1,721,046 research outputs found
The efficacy of a self-paced VO2max test during motorized treadmill exercise
No full textPURPOSE:To assess the utility of a self-paced maximal oxygen uptake (VO2max) test (SPV) in eliciting an accurate measure of VO2max in comparison with a traditional graded exercise test (GXT) during motorized treadmill exercise.DESIGN:This was a cross-sectional experimental study whereby recreationally trained men (n = 13, 25.5 ± 4.6 y) completed 2 maximal exercise tests (SPV, GXT) separated by a 72-h recovery period.METHODS:The GXT was continuous and incremental, with prescribed 1-km/h increases every 2 min until the attainment of VO2max. The SPV consisted of 5 × 2-min stages of incremental exercise, which were self-selected and adjusted according to 5 prescribed RPE levels (RPE 11, 13, 15, 17, and 20).RESULTS:Although no significant differences in VO2max were observed between the SPV and GXT (63.9 ± 3.3 cf 60.9 ± 4.6 mL · kg-1 · min-1, respectively, P > .05), the apparent 4.7% mean difference may be practically important. The 95% limits-of-agreement analysis was 3.03 ± 11.49 mL · kg-1 · min-1. Therefore, in the worst-case scenario, the GXT may underestimate measured VO2max as ascertained by the SPV by up to 19%. Conversely, the SPV could underestimate the GXT by 14%.CONCLUSIONS:The current study has shown that the SPV is an accurate measure of VO2max during exercise on a motorized treadmill and may provide a slightly higher VO2max value than that obtained from a traditional GXT. The higher VO2max during the SPV may be important when prescribing training or monitoring athlete progression
The Effect of Anodal Transcranial Direct Current Stimulation Over Left and Right Temporal Cortex on the Cardiovascular Response: A Comparative Study
Full text linkBackground: Stimulation of the right and left anterior insular cortex, increases and decreases the cardiovascular response respectively, thus indicating the brain’s lateralization of the neural control of circulation. Previous experiments have demonstrated that transcranial direct current stimulation (tDCS) modulates the autonomic cardiovascular control when applied over the temporal cortex. Given the importance of neural control for a normal hemodynamic response, and the potential for the use of tDCS in the treatment of cardiovascular diseases, this study investigated whether tDCS was capable of modulating autonomic regulation.
Methods: Cardiovascular response was monitored during a post-exercise muscle ischemia (PEMI) test, which is well-documented to increase sympathetic drive. A group of 12 healthy participants performed a PEMI test in a control (Control), sham (Sham) and two different experimental sessions where the anodal electrode was applied over the left temporal cortex and right temporal cortex with the cathodal electrode placed over the contralateral supraorbital area. Stimulation lasted 20 min at 2 mA. The hemodynamic profile was measured during a PEMI test. The cardiovascular parameters were continuously measured with a transthoracic bio-impedance device both during the PEMI test and during tDCS.
Results: None of the subjects presented any side effects during or after tDCS stimulation. A consistent cardiovascular response during PEMI test was observed in all conditions. Statistical analysis did not find any significant interaction and any significant main effect of condition on cardiovascular parameters (all ps > 0.316) after tDCS. No statistical differences regarding the hemodynamic responses were found between conditions and time during tDCS stimulation (p > 0.05).
Discussion: This is the first study comparing the cardiovascular response after tDCS stimulation of left and right TC both during exercise and at rest. The results of the current study suggest that anodal tDCS of the left and right TC does not affect functional cardiovascular response during exercise PEMI test and during tDCS. In light of the present and previous findings, the effect of tDCS on the cardiovascular response remains inconclusive
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
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
The use of the self-paced exercise test in assessing cardiorespiratory fitness in runners
Full text linkThe aim of this thesis was to investigate the utility of the self-paced exercise test (SPXT) in assessing the cardiorespiratory fitness of runners. Traditionally, cardiorespiratory fitness is assessed via an open-ended graded exercise test (GXT) which utilises fixed increments of work-rate and involves the participant continuing until volitional exhaustion. The SPXT is a closed-looped 10 minute (min) test which is made up of 5 x 2 min stages in which intensity is clamped by ratings of perceived exertion (RPE). The test starts at RPE 11, and this increases in an incremental fashion to encompass RPE 13, 15, 17, and finally 20. The test is more time-efficient than traditional protocols due to not requiring a known starting speed. Additionally, the SPXT may be more valid for runners compared to the GXT in which test duration is unknown.
