Effect of Hypoxia on the Oxygen Uptake Response to an Exhaustive Severe Intensity Run

It has been shown that highly aerobically trained individuals are unable to achieve maximal oxygen uptake (O2 max) during exhaustive running lasting ~2 min despite sufficient time for the response (Draper and Wood, 2005). However, hypoxia offers the opportunity to study the O2 response to an exhaustive run relative to a reduced O2 max. The purpose of the current study was to explore whether there is a difference in the percentage of O2 max attained (during a 2 minute exhaustive run) in normoxia and hypoxia. Fourteen trained middle-distance runners (mean ± SD; age 21.4 ± 3.4 y, height 1.76 ± 0.05 m, mass 66.0 ± 7.0 kg, O2 max 67.0 ± 5.2 ml.kg-1.min-1) volunteered for this study. Participants completed exhaustive treadmill ramp tests and square-wave tests (lasting 2 minutes), in normoxia and hypoxia (FiO2 0.13). Oxygen uptake was determined on a breath-by-breath basis throughout each test. The O2 data (excluding the first 15s) from the square-wave tests were modelled using a mono-exponential function. Repeated measures ANOVA (condition x test) was used to investigate the differences in O2 peak and post-hoc related samples t-tests for each condition were performed to explore a significant interaction. There was a significant interaction effect for O2 peak (P < 0.001). Post hoc tests revealed that the O2 peak achieved during the square-wave test was lower than the ramp test in normoxia (P < 0.001) but not in hypoxia (P = 0.49). The mean ± SD percentage of the ramp O2 peak achieved was; 86 ±0.06 vs. 102 ± 0.08%, for normoxia and hypoxia respectively. The phase II time constant was different between conditions (P = 0.029) demonstrating a slower oxygen uptake response to exercise in hypoxia (mean ± SD; 12.7 ± 2.8 vs. 10.4 ± 2.6 seconds, for hypoxia and normoxia respectively). The findings of the current study support the findings of Draper and Wood (2005) that suitably trained individuals do not achieve maximal oxygen uptake in running of this intensity. However, the present study has demonstrated that when maximal oxygen uptake is reduced through hypoxia it may then be achieved

Effects of priming and pacing strategy on VO2 kinetics and cycling performance

Copyright © 2015 Human KineticsThis is the author accepted manuscript. The final version is available from Human Kinetics via the DOI in this record.Purpose: To assess whether combining prior ‘priming’ exercise with an all-out pacing strategy was more effective at improving O2 uptake (VO2) kinetics and cycling performance than either intervention administered independently. Methods: Nine males completed target-work cycling performance trials using a self-paced or all-out pacing strategy with or without prior severe-intensity (70%Δ) priming exercise. Breath-by-breath pulmonary VO2 and cycling power output were measured during all trials. Results: Compared to the self-paced-unprimed control trial (22 ± 5 s), the VO2 mean response time (MRT) was shorter (VO2 kinetics was faster) with all-out pacing (17 ± 4 s) and priming (17 ± 3 s), with the lowest VO2 MRT observed when all-out pacing and priming were combined (15 ± 4 s) (P0.05). Conclusions: These findings suggest that combining an all-out start with severe-intensity priming exercise additively improves the VO2 MRT, but not total O2 consumption and cycling performance since these were improved by a similar magnitude in both primed trials relative to the self-paced-unprimed control condition. Therefore, these results support the use of priming exercise as a pre-competition intervention to improve oxidative metabolism and performance during short-duration high-intensity cycling exercise, independent of the pacing strategy adopted

