Changes In Metabolic Rate Research Articles

Seasonal muscle ultrastructure plasticity and resistance of muscle structural changes during temperature increases in resident black-capped chickadees (Poecile atricapillus) and rock pigeons (Columba livia)

Resident birds in temperate zones respond to seasonally fluctuating temperatures by adjusting their physiology, such as changes in basal metabolic rate or peak metabolic rate during cold exposure, or altering their organ sizes, so as to match the thermogenic requirements of their current environment. Climate change is predicted to cause increases in the frequency of heat and cold wave events, which could increase the likelihood that birds will face an environmental mismatch. Here, we examined seasonality and the effects of acute and chronic heat shock to 33°C and subsequent recovery from heat shock on the ultrastructure of the superficial pectoralis muscle fiber diameter, myonuclear domain (MND) and capillary density in two temperate bird species of differing body mass, the black-capped chickadee (Poecile atricapillus) and the rock pigeon (Columba livia). We found that muscle fiber ultrastructure did not change with heat treatment. However, in black-capped chickadees, there was a significant increase in fiber diameter in spring phenotype birds compared with summer phenotype birds. In rock pigeons, we saw no differences in fiber diameter across seasons. Capillary density did not change as a function of fiber diameter in black-capped chickadees, but did change seasonally, as did MND. Across seasons, as fiber diameter decreased, capillary density increased in the pectoralis muscle of rock pigeons. For both species in this study, we found that as fiber diameter increased, so did MND. Our findings imply that these two temperate birds employ different muscular growth strategies that may be metabolically beneficial to each.

Starvation resistance is associated with developmentally specified changes in sleep, feeding and metabolic rate.

Food shortage represents a primary challenge to survival, and animals have adapted diverse developmental, physiological and behavioral strategies to survive when food becomes unavailable. Starvation resistance is strongly influenced by ecological and evolutionary history, yet the genetic basis for the evolution of starvation resistance remains poorly understood. The fruit fly Drosophila melanogaster provides a powerful model for leveraging experimental evolution to investigate traits associated with starvation resistance. While control populations only live a few days without food, selection for starvation resistance results in populations that can survive weeks. We have previously shown that selection for starvation resistance results in increased sleep and reduced feeding in adult flies. Here, we investigate the ontogeny of starvation resistance-associated behavioral and metabolic phenotypes in these experimentally selected flies. We found that selection for starvation resistance resulted in delayed development and a reduction in metabolic rate in larvae that persisted into adulthood, suggesting that these traits may allow for the accumulation of energy stores and an increase in body size within these selected populations. In addition, we found that larval sleep was largely unaffected by starvation selection and that feeding increased during the late larval stages, suggesting that experimental evolution for starvation resistance produces developmentally specified changes in behavioral regulation. Together, these findings reveal a critical role for development in the evolution of starvation resistance and indicate that selection can selectively influence behavior during defined developmental time points.

Variation in metabolic rate and a test of differential sensitivity to temperature in populations of woolly sculpin (Clinocottus analis)

Variation in water temperature can have important effects on the energetics underlying metabolism, growth, and reproduction of many organisms. In order to anticipate how a species' allocation of energy may change in a warming ocean, we need to know the degree to which processes such as metabolic rate change with temperature (i.e., the thermal sensitivity of metabolism, Q10). In the context of long-term climate change, it will also be helpful to know whether local populations that experience different thermal regimes exhibit differences in thermal sensitivity. If so, it would indicate that thermal sensitivities of populations may adjust via acclimation or adaptation. We measured metabolic rates of Woolly Sculpin collected from two distant populations (Santa Cruz (SC) and Los Angeles (LA) counties, California, USA) and housed in a common environment. Using respirometry, we estimated resting mass-specific oxygen consumption (MO2) and calculated metabolic rates (MR) at temperatures of 12 °C, 16 °C, and 20 °C for 59 fish. The Q10 value across this range of temperatures was 2.92. Populations did not differ with respect to overall MO2, nor did they vary in their degree of thermal sensitivity. However, the LA population had greater variation in MO2 among individuals when compared to the SC population. Larger variation in overall MO2 among individuals within specific populations may reflect greater genetic diversity, and this may buffer some populations against the effect of future increases in water temperature.

