spatial distribution of species has long sparked interest among ecologists and biogeographers, increasingly so in studies of species responses to climate change. However, field studies on spatial patterns of distribution, useful to inform conservation actions at local scales, are still lacking for many regions, especially the tropics. We studied elevational trends and species‐area relationships among anurans in wetland habitats within Volcanoes National Park (VNP) in Rwanda, part of the biodiverse Albertine Rift region. In VNP, wetlands are key sites for anuran reproduction, and anurans are likely threatened by wetland desiccation which has occurred for the last few decades. Between 2012 and 2017, we sampled anuran communities in ten VNP wetlands located along an elevational gradient of c. 600 m (from 2,546 to 3,188 m a.s.l.) and found at least eight species, including at least two Albertine Rift Endemics. We show that species richness, diversity, and abundance likely decline with a decrease in wetland size and with an increase in elevation, though additional sampling (e.g., at night) might be needed to derive definite conclusions. Larger wetlands at lower elevations contained most species and individuals, which indicates the potential threat of wetland size reduction (through desiccation) for anuran conservation. However, we also found that wetlands differed in species composition and that some species (e.g., Sclerophrys kisoloensis) were likely restricted in distribution to only a few of the smaller wetlands—suggesting that the conservation of each individual wetland should be prioritized, regardless of size. We propose that all wetlands in VNP require additional conservation measures, which should be based on knowledge gathered through long‐term monitoring of anuran communities and research on drivers of wetland decline. Only such extended research will allow us to understand the response of anurans in VNP to threats such as climate change and wetland desiccation.     

Metabolic Correlates of Anuran Behavior

Frogs exhibit extensive diversity in their repertoires of social,reproductive, defensive, and predatory behavior, and in themetabolic processes that support these activities. Three aspectsof anuran biology (foraging mode, post-metamorphic ontogeneticchanges in ecology, and reproductive behavior) are analyzedfor their correlations with metabolic capacities. Anurans thatforage widely for prey have greater capacities for aerobic ATPproduction than do sedentary foragers. This relationship appearsto extend to intraspecific analyses; significant differencesin aerobic capacity among populations of a species of dart-poisonfrog are associated with differences in feeding ecology. Ontogenetic change in metabolic capacity is directly coupledwith ontogeny of behavior. The magnitude of post-metamorphicchanges in physiology, behavior, and ecology appears to be relatedto differences in life history. A relatively short larval stageand small body size at metamorphosis, such as that found inAmerican toads, are associated with extensive post-metamorphicchanges in oxygen carrying capacity of the blood, cardiac musclemass, and aerobic capacity of predispersal juveniles. In contrast,predispersal juveniles of species with long larval periods andlarge body size at metamorphosis possess adult physiologicaland behavioral features. Anuran reproductive activities, especially calling to attractmates, are energetically demanding, suggesting that the behaviorof male frogs at a breeding pond may be limited by their metaboliccapacities. However, the only study that has attempted to relateindividual variation in reproductive behavior to individualvariation in aerobic capacity found no correlation between thosecharacteristics. The complexity of anuran biology ensures that physiologicalcharacteristics of anurans reflect many aspects of ecologyandbehavior, some of which act independently, others in concert.Carefully designed experiments that incorporate both field andlaboratory data are required to assess these interlocking features.     

COMPARATIVE METHODS AT THE SPECIES LEVEL: GEOGRAPHIC VARIATION IN MORPHOLOGY AND GROUP SIZE IN GREY-CROWNED BABBLERS (POMATOSTOMUS TEMPORALIS)