THE RELATIONSHIP OF ANTHROPOMETRY AND BODY COMPOSITION WITH RUNNING ECONOMY

The aim of this study was to investigate the relationships of anthropometry and body composition with running economy within a large heterogeneous cohort of runners. Locomotory energy cost was determined in ninety-four healthy male and female endurance runners across a range of performance standards. Various anthropometric and body composition measurements were taken manually and via DXA scans. The relationships between anthropometry and running economy were assessed using independent Pearson’s correlation and stepwise multiple linear regression. Three parameters, normalised neck and calf perimeters and normalised whole body bone mass explained 30% of the variance in locomotory energy cost. Low locomotory energy cost was related solely to parameters indicating relative slenderness of the body

The maximal metabolic steady state: redefining the ‘gold standard’

The maximal lactate steady state (MLSS) and the critical power (CP) are two widely used indices of the highest oxidative metabolic rate that can be sustained during continuous exercise and are often considered to be synonymous. However, while perhaps having similarities in principle, methodological differences in the assessment of these parameters typically result in MLSS occurring at a somewhat lower power output or running speed and exercise at CP being sustainable for no more than approximately 20–30 min. This has led to the view that CP overestimates the ‘actual’ maximal metabolic steady state and that MLSS should be considered the ‘gold standard’ metric for the evaluation of endurance exercise capacity. In this article we will present evidence consistent with the contrary conclusion: i.e., that (1) as presently defined, MLSS naturally underestimates the actual maximal metabolic steady state; and (2) CP alone represents the boundary between discrete exercise intensity domains within which the dynamic cardiorespiratory and muscle metabolic responses to exercise differ profoundly. While both MLSS and CP may have relevance for athletic training and performance, we urge that the distinction between the two concepts/metrics be better appreciated and that comparisons between MLSS and CP, undertaken in the mistaken belief that they are theoretically synonymous, is discontinued. CP represents the genuine boundary separating exercise in which physiological homeostasis can be maintained from exercise in which it cannot, and should be considered the gold standard when the goal is to determine the maximal metabolic steady state

A new, long-term daily satellite-based rainfall dataset for operational monitoring in Africa

Rainfall information is essential for many applications in developing countries, and yet, continually updated information at fine temporal and spatial scales is lacking. In Africa, rainfall monitoring is particularly important given the close relationship between climate and livelihoods. To address this information gap, this paper describes two versions (v2.0 and v3.0) of the TAMSAT daily rainfall dataset based on high-resolution thermal-infrared observations, available from 1983 to the present. The datasets are based on the disaggregation of 10-day (v2.0) and 5-day (v3.0) total TAMSAT rainfall estimates to a daily time-step using daily cold cloud duration. This approach provides temporally consistent historic and near-real time daily rainfall information for all of Africa. The estimates have been evaluated using ground-based observations from five countries with contrasting rainfall climates (Mozambique, Niger, Nigeria, Uganda, and Zambia) and compared to other satellite-based rainfall estimates. The results indicate that both versions of the TAMSAT daily estimates reliably detects rainy days, but have less skill in capturing rainfall amount—results that are comparable to the other datasets

Extratropical cyclones and the projected decline of winter Mediterranean precipitation in the CMIP5 models

The Mediterranean region has been identified as a climate change "hot-spot" due to a projected reduction in precipitation and fresh water availability which has potentially large socio-economic impacts. To increase confidence in these projections, it is important to physically understand how this precipitation reduction occurs. This study quantifies the impact on winter Mediterranean precipitation due to changes in extratropical cyclones in 17 CMIP5 climate models. In each model, the extratropical cyclones are objectively tracked and a simple approach is applied to identify the precipitation associated to each cyclone. This allows us to decompose the Mediterranean precipitation reduction into a contribution due to changes in the number of cyclones and a contribution due to changes in the amount of precipitation generated by each cyclone. The results show that the projected Mediterranean precipitation reduction in winter is strongly related to a decrease in the number of Mediterranean cyclones. However, the contribution from changes in the amount of precipitation generated by each cyclone are also locally important: in the East Mediterranean they amplify the precipitation trend due to the reduction in the number of cyclones, while in the North Mediterranean they compensate for it. Some of the processes that determine the opposing cyclone precipitation intensity responses in the North and East Mediterranean regions are investigated by exploring the CMIP5 inter-model spread