Thyroid hormones mediate metabolic rate and oxidative, anti-oxidative balance at different temperatures in Mongolian gerbils (Meriones unguiculatus)

Oxidative damage is a potential physiological cost of thermoregulation during seasonal adjustments to air temperature (Ta) in small mammals. Here, we hypothesized that Ta affects serum thyroid hormone levels and these hormones can mediate the changes in metabolic rate and oxidative damage. Mongolian gerbils (Meriones unguiculatus) were acclimated at different Tas (5 °C, 23 °C and 37 °C) for 3 weeks. Serum tri-iodothyronine (T3) levels increased at 5 °C but decreased at 37 °C compared to the control (23 °C). Protein carbonyls increased in liver at 37 °C compared with control, however, lipid damage (malonaldehyde, MDA) in both serum and liver was unrelated to Ta. After the effects of different Tas on thyroid hormone levels and oxidative damage markers were determined, we further investigate whether thyroid hormones mediated metabolic rate and oxidative damage. Another set of gerbils received 0.0036% L-thyroxin (hyperthyroid), 0.04% Methylimazol (hypothyroid) or water (control). Hypothyroid group showed a 34% reduction in resting metabolic rate (RMR) also 42% and 26% increases in MDA and liver protein carbonyl respectively, whereas hyperthyroid group had higher RMR, liver mass and superoxide dismutase (SOD) compared to control. Serum T3 or T3/T4 levels were correlated positively with RMR, liver mass, and SOD, but negatively with MDA and uncoupling protein 2 (UCP2). We concluded that high Ta induced hypothyroidism, decreased RMR and increased oxidative damage, whereas low Ta induced hyperthyroidism, increased RMR and unchanged oxidative damage. These data supported our hypothesis that thyroid hormones can be a cue to mediate metabolic rate and different aspects of oxidative and antioxidant activities at different Tas.

Cerebral blood volume changes during the BOLD post-stimulus undershoot measured with a combined normoxia/hyperoxia method

Cerebral blood flow (CBF) and blood oxygenation level dependent (BOLD) signal measurements make it possible to estimate steady-state changes in the cerebral metabolic rate of oxygen (CMRO2) with a calibrated BOLD method. However, extending this approach to measure the dynamics of CMRO2 requires an additional assumption: that deoxygenated cerebral blood volume (CBVdHb) follows CBF in a predictable way. A test-case for this assumption is the BOLD post-stimulus undershoot, for which one proposed explanation is a strong uncoupling of flow and blood volume with an elevated level of CBVdHb during the post-stimulus period compared to baseline due to slow blood volume recovery (Balloon Model). A challenge in testing this model is that CBVdHb differs from total blood volume, which can be measured with other techniques. In this study, the basic hypothesis of elevated CBVdHb during the undershoot was tested, based on the idea that the BOLD signal change when a subject switches from breathing a normoxic gas to breathing a hyperoxic gas is proportional to the absolute CBVdHb. In 19 subjects (8F), dual-echo BOLD responses were measured in primary visual cortex during a flickering radial checkerboard stimulus in normoxia, and the identical experiment was repeated in hyperoxia (50% O2/balance N2). The BOLD signal differences between normoxia and hyperoxia for the pre-stimulus baseline, stimulus, and post-stimulus periods were compared using an equivalent BOLD signal calculated from measured R2* changes to eliminate signal drifts. Relative to the pre-stimulus baseline, the average BOLD signal change from normoxia to hyperoxia was negative during the undershoot period (p = 0.0251), consistent with a reduction of CBVdHb and contrary to the prediction of the Balloon Model. Based on these results, the BOLD post-stimulus undershoot does not represent a case of strong uncoupling of CBVdHb and CBF, supporting the extension of current calibrated BOLD methods to estimate the dynamics of CMRO2.

