Biomedical subjects

M Parnianpour

Publications and source records attributed to M Parnianpour.

At least 55 records · Page 3Linked to original sources

PubMed1997

Spectral and temporal responses of trunk extensor electromyography to an isometric endurance test.

STUDY DESIGN: This study investigated the effect of trunk extensor muscle location on the spectral and temporal electromyographic activity of the muscles during a fatiguing isometric extension of the torso against gravity. OBJECTIVES: To determine the spectral responses of the trunk extensor muscles at more locations than have been studied previously, to determine if fatigue in the knee flexors limits this test, and to quantify the recruitment patterns of the trunk extensor muscles in a group of healthy subjects. SUMMARY OF BACKGROUND DATA: Isometric endurance tests appear to have more value than strength tests in predicting the occurrence of low back pain. Electromyographic activity of trunk extensor muscles during these tests may provide clues to the etiology of neuromuscular-based low back pain. Spectral electromyographic measures appear to be successful discriminators between low back pain patient and normal populations, although which muscles provide the best information is unclear. Likewise, the recruitment patterns of the trunk extensors during fatiguing isometric tasks is not well quantified. METHODS: Ten healthy men performed an isometric trunk endurance test. Surface electromyography was recorded from the erector spinae medially and laterally at vertebral levels of L1 and L3, medially at L5, and from the biceps femoris and gastrocnemius. Spectral parameters were calculated from the Fast Fourier Transform, and temporal parameters were calculated from the root mean square of the raw data. Linear regression was used to determine their responses as a function of time. RESULTS: There was a significant effect of vertebral level and medial-lateral location on the initial median frequency and linear slope of the median frequency regressions. No significant evidence of fatigue in the lower extremities was observed. For most subjects, the temporal response of the surface electromyography was parabolic (concave-down), peaking at 30-50% of the endurance time. CONCLUSION: Establishment of which muscle locations provide the best information and knowledge of the recruitment patterns are essential for the development of clinical diagnostic procedures and rehabilitation protocols.

Adult↗

PubMed1997

Stability of the human spine in neutral postures.

The present study aimed to identify some of the mechanisms affecting spinal compressive load-bearing capacity in neutral postures. Two spinal geometries were employed in the evaluation of the stabilizing mechanisms of the spine in standing neutral postures. Large-displacement finite-element models were used for parametric studies of the effect of load distribution, initial geometry, and pelvic rotation on the compression stability of the spine. The role of muscles in stabilization of the spine was also investigated using a unique muscle model based on kinematic conditions. The model with a realistic load configuration supported the largest compression load. The compressive load-bearing capacity of the passive thoracolumbar spine was found to be significantly enhanced by pelvic rotation and minimal muscular forces. Pelvic rotation and muscle forces were sensitive to the initial positioning of T1 and the spinal curvatures. To sustain the physiological gravity load, the lordotic angle increased as observed in standing postures. These predictions are in good agreement with in vitro and in vivo observations. The load-bearing potential of the ligamentous spine in compression is substantially increased by controlling its deformation modes through minimal exertion of selected muscles and rotation of the pelvis.

Humans↗

PubMed1997

A method for measuring external spinal loads during unconstrained free-dynamic lifting.

Biomechanical lifting models often require the knowledge of the applied trunk moments and forces for model validation purposes and/or to determine loading levels experienced at various joints of the body. Trunk kinetic data under dynamic exertions are commonly difficult to attain without restrictive anatomic/anthropometric assumptions and cost or constraining body motion. The main objectives of the study were to present a new technique for determining continuous three-dimensional forces and moments about the L5/S1 spinal joint, and to validate the technique and assess its applicability under lifting situations. A combination of a force plate and two electrogoniometers facilitated the determination of trunk kinetics about L5/S1. An apparatus was devised to allow the application of various actual moments that were compared to their corresponding predicted moments. The results showed that, over all the conditions considered, the average percent error in estimating the actual applied moment(s) was about 4% (2.3 S.D.), with a test-retest reliability approaching unity. Given such agreement, along with the relative ease and directness of the method, it is believed that this approach should be applicable under most lifting conditions. The technique offers a fairly accurate measure of trunk moments without the need for constraining the motion of any body joint.

Biomechanical Phenomena↗

PubMed1997

The effect of fatigue on multijoint kinematics, coordination, and postural stability during a repetitive lifting test.