We show that a new comparative method that sheds light on evolutionary trends among species may also illuminate trends within species. This finding comes from a phylogenetic autocorrelation analysis of morphological traits among individuals sampled from ten populations of a cooperatively breeding songbird, the Grey-crowned Babbler (Pomatostomus temporalis). Highly variable mitochondrial DNA (mtDNA) sequences from both the eastern (Pomatostomus temporalis temporalis) and western (Pomatostomus temporalis rubeculus) lineages were used to define genetic distances among 120 individuals and to estimate correlations among individuals in wing length, tarsus length, and body weight via an intraspecific weighting matrix. The autoregressive model effectively removed intraspecific correlations for all three morphological variables, and the proportion of the total phenotypic variance due to genealogical relationships varied from 0.68 (weight) to 0.23 (tarsus). The analysis revealed correlations among the specific components of traits, in which none were previously detected (type-I error) and diminished correlations that appeared strong when phylogeny was ignored. Group size was the only trait for which the autoregressive model failed to remove intraspecific correlations, a result likely due to the plasticity, convergence, and clinal variation in this trait in both the eastern and western lineages. The autocorrelation analysis weakened significant negative correlations between group size and total values for wing length and body weight, but the interpretation of this result depends on the adaptive significance ascribed to the “phylogenetic component” of trait values removed by the analysis. Comparative methods employing distance matrices are one useful way of summarizing the pattern of nonhierarchical relationships among conspecific individuals (“tokogenetic” relationships, sensu Hennig).     

Abundance-occupancy dynamics in a human dominated environment: linking interspecific and intraspecific trends in British farmland and woodland birds

1. Range size, population size and body size, the key macroecological variables, vary temporally both within and across species in response to anthropogenic and natural environmental change. However, resulting temporal trends in the relationships between these variables (i.e. macroecological patterns) have received little attention. 2. Positive relationships between the local abundance and regional occupancy of species (abundance-occupancy relationships) are among the most pervasive of all macroecological patterns. In the absence of formal predictions of how abundance-occupancy relationships may vary temporally, we outline several scenarios of how changes in abundance within species might affect interspecific patterns. 3. We use data on the distribution and abundance of 73 farmland and 55 woodland bird species in Britain over a 32-year period encompassing substantial habitat modification to assess the likelihood of these scenarios. 4. In both farmland and woodland habitats, the interspecific abundance-occupancy relationship changed markedly over the period 1968-99, with a significant decline in the strength of the relationship. 5. Consideration of intraspecific dynamics shows that this has been due to a decoupling of abundance and occupancy particularly in rare and declining species. Insights into the intraspecific processes responsible for the interspecific trend are obtained by analysis of temporal trends in the distribution of individuals between sites, which show patterns consistent with habitat quality declines. 6. This study shows that a profitable approach to ascertaining the nature of human impacts is to link intra- and interspecific processes. In the case of British farmland and woodland birds, changes to the environment lead to species-specific responses in large-scale distributions. These species-specific changes are the driver of the observed changes in the form and strength of the interspecific relationship.     

The energetics of middle-distance running

In order to assess the relative contribution of aerobic processes to running velocity (v), 27 male athletes were selected on the basis of their middle-distance performances over 800, 1500, 3000 or 5000 m, during the 1987 track season. To be selected for study, the average running velocity (v) corresponding to their performances had to be superior to 90% of the best French v of the season. Maximum O2 consumption (VO2max) and energy cost of running (C) had been measured within the 2 months preceding the track season, which, together with oxygen consumption at rest (VO2rest) allowed us to calculate the maximal v that could be sustained under aerobic conditions: vamax = (VO2max - VO2rest) x C-1. The treadmill running v corresponding to a blood lactate of 4 mmol.l-1 (vla4), was also calculated. In the whole group, C was significantly related to height (r = -0.43; P less than 0.03). Neither C nor VO2max (with, in this case, the exception of the 3000 m athletes) were correlated to v. On the other hand, vamax was significantly correlated to v over distances longer than 800 m. These v were also correlated to vla4. However vla4 occurred at 87.5% SD 3.3% of vamax, this relationship was interpreted as being an expression of the correlation between vamax and v. Calculation of vamax provided a useful means of analysing the performances. At the level of achievement studied, v sustained over 3000 m corresponded to vamax.(ABSTRACT TRUNCATED AT 250 WORDS)     

