186,283 research outputs found
Concurrent validity of GPS for deriving mechanical properties of sprint acceleration
No full textPurpose: The purpose of this study was to test the concurrent validity of data from two different global positioning system (GPS) units for obtaining mechanical properties during sprint acceleration using a field method recently validated by Samozino et al. Methods: Thirty-two athletes performed maximal straight-line sprints, and their running speed was simultaneously measured by GPS units (sampling rate: 20 Hz or 5 Hz) and either a radar or laser device (devices taken as references). Lower limb mechanical properties of sprint acceleration (theoretical maximal force, F0; theoretical maximal speed, V0; maximal power, Pmax) were derived from a modeling of the speed-time curves using an exponential function in both measurements. Comparisons of mechanical properties from 20 Hz and 5 Hz GPS units with those from reference devices were performed for 80 and 62 trials, respectively. Results: The percentage bias showed a wide range of over or underestimation for both systems (-7.9-9.7% and -5.1-2.9% for 20 Hz and 5 Hz GPS), while the ranges of its 90% confidence limits for 20 Hz GPS were markedly smaller than those for 5 Hz GPS. These results were supported by the correlation analyses. Conclusions: Overall, the concurrent validity for all variables derived from 20 Hz GPS measurements was better than that obtained from the 5 Hz GPS units. However, in the current state of GPS devices accuracy for speed-time measurements over a maximal sprint acceleration, we recommend that radar, laser devices and timing gates remain the reference methods for implementing Samozino et al.'s computations
Optimal force-velocity profile in ballistic movements-Altius: Citius or Fortius?
No full textThe study's purpose was to determine the respective influences of the maximal power (P max) and the force-velocity (F-v) mechanical profile of the lower limb neuromuscular system on performance in ballistic movements. Methods: A theoretical integrative approach was proposed to express ballistic performance as a mathematical function of P max and F-v profile. This equation was (i) validated from experimental data obtained on 14 subjects during lower limb ballistic inclined push-offs and (ii) simulated to quantify the respective influence of P max and F-v profile on performance. Results: The bias between performances predicted and obtained from experimental measurements was 4%-7%, confirming the validity of the proposed theoretical approach. Simulations showed that ballistic performance was mostly influenced not only by P max but also by the balance between force and velocity capabilities as described by the F-v profile. For each individual, there is an optimal F-v profile that maximizes performance, whereas unfavorable F-v balances lead to differences in performance up to 30% for a given P max. This optimal F-v profile, which can be accurately determined, depends on some individual characteristics (limb extension range, P max) and on the afterload involved in the movement (inertia, inclination). The lower the afterload, the more the optimal F-v profile is oriented toward velocity capabilities and the greater the limitation of performance imposed by the maximal velocity of lower limb extension. Conclusions: High ballistic performances are determined by both maximization of the power output capabilities and optimization of the F-v mechanical profile of the lower limb neuromuscular system. Copyright © 2012 by the American College of Sports Medicine
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Bilateral deficit magnitude increases with velocity during a half-squat exercise
No full textMovement velocity has been viewed as one of the bilateral deficit (BLD) determinants. This research tested the velocity effect on BLD during a half-squat exercise. The role of muscle excitation in BLD was also assessed. BLD amplitude was assessed in 12 male soccer players while performing a half-squat exercise with incremental load. During the exercise’s pushing phase, the average force and velocity were measured in bilateral and unilateral conditions to provide the bilateral index (BI) at each interpolated velocity. The vastus lateralis and medialis excitation was assessed during the exercise by calculating the surface electromyography signal root mean square (sEMGRMS). The BI for sEMGRMS (sEMG BI) was calculated. The theoretical maximum force (F0) and velocity (v0) were also determined. F0 was +43
(28)% in bilateral compared with unilateral conditions (p < 0.001), whereas v0 was similar in both conditions (p = 0.386). The BI magnitude rose with the increase in velocity from −34 (7)% at 50%v0 to −70 (17)% at 90%v0 (p 0.03-<0.001), whereas no sEMG BI occurred (p: 0.07-0.991 in both muscles). The study reported velocity-dependent changes in the BLD amplitude, with the largest BLD amplitudes occurring at the highest velocities. This behaviour could provide useful information for setting specific contraction velocities to exploit/limit the BLD amplitude as a possible training stimulus
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Dr. Edward P. Wimberly, ITC, July 2011
No full textThis video is a conversation with Dr. Edward P. Wimberly. Dr. Wimberly talks about his book, "No Shame in Wesley's Gospel: A Twenty-First Century Pastoral Gospel". Brad Ost, AUC Woodruff Library, is the interviewer
Lower Limb Force, Velocity, Power Capabilities during Leg Press and Squat Movements
No full textThe aim was to compare lower-limb power, force, and velocity capabilities between squat and leg press movements. Ten healthy sportsmen performed ballistic lower-limb push-offs against 5-to-12 different loads during both the squat and leg press. Individual linear force-velocity and polynomial power-velocity relationships were determined for both movements from push-off mean force and velocity measured continuously with a pressure sensor and linear encoder. Maximal power output, theoretical maximal force and velocity, force-velocity profile and optimal velocity were computed. During the squat, maximal power output (17.7±3.59 vs. 10.9±1.39 W·kg-1), theoretical maximal velocity (1.66±0.29 vs. 0.88±0.18 m·s-1), optimal velocity (0.839±0.144 vs. 0.465±0.107 m·s-1), and force-velocity profile (-27.2±8.5 vs. -64.3±29.5 N·s·m-1·kg-1) values were significantly higher than during the leg press (p=0.000, effect size=1.72-3.23), whereas theoretical maximal force values (43.1±8.6 vs. 51.9±14.0 N·kg-1, p=0.034, effect size=0.75) were significantly lower. The mechanical capabilities of the lower-limb extensors were different in the squat compared with the leg press with higher maximal power due to much higher velocity capabilities (e.g. ability to produce force at high velocities) even if moderately lower maximal force qualities
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