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Julien Morlier, Michel Mesnard and Mariano Cid

The development of composite material poles since 1960 has played a prominent part in performance improvement in pole-vaulting. Previous studies devoted to pole-vaulting models were based on constant mechanical characteristics. It is thus necessary to identify the local bending rigidities of the pole to build realistic pole-vaulting models. Updating methods developed for dynamic structure studies allow us to describe local mechanical characteristics. These methods are based on the comparison between experimental results and those determined numerically by finite element models. This study presents an adaptation of these methods to determine the local bending rigidities of the pole. The updating technique is validated by a deflection test of a homogeneous beam. Then, a study of the model sensitivity is carried out to investigate the procedure robustness. Finally, the updating method is applied to an old design pole and to a recent one. The results obtained vary greatly from one pole to the other; they highlight the evolutions in pole design.

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Cecilia Persson, Jon Summers and Richard M. Hall

A spinal cord injury may lead to loss of motor and sensory function and even death. The biomechanics of the injury process have been found to be important to the neurological damage pattern, and some studies have found a protective effect of the cerebrospinal fluid (CSF). However, the effect of the CSF thickness on the cord deformation and, hence, the resulting injury has not been previously investigated. In this study, the effects of natural variability (in bovine) as well as the difference between bovine and human spinal canal dimensions on spinal cord deformation were studied using a previously validated computational model. Owing to the pronounced effect that the CSF thickness was found to have on the biomechanics of the cord deformation, it can be concluded that results from animal models may be affected by the disparities in the CSF layer thickness as well as by any difference in the biological responses they may have compared with those of humans.

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John H. Challis

Segmental moment of inertia values, which are often required to perform mechanical analyses of human movement, are commonly computed using statistical models based on cadaver data. Two sets of equations for estimating human limb moments of inertia were evaluated: linear multivariable equations and nonlinear equations. Equation coefficients for both sets of equations were determined using the cadaver data of Chandler et al. (1975). A cross-validation procedure was used to circumvent the problem of model evaluation when there is limited data with which to develop and evaluate the model. Moment of inertia values for the longitudinal axes were predicted with similar degrees of accuracy with either set of equations, while for the transverse axes the nonlinear equations were superior. An evaluation of the influence of the accuracy of moment of inertia estimates on resultant joint moments for three activities showed that the influence of these errors was generally small.

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Kathleen J. Ashmen, C. Buz Swanik and Scott M. Lephart

The purpose of this study was to identify strength and flexibility deficits in subjects with chronic low-back pain (CLBP). Subjects were 16 female Division I athletes: 8 athletes who had experienced CLBP for at least 6 months prior to testing and a control group of 8 matched subjects. Athletes with neurological symptoms, previous back operations, and leg length discrepancies and those who were diagnosed with scoliosis, spondylolisthesis, or spondylolysis were excluded from this study. Variables assessed included abdominal strength, erector spinae endurance, hip flexion and extension endurance, torso lateral flexibility, and low-back flexibility. Strength and endurance were calculated as a function of time in seconds. Goniometric measurements were used to determine flexibility. Significant mean differences were found by using dependent t tests for abdominal strength, erector Spinae endurance, hip extension, and right lateral flexion of the torso. The results validate the necessity for pelvic stabilization and indicate that strength and flexibility deficits vary among populations.

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Kathleen A. Swanik, C. Buz Swanik, Scott M. Lephart and Kellie Huxel

Objective:

To determine whether functional training reduces the incidence of shoulder pain and increases strength in intercollegiate swimmers.

Design:

Pretest–posttest.

Setting:

Laboratory and weight room.

Participants:

26 intercollegiate swimmers (13 men, 13 women).

Intervention:

6-wk functional training program.

Main Outcome Measures:

Incidence of shoulder pain was recorded throughout the study. Isokinetic shoulder strength was assessed before and after training.

Results:

A t test showed significant differences (P < .05) for the incidence of shoulder pain between the experimental (mean episodes = 1.8 ± 2.1) and control (mean episodes = 4.6 ± 4.7) groups. ANOVA with repeated measures revealed no significant strength differences between groups but exhibited significant within-group increases.

Conclusions:

Incorporating functional exercises might reduce incidence of shoulder pain in swimmers. The results also validate the need to modify preventive programs as the demands of the sport change throughout the season.