Aerobic power and cardiovascular response to stress

The relationship between aerobic fitness as measured by maximal O2 uptake (VO2max) and the cardiovascular response to laboratory stressors was examined in two experiments. First, 34 male college students were screened on the basis of their heart rate (HR) response to a reaction time-shock avoidance (RT-AV) task. The six individuals showing an average HR increase of 45 beats/min (reactives) and the six subjects showing an average increase of 8 beats/min (nonreactives) did not differ in VO2max (47.7 +/- 2 vs. 48.7 +/- 1 ml.kg-1.min-1, respectively). However, a statistically significant association between a reported family history of hypertension and peak HR response to RT-AV was seen. In the second series of experiments, the plasma catecholamine and cardiovascular responses of eight elite endurance-trained athletes (VO2max 70.6 +/- 1 ml.kg-1.min-1) and eight untrained volunteers (VO2max 45.5 +/- 1 ml.kg-1.min-1) were compared on the following: RT-AV, reaction time for monetary reward (RT-AP), cold pressor, isometric handgrip, and orthostatic challenge (standing). The trained group exhibited a significantly lower mean HR at rest (P less than 0.05), otherwise there were no significant differences between the two groups. The results indicate that although individual differences (e.g., family history of hypertension and high resting HR) can be related to the potential for cardiovascular responses to novel laboratory challenges, the contribution of fitness to this characteristic is much less clear. Further exploration of questions pertaining to fitness and stress should focus on individuals with a predisposition to stress reactivity.     

两代AVHRR GIMMS NDVI数据集的对比分析——以新疆地区为例

最新发布的1981—2012年的AVHRR GIMMS NDVI3g数据为了解区域植被的近期变化状况提供了数据基础。深入理解该版本与老版本GIMMS NDVIg(1981—2006年)之间的关系,对于使用新数据时充分利用已有老版本的研究结果具有重要意义。以我国西北干旱区的典型区域——新疆为例,研究了两个数据集在反映生长季、春季、夏季和秋季植被现状,植被变化趋势及其对气候变化响应方面的异同。研究结果表明:两个数据集在描述植被活动空间分布、变化趋势及其与气候的相关性方面大体相似,但在数值、动态变化率及其对气候变化响应强度等方面存在的差异也不容忽略。NDVI3g数据生长季和各季节NDVI数值多大于NDVIg,尤其是在夏季和在植被覆盖较好的区域。区域尺度,NDVI3g所反映的植被变化趋势更为平稳,尤其是在夏季和较长的时段,这可能与像元尺度NDVI3g显著增加范围小于NDVIg,而显著减少范围多于NDVIg有关。两个数据集对气温、降水量、潜在蒸散发和湿润指数的响应具有大体一致的空间格局,但对气候因子变化的敏感性存在差异,哪一个数据集更为灵敏依赖于不同的气候因子和时段。一般规律是NDVI3g与热量因子显著正相关的区域小于NDVIg,而与水分因子显著正相关的区域则大于NDVIg。利用长期的生态数据集,尽快理清两个数据集在表征植被变化之间的异同并建立两者的转换关系,对于合理开展植被变化、碳平衡、生态系统服务功能评估等广泛利用NDVI数据的相关研究十分重要。     

