1,720,971 research outputs found
Critical oxygenation: Can muscle oxygenation inform us about critical power?
Get PDFThe power-duration relationship is well documented for athletic performance and is formulated out mathematically
in the critical power (CP) model. The CP model, when applied properly, has great predictive power, e.
g. pedaling at a specific power output on an ergometer the model precisely calculates the time over which an
athlete can sustain this power. However, CP presents physiological inconsistencies and process-oriented problems.
The rapid development of near-infrared spectroscopy (NIRS) to measure muscle oxygenation (SmO2) dynamics
provides a physiological exploration of the CP model on a conceptual and empirical level. Conceptually,
the CP model provides two components: first CP is defined as the highest metabolic rate that can be achieved
through oxidative means. And second, work capacity above CP named W’. SmO2 presents a steady-state in oxygen
supply and demand and thereby represents CP specifically at a local level of analysis. Empirically,
exploratory data quickly illustrates the relationship between performance and SmO2, as shown during 3-min allout
cycling tests to assess CP. During these tests, performance and SmO2 essentially mirror each other, and both
CP and W’ generate solid correlation with what would be deemed their SmO2 counterparts: first, the steady-state
of SmO2 correlates with CP. And second, the tissue oxygen reserve represented in SmO2, when calculated as an
integral corresponds to W’. While the empirical data presented is preliminary, the proposition of a concurring
physiological model to the current CP model is a plausible inference. Here we propose that SmO2 steady-state
representing CP as critical oxygenation or CO. And the tissue oxygen reserve above CO would then be identified
as O’. This new CO model could fill in the physiological gap between the highly predictive CP model and at
times its inability to track human physiology consistently. For simplicity’s sake, this would include acute changes
in physiology as a result of changing climate or elevation with travel, which can affect performance. These types
of acute fluctuations, but not limited to, would be manageable when applying a CO model in conjunction with
the CP model. Further, modeling is needed to investigate the true potential of NIRS to model CP, with a focus on
repeatability, recovery, and systemic vs local workloads
NIRS on a functional scale of 0-100%: Establishing practicality of the Moxy Monitor for sport science
No full textNear-infrared spectroscopy (NIRS) has become readily available technology to monitor muscle oxygenation (SmO2) in applied sport settings. However, the technology is limited by its inability to convey quantifiable values, but rather offers relative change of oxy- and deoxyhemoglobin (O2Hb, HHb). In order to generate robustness for inter-individual and inter-location analysis and comparison an arterial occlusion method (AOM; 1) can be applied to generate a functional scale of 0-100%. On this scale 0% represents a maximally deoxygenated state defined by a disappearance of O2Hb in relation to the sum of O2Hb and HHb, and 100% a maximally oxygenated state and the disappearance of HHb to the sum. The purpose of this study is to examine the practicality and reliability of an a priori determined 0-100% scale by a commercially available NIRS device, the Moxy Monitor (Fortiori Designs LLC, US), using the AOM.
22 participants completed a series of tests to scrutinize the a priori 0-100% scale modeled by the device. First, reliability was tested with AOM in back to back weeks. Then the feasibility of the 0-100% scale was tested firstly by comparing the AOM during passive and active conditions, and secondly by comparing the results for minimally and maximally obtained SmO2 (SmO2min and SmO2max) to a priori defined limits from invasive measurement results of mixed venous oxygen saturation (SvO2). Four devices were mounted on participant’s legs.
The reliability test resulted in significant equivalency between all trials for SmO2min, TOST: -5.38 to 4.62, t(54) = 4.85, p < 0.001, and SmO2max, TOST: -6.13 to 3.87, t(55) = -3.5, p < 0.001.The 0-100% functional scale showed a good dynamic range for all muscle groups (Mmin = 10.1%±5.7; Mmax = 78.1%±6.0). During active and passive conditions the results for SmO2min were significantly equivalent, TOST: -7.69 to 2.32, t(39) = 2.77, p = 0.004. Tested against the a priori defined limits of SvO2, SmO2min was significantly lower than the SvO2 limit of 26% (2), t(54) = -20.69, p < 0.001; as was SmO2max, t(54) = -8.53, p < 0.001, for the SvO2 limit of 85%(3), as predicted.