Early screening and treatment of gestational diabetes in high-risk women improves maternal and neonatal outcomes: A retrospective clinical audit

AimsEvidence suggests that screening for gestational diabetes (GDM) occurs too late in pregnancy, when changes in glucose metabolism and fetal growth rates can already be detected. In August 2016 NHS Lothian began screening women with risk factors for GDM during early pregnancy (11–13 weeks). We hypothesised that an earlier identification and treatment of dysglycaemia would improve pregnancy outcomes compared to previous standard care. MethodsWe compared management and outcomes for singleton pregnancies with GDM delivering at Royal Infirmary Edinburgh, UK, diagnosed through routine or early screening from 01/01/2015–31/10/2017 (routine screening n = 335, early screening n = 241). ResultsEarly screening increased the proportion of women diagnosed before 24 weeks’ gestation (n = 59/335, 17.6% vs n = 103/241, 42.7%, p < 0.001) but did not change the average monthly rate of diagnosis. Early screening increased the median duration of GDM during pregnancy (71 vs 93 days of gestation, p < 0.001) with no significant changes in the pharmacological management. Early screening improved the primary composite outcome (emergency caesarean section, neonatal hypoglycaemia and macrosomia; n = 138/335, 41.2% vs n = 73/241, 30.3%, adjusted Odds Ratio [95% confidence interval] 0.62 [0.43–0.91]. ConclusionsThere is a role for early screening and management of GDM however it is unclear whether this represents a cost-effective intervention.

A new method to study human metabolic rate changes and thermal comfort in physical exercise by CO2 measurement in an airtight chamber

The human metabolic rate is probably the most fundamental but least accurately assessed parameter in thermal comfort research and practice. This study aims to test the dynamic changes of the metabolic rate and its effects on thermal comfort perception. An airtight chamber (2 × 2 × 2 m3) was utilized to measure subjects’ accumulated CO2 production, and metabolic values then were calculated based on indirect calorimetry theory. During the test, 31 subjects were first asked to ride a spinning bike for 8 min at different intensities, and then asked to remain sitting for 22 min. The results showed how the human metabolic rate changed during different exercise periods. It took the human body 5–6 min to reach a new exercising metabolic level while the human body needed 7–9 min to recover from exercise to a normal sedentary state. The dramatic changes in metabolic rate markedly influenced subjects’ thermal sensation and thermal comfort perception. These findings provide a general principle of metabolic rate changes and could serve as a reference for future thermal comfort research.

Spatiotemporal dynamics and genome-wide association genome-wide association analysis of desiccation tolerance in Drosophila melanogaster.

Water availability is a major environmental challenge to a variety of terrestrial organisms. In insects, desiccation tolerance varies predictably over spatial and temporal scales and is an important physiological determinant of fitness in natural populations. Here, we examine the dynamics of desiccation tolerance in North American populations of Drosophila melanogaster using: (a) natural populations sampled across latitudes and seasons; (b) experimental evolution in field mesocosms over seasonal time; (c) genome-wide associations to identify SNPs/genes associated with variation for desiccation tolerance; and (d) subsequent analysis of patterns of clinal/seasonal enrichment in existing pooled sequencing data of populations sampled in both North America and Australia. A cline in desiccation tolerance was observed, for which tolerance exhibited a positive association with latitude; tolerance also varied predictably with culture temperature, demonstrating a significant degree of thermal plasticity. Desiccation tolerance evolved rapidly in field mesocosms, although only males showed differences in desiccation tolerance between spring and autumn collections from natural populations. Water loss rates did not vary significantly among latitudinal or seasonal populations; however, changes in metabolic rates during prolonged exposure to dry conditions are consistent with increased tolerance in higher latitude populations. Genome-wide associations in a panel of inbred lines identified twenty-five SNPs in twenty-one loci associated with sex-averaged desiccation tolerance, but there is no robust signal of spatially varying selection on genes associated with desiccation tolerance. Together, our results suggest that desiccation tolerance is a complex and important fitness component that evolves rapidly and predictably in natural populations.

