1,720,956 research outputs found
Analysis of human underwater undulatory swimming using musculoskeletal modelling
No full textElite swimming is a highly competitive sport. At this professional level, the difference between a podium finish or not, is measured in fractions of a second. While improvements in specific performance metrics may deliver a marginal improvement, it is through the accumulation of marginal gains that the winning margins are created. Quantifying performance in elite sport is therefore fundamental in identifying and implementing improvements. The trade-off between energy expenditure, thrust generated and attained velocity are identified as key aspects to performance. From a review of previous swimming research it was identified that there was a lack of suitable methods for simultaneously quantifying the energy expenditure, thrust and velocity for a particular swimming technique. The aim of this thesis is to analyse the performance of human underwater undulatory swimming (UUS) |a significant proportion of a race for multiple events. This encompasses experimentally gathered data and computational musculoskeletal modelling in the analysis and evaluation of UUS technique. This thesis has developed a novel, fully functional musculoskeletal model with which detailed analysis of human UUS can be performed. The experimental and processing methods for two methods of acquiring the athlete's kinematics have also been developed. A model based upon fish locomotion is coupled with the musculoskeletal model to provide the fluid loadings for the simulation. Detailed analysis of two techniques of an elite athlete has demonstrated this process in a case study. Energy expended by the simulated muscles is estimated. Combined with the measured velocity and predicted thrust, the propulsive efficiency for each technique is determined
Comparison of kinematic acquisition methods for musculoskeletal analysis of underwater flykick
Get PDFThe use of musculoskeletal modeling as a tool for analysing performance sport is increasing. This typically involves simulating an athlete's motion as well as the external loads they experience and assessing muscle activities with respect to the given kinematics. The findings of any analysis are therefore dependent on the accuracy of the kinematics. Furthermore, for sports where the environment directly influences the kinematics, for example swimming, it is preferable to capture the athlete's motion in this environment. For the example of swimming, using typical optical based systems is challenging due to marker occlusions and the reflection of the water, while the frequently used manual digitisation of video data is laborious and time intensive. Inertial measurement units (IMU), however, have been shown to be suitable alternative for capturing gait kinematics.This paper compares results from a musculoskeletal model of human underwater flykick where the kinematics have been determined from two sources; manual digitisation and IMUs. The model simulates the anatomy of the trunk and lower limbs while motion is prescribed for; pelvic-pitch and pelvis-thorax, hip, and knee flexion-extension. It is found that the knee, hip and pelvic-pitch angles derived from the IMU exhibit close agreement to the manual digitisation process and captures the swimmer's motion well as compared to the respective video frames. The musculoskeletal model was executed for both input types and the observed maximum muscle activities were similar in both trend and mean. It is therefore suggested the multiple IMUs can be reliably employed in determining joint kinematics of underwater flykic
Optimisation of a bicycle chainring to aid in rehabilitation of athletes suffering from patellofemoral pain syndrome (PFPS)
Get PDFPatellofemoral Pain Syndrome (PFPS) is a frequently occurring problem whose causation is multifactorial. Supposed triggers include mal-tracking patella due to an imbalance in the muscles of the quadriceps. There are numerous treatments for the pain; for example, strengthening of the quadriceps shows good clinical results. In this study, the geometry of a bicycle chainring has been optimised to increase the recruitment of Vastus Medialis Oblique (VMO). The intention is to strengthen VMO as part of a rehabilitation program to relieve the pain associated with PFPS
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
Prediction of passive and active drag in swimming
Get PDFIn order to understand the physical origin of passive resistance in swimming the resistance breakdown fora swimmer is investigated. A combination of empirical methods and theoretical analysis is used to predictpassive resistance in the speed range 0 – 2 ms-1 and is shown to provide similar results to those from experimental testing. Typical magnitudes of wave, viscous pressure and skin friction resistance contribute 59%, 33% and 8% of total passive resistance respectively at free swim speed. A comparison is made between the widely used Velocity Perturbation Method and a Naval Architecture based approach in predicting active drag. For the swimmer investigated the two approaches predict active drag of 131.4 N and 133.9 N for a swimming speed of 1.53 ms-1. However, the results predicted from the Velocity Perturbation Method have a much higher uncertainty and the Naval Architecture based approach is suggested as a more robust method of predicting active drag
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
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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