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Mary M. Rodgers, Srinivas Tummarakota and Junghsen Lieh

A three-dimensional (3-D) inverse dynamic model of wheelchair propulsion was developed using the Newton-Euler method based on body coordinate systems. With this model, the arm was assumed to be three rigid segments (hand, forearm, and upper arm) connected by the wrist, elbow, and shoulder joints. A symbolic method was adopted to generate the equations of motion. The model was used to compute the joint forces and moments based on the inputs obtained from a 3-D motion analysis system, which included an instrumented wheelchair, video cameras, and a data acquisition system. The linear displacements of markers placed on the joints were measured and differentiated to obtain their velocities and accelerations. Three-dimensional contact forces and moments from hand to handrim were measured and used to calculate joint forces and moments of the segments.

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Peter M. McGinnis and Lawrence A. Bergman

An inverse analysis of the pole vault was completed using a nine-segment rigid-body model of the vaulter in two dimensions. Competitive vaults by five elite vaulters were recorded on film using a high-speed 16-mm motion picture camera. The films were digitized and the digitized data were smoothed. The resultant joint moment histories at the shoulder, left hip, left knee, right hip, and right knee were computed for each vaulter. The moments produced about the top hand by the lower hand on the pole were also computed. The resultant joint moments at each joint were compared between vaulters and related to observed vault techniques. The moment produced by the lower hand on the pole and the resultant shoulder moment showed the most variance between vaulters. The pole moment indicated that the lower arm pulled on the pole throughout much of the vault. The resultant shoulder joint moment indicated the need for strength in the shoulder joint extensor muscles. Variations in the resultant moments at the lower extremity joints were small despite large apparent differences in the observed kinematics between vaulters.

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John P. Miller, James C. Vailas, Ronald V. Croce, Robert Confessore and Kerriann Catlaw

This study examined the effects of (a) functional knee braces on thigh muscle EMG and (b) physical activity and leg shape on knee brace migration. Ten female college ice hockey players were fitted with a strap-secured functional knee brace (SSB) and a hard-shell functional knee brace with strapping. Participants performed a side-step maneuver, a treadmill ran, and an obstacle course. Significant differences were noted in hamstring and quadriceps EMG median frequency (mfEMG) while wearing the SSB compared with the control condition. Significant downward shifts were noted in hamstring mfEMG for both braces when compared with the control condition. There was greater brace migration for the obstacle course for both brace types. No relation was found between leg shape and the amount of migration. This study suggests that custom-fitted functional knee braces alter the motor unit recruitment patterns of the thigh musculature during physical activity and that they do not migrate significantly during physical activity.

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Felix Stief, Frank I. Kleindienst, Josef Wiemeyer, Florian Wedel, Sebastian Campe and Berthold Krabbe

Compared with walking (W), Nordic walking (NW) exhibits greater cardiopulmonary and cardiovascular benefits. Some authors conjecture that compared with W or running (R), NW imposes smaller mechanical loads on the musculoskeletal system. The purpose of the current study was to quantify any differences in joint loading of the lower extremities among NW, W, and R. Fifteen experienced adults participated. Kinematic and force measurements were combined using an inverse dynamics approach to yield joint moments. The results showed no biomechanical benefit of NW. Instead, NW involved greater knee joint loading just after heel strike compared with W. This was due to the longer steps and the higher sole angle during the first part of the stance phase. The sagittal and frontal plane moments were smaller for NW compared with R, but in the transverse plane, the ankle moments were greater in NW than in W or R. Based on these results, NW is not recommended as an exercise for persons who seek to reduce biomechanical loading of the lower extremities.

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Gregory S. Rash and Robert Shapiro

Twelve collegiate football quarterbacks were videotaped while performing drop back passes. The video images were digitized using a Peak Performance system, and three-dimensional (3-D) kinematic and kinetic data were calculated from the 3-D coordinate data using standard analytical procedures. The sequential timing of peak shoulder torques in the delivery for the football throw was peak abduction torque prior to the point of maximum shoulder external rotation (MER), peak internal rotation torque just after MER, and peak horizontal adduction torque just prior to release. As anticipated, large medial deviation torques at the elbow were found in the acceleration phase. However, in many cases the quarterbacks demonstrated larger elbow lateral deviation torques during the follow-through than found in the acceleration phase. This paper will describe these and other kinetic results and the kinematic findings observed during the football pass.

