1,721,041 research outputs found
Relationships between anthropometric characteristics, block settings, and block clearance technique during the sprint start
No full textThis study aimed to identify how body dimensions interact with anteroposterior block distances to influence lower limb joint angles in the "set" position, how these angles relate to block clearance kinetic and kinematic parameters, and how these biomechanical parameters influence sprint start performance in sprinters of both sexes and of different ability levels. Seventy-eight sprinters performed six maximal-effort 10 m sprints. Joint angles in the "set" position were quantified through 2D video analysis, and the forces generated during block exit were measured by dynamometric starting blocks. Lower limb length was associated with the front block-starting line distance ([FB/SL], partial correlation [rPC] = 0.48) and was a significant predictor of FB/SL (R2 = 0.39). The FB/SL was associated with front hip angle (rPC = 0.38), which was consequently associated with numerous kinetic variables during block clearance (rPC from -0.41 to -0.61). Coaches should be encouraged to explore the interactions between individual lower limb lengths and the FB/SL distance in both male and female sprinters to manipulate the front hip angle in the "set" position in an attempt to achieve more favourable block clearance kinetics
Effect of different anthropometry-driven block settings on sprint start performance
No full textThe effects of different front-block starting line distances on "set" position kinematics, block clearance kinetics and sprint start performance are largely consistent irrespective of ability level.When using a medium inter-block distance (45% of leg length), shorter front block-starting line distances (down to 50% of the leg length) led to improved sprint start performance.From shorter front block-starting line distances, sprint start performance was primarily improved through greater force production against the rear block which led to greater impulses due to no change in push durations or resultant front foot forces.Lower-limb length is an important consideration when adjusting anteroposterior block distances
Two Wearable Sensor Datasets recording the Countermovement Jump
No full text<p>These datasets come from two independent studies using wearable inertial sensors to estimate countermovement jump performance. The participants were healthy sports science students, free of injury, all of whom had given their prior written consent. Ethical approval was given by the governing institutions’ ethics committees, which included further analysis of the data.</p>
<ul>
<li><strong>Smartphone Dataset:</strong>
<ul>
<li>119 valid jumps</li>
<li>Peak power 40.7 +/- 8.9 W/kg</li>
<li>22 males, 10 females (26.5 +/- 4.1 yrs; standing height 1.74 +/- 0.08 m; body mass 70.0 +/- 10.9 kg)</li>
<li>Redmi 9T phone (Xiaomi Technology, Beijing, China)</li>
<li>128 Hz sampling frequency</li>
<li>Accelerometer & gyroscope</li>
<li>Handheld at sternum level</li>
<li>Mascia, G.; De Lazzari, B.; Camomilla, V. Machine learning aided jump height estimate democratization through smartphone measures. Frontiers in Sports and Active Living 2023, 5, 1112739. <a href="https://doi.org/10.3389/fspor.2023.1112739">https://doi.org/10.3389/fspor.2023.1112739</a>.</li>
</ul>
</li>
<li><strong>Accelerometer Dataset:</strong>
<ul>
<li>347 valid jumps</li>
<li>Peak power 45.1 +/- 7.6 W/kg</li>
<li>48 males, 25 females (21.6 +/- 3.3 yrs; standing height 1.75 +/- 0.10 m; body mass 71.2 +/- 15.1 kg)</li>
<li>Trigno sensor (Delsys Inc, MA, USA)</li>
<li>250 Hz sampling frequency</li>
<li>Accelerometer</li>
<li>Taped to lower back (L4)</li>
<li>White, M.G.E.; Bezodis, N.E.; Neville, J.; Summers, H.; Rees, P. Determining jumping performance from a single body-worn accelerometer using machine learning. PLOS ONE 2022, 17, e0263846. <a href="https://doi.org/10.1371/journal.pone.0263846">https://doi.org/10.1371/journal.pone.0263846</a></li>
</ul>
</li>
</ul>
<p>MATLAB .mat files</p>
<p>This repository was used by the paper currently under review for the open journal Mathematics:</p>
<p>White, M.; De Lazzari, B.; Bezodis, N., Camomilla, V. Title. Mathematics 2024, 1, 0. Wearable Sensors for Athletic Performance: A Comparison of Discrete and Continuous Feature Extraction Methods for Prediction Models</p>
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
Sprint Running With Lower-limb Wearable Resistance: Acute Mechanical Responses and Training Outcomes
No full textSprint running, and in particular one’s ability to perform maximal acceleration over short distances, is a key component of performance for many sports. Thus, the best methods to develop an athlete’s sprint running capabilities is of interest to many coaches. Lower-limb wearable resistance (WR) is a movement- and speed-specific training method for sprint running that allows close adherence to the principle of training specificity. Therefore, lower-limb WR could be well suited for producing adaptations that transfer to unloaded sprint running. This thesis aimed to answer the overarching question, “What are the effects of lower-limb WR on short distance sprint running?”
A review of the literature (Chapter 2) found that lower-limb WR loading schemes of 0.6−5% body mass (BM) significantly increased contact time (2.9−8.9%), decreased step frequency (−1.4 to −3.7%), and slowed total sprint times (0.6−7.4%). However, minimal kinetic and joint kinematic information had been published which limited the understanding of the underlying mechanics associated with sprint running with lower-limb WR. Also, no prior investigations had employed a shank- or thigh-only load configuration. Further, there was no research-based evidence detailing how an athlete population might respond to lower-limb wearable resistance training (WRT) for sprint running. These important gaps and limitations provided a framework for the research undertaken in this thesis.
