The metabolic and mechanical costs of step time asymmetry in walking

Animals use both pendular and elastic mechanisms to minimize energy expenditure during terrestrial locomotion. Elastic gaits can be either bilaterally symmetric (e.g. run and trot) or asymmetric (e.g. skip, canter and gallop), yet only symmetric pendular gaits (e.g. walk) are observed in nature. Does minimizing metabolic and mechanical power constrain pendular gaits to temporal symmetry? We measured rates of metabolic energy expenditure and calculated mechanical power production while healthy humans walked symmetrically and asymmetrically at a range of step and stride times. We found that walking with a 42 per cent step time asymmetry required 80 per cent (2.5 W kg⁻¹) more metabolic power than preferred symmetric gait. Positive mechanical power production increased by 64 per cent (approx. 0.24 W kg⁻¹), paralleling the increases we observed in metabolic power. We found that when walking asymmetrically, subjects absorbed more power during double support than during symmetric walking and compensated by increasing power production during single support. Overall, we identify inherent metabolic and mechanical costs to gait asymmetry and find that symmetry is optimal in healthy human walking.     

Gait‐specific metabolic costs and preferred speeds in ring‐tailed lemurs (Lemur catta), with implications for the scaling of locomotor costs

Metabolic costs of resting and locomotion have been used to gain novel insights into the behavioral ecology and evolution of a wide range of primates; however, most previous studies have not considered gait‐specific effects. Here, metabolic costs of ring‐tailed lemurs (Lemur catta) walking, cantering and galloping are used to test for gait‐specific effects and a potential correspondence between costs and preferred speeds. Metabolic costs, including the net cost of locomotion (COL) and net cost of transport (COT), change as a curvilinear function of walking speed and (at least provisionally) as a linear function of cantering and galloping speeds. The baseline quantity used to calculate net costs had a significant effect on the magnitude of speed‐specific estimates of COL and COT, especially for walking. This is because non‐locomotor metabolism constitutes a substantial fraction (41–61%, on average) of gross metabolic rate at slow speeds. The slope‐based estimate of the COT was 5.26 J kg^?1 m^?1 for all gaits and speeds, while the gait‐specific estimates differed between walking (0.5 m s^?1: 6.69 J kg^?1 m^?1) and cantering/galloping (2.0 m s^?1: 5.61 J kg^?1 m^?1). During laboratory‐based overground locomotion, ring‐tailed lemurs preferred to walk at ～0.5 m s^?1 and canter/gallop at ～2.0 m s^?1, with the preferred walking speed corresponding well to the COT minima. Compared with birds and other mammals, ring‐tailed lemurs are relatively economical in walking, cantering, and galloping. These results support the view that energetic optima are an important movement criterion for locomotion in ring‐tailed lemurs, and other terrestrial animals. Am J Phys Anthropol, 2012. © 2012 Wiley Periodicals, Inc.     

Accuracy of predicted resting metabolic rate and relationship between resting metabolic rate and cardiorespiratory fitness in obese men

[Purpose]

The purpose of this study is to examine that not only the relationship of the resting metabolic rate (RMR) and cardiorespiratory fitness(VO2peak), but also the comparison between measured and predicted results of RMR in obese men.

[Methods]

60 obese men (body fat>32%) were recruited for this study. They did not participate in regular exercising programs at least 6 months. The RMR was measured with indirect calorimetry and predicted RMR using Herris-Benedicte equation. The cardiorespiratory fitness was determined by directly measuring the oxygen consumption (VO2peak) during the exercise on the treadmill.

[Results]

The significance for the difference between the measured results and predicted result of RMR were tested by paired t-test. Correlation of measured date was obtained by Pearson correlation coefficient. The value of predicted RMR and measured RMR were significantly different in these obese subjects. (p < 0.001). The difference between RMR cardiorespiratory fitness and cardiorespiratory fitness showed significant correlation (r=0.67, p < 0.05).