Familial resemblance in maximal heart rate, blood lactate and aerobic power

There are considerable interindividual differences in maximal oxygen uptake per kilogram of body weight (VO2 max/kg), maximal heart rate (max HR) and maximal blood lactate (max blood La) measured during a progressive exercise test. The aim of the study was to quantify the familial relationships for these variables. Parents and children of 38 families of French-Canadian descent were submitted to a modified Balke treadmill test. VO2 max/kg and max HR were the highest values reached during the test for 1 min. Max blood La was obtained from a blood sample taken 2 min after the test. The effects of age and sex were significant for max blood La and VO2 max/kg in each generation. Scores were thus adjusted through multiple regression procedures (age + sex + age X sex + age2), yielding residuals which were submitted to further analysis. Intraclass correlations (ri) were significant in pairs of sibs for max blood La and max HR, i.e. 0.28 (p less than 0.01) and 0.43 (p less than 0.05), respectively. For VO2 max/kg, pairs of spouses and sibs were about similarly correlated (ri = 0.20 and 0.15; p less than 0.05). Data suggested that children were more related to their mother than to their father for VO2 max/kg, VO2 max/kg of fat-free weight, and particularly for max HR. It was concluded that familial resemblance and heritability estimates for maximal aerobic power, max HR and max blood La were quite low and generally nonsignificant. Correlations between biological sibs were, however, consistently significant for max HR and max blood La. The suggestion of a maternal effect in maximal aerobic power should be further investigated.     

Validity of VO(2 max) in predicting blood volume: implications for the effect of fitness on aging

A multiple regression model was constructed to investigate the premise that blood volume (BV) could be predicted using several anthropometric variables, age, and maximal oxygen uptake (VO(2 max)). To test this hypothesis, age, calculated body surface area (height/weight composite), percent body fat (hydrostatic weight), and VO(2 max) were regressed on to BV using data obtained from 66 normal healthy men. Results from the evaluation of the full model indicated that the most parsimonious result was obtained when age and VO(2 max) were regressed on BV expressed per kilogram body weight. The full model accounted for 52% of the total variance in BV per kilogram body weight. Both age and VO(2 max) were related to BV in the positive direction. Percent body fat contributed <1% to the explained variance in BV when expressed in absolute BV (ml) or as BV per kilogram body weight. When the model was cross validated on 41 new subjects and BV per kilogram body weight was reexpressed as raw BV, the results indicated that the statistical model would be stable under cross validation (e.g., predictive applications) with an accuracy of +/- 1,200 ml at 95% confidence. Our results support the hypothesis that BV is an increasing function of aerobic fitness and to a lesser extent the age of the subject. The results may have implication as to a mechanism by which aerobic fitness and activity may be protective against reduced BV associated with aging.     

Effects of adrenergic agonists and antagonists on muscle O2 uptake and lactate metabolism

To investigate adrenergic receptor-mediated responses in dog gastrocnemius-plantaris muscle, several catecholamine agonists, isoproterenol, epinephrine, norepinephrine, and phenylephrine, and two antagonists, propranolol and phenoxybenzamine, were given during repetitive, isotonic, tetanic contractions. The response variables that were measured were muscle blood flow, shortening during constant load contractions, and arterial and venous O2 and lactate concentrations. The calculated variables were O2 uptake (VO2), net lactic acid output (L), and power output. In the control experiments, the contractions increased VO2 to approximately 50 times rest by 2 min. Thereafter, shortening, work, and VO2 declined together by 17% at 30 min, indicating muscle fatigue. L increased rapidly to nearly 0.8 mumol X g-1 X min-1 by 2 min, declined to 0.3-0.4 mumol X g-1 X min-1 by 7 min, and was like rest at 15, 22.5, and 30 min. The arterial lactate concentration rose steadily from rest to 30 min of contractions. Epinephrine infusion stopped the decline of VO2 during the contractions, but this effect was not observed with the other agonists. Propranolol decreased VO2 compared with controls at 22.5 and 30 min of contractions. Phenoxybenzamine decreased VO2 compared with controls at all times during contraction, and the decline with time was present. Coinfusion of epinephrine with propranolol reduced the decline in VO2 observed with propranolol alone. Both epinephrine and isoproterenol increased L compared with controls. This epinephrine response was antagonized by propranolol but enhanced by phenoxybenzamine. Both isoproterenol and epinephrine infusions increased arterial lactate concentration.(ABSTRACT TRUNCATED AT 250 WORDS)