Postural control during lifting.

Any voluntary motion of the body causes an internal perturbation of balance. Load transfer during manual material handling may increase these perturbations. This study investigates effects of stance condition on postural control during lifting. Nineteen healthy subjects repeatedly lifted and lowered a load between a desk and a shelf. The base of support was varied between parallel and step stance. Ground reaction force and segmental kinematics were measured. Load transfer during lifting perturbed balance. In parallel stance postural response consisted of axial movements in the sagittal plane. Such strategy was accompanied by increased posterior shear forces after lift-off. Lifting in step stance provided extended support in anterior/posterior direction. The postural control mechanisms in the sagittal plane are less complex as compared to parallel stance. However, lifting in step stance was asymmetrical and thus accompanied by distinct lateral transfer of the body. Lateral shear forces were larger as compared to parallel stance. Both lifting techniques exhibit positive and negative aspects. We cannot recommend either one as being better in terms of postural control.

The pain of being borderline: dysphoric states specific to borderline personality disorder.

The objective of this study was to identify the dysphoric states that best characterize patients meeting criteria for borderline personality disorder and distinguish them from those in patients with other forms of personality disorder. One hundred forty-six patients with criteria-defined borderline personality disorder and 34 Axis II controls filled out the Dysphoric Affect Scale, a 50-item self-report measure that was designed for this purpose and has good internal consistency and test-retest reliability. Twenty-five dysphoric states (mostly affects) were found to be significantly more common among borderline patients than controls but nonspecific to borderline personality disorder. Twenty-five other dysphoric states (mostly cognitions) were found to be both significantly more common among borderline patients than controls and highly specific to borderline personality disorder. These states tended to fall into one of four clusters: (1) extreme feelings, (2) destructiveness or self-destructiveness, (3) fragmentation or "identitylessness," and (4) victimization. In addition, three of the 25 more-specific states (feeling betrayed, like hurting myself, and completely out of control), when occurring together, were particularly strongly associated with the borderline diagnosis. Equally important, overall mean Dysphoric Affect Scale scores correctly distinguished borderline personality disorder from other personality disorders in 84% of the subjects. Taken together, the results of this study suggest that the subjective pain of borderline patients may be both more pervasive and more multifaceted than previously recognized, and that the overall "amplitude" of this pain may be a particularly good marker for the borderline diagnosis.

Electrically evoked myoelectric signals.

Electrical stimulation of the nervous system is attracting increasing attention because of the possibilities it offers for physiological investigations, clinical diagnosis, muscle function assessment, noninvasive muscle characterization, and functional control of paralyzed extremities. Parameters of the myoelectric signal evoked by surface stimulation of a muscle motor point or by stimulation of a nerve trunk by means of implanted electrodes provide information about muscle performance and properties if the stimulation artifact is properly removed or suppressed. Comparison of these parameters with those obtained during voluntary contractions provides additional insight into muscle physiology. The relationships between myoelectric signal amplitude parameters, spectral parameters, and conduction velocity are discussed with special reference to muscle fatigue. This review focuses on a few methodological aspects concerning electrical stimulation of the peripheral nervous system, detection, and processing of the electrically evoked myoelectric signals in skeletal muscles. The state of the art of the following issues is discussed: (1) properties of voluntary and electrically evoked myoelectric signals; (2) techniques for evoking and detecting myoelectric signals; (3) techniques for suppression of stimulation artifacts; (4) effect of stimulation waveforms and electrode properties; (5) signal processing techniques for electrically evoked myoelectric signals; (6) physiological significance of myoelectric signal variables; (7) order of recruitment of motor units during electrical stimulation; (8) myoelectric manifestations of fatigue in electrically stimulated muscles; (9) assessment of crosstalk by electrical stimulation; and (10) applications in sport, rehabilitation, and geriatric medicine.

Comparison of spinal mobility and isometric trunk extensor forces with electromyographic spectral analysis in identifying low back pain.

This study compared conventional clinical measurements with electromyographic (EMG) spectral measurements for identification of individuals with low back pain (LBP). Twenty freshman sweep rowers were subjects for this study. Range-of-motion (ROM) measurements were taken for forward bending (FB), backward bending (BB) (double inclinometers), lateral bending (LB) (tape measure), and rotation (double-arm goniometer). Intratester reliability for ROM was also assessed. The Back Analysis System was used to determine static trunk extensor strength (ie, maximal voluntary contraction [MVC]) and to compute EMG spectral parameters from a paraspinal multi-electrode array. A two-group stepwise discriminant-analysis procedure for the ROM and MVC variables correctly identified 57% of the rowers with LBP and 63% of the rowers without LBP. A similar discriminant-analysis procedure for EMG spectral parameters correctly identified either 88% of the rowers with LBP and 100% of the rowers without LBP or 100% of the rowers with LBP and 88% of the rowers with LBP, depending on whether EMG measurements of recovery were calculated at 1 minute or at 2 minutes into the recovery period. Sensitivity (66%) and specificity (71%) results from the more traditional tests suggest that these techniques may be of limited usefulness for LBP screening or diagnosis.

Standardized evaluation of techniques for measuring the spectral compression of the myoelectric signal.

A digital algorithm was designed to produce band-limited noise with adjustable median frequency and amplitude. This algorithm produces test signals with spectral characteristics typical of those of the surface myoelectric signals encountered in muscle fatigue studies. These synthesized signals provide the basis for standardized evaluation of the performance of various techniques which monitor the spectral compression of the myoelectric signal during muscle fatigue.