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Li-Xin Guo, Zhao-Wen Wang, Yi-Min Zhang, Kim-Kheng Lee, Ee-Chon Teo, He Li and Bang-Chun Wen

The aim of this study is to investigate the effect of material property changes in the spinal components on the resonant frequency characteristics of the human spine. Several investigations have reported the material property sensitivity of human spine under static loading conditions, but less research has been devoted to the material property sensitivity of spinal biomechanical characteristics under a vibration environment. A detailed three-dimensional finite element model of the human spine, T12– pelvis, was built and used to predict the influence of material property variation on the resonant frequencies of the human spine. The simulation results reveal that material properties of spinal components have obvious influences on the dynamic characteristics of the spine. The annulus ground substance is the dominant component affecting the vertical resonant frequencies of the spine. The percentage change of the resonant frequency relative to the basic condition was more than 20% if Young’s modulus of disc annulus is less than 1.5 MPa. The vertical resonant frequency may also decrease if Poisson’s ratio of nucleus pulposus of intervertebral disc decreases.

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Jos J. de Koning, Gert de Groot and Gerrit Jan van Ingen Schenau

The purpose of this study was to describe the intermuscular coordination and power production for the constrained asymmetrical movement during skating the curves. Seven elite male speed skaters took part in the experiments. The speed skaters were simultaneously filmed from frontal and sagittal views. EMGs were obtained telemetrically and push-off force was registered with special skates. Inverse dynamic analysis yielded power production data, which differed for left and right leg. Marked differences were also found in intermuscular coordination of each leg. The activation patterns of the muscles were influenced by the asymmetrical nature and the typical body position during the speed skating movement. External power output was determined by three methods. The mean joint power output for left and right leg showed similar values as the external power output calculated from air and ice friction. These values were lower than the values predicted with a geometrical model for skating the curves.

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Steven T. McCaw, Jacob K. Gardner, Lindsay N. Stafford and Michael R. Torry

An inverse dynamic analysis and subsequent calculation of joint kinetic and energetic measures is widely used to study the mechanics of the lower extremity. Filtering the kinematic and kinetic data input to the inverse dynamics equations affects the calculated joint moment of force (JMF). Our purpose was to compare selected integral values of sagittal plane ankle, knee, and hip joint kinetics and energetics when filtered and unfiltered GRF data are input to inverse dynamics calculations. Six healthy, active, injury-free university student (5 female, 1 male) volunteers performed 10 two-legged landings. JMFs were calculated after two methods of data filtering. Unfiltered: marker data were filtered at 10 Hz, GRF data unfiltered. Filtered: both GRF and marker data filtered at 10 Hz. The filtering of the GRF data affected the shape of the knee and hip joint moment-time curves, and the ankle, knee and hip joint mechanical power-time curves. We concluded that although the contributions of individual joints to the support moment and to total energy absorption were not affected, the attenuation of high-frequency oscillations in both JMF and JMP time curves will influence interpretation of CNS strategies during landing.

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. Hartsell * Sandi J. Spaulding * 5 1999 8 2 83 98 10.1123/jsr.8.2.83 Effect of Gallium Aluminum Arsenide Triple-Diode Laser on Median Nerve Latency in Human Subjects William P. Bartlett * William S. Quillen * Jeanne L. Gonzalez * 5 1999 8 2 99 108 10.1123/jsr.8.2.99 Dynamic Analysis of Custom

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. Elliott * Robert N. Marshall * Guillermo J. Noffal * 11 1995 11 4 433 442 10.1123/jab.11.4.433 A Three-Dimensional Dynamic Analysis of the Quarterback's Throwing Motion in American Football Gregory S. Rash * Robert Shapiro * 11 1995 11 4 443 459 10.1123/jab.11.4.443 Desirable Gliding Styles and