Body size shifts influence effects of increasing temperatures on ectotherm metabolism

AbstractAimWarmer temperatures directly increase metabolic rates of ectotherms, but temperature also indirectly affects metabolic rates. Higher temperatures result in smaller body sizes and associated decreases in metabolic rates, and it remains unknown whether this indirect effect of temperature increase could mitigate the direct positive effect of temperature on metabolic rate. Here, we assess whether temperature‐induced shifts in body size are likely to offset the direct influence of temperature on metabolic rate.LocationGlobal.Time period1940–2011.Major taxa studiedEctotherms.MethodsWe compiled literature‐derived data on mass and temperature for 109 ectotherm species raised at various constant temperatures. Using an allometric equation to estimate metabolic rate from size and temperature, we determined the body masses necessary for species to maintain constant metabolic rates under increased temperatures. We also calculated and compared (a) change in metabolic rate attributable to increased temperature where body size does not change with (b) change in metabolic rate including empirical size change.ResultsWarmer temperatures resulted in increased metabolic rate estimates, but this was partly offset by decreased body sizes for the majority of species. For most species, observed decreases in body size at higher temperatures were insufficient to avoid metabolic rate increases.Main conclusionsAlthough the indirect effect of temperature on metabolic rate via body size is not sufficient to counterbalance the direct effect, it limits the magnitude of the increase in metabolic rate. Thus, in a warming climate, ectotherms are likely to experience increases in energy use that are smaller than anticipated. Given that metabolic rates have substantial, diverse impacts on individuals, populations, and ecosystems, these indirect effects of temperature change will have complex cascading effects on ecological communities, but the impacts of increases in metabolic rate of these varying magnitudes are unknown.

Feeding plasticity more than metabolic rate drives the productivity of economically important filter feeders in response to elevated CO2 and reduced salinity

AbstractClimate change driven alterations in salinity and carbonate chemistry are predicted to have significant implications particularly for northern costal organisms, including the economically important filter feeders Mytilus edulis and Ciona intestinalis. However, despite a growing number of studies investigating the biological effects of multiple environmental stressors, the combined effects of elevated pCO2 and reduced salinity remain comparatively understudied. Changes in metabolic costs associated with homeostasis and feeding/digestion in response to environmental stressors may reallocate energy from growth and reproduction, affecting performance. Although these energetic trade-offs in response to changes in routine metabolic rates have been well demonstrated fewer studies have investigated how these are affected by changes in feeding plasticity. Consequently, the present study investigated the combined effects of 26 days’ exposure to elevated pCO2 (500 µatm and 1000 µatm) and reduced salinity (30, 23, and 16) on the energy available for growth and performance (Scope for Growth) in M. edulis and C. intestinalis, and the role of metabolic rate (oxygen uptake) and feeding plasticity [clearance rate (CR) and absorption efficiency] in this process. In M. edulis exposure to elevated pCO2 resulted in a 50% reduction in Scope for Growth. However, elevated pCO2 had a much greater effect on C. intestinalis, with more than a 70% reduction in Scope for Growth. In M. edulis negative responses to elevated pCO2 are also unlikely be further affected by changes in salinity between 16 and 30. Whereas, under future predicted levels of pCO2C. intestinalis showed 100% mortality at a salinity of 16, and a &amp;gt;90% decrease in Scope for Growth with reduced biomass at a salinity of 23. Importantly, this work demonstrates energy available for production is more dependent on feeding plasticity, i.e. the ability to regulate CR and absorption efficiency, in response to multiple stressors than on more commonly studied changes in metabolic rates.

A combined study of 18F-FDG PET-CT and fMRI for assessing resting cerebral function in patients with major depressive disorder.