[Conclusion]

The current formulas of predicted RMR have limited the evaluation of measured RMR for Korean obese men. Therefore, this study suggests that new formula should be designed for Korean in order to obtain more accurate results in obese.     

Allometry of resting metabolic rate in cockroaches

1. Resting VO2 at 22.7 degrees C was 0.217 +/- 0.007 ml O2/g/hr in Nauphoeta cinerea of 0.51 +/- 0.008 g body mass. 2. Whole animal resting metabolic rate for 11 cockroach species scaled allometrically: VO2 = 0.261 M0.776. 3. Allometry of resting VO2 among cockroach species is similar to that in vertebrates, and is consistent with models based on both "elastic similarity" and "biological similitude."     

A unified theory for the energy cost of legged locomotion

Small animals are remarkably efficient climbers but comparatively poor runners, a well-established phenomenon in locomotor energetics that drives size-related differences in locomotor ecology yet remains poorly understood. Here, I derive the energy cost of legged locomotion from two complementary components of muscle metabolism, Activation–Relaxation and Cross-bridge cycling. A mathematical model incorporating these costs explains observed patterns of locomotor cost both within and between species, across a broad range of animals (insects to ungulates), for a wide range of substrate slopes including level running and vertical climbing. This ARC model unifies work- and force-based models for locomotor cost and integrates whole-organism locomotor cost with cellular muscle physiology, creating a predictive framework for investigating evolutionary and ecological pressures shaping limb design and ranging behaviour.     

Effects of feeding and habitat on resting metabolic rates of the Pacific walrus

Arctic marine mammals live in a rapidly changing environment due to the amplified effects of global warming. Pacific walruses (Odobenus rosmarus divergens) have responded to declines in Arctic sea-ice extent by increasingly hauling out on land farther from their benthic foraging habitat. Energy models can be useful for better understanding the potential implications of changes in behavior on body condition and reproduction but require behavior-specific metabolic rates. Here we measured the resting metabolic rates (RMR) of three captive, adult female Pacific walruses through breath-by-breath respirometry when fed and fasted resting out of water (sitting and lying down) and while fed resting in water. RMR in and out of water were positively related with pretrial energy intake when not fasted and 25% higher than RMR when walruses were fasted and out of water. Overall, RMR was higher than previously estimated for this species. Fasting RMR out of water was only 25% lower than subsurface swimming metabolic rates suggestive of relatively efficient swimming in adult females. Our results identify the importance of considering feeding status and species-specific differences in affecting metabolic costs. Further research is needed to better understand potential energetic costs of thermoregulation at temperatures experienced by wild walruses.     

The standard metabolic rate of dolphin fish

The standard metabolic rates (SMRs) of 11 (1.395–4.125 kg) dolphin fish (mahimahi or dorado, Coryphaena hippurus ) were measured at 25°± 0.5°C. Fish were prevented from swimming with neuromuscular blocking agents and force ventilated. Heart rates were determined simultaneously. SMRs (358–726 mg O₂ h ^–1) were several times those of other similarly sized active teleosts such as salmonids, but close to those of tunas. Heart rates (84–161 beats min ^–1) were also high, but alike those of tunas under similar circumstances. As in tunas, the high SMR of dolphin fish may result from high osmoregulatory costs engendered by their large gill surface areas and/or other adaptations necessary for achieving exceptionally high maximum metabolic rates.     

Pendular mechanics and the kinematics and energetics of brachiating locomotion

Because brachiating locomotion is characterized by a pattern of swinging movements, brachiation has often been analogized to pendular motion, and aspects of the mechanics of pendular systems have been used to provide insight into both energetic and structural design aspects of this locomotor mode. However, there are several limitations to this approach. First, the motions of brachiating animals only approximate pendular motion, and therefore the energetics of these two systems are only roughly comparable. Second, the kinematic similarity between brachiation and pendular motion will be maximal at only one velocity, and the correspondence will be even less at greater or lesser speeds. Third, all forms of terrestrial locomotion that involve the use of limbs incorporate elements of pendular systems, and therefore brachiation is not unusual in this respect. Finally, it has been suggested that the mechanics of pendular motion will constrain the maximum attainable body size of brachiating animals and that this mechanical situation explains the lack of brachiating primates of greater than 30-kg body size; the present analysis provides evidence that the constraints on body size are far less strict than previously indicated and that extrinsic factors such as the geometry of the forest environment are more likely to dictate maximum body size for brachiators.     

