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Young-Hoo Kwon

The purpose of this study was twofold: (a) to investigate the effect of the method of body segment parameter (BSP) estimation on the accuracy of the experimental simulation of a complex airborne movement; and (b) to assess the applicability of selected BSP estimation methods in the experimental simulation. It was hypothesized that different BSP estimation methods would provide different simulation results. A sensitivity analysis was performed to identify the BSP items and segments responsible for the inter-method differences in the simulation accuracy. The applicability of the estimation methods was assessed based on the simulation results and the number of anthropometric parameters required. Ten BSP estimation methods classified into 3 groups (4 cadaver-based, 4 gamma mass scanning-based, and 2 geometric) were employed in a series of experimental simulations based on 9 double-somersault-with-full-twist H-bar dismounts performed by 3 male college gymnasts. The simulated body orientation angles were compared with the corresponding observed orientation angles in computing the simulation errors. The inclination and twist simulation errors revealed significant (p < .05) differences among the BSP estimation groups and methods. It was concluded that: (a) the method of BSP estimation significantly affected the simulation accuracy, and more individualized BSP estimation methods generally provided more accurate simulation results; (b) the mass items, and the lower leg and thorax/ abdomen were more responsible for the intermethod differences in the simulation accuracy than other BSP items and segments, respectively; (c) the ratio methods and the simple regression methods were preferable in simulation of the somersaulting motion due to the fewer anthropometric parameters required; (d) the geometric models and the cadaver-based stepwise regression method were superior to the other methods in the simulation of the complex airborne motion with twist.

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Milda Bilinauskaite, Vishveshwar R. Mantha, Abel I. Rouboa, Pranas Ziliukas, and António J. Silva

The aim of the article is to determine the hydrodynamic characteristics of a swimmer’s scanned hand model for various possible combinations of both the angle of attack and the sweepback angle, simulating separate underwater arm stroke phases of front crawl swimming. An actual swimmer’s hand with thumb adducted was scanned using an Artec L 3D scanner. ANSYS Fluent code was applied for carrying out steady-state computational fluid dynamics (CFD) analysis. The hand model was positioned in nine different positions corresponding to the swimmer’s hand orientations (angle of attack and sweepback angle) and velocities observed during the underwater hand stroke of front crawl. Hydrodynamic forces and coefficients were calculated. Results showed significantly higher drag coefficient values in the pull phase, when compared with previous studies under a steady-state flow condition. The mean value of the ratio of drag and lift coefficients was 2.67 ± 2.3 in underwater phases. The mean value of the ratio of drag and lift forces was 2.73 ± 2.4 in underwater phases. Moreover, hydrodynamic coefficients were not almost constant throughout different flow velocities, and variation was observed for different hand positions corresponding to different stroke phases. The current study suggests that the realistic variation of both the orientation angles influenced higher values of drag, lift and resultant coefficients and forces.

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Maurice R. Yeadon

At the 1992 Olympic Games six full twisting double somersault dismounts were recorded with two video cameras during the rings individual apparatus finals in the men's Artistic Gymnastics competition. Angles describing body configuration were determined from video data and were input, together with initial orientation angle values and angular momentum components, into a computer simulation model of aerial movement. Mean absolute deviations between simulation and video after the completion of one half twist were 0.01 rev for somersault, 2.8° for tilt, and 0.08 rev for twist. When the estimate of the initial tilt angle was adjusted by up to 1° these deviations fell to 1.6° for tilt and 0.02 rev for twist. All 6 competitors produced the majority of the tilt using aerial techniques that were predominantly asymmetrical movements of the arms. Contributions to the subsequent removal of tilt were determined using reverse simulations, and again arm movements were the main contributors.

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Maurice R. Yeadon

A method is presented for the three-dimensional analysis of ski jumping using two pan and tilt cameras. In each film frame two reference markers are digitized and identified so that a pseudo focal length and three angles defining camera orientation can be calculated from a knowledge of the positions of camera and markers. In each film frame 12 body landmarks are digitized and the films taken by the two cameras are synchronized using the digitized displacement data. The time histories of the center of mass location and 15 angles describing the orientation and configuration of the jumper are calculated. Digitization errors lead to an error of 0.05 m in center of mass location and an error of 1° in orientation angles.

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Paul J. Felton, Maurice R. Yeadon, and Mark A. King

(toe, metatarsophalangeal (MTP), ankle, knee, hip, shoulder, elbow, wrist, and hand) onto the sagittal plane were used to determine the trunk orientation angle (angle of the trunk in the global coordinate system) and the joint configuration angles. The distance between the projected hip joint centers

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Pedro Paulo Deprá, Avelino Amado, and Richard E.A. van Emmerik

left and right back. These markers were used to calculate the tracking error and head orientation angle. To visually track the target, the participant wore a laser pointer attached to a headband that projected a dot on the wall (Figure  1 ). Figure 1 —Experimental setup. An eight-camera ProReflex

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Brendan L. Pinto, Daniel Viggiani, and Jack P. Callaghan

calculated (Figure  1 ). The height of the rectangle was extracted as the thickness of the muscle (Figure  1 ). When analyzing the images, the researcher was blinded to posture and condition. Figure 1 —Sample ultrasound image showing how the fiber orientation angle and thickness were measured. This image was

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Katherine A.J. Daniels, Eleanor Drake, Enda King, and Siobhán Strike

. 16 – 19 At more acute angles, larger changes to the direction in which the COM is traveling (COM heading angle) and the direction in which the body is facing (body orientation angle) are necessitated. Greater deceleration in the original direction of travel is thus required, and braking impulses

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Kazumichi Ae, Dave Burke, Takashi Kawamura, and Sekiya Koike

dependent on the measured kinetic variables of the individual hands. 24 , 27 , 28 A root mean squared error (RMSE) and %RMSE for evaluating the accuracy of the simulation model were calculated between the measured and simulation model data for the time histories of bat-head speed, bat orientation angle

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Michael A. Hunt, Christopher K. Cochrane, Andrew M. Schmidt, Honglin Zhang, David J. Stockton, Alec H. Black, and David R. Wilson

, α was set at .05. Pairwise comparisons were then conducted using a least significant differences correction. Additional repeated-measures analyses of variance were conducted for the joint orientation angles and pressure data from each standing condition in order to characterize these positions. All