Because of the inability of strength tests to accurately discriminate between low back pain patients and healthy subjects, a multifactorial evaluation of low back pain patients is warranted. It is postulated that measurements of endurance, kinematics, postural stability, and coordination, in addition to strength, are necessary to fully document the patients' functional capabilities. This research study was conducted in order to understand the effects of fatigue on the above factors. Twelve healthy male subjects performed a repetitive lifting test in which a submaximal load was lifted at a maximal rate. Knee, hip, and trunk motion was measured using videography and electrogoniometry, postural stability was measured using a forceplate, and coordination parameters were determined using phase-plane analysis. Fatigue was documented by a 31% reduction in lifting power. At the end of the endurance test, there was less knee and hip range of motion and greater spine peak flexion, while the coordination measures demonstrated that there was greater hip and lumbar spine extension earlier in the lifting phase. The postural stability declined as the test endured. Utilization of these measures may guide physical therapists in their rehabilitation of low back pain patients.

Adult↗

PubMed1997

Neuromuscular trunk performance and spinal loading during a fatiguing isometric trunk extension with varying torque requirements.

A novel testing protocol was used to investigate changes in neuromuscular performance, muscle recruitment, and spinal loading as subjects became fatigued while performing an isometric endurance test of varying torque requirements. There was decreased accuracy in maintenance of a reference torque but no change in response time as subjects became fatigued. The study of trunk-muscle recruitment indicated significant increases in internal oblique and latissimus dorsi muscle activity. This change in recruitment led to changes in spinal loading despite a relatively constant torque output. The use of an electromyogram (EMG)-assisted model demonstrated that when subjects are expected to become fatigued during test performance, the assumption of a constant maximal stress capacity of the muscle may not be robust.

Adult↗

PubMed1997

Modeling of functional trunk muscle performance: interfacing ergonomics and spine rehabilitation in response to the ADA.

The combination of increasing costs of musculoskeletal injuries and the implementation of the Americans with Disabilities Act (ADA) has created the need for a more objective functional understanding of dynamic trunk performance. In this study, trunk extensor and flexor strengths were measured as a function of angular position and velocity for 20 subjects performing maximum isometric and isokinetic exertions. Results indicate that trunk strength is significantly influenced by trunk angular position, trunk angular velocity, gender, and direction, as well as by the interaction between trunk angular position and velocity. Three-dimensional surfaces of trunk strength in response to trunk angular position and velocity were constructed for each subject per direction. Such data presentation is more accurate and gives better insight about the strength profile of an individual than does the traditional use of a single strength value. The joint strength capacity profiles may be combined with joint torque requirements from a manual material handling task, such as a lifting task, to compute the dynamic utilization ratio for the trunk muscles. This ratio can be used as a unified measure of both task demand and functional capacity to guide job assignment, return to work, and prognosis during the rehabilitation processes. Furthermore, the strength regressions developed in this study would provide dynamic strength limits that can be used as functional constraints in the computer simulation of physical activities, such as lifting. In light of the ADA, this would be of great value in predicting the consequences of task modifications and/or workstation alterations without subjecting an injured worker or an individual with a disability to unnecessary testing.

Adult↗

PubMed1997

Feature extraction and modeling of the variability of performance in terms of biomechanical motion patterns during MMH tasks.

In investigating manual material handling (MMH) jobs, such as lifting, the quantification of the various kinematic and kinetic parameters of the lift is an important step towards functional assessment and evaluation. Experimental data collection generates a large quantity of data for the different kinetic, kinematic, and electromyographic parameters over the various lifting cycles. In order to efficiently manage and interpret the data, it is important to use appropriate tools which would reduce the dimension of the original data set without sacrificing any important features. Furthermore, the generated parameters are often expressed as a function of the lifting cycle resulting in complex waveforms as the unit of analysis. Appropriate statistical analysis of these waveforms or motion profiles should reflect their vectorial constitution as a function of the lifting cycle rather than the usual method of using traditional descriptive statistics based on collapsing the data over the cycle.

Adult↗

PubMed1997

Using CAI to accommodate a variety of learning styles in a biomechanics course.

Multimedia technology offers a more interactive approach to instruction than the traditional classroom lectures. Through computer-aided instruction (CAI), a number of teaching styles can be used that take into account the different preferences of the students. The Biomechanics Tutorial program that the authors have written is a CAI that incorporates audio, video, simulations, and graphics to: review concepts of mechanics (kinematics and kinetics of interconnected rigid bodies), familiarize students with functional anatomy, and allow students to interactively evaluate the law of mechanics applied to physical performance of activities modeled by a set of biomechanical models of the joints. Principles of ergonomics are reinforced by enabling the student to perform numerous numerical experiments within the context of workplace or task redesign and see the real time consequences of these alterations. For example, the task of holding a load is simulated by allowing the student to change elbow and shoulder angles and the orientation and magnitude of the load. The consequences of these in terms of required muscle forces and joint reaction forces at the elbow and shoulder will be updated on the screen. The detailed rationale of developing this Biomechanics Tutorial which integrates a variety of learning styles will be presented.