The present study investigated changes in the regional cerebral metabolic rates of glucose uptake (rCMRglc) using 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) and regional homogeneity (ReHo), together with resting-state blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI), in patients with major depressive disorder (MDD). In total, 18 patients with untreated MDD and 17 healthy control subjects underwent 18F-FDG PET and BOLD-fMRI scanning. The MDD patients' cerebral changes, measured as rCMRglc and ReHo values, were mapped and statistically analyzed. Compared with the control group, the patients with MDD had a decreased rCMRglc in the bilateral superior, middle and inferior frontal gyrus, in the bilateral superior and middle temporal gyrus, in the bilateral anterior cingulate cortex, in the bilateral putamen and caudate, and in the left pallidum, but an increased rCMRglc in the bilateral hippocampus and left thalamus. The ReHo values in the patient group were decreased in the bilateral superior and middle frontal gyrus, left pallidum, bilateral putamen and left anterior cingulate cortex, but increased in the right hippocampus and thalamus. No statistically significant differences were identified between decreased metabolism and ReHo brain regions of MDD patients (χ2=9.16; P=0.90) and between increased metabolism and ReHo brain regions (χ2=3.96; P=0.27), when comparing activated brain regions of PET and MRI. The standardized uptake values (SUV) of the bilateral superior, middle and inferior frontal gyrus, bilateral superior and middle temporal gyrus, bilateral putamen, the left caudate and pallidum, the left anterior cingulate cortex, and the bilateral hippocampus and thalamus were correlated with the ReHo (r=0.51–0.83; P<0.05). However, no correlation was detected between the SUV and ReHo in the right caudate and anterior cingulate cortex (r=0.41 and 0.37, respectively; P>0.05). Taken together, these results demonstrated that patients with MDD displayed characteristic patterns regarding changes of brain glucose uptake and ReHo in the resting state. Furthermore, 18F-FDG PET may be a more sensitive technique compared with BOLD-fMRI for the identification of brain lesions in patients with MDD.

Responses mechanism of C:N:P stoichiometry of soil microbial biomass and soil enzymes to climate change.

Microorganisms and soil enzymes are important drivers for biogeochemical cycles in terrestrial ecosystems. Understanding the role of microorganisms in the regulation of ecosystems and the response mechanisms of microbial biomass and soil enzymes to climate change are important topic in ecology. From the perspective of climatic factors, this review introduced the roles of microorganisms and soil enzymes in the carbon, nitrogen and phosphorus cycles of terrestrial ecosystems based on the theory of ecological stoichiometry. Moreover, we synthesized the responses mechanisms of soil microbial and soil enzyme stoichiometry, i.e., changes of microbial metabolic rate, enzymatic acti-vity, microbial community structure, ecological stoichiometry of soil microbial biomass and soil enzymes, and nutrient use efficiency. Finally, we analyzed the current research inadequacies and proposed the scientific problems in this field, i.e., to comprehensively elucidate the response mecha-nism of soil microbes and soil enzymes to climate change; to examine the nutrient coupling mechanism of soil microbes and extracellular enzymes; and to explore the adaptive strategies of C:N:P stoichiometry of soil microbial biomass and soil enzymes to climate change.

Changes in Metabolic Activities and Gene Expression Associated with Gamma Irradiation of HoneybeeApis melliferaWorkers

ABSTRACT: This study was carried out to explore the possible stimulatory effect of a low dose of gamma irradiation on the expression profile of a number of genes and suspected metabolic mediators involved in honeybee (Apis mellifera) foraging activity. Honeybee workers were subjected to two gamma ray doses (0.2 and 2Gy) and the expression levels of Apis mellifera foraging gene (Amfor), juvenile hormone (JH), Octopamine receptor 1 (OctR1), heat shock protein- 70 (HSP- 70) and Troponin T (TpnT) mRNA levels were estimated using RT-PCR. In addition, the indicators of metabolic and flight rate changes such as citrate synthase (CS), pyruvate kinase (PK) and adenosine triphosphatase (ATPase) were estimated. The results revealed a marked increase in the expression of Amfor, JH, OctR1, HSP-70 and TpnT genes in the bees irradiated with the low dose of radiation (0.2Gy) as compared to the non-irradiated control workers and those irradiated with the higher dose (2Gy). In addition, CS, PK and ATPase activities were si...

