1,720,980 research outputs found
Slow V̇O2 kinetics during moderate-intensity exercise as markers of lower metabolic stability and lower exercise tolerance
No full textAn analysis of previously published data obtained by our group on patients characterized by markedly slower pulmonary V̇O2 kinetics (heart transplant recipients, patients with mitochondrial myopathies, patients with McArdle disease) was carried out in order to suggest that slow V̇O 2 kinetics should not be considered the direct cause, but rather a marker, of impaired exercise tolerance. For a given ATP turnover rate, faster (or slower) V̇O2 kinetics are associated with smaller (or greater) muscle [PCr] decreases. The latter, however, should not be taken per se responsible for the higher (or lower) exercise tolerance, but should be considered within the general concept of "metabolic stability". Good muscle metabolic stability at a given ATP turnover rate (∼power output) is associated with relatively smaller decreases, compared to rest, in [PCr] and in the Gibbs free energy of ATP hydrolysis, as well as with relatively smaller increases in [Pi], [ADPfree], [AMPfree], and [IMP free], metabolites directly related to fatigue. Disturbances in muscle metabolic stability can affect muscle function in various ways, whereas good metabolic stability is associated with less fatigue and higher exercise tolerance. Smaller [PCr] decreases, however, are strictly associated with a faster V̇O2 kinetics. Thus, faster V̇O2 kinetics may simply be an "epiphenomenon" of a relatively higher metabolic stability, which would then represent the relevant variable in terms of fatigue and exercise tolerance. © 2010 Springer-Verlag
Recovery from the ultraendurance race MAGRAID 2009: muscle and cardiac damage biomarkers
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Heterogeneity of human adaptations to bed rest and hypoxia: A retrospective analysis within the skeletal muscle oxidative function
No full textThis retrospective study was designed to analyze the interindividual variability in the responses of different variables characterizing the skeletal muscle oxidative function to normoxic (N-BR) and hypoxic (H-BR) bed rests and to a hypoxic ambulatory confinement (H-AMB) of 10 and 21 days. We also assessed whether and how the addition of hypoxia to bed rest might influence the heterogeneity of the responses. In vivo measurements of O2 uptake and muscle fractional O2 extraction were carried out during an incremental one-leg knee-extension exercise. Mitochondrial respiration was assessed in permeabilized muscle fibers. A total of 17 subjects were included in this analysis. This analysis revealed a similar variability among subjects in the alterations induced by N-BR and H-BR both in peak O2 uptake (SD: 4.1% and 3.3% after 10 days; 4.5% and 8.1% after 21 days, respectively) and peak muscle fractional O2 extraction (SD: 5.9% and 7.3% after 10 days; 6.5% and 7.3% after 21 days), independently from the duration of the exposure. The individual changes measured in these variables were significantly related (r = 0.66, P = 0.004 after N-BR; r = 0.61, P = 0.009 after H-BR). Mitochondrial respiration showed a large variability of response after both N-BR (SD: 25.0% and 15.7% after 10 and 21 days) and H-BR (SD: 13.0% and 19.8% after 10 and 21 days); no correlation was found between N-BR and HBR changes. When added to bed rest, hypoxia altered the individual adaptations within the mitochondria but not those intrinsic to the muscle oxidative function in vivo, both after the short- and medium-term exposures
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Study of the effect on oxidative metabolism, muscle composition, and metabolic cost in high altitude walking women
No full textAim: During Hypobaric hypoxia (Hh) the oxygen level in the bloodstream is reduced and body responses lead to physiological adaptations that determines the modulation of oxygen transport/utilization and, for more than 4 weeks exposure to Hh, changes in structural and functional properties take place. Permanence to 4000–5000 m altitude lead to muscular arrangements similar to those resulting after endurance training and the addition of physical exercise further improve aerobic performance through adaptations of muscle oxidative metabolism. Even if a sex dependent response to
chronic hypoxia has been described, only few studies involving female about physiological adaptation to high-altitude are published1,2.
Methods: Seven healthy women (36.3yy ± 7.1; 65.8kg ± 11.7; 165cm ± 8) were enrolled to participate in two 20-day trekking expeditions, respectively at 598 m and 4132 m of altitude, separated by 4 months of recovery. Before (B1, B2) and after (P1, P2) each expedition we measured maximal oxygen uptake, VO2 and systemic O2 delivery (QaO2) kinetics during moderate-intensity exercise and energy cost of locomotion. Furthermore, muscle structure (slow/fastMyHC isoforms), mitochondrial features and mass were analyzed from muscular biopsies obtained at B1, P1 and P2.
Results: Both of altitude trekking reveal: No changes in QaO2 kinetics, faster mean response time of VO2 kinetics (P = 0.002, P = 0.001) and smaller oxygen deficit (P = 0.001, P = 0.0004). No changes in MyHC isoforms expression and mitochondrial mass. Decrease in ADP-stimulate mitochondrial respiration (P = 0.016), increase in leak respiration (P = 0.031) and in the respiratory control ratio (P = 0.016)
Conclusion Training don’t affect muscle phenotype but it induced beneficial adaptations of the oxygen transport-utilization systems demonstrated by faster VO2 kinetics at exercise onset
Skeletal muscle oxygen uptake in obese patients: Functional evaluation by knee-extension exercise
No full textWe hypothesized, in a group of obese women (OB), a more significant impairment of aerobic metabolism during knee extension (KE) exercise vs. that described during cycle ergometer exercise, lending support to the role of skeletal muscles in limiting exercise tolerance in OB. Eleven OB (age 29.5 ± 5.5 years, body mass index 43.2 ± 5.4 kg m-2) and 10 non-obese controls (CTRL) women were tested. Fat-free mass of a lower-limb (FFMLL) was assessed by a densitometer. Heart rate (HR) and pulmonary O2 uptake (VO2) were determined during incremental exercise tests to voluntary exhaustion carried out on a custom-built KE ergometer and on a cycle ergometer (CE). FFMLL and maximal isometric force of KE muscles were higher in OB vs. CTRL (+42.4 and +46.2 %, respectively). Peak work rate was significantly lower in OB (-18.4 %) vs. CTRL in CE, but not in KE. Expressed in mL min-1, peak VO2 was not different in OB vs. CTRL in CE and in KE. After it was divided per unit of FFM involved in the exercises, peak VO2 was significantly lower in OB vs. CTRL, both for CE (-19 %) and KE (-33 %). Expressed per unit of exercising muscle mass, peak oxidative function is impaired in OB. The impairment is more pronounced after limitations related to cardiovascular O2 delivery are reduced. In OB muscle hypertrophy and the increased muscle force allow to preserve exercise tolerance during aerobic exercises carried out by relatively small muscle masses. © 2013 Springer-Verlag Berlin Heidelberg
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Effects of marked skeletal muscle hypertrophy in humans on oxidative function in vivo and in vitro
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