The device exhibits an appropriate a priori defined functional scale between 0-100% that can be consider reliable and functional for application in sport.
1. Hamaoka, T., et al. (2007). Near-infrared spectroscopy/imaging for monitoring muscle oxygenation and oxidative metabolism in healthy and diseased humans. Journal of Biomedical Optics, 12(6), 062105.
2. Hamaoka, T., et al. (2000). Quantification of ischemic muscle deoxygenation by near infrared time-resolved spectroscopy. Journal of Biomedical Optics, 5(1), 102.
3. Langham, M. C., et al. (2010). Evaluation of Cuff-Induced Ischemia in the Lower Extremity by Magnetic Resonance Oximetry. Journal of the American College of Cardiology, 55(6), 598–606
Muscle oxygen dynamics in elite climbers during finger-hang tests at varying intensities
No full textIntroduction:
Failure in elite sport climbing is associated with an inability to maintain isometric muscle contraction. The ability to supply and utilise oxygen is the primary bioenergetic contributor to muscle contraction and can be examined locally using near-infrared spectroscopy (NIRS). Examining changes in NIRS derived muscle oxygenation (SmO2) have shown to be related to changes in performance output during gripping exercises.
Purpose:
The aim of this study is to measure SmO2 dynamics in a climbing specific test until task failure in varying conditions. Our prediction is that SmO2 should be a good marker to predict task failure.
Methods:
Eight elite level climbers performed a finger-hang test with four different intensities maintaining grip until voluntary exhaustion. During each trial SmO2 and time to failure (TTF) were measured. TTF was then compared to the minimally attainable value of SmO2 (SmO2min) and time to SmO2min (TTmin).
Results
Two-one-sided tests (TOST) resulted in SmO2min equivalence for the high intensity conditions (M1 = 21.9% SD1 = 5.0%; M2 = 25.4%; SD2 = 6.5%; M3 = 24.1%, SD3 = 5.9%), t(7) = 2.72, p = 0.015; t(7) = 3.85, p = 0.003, but failed to show equality for the fourth and lowest intensity condition (M4 = 32.4%, SD4 = 8.8%), t(7) = -1.01, p = 0.173. Equivalence was also found between TTF and TTmin for the high intensity conditions.
Conclusion:
The duration with which oxygen is extracted and utilised changes, while the attainable SmO2min remains constant at high intensity conditions and is related to the ability to maintain task performance
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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
Near-infrared spectroscopy-derived muscle oxygen saturation on a 0% to 100% scale: reliability and validity of the Moxy Monitor
Get PDFNear-infrared spectroscopy (NIRS) to monitor muscle oxygen saturation (SmO2) is rapidly expanding into applied sports settings. However, the technology is limited due to its inability to convey quantifiable values. A test battery to assess reliability and validity of a 0% to 100% scale modeled by a commercially available NIRS device was established. This test battery applies a commonly used technique, the arterial occlusion method (AOM) to assess repeatability, reproducibility, and face validity. A total of 22 participants completed the test battery to scrutinize the 0% to 100% scale provided by the device. All participants underwent repeated AOM tests in passive and active conditions. The SmO2 minimum and SmO2 maximum values were obtained from the AOM and were used in the subsequent analysis. Repeatability and reproducibility were tested for equivalency and Bland–Altman plots were generated. Face validity was assessed by testing SmO2 values against an a priori defined threshold for mixed venous blood during AOM response. The device exhibits an appropriately functional 0% to 100% scale that is reliable in terms of repeatability and reproducibility. Under the conditions applied in the test battery design, the device is considered valid for application in sports
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