Changes in metabolic rate of spiny lobster under predation risk

Animals exposed to high levels of predation risk may exhibit a variety of changes in life history, behaviour, physiology and morphology that can affect survival. Under predation threat, prey individuals may increase their aerobic metabolism to allocate energy toward escaping behaviours (e.g. ‘fight or flight’), although the associated energetic cost of such behaviour remains largely unknown. Lobsters display different anti-predatory responses, such as sheltering and/or escaping, but the underlying energetic cost of such responses has not been examined. Here, we tested the aerobic metabolic response of southern rock lobsters Jasus edwardsii in the presence of predator (Maori octopus Octopus maorum) olfactory cues (kairomones) using open-flow respirometry. We examined the routine metabolic rate of lobsters in response to predator kairomones during the active phase of their diurnal cycle (at night) to investigate the physiological anti-predator response when lobsters are most vulnerable. Our findings revealed that lobsters strongly reduced their routine metabolism for 3 h by 31.4% when exposed to kairomones in comparison to controls. Our findings suggest that under laboratory conditions, lobsters exposed to predation risk during the night reduce their activity to avoid predators, i.e. the anti-predator mechanism is to be immobile or inactive rather than showing a fight-or-flight response. Lobster immobility may be an energetically advantageous anti-predator response in the short term; however, prolonged or regular predator exposure could have significant consequences on foraging time and foraging area, with an overall impact on lobster performance, particularly in environments with high predator presence such as fishing grounds.

Pathogenetic role of visceral adipose tissue in the development of non-alcoholic fatty liver disease in patients with metabolic syndrome

Objective — to study the nature of changes in carbohydrate and lipid metabolism, depending on the distribution and activity of visceral adipose tissue (VAT), and the degree of liver steatosis in patients with nonalcoholic fatty liver disease (NAFLD) against the background of a metabolic syndrome (MS). Materials and methods. Were examined 62 patients with NAFLD: 26 men (40 %) and 36 women (60 %). The mean age of patients was 57.3 ± 9.2 years. The control group consisted of 30 healthy donors of the same age group of males and females. All patients were assessed the parameters of an objective examination and laboratory and instrumental examination in accordance with the current order MOH № 826 from 06.11.2014. In addition to the standard survey, the body composition of patients was monitored, and the visceral adiposity index (VAI) was calculated by the method of Amato MC (2010) to determine visceral adipose tissue dysfunction (VAT). Statistical processing of data was carried out using the SPSS 17.0 software package. Results. In patients with NAFLD, elevated insulin levels 29.23 ± 5.26 μS/ml were established in comparison with control group 6.83 ± 2.08 μS/ml and a significant increase in the HOMA index to 8.93 ± 3.01 μmol fructose/1 g Nv (p < 0.05). The maximum levels of insulin and the HOMA-IR index were found in patients with high IVO that exceeded 5μm. unit. Concentrations of total cholesterol (CH), triglycerides (TG), low density lipoprotein (LDL) in patients with NAFLD were also significantly higher than those in the control group (p < 0.05). The maximal TG level 2.87 ± 0.14 mmol was observed in patients with high IVO (p < 0.05). In addition to the changes in carbohydrate and lipid metabolism rates, with the degree of fusion of IVO, the steatosis rates (p < 0.05) also increased. Conclusions. The obtained data evidence about the dependence of the depth of the carbohydrate and lipid metabolism violations on the activity. In patients with NAFLD against the background of MS, index HOMA-IR and CH, TG, LDL and degree of steatosis significantly increased with the growth of IVO (p < 0.05), which makes it possible to consider IVO as a significant additional prognostic criterion for the risk of development of not only metabolic disorders, but also as a risk factor for the progression of fibroblastic processes.