Genetic correlation between resting metabolic rate and exploratory behaviour in deer mice (Peromyscus maniculatus)

According to the 'pace-of-life' syndrome hypothesis, differences in resting metabolic rate (RMR) should be genetically associated with exploratory behaviour. A large number of studies reported significant heritability for both RMR and exploratory behaviour, but the genetic correlation between the two has yet to be documented. We used a quantitative genetic approach to decompose the phenotypic (co)variance of several metabolic and behavioural measures into components of additive genetic, common environment and permanent environment variance in captive deer mice. We found significant additive genetic variance for two mass-independent metabolic measures (RMR and the average metabolic rate throughout the respirometry run) and two behavioural measures (time spent in centre and distance moved in a novel environment). We also detected positive additive genetic correlation between mass-independent RMR and distance moved (r(A) = 0.78 ± 0.23). Our results suggest that RMR and exploratory behaviour are functionally integrated traits in deer mice, providing empirical support for one of the connections within the pace-of-life syndrome hypothesis.     

Genetic correlations between basal and maximum metabolic rates in a wild rodent: consequences for evolution of endothermy

According to the aerobic capacity model, endothermy in birds and mammals evolved as a correlated response to selection for an ability of sustained locomotor activity, rather than in a response to direct selection for thermoregulatory capabilities. A key assumption of the model is that aerobic capacity is functionally linked to basal metabolic rate (BMR). The assumption has been tested in several studies at the level of phenotypic variation among individuals or species, but none has provided a clear answer whether the traits are genetically correlated. Here we present results of a genetic analysis based on measurements of the basal and the maximum swim- and cold-induced oxygen consumption in about 1000 bank voles from six generations of a laboratory colony, reared from animals captured in the field. Narrow sense heritability (h2) was about 0.5 for body mass, about 0.4 for mass-independent basal and maximum metabolic rates, and about 0.3 for factorial aerobic scopes. Dominance genetic and common environmental (= maternal) effects were not significant. Additive genetic correlation between BMR and the swim-induced aerobic capacity was high and positive, whereas correlation resulting from specific-environmental effects was negative. However, BMR was not genetically correlated with the cold-induced aerobic capacity. The results are consistent with the aerobic capacity model of the evolution of endothermy in birds and mammals.     

The measurement of resting metabolic rate in preschool children

Objective: This study examined the repeatability of measuring resting metabolic rate (RMR) in preschool children and the effect of different calculation protocols. Research Methods and Procedures: Eleven children (4 females and 7 males) participated in the project. They were recruited through advertisements in local schools and community centers. Resting metabolic rate was measured on 3 occasions over a 2‐week period, each after an overnight fast and each lasting ～20 to 25 minutes. Results were compared using repeated‐measures ANOVA to check for repeatability, and a number of methods of calculating RMR were assessed. Results: Repeatability of RMR measurements was good (coefficient of variation of replicates, 6.8%), with no significant difference between days of measurement. The lowest RMR measurement was obtained when the first 10 minutes were excluded and periods during which large activity was observed were excluded. This measurement was, on average, 4% lower than averaging the measurements after the first 5 minutes, including body movements. Discussion: This study suggests that RMR can be measured in preschool children and that the best method for calculating RMR in these subjects is to exclude periods when large body movements occur and the first 10 minutes of the measurement period. Only a single measurement of RMR is needed to obtain a reliable estimate.     

