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Understanding the role of shaft stiffness in the golf swing 总被引:3,自引:3,他引:0
Theoretically, shaft stiffness can alter shot distance by increasing clubhead speed or altering clubhead orientation at impact.
A 3D forward dynamics model of a golfer and flexible club simulated the downswing. A genetic algorithm optimized the coordination
of the model’s muscles (four torque generators) to maximize clubhead speed. The maximum torque output and maximum rate of
torque development from the torque generators were varied to simulate the swing of golfers that generate different clubhead
speeds. Four shafts of varying stiffness (flexible, regular, stiff, and completely rigid) were entered into these simulations
to examine the role that shaft flexibility had on clubhead speed and orientation at impact. Shaft stiffness was found to have
a meaningful effect only on clubhead orientation (dynamic loft and dynamic close) at impact. There was no evidence to support
the premise that matching the stiffness properties of the shaft with the golfer would improve clubhead speed. 相似文献
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Guillaume Costalat Jeremy Coquart Ingrid Castres Fabrice Joulia Olivier Sirost Eric Clua 《Journal of sports sciences》2017,35(7):678-687
We investigated the oxygen-conserving potential of the human diving response by comparing trained breath-hold divers (BHDs) to non-divers (NDs) during simulated dynamic breath-holding (BH). Changes in haemodynamics [heart rate (HR), stroke volume (SV), cardiac output (CO)] and peripheral muscle oxygenation [oxyhaemoglobin ([HbO2]), deoxyhaemoglobin ([HHb]), total haemoglobin ([tHb]), tissue saturation index (TSI)] and peripheral oxygen saturation (SpO2) were continuously recorded during simulated dynamic BH. BHDs showed a breaking point in HR kinetics at mid-BH immediately preceding a more pronounced drop in HR (?0.86 bpm.%?1) while HR kinetics in NDs steadily decreased throughout BH (?0.47 bpm.%?1). By contrast, SV remained unchanged during BH in both groups (all P > 0.05). Near-infrared spectroscopy (NIRS) results (mean ± SD) expressed as percentage changes from the initial values showed a lower [HHb] increase for BHDs than for NDs at the cessation of BH (+24.0 ± 10.1 vs. +39.2 ± 9.6%, respectively; P < 0.05). As a result, BHDs showed a [tHb] drop that NDs did not at the end of BH (?7.3 ± 3.2 vs. ?3.0 ± 4.7%, respectively; P < 0.05). The most striking finding of the present study was that BHDs presented an increase in oxygen-conserving efficiency due to substantial shifts in both cardiac and peripheral haemodynamics during simulated BH. In addition, the kinetic-based approach we used provides further credence to the concept of an “oxygen-conserving breaking point” in the human diving response. 相似文献
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Eric Ma 《Inter-Asia Cultural Studies》2013,14(2):187-200
The paper attempts to work out the link between the structuring of the public domain and hegemonic masculinities in contemporary Kerala, South India. Using the debates around an incident of sexual harassment that happened in 1999, it argues for a conjunctural understanding of the contemporary where various events and moments in history are replayed through narrativization and popular memory. The paper goes on to analyse the debates around the incident that produce a ‘narrative public domain’, to foreground the various notions of masculinity that construct and structure it in relation to notions of female sexuality and changing structures of family. These notions of masculinity could be, the paper argues, a starting point for a historical inquiry into Kerala's modernity – an inquiry that would throw light on the past and the ways in which the contemporary is produced through its historical legacies. 相似文献
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Maria A. Ruiz‐Primo Min Li Carlos Ayala Richard J. Shavelson 《International Journal of Science Education》2013,35(12):1477-1506
The idea of using science notebooks as a classroom assessment tool is not new. There is general agreement that science notebooks allow teachers to assess students' conceptual and procedural understanding and to provide the feedback students need for improving their performance. In this study we examined the use of science notebooks as an unobtrusive assessment tool that can also be used by individuals outside the classroom (for example, school district personnel), and as a means for obtaining information about students' learning and their opportunities to learn. More specifically, in this study students' science notebooks were used as a source of data about the (a) implementation of a curriculum's intended activities, (b) students' performance, and (c) quality of teachers' feedback. Our results indicated that: (1) Students' science notebooks can be reliably scored. Unit implementation, student performance, and teacher feedback scores were highly consistent across raters and units. (2) High and positive correlations with other performance assessment scores indicated that the student performance score can be considered as an achievement indicator. And (3) low performance scores across the two units revealed that students' communication skills and understanding were far away from the maximum score and did not improve over the course of instruction during the school year. This result may be due, in part, to the fact that no teacher feedback was found in any of the students' notebooks across the six classrooms studied. This may reflect some characteristics of the teachers' assessment practices that may require further professional development. 相似文献
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