Biomechanical Phenomena↗

PubMed1997

Wavelet analysis of electromyography for back muscle fatigue detection during dynamic constant-torque exertions.

The fatigue of the back muscles appears to be strongly implicated as a risk factor for acquisition of low back pain, which is one of the leading ills of our industrial society. Previously, researchers have successfully measured the level of muscular fatigue by using the Fourier transform to analyze the frequency content of the electromyogram (EMG). However, due to the requirement that the EMG signal be stationary, the Fourier transform is suitable only for the analysis of static muscle exertions in which the muscle is held at constant length and tension. Because the majority of industrial work tasks are not static in nature, new methods for quantifying fatigue during dynamic work are needed. The wavelet transform is a novel, although mathematically well developed, technique for analyzing non-stationary signals that has only recently been applied to the study of EMG. Consequently, the main objective of this project is to develop techniques, using the wavelet transform, for the quantification of back muscle fatigue during dynamic repetitive working conditions.

Back Pain↗

PubMed1997

Effect of aging on human postural control during cognitive tasks.

The purpose of this study was to investigate the effect of aging on human postural control during cognitive tasks. Forty-eight subjects between the ages of 20 to 60 years underwent a series of balance tests that placed increasingly more demand on sensorimotor and cognitive mechanisms. Balance tests were based on a dynamic posturography device called EquiTest. The standard clinical protocol consisted of assessing the subject's stability in six different sensory conditions as the inputs from the proprioceptive and visual systems were altered in a systematic manner. The subjects were also tested with the head extended backwards. This represents an additional sensory condition in which the input from the vestibular system is modified. In order to investigate the role of cognitive function on the postural control mechanisms, the balance tests were performed either with or without an attention-demanding task. The test sequence was randomized to account for simple order effects. The relative contribution and interaction of sensory modification, cognitive tasking, and age were assessed. The results showed that head extension significantly increased postural sway in sensory conditions in which the proprioceptive input was altered. The effects of cognitive tasking and age group assignment were only approaching significance.

Adult↗

PubMed1997

Validation of electrolytic-liquid tilt sensors for human motion measurement.

The development of inexpensive, low-weight, no-invasive sensors that can be used to accurately measure human motion is important for the evaluation of biomechanical risk during a variety of industrial work activities. Electrolytic liquid tilt sensors that measure the angular position of an object relative to the gravitational force vector may provide a valuable means for assessing the postural demand of work tasks. For example, the biomechanical cost to the low back could be assessed during manual material handling activities, or the demand to the shoulders could be evaluated during overhead construction work. Tilt sensors were tested during static and dynamic activities, using isovelocity and isoacceleration dynamometers to move the sensor. The output voltage of the sensors was found to be linearly proportional to the angular deviation of the dynamometer within an 150 degree range (r > 0.99). During constant angular velocity and constant angular acceleration movements, the correlation between the output of the dynamometer and sensor was high and linearly dependent on angular position. Hence, the sensors are capable of accurate motion measurement during static and controlled dynamic movements. Because of the inertia of the liquid within the sensor, its output during sudden acceleration/deceleration may cause some artifact which requires more extensive investigation.

Biomechanical Phenomena↗

PubMed1996

Quantitative assessment of the control capability of the trunk muscles during oscillatory bending motion under a new experimental protocol.

OBJECTIVE: A new quantitative technique for measuring the trunk control capability/coordination was to be developed in this study. DESIGN: Fitts' experimental paradigm was employed to quantify the information processing capacity (bits/s) of the trunk as well as dynamic motor performance such as velocity and acceleration during flexion and extension. BACKGROUND: The quantification of functional capability of the trunk such as range of motion, strength, and endurance have been used to evaluate low back pain patient. Especially, dynamic trunk motion during flexion and extension has been studied not only to quantify the severity of the low-back impairment but to classify patients. METHOD: A lumbar motion monitor was used to record the time series of range of motion (RoM) and compute the velocity and acceleration of the trunk motion. Twenty male subjects without any back pain in the past 6 months and previous history of back injury participated. Each subject performed 22 controlled flexion/extension at predetermined RoMs as well as one ballistic trunk flexion/extension at a self-selected RoM. RESULTS: The information processing capacity of the trunk among healthy subjects was found to have a mean of 4.23 (SD 1.43) bits/s based on Fitts' law. Also, the velocity of dynamic trunk motion was measured with a considerable reduction in intersubject variability when the RoMs were controlled. A short but still accurate experimental protocol was suggested via a series of statistical analyses to provide an objective and easy-to-use method to evaluate the functional capacity of low-back pain patients.