Resting metabolic rate and lung function in fasted and fed rough-toothed dolphins,Steno bredanensis

We measured resting metabolic rate (RMR), tidal volume (V_T), breathing frequency (f_R), respiratory flow, and end-expired gases in rough-toothed dolphins (Steno bredanensis) housed in managed care after an overnight fast and 1–2 hr following a meal. The measured average (± standard deviation) V_T (4.0 ± 1.3 L) and f_R (1.9 ± 1.0 breaths/min) were higher and lower, respectively, as compared with estimated values from both terrestrial and aquatic mammals, and the average V_T was 43% of the estimated total lung capacity. The end-expired gas levels suggested that this species keep alveolar O₂ (10.6% or 80 mmHg) and CO₂ (7.6% or 57 mmHg), and likely arterial gas tensions, low and high, respectively, to maximize efficiency of gas exchange. We show that following an overnight fast, the RMR (566 ± 158 ml O₂/min) was 1.8 times the estimated value predicted by Kleiber for terrestrial mammals of the same size. We also show that between 1 and 2 hr after ingestion of a meal, the metabolic rate increases an average of 29% (709 ± 126 ml O₂/min). Both body mass (M_b) and f_R significantly altered the measured RMR and we propose that both these variables should be measured when estimating energy use in cetaceans.     

Trapped in the darkness of the night: thermal and energetic constraints of daylight flight in bats

Bats are one of the most successful mammalian groups, even though their foraging activities are restricted to the hours of twilight and night-time. Some studies suggested that bats became nocturnal because of overheating when flying in daylight. This is because--in contrast to feathered wings of birds--dark and naked wing membranes of bats efficiently absorb short-wave solar radiation. We hypothesized that bats face elevated flight costs during daylight flights, since we expected them to alter wing-beat kinematics to reduce heat load by solar radiation. To test this assumption, we measured metabolic rate and body temperature during short flights in the tropical short-tailed fruit bat Carollia perspicillata at night and during the day. Core body temperature of flying bats differed by no more than 2°C between night and daytime flights, whereas mass-specific CO(2) production rates were higher by 15 per cent during daytime. We conclude that increased flight costs only render diurnal bat flights profitable when the relative energy gain during daytime is high and risk of predation is low. Ancestral bats possibly have evolved dark-skinned wing membranes to reduce nocturnal predation, but a low degree of reflectance of wing membranes made them also prone to overheating and elevated energy costs during daylight flights. In consequence, bats may have become trapped in the darkness of the night once dark-skinned wing membranes had evolved.     

Effect of fasting on resting metabolic rate and postprandial metabolic response in Silurus meridionalis

Resting metabolic rate in southern catfish of 2 and 5 day fasting groups were significantly higher than that of the 15 day fasting group ( P  < 0·05). After feeding, peak metabolic rate of specific dynamic action (SDA) of the 15 day fasting group was significantly lower than that of the 2 and 5 day fasting groups ( P  < 0·05). The duration of the SDA of the 15 day fasting group was significantly longer than that of the 2 day fasting group ( P  < 0·05) and the SDA coefficient of the 15 day fasting group was significantly lower than that of the 2 day fasting group ( P  < 0·05).     

Relation between average daily metabolic rate and resting metabolic rate of the mongolian gerbil (Meriones unguiculatus)

Summary Some early reports have claimed that the Mongolian gerbil is a diurnal rodent, but we found it to be active both night and day, being more active at night. A circadian rhythm was found both in locomotory activity under laboratory conditions and in average daily metabolic rate (ADMR).The ADMR of the Mongolian gerbil observed at 20° C in our study was 2.921 ml O₂/g·h which was near the value expected from Grodzinski's equation (ADMR=19.94 W^-0.50).Both ADMR and RMR were found to be negatively correlated with ambient temperature, with the slope of the regression line for ADMR being less than that for RMR. These two lines intersected at 20° C, lower below 20° C.According to Grodzinski, the ADMR is usually lower than RMR, but in our study the ADMR was found to be lower than the RMR only below 20° C, which suggests that the ambient temperature acts differently on ADMR and RMR. The temperature-dependent variation of both ADMR and RMR as well as their differences should be taken into account in the estimation of the productivity of animal population.