The Role of Cargo Proteins in GGA Recruitment

Coat proteins are recruited onto membranes to form vesicles that transport cargo from one compartment to another, but the extent to which the cargo helps to recruit the coat proteins is still unclear. Here we have examined the role of cargo in the recruitment of Golgi-localized, γ-ear-containing, ADP ribosylation factor (ARF)-binding proteins (GGAs) onto membranes in HeLa cells. Moderate overexpression of CD8 chimeras with cytoplasmic tails containing DXXLL-sorting signals, which bind to GGAs, increased the localization of all three GGAs to perinuclear membranes, as observed by immunofluorescence. GGA2 was also expressed at approximately twofold higher levels in these cells because it was degraded more slowly. However, this difference only partially accounted for the increase in membrane localization because there was a approximately fivefold increase in GGA2 associated with crude membranes and a ∼12-fold increase in GGA2 associated with clathrin-coated vesicles (CCVs) in cells expressing CD8-DXXLL chimeras. The effect of cargo proteins on GGA recruitment was reconstituted in vitro using permeabilized control and CD8-DXXLL-expressing cells incubated with cytosol containing recombinant GGA2 constructs. Together, these results demonstrate that cargo proteins contribute to the recruitment of GGAs onto membranes and to the formation of GGA-positive CCVs

A mechanistic understanding of polyethylene biodegradation by the marine bacterium Alcanivorax

Polyethylene (PE) is one of the most recalcitrant carbon-based synthetic materials produced and, currently, the most ubiquitous plastic pollutant found in nature. Over time, combined abiotic and biotic processes are thought to eventually breakdown PE. Despite limited evidence of biological PE degradation and speculation that hydrocarbon-degrading bacteria found within the plastisphere is an indication of biodegradation, there is no clear mechanistic understanding of the process. Here, using high-throughput proteomics, we investigated the molecular processes that take place in the hydrocarbon-degrading marine bacterium Alcanivorax sp. 24 when grown in the presence of low density PE (LDPE). As well as efficiently utilising and assimilating the leachate of weathered LDPE, the bacterium was able to reduce the molecular weight distribution (M from 122 to 83 kg/mol) and overall mass of pristine LDPE films (0.9 % after 34 days of incubation). Most interestingly, Alcanivorax acquired the isotopic signature of the pristine plastic and induced an extensive array of metabolic pathways for aliphatic compound degradation. Presumably, the primary biodegradation of LDPE by Alcanivorax sp. 24 is possible via the production of extracellular reactive oxygen species as observed both by the material's surface oxidation and the measurement of superoxide in the culture with LDPE. Our findings confirm that hydrocarbon-biodegrading bacteria within the plastisphere may in fact have a role in degrading PE

Assessing Network Scale-up Estimates for Groups Most at Risk of HIV/AIDS: Evidence From a Multiple-Method Study of Heavy Drug Users in Curitiba, Brazil

One of the many challenges hindering the global response to the human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) epidemic is the difficulty of collecting reliable information about the populations most at risk for the disease. Thus, the authors empirically assessed a promising new method for estimating the sizes of most at-risk populations: the network scale-up method. Using 4 different data sources, 2 of which were from other researchers, the authors produced 5 estimates of the number of heavy drug users in Curitiba, Brazil. The authors found that the network scale-up and generalized network scale-up estimators produced estimates 5–10 times higher than estimates made using standard methods (the multiplier method and the direct estimation method using data from 2004 and 2010). Given that equally plausible methods produced such a wide range of results, the authors recommend that additional studies be undertaken to compare estimates based on the scale-up method with those made using other methods. If scale-up-based methods routinely produce higher estimates, this would suggest that scale-up-based methods are inappropriate for populations most at risk of HIV/AIDS or that standard methods may tend to underestimate the sizes of these populations