In study one, gradient and speed-based SPXT protocols were compared to a laboratory based GXT to investigate the validity of the SPXT in producing maximal oxygen uptake (V?O2max). The gradient-based SPXT [which has not previously been investigated] produced higher V?O2max than the GXT (71 ± 4.3 vs. 68.6 ± 6.0 mL·kg-1·min-1, P = .03, ES = .39) but the speed-based SPXT produced similar V?O2max to the GXT (67.6 ± 3.6 vs. 68.6 ± 6.0 mL·kg-1·min-1, P = .32, ES = .21). Results also demonstrated that the oxygen (O2) cost of ventilation may differ between the SPXT and GXT (26.4 ± 2.8 vs. 28.2 ± 2.8 mL.min-1, respectively) (P = .02).
In study two, the oxygen cost of breathing during the SPXT was investigated. When assessed via separate ventilation trials, there were no differences in the oxygen cost of breathing between the SPXT and GXT (26.1 ± 5.3 vs. 26.9 ± 4.2 mL.min-1, respectively) (t7 = -1.00, P = .34,), and V?O2max was again similar between the SPXT and GXT (Z = -.43, P = .67,). The mean velocity at RPE20 (vRPE20) measured via the SPXT was also similar to the maximal velocity (Vmax) derived from the GXT (t8 = .74, P = .48).
In study three, the ability of the SPXT to provide novel parameters that could be used to prescribe six-weeks of running training for recreationally active runners was investigated. Results demonstrated that vRPE20 was effective in improving V?O2max (6 ± 6 %), critical speed (3 ± 3 %) and lactate threshold (7 ± 8%) and these improvements were similar to a separate group who trained using GXT-derived parameters including Vmax (4 ± 8, 7 ± 7, 5 ± 4 %, for V?O2max, critical speed, and lactate threshold, respectively). Prescribing training via the SPXT may be beneficial as it does not require additional testing that is usually associated with the GXT.
In study four, the ability of the SPXT to accurately determine ventilatory thresholds (VT) was investigated. The first and second VT (VT1 and VT2, respectively) were not significantly different when measured as V?O2 between the SPXT (4.03 ± 0.5 and 4.37 ± 0.6 L.min-1, for VT1 and VT2, respectively) and GXT (4.18 ± 0.5 and 4.54 ± 0.7 L.min-1, respectively) in highly trained runners. In recreationally trained runners VT1 was significantly different when measured via the SPXT and GXT (2.78 ± 0.5 vs. 2.99 ± 0.5 L.min-1, respectively) (t23 = -4.51, P < .01, ES = .42) whilst VT2 was also significantly different (3.10 ± 0.6 vs. 3.22 ± 0.6 L.min-1) (t21 = -2.35, P = .03, ES = .20). However, when calculated using different variables such as velocity, RPE, and HR, VT1 and VT2 were similar between protocols. This demonstrated that the SPXT can provide valid VT for runners.
The conclusion from this thesis is that the SPXT is a valid protocol for measuring V?O2max and can also be used to prescribe a programme of endurance training, and provide an accurate marker of VT
The Efficacy of Transcranial Direct Current Stimulation to Enhance Endurance Exercise Performance
Full text linkIn the last two decades, non-invasive brain stimulation techniques such as transcranial direct current stimulation (tDCS) have been proposed to increase endurance capacity within exhaustive exercise trials. Consequently, interest in the use of tDCS has spread throughout research, commercial and public communities. Despite the promising findings of an ergogenic effect detailed within exhaustive exercise, the mechanisms of action underlying tDCS are uncertain and the efficacy of tDCS to enhance self-paced performance is inconclusive. Therefore, this thesis explored the efficacy of tDCS to enhance endurance exercise performance. The first experimental chapter (chapter 2) demonstrated that anodal tDCS applied to the dorsolateral prefrontal cortex (DLPFC) in a bilateral montage had no significant effect on 15 minute cycling TT performance. Study two explored the effect of tDCS delivered to the DLPFC in an extracephalic montage on cycling TT performance. An extracephalic montage is suggested to avoid the complications associated with the cathodal electrode seen in cephalic and bilateral montages. This study also demonstrated that tDCS had no significant effect on TT performance. Study three explored the effect of anodal tDCS applied through the Halo Sport Neurostimulation system on physiological adaptation to endurance training. This study demonstrated that tDCS applied to the motor cortex (M1) during 6 weeks of high intensity interval training did not augment the training response to a greater extent than the sham group. Finally, study four investigated the capability of the Halo Sport Neurostimulation System to induce changes in corticospinal excitability. The results demonstrated that this device had no effect on the corticospinal excitability of the M1 when delivered at rest and during submaximal exercise. The present thesis demonstrates that the acute and chronic applications of conventional tDCS are not viable methods of enhancing endurance performance or increasing the physiological adaptations to training. Therefore, the use of tDCS to enhance performance of recreationally active participants cannot be recommended
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
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