Journal Article↗

PubMed1996

Clinical applications of power spectral analysis of electromyographic investigations in muscle function.

Electromyographic (EMG) power spectral analysis of the electrical signals produced by a contracting muscle is emerging as a useful clinical tool. It has the potential to measure objectively the fatigue rate of individual muscles during an exertion. This technical note gives a simple introduction to the spectral changes of the EMG signals during fatigue. It outlines the technical aspects of EMG investigations including the data collection, signal analysis and its interpretation. The clinical applications, its present limitations and future applications are also given. The correct use and interpretation of the power spectral analysis in the clinical environment is important for its further development as a clinical measurement.

Journal Article↗

PubMed1996

Trunk kinematics of one-handed lifting, and the effects of asymmetry and load weight.

This study investigated trunk kinematic differences between lifts performed using either one hand (unsupported) or two hands. These effects were studied while beginning the lifts from different asymmetric starting positions and while lifting different load weights. Each subject lifted a box from a lower to an upper platform under one- and two-handed lifting conditions. Subjects wore a lumbar spine electrogoniometer, from which relative motion components were calculated in the trunk's three cardinal planes. Results of this study showed that one-handed lifting resulted in significantly higher ranges of motion in the lateral and transverse planes and greater flexion in the sagittal plane. Back motion characteristics previously found to be associated with low back disorders were all significantly higher for one-handed lifts. The two-handed lift technique, on the other hand, produced overall faster trunk motions in the sagittal plane and equal or larger acceleration and deceleration magnitudes in all planes of motion. Increases in load asymmetry affected trunk kinematics, in that magnitude values for range of motion, velocity and acceleration became much greater with increasingly asymmetric load positions. Increasing the load weight appeared to have less of an effect on trunk kinematics, with increases in position mostly occurring during sagittal and lateral bending. These results suggest that unsupported one-handed lifting loads the spine more than two-handed lifts, due to the added coupling. Applying these results to a previously developed model, one-handed lifting was also found to increase one's risk of suffering a low back disorder.

Adult↗

PubMed1996

Stabilizing role of moments and pelvic rotation on the human spine in compression.

The mechanisms by which the human spinal column in neutral postures can resist relatively large axial compression forces with no abnormal motions or instabilities remain yet unknown. A nonlinear finite element study of the ligamentous thoracolumbar spine was performed to investigate the stabilizing role of two plausible mechanisms of combined moments and pelvic rotation on the human spine in axial compression. The passive system, by itself was able to carry only a negligible fraction of physiological compression loads without exhibiting large motions. The unconstrained spine was most flexible in the sagittal plane (least stiff plane). The existence of combined moments and pelvic rotation significantly increased the load-bearing capacity of the spine so that the free standing passive thoracolumbar spine resisted the axial compression forces of more than 1000 N with minimal displacements. The former mechanism is much more effective in stabilizing the spine in compression than is the latter one. It is postulated that the pelvic rotation and the off-centered anterior placement of the gravity force are exploited to partially stabilize the passive spine in compression and relieve the musculature. Previous and on- going studies support the validity of the proposed mechanisms.

Humans↗

PubMed1996

Role of posture in mechanics of the lumbar spine in compression.

Biomechanics of the entire lumbar spine L1-S1 in erect postures was investigated under physiological axial compression loads of up to 800 N with and without right axial torques of up to 10 Nm using a nonlinear finite-element model. The sagittal curvature is varied from an initial value of 46 degrees by +15 degrees to model more lordotic posture and by -7.5 degrees as well as -15 degrees to model flattened lumbar spines. The primary/coupled displacements, disc pressures, ligament forces, facet forces, disc fiber strains, along with the required stabilizing sagittal/lateral moments, are computed at different levels, loadings, and lordotic postures. The role of facetectomy and partial nucleotomy at some levels is also studied for a few cases. The primary/coupled motions, disc pressures, facet loads, and disc fiber strains are all affected by postural changes and the addition of 10-Nm axial torque. The primary responses are stiffened when axial compression and axial torque are applied together rather than separately. Flexion and left lateral moments are required to stabilize the lumbar spine in compression. The changes in lordosis markedly affect the stabilizing sagittal moments. The lateral moments, however, are significantly influenced only in the presence of axial torque. Axial compression generates small disc fibers that decrease from the innermost layer to outer ones at all disc levels. The contact forces are largest at the L5-S1 facets. These forces cause large differences in rotation between L5 anterior and posterior bony structures, suggesting the high stresses on corresponding pedicles and pars interarticularis. Finally, the stabilizing flexion moments are generated primarily by the off-centeredness of the gravity load. Relatively small muscle forces are required to balance the remaining portion.