Age and life histories of black and smooth oreos inferred using bomb radiocarbon dating and stable isotope analysis

ABSTRACTBlack oreo (Allocyttus niger) and smooth oreo (Pseudocyttus maculatus) are commercially exploited deepwater fishes in New Zealand. They are considered to be long-lived with unvalidated maximum otolith growth zone counts of 153 years and 86 years, respectively. Bomb radiocarbon dating results supported the otolith age estimates for A. niger, but those for P. maculatus provided only partial support. Oxygen isotope (δ18O) results for A. niger otoliths suggested that juveniles were in near-surface waters and adults in depths of 700–1300 m. In contrast, P. maculatus otoliths suggested a variable depth history (500 to at least 1500 m) throughout life. Carbon isotope (δ13C) results showed a steady enrichment from core values to c. 20 years for both species, owing to changes in diet and metabolic rate from the juvenile to the adult fish, associated with a depth increase. Von Bertalanffy growth parameters are provided for both species.

The influence of increased distal loading on metabolic cost, efficiency, and kinematics of roller ski skating.

The purpose of the present study was to examine the influence of increased loading of the roller ski on metabolic cost, gross efficiency, and kinematics of roller ski skating in steep and moderate terrain, while employing two incline-specific techniques. Ten nationally ranked male cross-country skiers were subjected to four 7-minute submaximal intervals, with 0, 0.5, 1.0, and 1.5 kg added beneath the roller-ski in a randomized order. This was done on two separate days, with the G2 skating at 12% incline and 7 km/h speed and G3 skating at 5% incline and 14 km/h speed, respectively. At 12% incline, there was a significant increase in metabolic rate and a decrease in gross efficiency with added weight (P<0.001 and P = 0.002). At 5% incline, no change in metabolic rate or gross efficiency was found (P = 0.89 and P = 0.11). Rating of perceived exertion (RPE) increased gradually with added weight at both inclines (P>0.05). No changes in cycle characteristics were observed between the different ski loadings at either incline, although the lateral and vertical displacements of the foot/skis were slightly altered at 12% incline with added weight. In conclusion, the present study demonstrates that increased loading of the ski increases the metabolic cost and reduces gross efficiency during steep uphill roller skiing in G2 skating, whereas no significant effect was revealed when skating on relatively flat terrain in G3. Cycle characteristics remained unchanged across conditions at both inclines, whereas small adjustments in the displacement of the foot coincided with the efficiency changes in uphill terrain. The increased RPE values with added ski-weight at both inclines indicates that other factors than those measured here could have influenced effort and/or fatigue when lifting a heavier ski.

Evaluating Near Infrared Spectroscopy Signals From Skeletal Muscle

Near Infrared Spectroscopy (NIRS) uses the relative absorption of light at 850 and 760nm to determine skeletal muscle oxygen saturation. There are currently disagreements in the literature over how to report oxygen saturation and the relative contributions of hemoglobin and myoglobin. PURPOSE: 1) Compare the separate 850nm (HbO2) and 760nm (HHb)signals during rest, ischemia, and reperfusion, and 2) test whether electrical stimulation to increase metabolic rate changes oxygen saturation values during 5-6 minutes of complete ischemia. METHOD: Ten participants ages = 20-29 years were measured. NIRS measurements were made in the forearm flexor muscles at rest, after 30 seconds of 6 Hz electrical stimulation, during and after 5-6 minutes of complete ischemia produced by arterial occlusion preceded by 30 seconds of 6 Hz electrical stimulation. After 5-6 minutes of ischemia 30 seconds of 6 Hz electrical stimulation was performed. RESULTS: Six Hz stimulation for 30 s increased metabolic rate for HbO2 and HHb; 6.2+3.1 and 5.5+2.7 fold over rest, respectively. Six Hz stimulation during cuff ischemia did not change either the HHb or HbO2 values (p>0.05). There was significantly greater (p<0.05) pulsitility associated with heart rate in the HbO2 (0.78+0.41% range) compared to HHb (0.16+0.09% range). Pulse size increased during reperfusion; HbO2 (2.37+0.38% range) compared to HHb (0.96+0.32% range). CONCLUSIONS: The difference in the magnitude of pulsitility between HbO2 and HHb signals suggests different anatomical locations for these signals, further suggesting that using various ratios of HbO2 and HHb signals should be performed with caution. Increasing metabolic rate with electrical stimulation during complete ischemia did not further change the NIRS signals, suggesting complete ischemia is obtained with 5-6 minutes of complete cuff occlusion. Keywords: Skeletal Muscle, Near Infrared Spectroscopy (NIRS), Oxygen consumption, Hemoglobin, Myoglobin

