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Robert K. Jensen, Tina Treitz, and Sylvie Doucet

The purpose of this study was to develop prediction equations to estimate mass, radius to the center of mass (CM), and principal moments of the segments during pregnancy. Nonlinear regression equations were determined for the lower trunk, upper trunk, and thigh. The third sampling month of a longitudinal study was used (Sample 1, n = 15). The nonlinear regressions were then used to predict segment inertias above and below the third sampling month (Sample 2, the remaining 74 measurements). For the remaining segments, body mass and segment lengths were used as predictor variables for mass, radius to CM, and radius of gyration about the centroidal axes. The remaining seven segments did not change substantially during pregnancy, and the means of the repeated measures were used for the simple linear regressions. Eighteen of the 28 regressions and all of the CM regressions were significant. With pregnant subjects it is recommended that these regressions be used if application of the elliptical cylinder model is not possible.

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Robert K. Jensen, Tina Treitz, and Han Sun

The purpose of the study was to use the elliptical cylinder model adapted for infants (Sun & Jensen, 1994) with a cross-sectional sample to select appropriate multiple linear regression equations for predicting masses and nonlinear regression equations for predicting principal moments of inertia (Yeadon & Morlock, 1989). The linear and nonlinear predictions were evaluated with an independent cross-validation sample of infants and a sample where inertias ranged below and above the cross-sectional sample. The cross-validation for masses was compared to a cross-validation of four linear regressions for masses developed by Schneider and Zernicke (1992). It is recommended that the linear regression equations developed in this study be used to predict infant segment masses. It is also recommended that the nonlinear regression equations developed in this study be used to predict the principal moments of inertia of all infant segments, other than head Ix and lower trunk Ix and Iy.

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Matthew T.G. Pain and John H. Challis

This study had two purposes: to evaluate a new method for measuring segmental dimensions for determining body segment inertial parameters (BSIP), and to evaluate the changes in mass distribution within a limb as a consequence of muscular contraction. BSIP were calculated by obtaining surface data points of the body under investigation using a sonic digitizer, interpolating them into a regular grid, and then using Green’s theorem which relates surface to volume integrals. Four skilled operators measured a test object; the error was approximately 2.5% and repeatability was 1.4% (coefficient of variation) in the determination of BSIP. Six operators took repeat measures on human lower legs; coefficients of variation were typically around 5%, and 3% for the more skilled operators. Location of the center of mass of the lower leg was found to move up 1.7 cm proximally when the triceps surae muscles went from a relaxed state to causing plantar flexion. The force during an impact associated with such motion of the soft tissue of the lower leg was estimated to be up to 300 N. In summary, a new repeatable and accurate method for determining BSIP has been developed, and has been used to evaluate body segment mass redistribution due to muscular contraction.

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Ross H. Sanders, Barry D. Wilson, and Robert K. Jensen

This study investigated whether force data could be derived accurately using segment inertia data determined by the elliptical zone method (Jensen, 1976), automatic digitizing from high-speed video using a Motion Analysis VP110 system, and for an activity that does not require flexion of the thorax. The criterion fonctions were the force-time records of the jumps recorded at 500 Hz by a Kistler 9281B force platform. A second-order Butterworth digital filter was used to smooth the derived data, with frequency cutoffs being selected on the basis of root mean square error of the smoothed function with respect to the criterion force function. In a second procedure, the criterion function was the directly measured force-time record after filtering with a second-order Butterworth digital filter at 5 Hz to remove the high frequency part of the force signal. The closeness of fit of the derived data to the low frequency part of the criterion force was then assessed. It was concluded that, using the techniques described, the low frequency components of the ground reaction forces of drop jumps could be derived accurately.

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Gary D. Heise

The purpose of this investigation was to determine, for a planar, multijoint throwing skill, if the interactions of segment energetics change over the course of practice. Eighteen men threw a weighted ball with their dominant arm at a target while the motion was restrained to a horizontal plane. From video data and body segment inertia! estimations, the energy transferred by the net joint force and the mechanical work attributed to the net joint moment were calculated for selected practice trials. Performance scores showed an expected improvement over trial blocks. An energetics analysis indicated that, for the throw, the mechanical work generated by muscle and transferred through muscle (i.e., via the net joint moment) across the elbow joint and the energy transferred by the net joint force across the wrist joint increased early in practice; however, no changes were observed in the relative contributions made by these components. The results indicated that, although performance increased significantly, the movement strategy used by subjects was intact throughout practice.

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Shohei Shibata, Yuki Inaba, Shinsuke Yoshioka, and Senshi Fukashiro

Muraoka ( 1998 ) studied the effects of the body segment inertia parameter (athlete or general adult) on the results of kinematic and kinetic analyses of human movement. This study revealed that the selection of body segment parameter apparently has little effect on the results of biomechanical analysis

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

calculated as the difference between a data value and the mean of adjacent values. 15 , 16 The center of mass position was calculated using segmental inertia parameters determined via the inertia model of Yeadon using 95 anthropometric measurements of the bowler. 17 Front foot contact was identified as the

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Noah X. Tocci, David R. Howell, Dai Sugimoto, Corey Dawkins, Amy Whited, and Donald Bae

-directions, to the left. To calculate the torques about the elbow joint during each pitch from the kinematic data, segment inertia parameters, and conventional inverse dynamics equations were used. Using 3-dimensional (3D) inverse dynamics, elbow kinetic parameters were calculated as the torque applied by the

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Zachary Merrill, Grace Bova, April Chambers, and Rakié Cham

: 1211 – 1221 . doi:10.1152/jn.1998.80.3.1211 10.1152/jn.1998.80.3.1211 15. de Leva P . Adjustments to Zatsiorsky–Seluyanov’s segment inertia parameters . J Biomech . 1996 ; 29 : 1223 – 1230 . PubMed ID: 8872282 doi:10.1016/0021-9290(95)00178-6 10.1016/0021-9290(95)00178-6 16. Chambers AJ

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Ghazaleh Azizpour, Matteo Lancini, Giovanni Incerti, Paolo Gaffurini, and Giovanni Legnani

.1016/0021-9290(89)90051-1 2745471 5. De Leva P . Adjustments to Zatsiorsky–Seluyanov’s segment inertia parameters . J Biomech . 1996 ; 29 ( 9 ): 1223 – 1230 . doi:10.1016/0021-9290(95)00178-6 10.1016/0021-9290(95)00178-6 6. Huang HK , Suarez FR . Evaluation of cross-sectional geometry and mass density distributions of