The first study (Chapter 3) investigated the effects of 2% BM thigh and shank WR on joint kinematics during early acceleration. It was found that significant differences in maximal joint angles between loaded and unloaded sprint running were small (ES = 0.23–0.38), limited to the hip and knee joints, and < 2° on average. Also, average hip flexion and extension velocity were significantly overloaded with the thigh and shank WR, which suggested a specific application for lower-limb WR to target the hip flexion and extension actions associated with fast sprint running. In study two (Chapter 4), it was found that athletes were largely able to maintain propulsive and net anterior-posterior impulse values using 2% BM thigh and shank WR. However, greater increases to braking and vertical impulses were observed with shank WR (2.72−26.3% compared to unloaded) than with thigh WR (2.17−12.1% compared to unloaded). Considering these findings and the greater practitioner interest in shank WR for training applications due to practical utility, a third study (Chapter 5) was undertaken to compare the force waveforms between unloaded and 2% BM shank WR sprint running to better understand the underlying cause(s) for increased horizontal braking and vertical impulses and determine if there are significant differences in the magnitude of forces around impact. Significant differences in the anterior-posterior component of the ground reaction force (i.e. greater levels of braking force) between unloaded and shank WR occurred between 20.8−28.3% of ground contact at 10 m, 20 m, and 30 m. Thus, there was no indication that greater horizontal braking or vertical forces occur during the impact portion of ground contact. These studies identified specific underlying mechanisms that may render thigh and shank WR as effective training tools for sprint acceleration performance.
Two training studies were subsequently undertaken in this thesis to investigate the longitudinal effects of shank WRT for sprint running in field-based sports athletes. Six weeks of WRT was found to be superior to unloaded training in maintaining the technical ability to produce horizontal force at low velocities and maintaining a horizontally oriented ground reaction force with increasing speed in collegiate/semi-professional rugby athletes (Chapter 6). Nine weeks of WRT in high school American football athletes did not result in significant post-training differences between the WR and unloaded training (Chapter 8). Detailed inspection of the training protocols employed and athlete responses provided evidence that shank-placed WR can be used to amplify the nuances of a sprint running training protocol.
Prior to Chapter 8, a study was completed to establish the level of agreement between the horizontal F-v profile variables obtained from two field-based velocity measurement devices, a 1080 Sprint and a Stalker ATS II radar gun (Chapter 7). This provided the necessary information to determine if the two devices could be used interchangeably to inform device selection, and thus, number of testing time points to be included in the training study that followed (Chapter 8).
The research presented in this thesis has identified the mechanical determinants that are overloaded by lower-limb WR, and thus, may be influenced over time to produce positive speed adaptations. Also, this thesis has identified lower-limb WRT as a time-efficient method to retain mechanical characteristics of sprint performance, which may have beneficial implications for sports with constrained schedules. In conclusion, it is suggested that this method of resistance training could be used concurrently with other resistance training methods in a mixed-method training approach to provide a unique stimulus to encourage continued improvement in speed development or further target velocity-based individual weaknesses
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
Biomechanical investigations of coordination during initial acceleration in highly trained to world class sprinters
Get PDFThesis (Sport Science (Biomechanics))--University of Pretoria, 2023.Initial sprint acceleration is a complex and dynamic skill, requiring the application of large forces to propel the body forwards. Effective force application is achieved through the use of joint and segment rotations in an organised and inter-related manner. While many of the isolated angular kinematic features associated with effective external force profiles are established, little is currently known about the relationships that exist between the key segments during the first steps of acceleration, i.e., the coordination of movement between functionally related elements. Through a series of three studies, this thesis explores inter- and intra-limb coordination during initial acceleration in sprinters ranging from highly trained to world class level, to enhance the understanding of sprint acceleration technique and performance.
The first study provided a detailed description and quantification of inter-limb thigh-thigh, intra-limb shank-foot, and trunk-shank coordination during the first four steps of acceleration, and investigated changes in coordination between steps. Specific coordination features were identified and between-individual variation in coordination patterns in preparation for, or response to, the major transitions in the step cycle, i.e., touchdown and toe-off, were observed. Additionally, step-to-step changes in coordination and angular kinematics were identified, showing clearly differentiated coordination in step 1 compared to later steps.
The second study utilised a novel application of hierarchical cluster analysis to vector coding data in order to identify and characterise sub-groups of sprinters with similar thigh-thigh and shank-foot coordination patterns, and subsequently explored discrete kinematic and performance differences between sub-groups. Three sub-groups were identified in step 1 and two sub-groups over steps 2-4. Sub-groups tended to be differentiated by differences in thigh-thigh coordination at the beginning and end of the step, and shank-foot coordination during flight as well as during ankle dorsiflexion in early stance. Combining sub-groups from step 1 and steps 2-4 to describe entire initial acceleration strategies, cluster combinations identified coordination approaches more likely to be associated with higher level sprinters and better performance.
In the final investigation, relationships between coordination and lower body strength were evaluated in the context of dynamical systems theory, and the interaction of these two factors with regard to acceleration performance was explored. Several correlations existed between measures of lower body strength and features of thigh-thigh and shank-foot coordination, while multiple regression analysis suggested the presence of interaction effects between coordination and tests associated with lower body power in relation to performance. Thus, lower body power appeared to influence the relationships between coordination features and performance, such that the effectiveness of particular coordination patterns varied depending the lower body power of the athlete.
The work included in this thesis provides a basis for understanding coordination during initial sprint acceleration, and includes several novel and exploratory approaches to investigating these questions which provides relevant information for practitioners and coaches interested in exploring the organisation of the body and coordination of segments during initial acceleration. Moreover, this work facilitate the generation of new hypotheses and encourages new directions in future research.PhysiologyPhD Sport Science (Biomechanics)UnrestrictedFaculty of Health Science
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
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