Changes in Oxidative Stress and Resting Metabolic Rate after Acute Dietary Nitrate Supplementation

BACKGROUND: Cardiovascular disease is the leading cause of preventable death in the United States and the Western world. A major component of cardiovascular disease is the deterioration of the cardiovascular system by increased oxidative stress. Dietary nitrate supplementation could increase nitric oxide bioavailability, decreasing oxidative stress. PURPOSE: The purpose of the present study is twofold: 1) to determine the impact of an acute dietary nitrate supplementation on oxidative stress and 2) to assess the oxygen dependent nature of a dietary nitrate supplementation. METHODS: Eighteen (7 females and 11 males) apparently healthy subjects, aged 18-30 years of age, participated in a randomized, double blind, placebo-controlled crossover study. Following a 12-hour fast and adherence to an NIH-approved low-nitrate diet for 48 hours, subjects visited the lab on 4 occasions (identical procedures) within 2 weeks. A resting blood draw preceded 15 minutes of supine rest followed by a 20-minute period of metabolic gas analysis for determination of resting metabolic rate; RMR (True One, ParvoMedics, Sandy, Utah, USA). Visits 2 and 4 served as baseline controls for the placebo or dietary nitrate treatments (negligible and 800mg nitrate, respectively) which were consumed 2.5 hours prior to visits 3 and 5. The resting concentration of the oxidative stress marker 8-isoprostane (8-ISO) was determined by ELISA testing using a commercial available kit (Cayman Chemical, USA). A 2-way repeated measures ANOVA was used to determine differences between protocols and over time, with an alpha of 0.05. RESULTS: There was no significant difference between placebo and dietary nitrate supplementation in oxidative stress (Placebo: 158±59 vs. 181±62 pg/ml; Active: 176±74 vs. 171±59 pg/ml, p=0.84) or in RMR (Placebo: 1839±308 vs. 1790±307 kcal/day; Active: 1828±318 vs. 1859±324 kcal/day, p=0.20). CONCLUSION: These data showed that acute dietary nitrate supplementation does not decrease resting oxidative stress. The conversion of nitrate to nitrite to nitric oxide has been previously described to be oxygen-independent. Our data supported this statement, as RMR did not change following the dietary nitrate supplementation.

Nutrient limitation suppresses the temperature dependence of phytoplankton metabolic rates

Climate warming has the potential to alter ecosystem function through temperature-dependent changes in individual metabolic rates. The temperature sensitivity of phytoplankton metabolism is especially relevant, since these microorganisms sustain marine food webs and are major drivers of biogeochemical cycling. Phytoplankton metabolic rates increase with temperature when nutrients are abundant, but it is unknown if the same pattern applies under nutrient-limited growth conditions, which prevail over most of the ocean. Here we use continuous cultures of three cosmopolitan and biogeochemically relevant species (Synechococcus sp., Skeletonema costatum and Emiliania huxleyi) to determine the temperature dependence (activation energy, Ea) of metabolism under different degrees of nitrogen (N) limitation. We show that both CO2 fixation and respiration rates increase with N supply but are largely insensitive to temperature. Ea of photosynthesis (0.11 ± 0.06 eV, mean ± SE) and respiration (0.04 ± 0.17 eV) under N-limited growth is significantly smaller than Ea of growth rate under nutrient-replete conditions (0.77 ± 0.06 eV). The reduced temperature dependence of metabolic rates under nutrient limitation can be explained in terms of enzyme kinetics, because both maximum reaction rates and half-saturation constants increase with temperature. Our results suggest that the direct, stimulating effect of rising temperatures upon phytoplankton metabolic rates will be circumscribed to ecosystems with high-nutrient availability.