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Neil E. Fowler and Adrian Lees

The aim of this study was to compare the kinetic and kinematic characteristics of plyometric drop-jump and pendulum exercises. Exercises were filmed (100 Hz) from the sagittal view and manually digitized; the data were smoothed and differentiated using cross-validated quintic splines. Ground reaction force data were sampled using a Kistler force platform sampling at 500 Hz. Differences between movement amplitudes and coordination strategies were assessed using t tests and conjugate cross-correlations. Pendulum exercises involved a greater range of motion at the ankle and knee but less motion at the hip joint than drop-jumps. Although different in absolute terms, the exercises used a similar coordination strategy. Drop-jumps resulted in greater peak vertical ground reaction forces than the pendulum exercises although the latter involved a greater net impulse. The similarity between the movement patterns for the two modes of exercise led to the conclusion that pendulum exercises offer a training stimulus similar to that of drop-jumps.

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Judith A. Rock and Marc V. Jones

Objectives:

To explore the usefulness of counseling skills for 3 athletes undergoing rehabilitation from anterior-cruciate-ligament-reconstruction surgery.

Design:

A series of 3 case studies explored the impact of a counseling-skills intervention over 12 weeks postsurgery. Semistructured interviews were conducted 12 weeks postsurgery for triangulation and social validation of intervention.

Participants:

3 athletes meeting selection criteria, recruited from a hospital waiting list and receiving standardized rehabilitation regime.

Intervention:

Participants each received 6 counseling skills interventions at 2-week intervals.

Main Outcome Measures:

Mood, perceived rehabilitation, pain ratings, social support.

Results:

Triangulation of interview data and outcome measures provided some evidence of the beneficial impact of counseling skills on psychological outcomes. It also indicated that setbacks could present challenges to rehabilitation.

Conclusions:

Counseling skills can enhance psychological well-being of athletes during rehabilitation and be especially important during setbacks.

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Robert Rein, Chris Button, Keith Davids and Jeffery Summers

The present paper proposes a technical analysis method for extracting information about movement patterning in studies of motor control, based on a cluster analysis of movement kinematics. In a tutorial fashion, data from three different experiments are presented to exemplify and validate the technical method. When applied to three different basketball-shooting techniques, the method clearly distinguished between the different patterns. When applied to a cyclical wrist supination-pronation task, the cluster analysis provided the same results as an analysis using the conventional discrete relative phase measure. Finally, when analyzing throwing performance constrained by distance to target, the method grouped movement patterns together according to throwing distance. In conclusion, the proposed technical method provides a valuable tool to improve understanding of coordination and control in different movement models, including multiarticular actions.

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Armin Kibele

Possibilities and limitations in the biomechanical analysis of countermovement jump performance were examined using force plate data. Four male and 4 female sport students participated in the study. Software designed to test jumping performance was used to evaluate recordings from a force plate and to compute net velocity and net displacement measures for the center of gravity. In parallel, a film analysis incorporating Dempster's center of gravity model was used for a comparison. Validity of the computed kinetic measures was evaluated with a general analysis of the major error sources including the data acquisition and numerical computations. Numerical integration procedures were found to be a reasonable tool for calculating net velocity and net displacement parameters for a more detailed analysis of athletic jumping performance. On the other hand, it appeared that Dempster-like center of gravity models can cause errors that disqualify their use as validation criteria for kinetic parameters.

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Hong-Wan Ng, Ee-Chon Teo and QingHang Zhang

Posterior decompressive techniques including one- and two-level laminotomies and laminectomies are often used in treating cervical stenosis. Previously, several in vitro studies were conducted to help us understand the biomechanical changes occurring in the cervical spine after these surgical techniques. However, changes in the intersegmental flexibility under combined flexion-extension remain unclear. In this study, a 3-D nonlinear intact model of the C2–C7 was developed to evaluate the influence of one- and two-level laminotomies and laminectomies on the intersegmental moment rotational responses and internal stresses. The intact model was validated by comparing the predicted responses against experimental data. The validated model was then modified to simulate various surgical techniques for finite element analysis. Results showed that one- and two-level laminectomies increase the C2–C7 rotation motions by about 15% and 20%, respectively. The predicted increase in rotational motions also correlated well with the published data. Furthermore, results indicated that laminectomies would influence the biomechanical responses on both the affected and adjacent motion segments. In contrast, laminotomies have no significant effects on cervical biomechanics. To conduct a one-level laminectomy study, current findings indicate that it takes at least five motion segments to capture the immediate postsurgical biomechanical changes accurately and realistically. Minimally invasive cervical spine surgeries with one- or two-level laminotomies are preferred over one- and two-level laminectomies. Also, there is no consideration as to the efficacy of the two techniques in decompressing the spinal cord or nerve roots, which is the goal of the surgery, but is not examined in this study.