Aged↗

PubMed1995

The classification of anatomic- and symptom-based low back disorders using motion measure models.

STUDY DESIGN: This study observed the trunk angular motion features of healthy subjects and those experiencing chronic low back disorders as they flexed and extended their trunks in five symmetric and asymmetric planes of motion. Trunk angular position, velocity, and acceleration were evaluated during several cycles of motion. OBJECTIVE: The trunk angular motion features of the low back disorder group were normalized relative to the healthy subjects and used to 1) evaluate the repeatability and reliability of trunk motion as a measure of trunk musculoskeletal status, 2) quantify the extent of the disorder, 3) determine the extent to which trunk motion measures might be used as quantifiable means to help classify low back disorders. SUMMARY OF BACKGROUND DATA: Given the magnitude of the low back disorder problem, it is problematic that there are few quantitative methods for objectively documenting the extent of a disorder. Impairment ratings of low back disorders can vary by as much as 70% using current systems. Diagnoses and classification schemes are rarely based upon quantitative indicators and we are unable to easily assess and diagnose low back disorders. It is important to quantitatively evaluate low back disorders so that proper treatment can be administered and the risk of exacerbating the problem can be minimized. METHODS: Three-hundred-thirty-nine men and women between 20 and 70 years old who had not experienced significant back pain were recruited as the healthy subjects in this study. One hundred-seventy-one patients with various chronic low back disorders also were recruited and compared with the healthy group of subjects. All subjects wore a triaxial goniometer on their trunks that documented the angular position, velocity, and acceleration of the trunk as the subjects flexed and extended their trunks in each of five planes of motion. Trunk motion features first were normalized for subject gender and age. Several two-stage eight-variable models that account for trunk motion interactions were developed to classify the 510 healthy and low back injured subjects into one of 10 anatomic and symptom-based low back disorder classification categories. RESULTS: Using conservative cross-validation measures, it was found that the stage one eight-variable model could correctly classify more than 94% of the subjects as either healthy or having a low back disorder. One of the stage two eight-variable models was able to reasonably classify the patients with low back disorders into one of 10 low back disorder classification groups. CONCLUSION: The motion-related parameters may relate to biomechanical or learned sensitivities to spinal loading. This study suggests that higher-order trunk motion characteristics hold great promise as a quantitative indicator of the trunk's musculoskeletal status and may be used as a measure of the extent of a disorder and as a measure of rehabilitative progress. Furthermore, once the interactive nature of these trunk motion characteristics is considered, the model could help diagnose low back disorders. However, independent data sets are needed to validate these findings.

Adult↗

PubMed1995

Effects of various isoresistive training programmes on trunk muscle performance.

Isoresistive movements provide a functional method of testing muscle performance and of providing exercise; the resistance applied is usually a percentage of the maximal isometric torque which can be developed by individual subjects. The aim of the current study was to compare the effectiveness of dynamic isoresistive exercise programmes using 25, 50 or 75% of the maximum isometric flexion torque and static isometric exercises for improving the performance of the trunk flexors and extensors. Subjects comprised 42 asymptomatic females aged 18-25 years who were randomly assigned to control or exercise groups. The exercise groups undertook 2 min of exercise 3 times per week. The control subjects showed significant improvement between tests indicating a strong learning effect. The study showed that the subjects who exercised at 50% of maximum flexion isometric torque achieved the greatest increases in muscle performance on most measures. maximal isometric flexion and extension torques did not significantly change in any of the groups. Flexion and extension velocity and power were the muscle performance characteristics which improved the most in response to the training programmes. RELEVANCE:--This paper attempts to determine which among several options is the most effective isoresistive protocol for conditioning trunk muscle performance, as improved strength and power of these muscles may contribute in preventing episodes of LBP.

Journal Article↗