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Jinsung Wang and George E. Stelmach

Smeets and Brenner propose a model that attempts to account for the action patterns involved in prehensile behaviors. However, the model does not provide a full account of the available data on temporal and spatial relationships between the transport and grasp components. Predictions from the model in its current form appear to correspond only to experimental results in a very general way.

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Anthony J. Lisi, Conor W. O’Neill, Derek P. Lindsey, Robert Cooperstein, Elaine Cooperstein and James F. Zucherman

This paper presents the first reported measurements of lumbar intervertebral disc pressure in vivo during spinal manipulation. A pressure transducer was inserted into the nucleus pulposus of one normal-appearing lumbar disc in an asymptomatic adult volunteer. Pressures were recorded during several body positions and maneuvers, then during spinal manipulation, and lastly during a repetition of the preintervention body positions. Baseline pressures in the prone and side-lying positions measured 110 kPa and 150 kPa, respectively. During the manipulation, pressure rose to a peak of 890 kPa over 250 ms. Immediately following, pressures in the prone and side-lying positions measured 150 kPa and 165 kPa, respectively. These data do not support the hypotheses that manipulation can reduce a herniation by decreasing intradiscal pressure, or cause a herniation by raising pressure to failure levels. Further work may lead to a better understanding of this treatment method.

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Kyriaki Kaplanidou

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Alex V. Nowicky, Alison H. McGregor and Nick J. Davey

We used transcranial magnetic stimulation (TMS) to study corticospinal excitability to erector Spinae (ES) muscles during graded voluntary contractions in bilateral trunk extension (BTE) and forced expiratory breath holding (FEBH) in normal individuals. Motor evoked potentials (MEPs) could be produced in all subjects in the absence of voluntary activation. At maximum voluntary contraction, levels of surface electromyographic (EMG) activity were 4 times greater during BTE than FEBH. When EMG was normalized to maximum. MEP amplitudes increased in proportion to contraction in both tasks. MEPs in FEBH were compared with extrapolated values at similar EMG levels in BTE and were found to be larger. EMG and MEPs in left and right ES were symmetrical throughout the range of contractions in both tasks. ES muscles have a facilitation pattern similar to that previously shown in leg muscles, but subtle differences at low levels of EMG suggest that the facilitation is dependent on the task.

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Richard E.A. van Emmerik and Erwin E.H. van Wegen

Current research in biology and physiology has unequivocally demonstrated the significance of variability for the optimal functioning of healthy and adaptable systems. Different pathologies are characterized by reductions in complexity of organization, often signified by loss of variability and adaptability. It is argued that the traditional perspective on biology in general and movement science in particular that tended to associate noise and variability with performance decrements and pathology is no longer tenable. Tools and methodologies that have emerged from the dynamical systems perspective to coordination and control are discussed in the context of postural control and transitions in interlimb coordination and locomotion. First, it is shown that variability can play a functional role in the detection and exploration of stability boundaries during balance control. Second, pattern transitions are characterized by increased variability in movement coordination dynamics. Under conditions of movement pathologies, such as in Parkinson’s disease, reductions in variability in coordination dynamics clearly identify movement coordination and transition problems so characteristic for these patients. It is concluded that the relation between variability and stability is complex and that variability cannot be equated with instability without knowledge of the underlying movement dynamics.

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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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Fink Philip

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Oleg Verbitsky, Joseph Mizrahi, Arkady Voloshin, July Treiger and Eli Isakov

The goal of this research was to analyze the effects of fatigue on the shock waves generated by foot strike. Twenty-two subjects were instrumented with an externally attached, lightweight accelerometer placed over the tibial tuberosity. The subjects ran on a treadmill for 30 min at a speed near their anaerobic threshold. Fatigue was established when the end-tidal CO2 pressure decreased. The results indicated that approximately half of the subjects reached the fatigue state toward the end of the test. Whenever fatigue occurred, the peak acceleration was found to increase. It was thus concluded that there is a clear association between fatigue and increased heel strike–induced shock waves. These results have a significant implication for the etiology of running injuries, since shock wave attenuation has been previously reported to play an important role in preventing such injuries.