Showing papers by "Mohamad Parnianpour published in 2000"

Viscoelastic finite-element analysis of a lumbar motion segment in combined compression and sagittal flexion. Effect of loading rate.

Abstract: Study Design.A study using a validated viscoelastic finite-element model of a L2–L3 motion segment to identify the load sharing among the passive elements at different loading rates.Objective.To enhance understanding concerning the role of the loading rate (i.e., speed of lifting and lowering during

Wavelet and short-time Fourier transform analysis of electromyography for detection of back muscle fatigue

Abstract: Measurement of the time-varying characteristics of the frequency content of trunk muscle electromyography is a method to quantify the amount of fatigue endured by workers during industrial tasks, as well as a tool that may guide the training and rehabilitation of healthy and injured workers. Quantification of the change of signal power within specific frequency ranges may shed greater insight into the fatigue process. Sixteen healthy male subjects performed isometric trunk extension at 70% of their maximum voluntary contraction. Surface electromyography from medial and lateral erector spinae, and latissimus dorsi locations were processed using the short-time Fourier transform (STFT) and wavelet transform. Linear regression quantified the time rate of change of median frequency as well as frequency specific STFT filter and wavelet scale measures. The median frequency from the short-time Fourier transform declined by 22 Hz/min from an initial value of 77 Hz on average. The wavelet and STFT filter measures demonstrated this decline to be caused by a reduction in 209-349 Hz signal power in addition to an increase in 7-88 Hz signal power. A significant reduction in median frequency and significant elevation in 13-22 Hz wavelet signal component was detected in about 90% of the cases, indicating their use for detecting and quantifying fatigue.

Impairment magnification during dynamic trunk motions

Abstract: Study Design. An examination of a group of patients with low back disorder and a group of healthy (asymptomatic) individuals asked to produce trunk motions under sincere and insincere experimental conditions. Trunk motion components were examined to determine which combination of motion components could best distinguish between sincere and insincere efforts. Objective. To determine whether examination of trunk motion components could be used to identify impairment magnification during unresisted repeated bending tasks. Summary of Background Data. Trunk motion measures can be used to assess and “benchmark” the status of the low back. However, these measures typically are clinically useful only if the individual is producing an effort that does not magnify the impairment during the functional evaluation. This study addressed the issue of impairment magnification during the production of free dynamic trunk motion. Methods. The trunk motion characteristics of 100 healthy individuals and 100 patients with chronic low back disorders were documented. All participants were asked to produce the trunk motions in two different types of conditions. In the one experimental condition, they were asked to produce sincere trunk motions. In the other experimental condition they were asked to pretend either that they were experiencing low back pain (the asymptomatic group) or that their pain was worse than it actually was (group with low back pain). Results. A combination of trunk motion measures was able to distinguish well between the conditions. Sensitivity and specificity for the asymptomatic group were 92%, whereas they were 75% for the group with low back pain. Overall, sensitivity and specificity were 81.5% for all the participants combined. Conclusions. These results indicate that motion measures can be used to help assess impairment magnification during functional trunk motion testing. These measures can provide a means by which to scrutinize the quality of quantitative measures indicating the extent of a low back disorder. These objective motion measures also can be used to complement other subjective observational methods for the assessment of impairment.

A well-posed, embedded constraint representation of joint moments from kinesiological measurements

Abstract: Joint moment estimation using the traditional inverse dynamics analysis presents two challenging problems, which limit its reliability. First, the quality of the computed moments depends directly on unreliable estimates of the segment accelerations obtained numerically by differentiating noisy marker measurements. Second, the representation of joint moments from combined video and force plate measurements belongs to a class of ill-posed problems, which does not possess a unique solution. This paper presents a well-posed representation derived from an embedded constraint equation. The proposed method, referred to as the embedded constraint representation (ECR), provides unique moment estimates, which satisfy all measurement constraints and boundary conditions and require fewer acceleration components than the traditional inverse dynamics method. Specifically, for an n-segment open chain planar system, the ECR requires n-3 acceleration components as compared to 3(n-1) components required by the traditional (from ground up) inverse dynamics analysis. Based on a simulated experiment using a simple three-segment model, the precision of the ECR is evaluated at different noise levels and compared to the traditional inverse dynamics technique. At the lowest noise levels, the inverse dynamics method is up to 50 percent more accurate while at the highest noise levels the ECR method is up to 100 percent more accurate. The ECR results over the entire range of noise levels reveals an average improvement on the order 20 percent in estimating the moments distal to the force plate and no significant improvement in estimating moments proximal to the force plate. The new method is particularly advantageous in a combined video, force plate, and accelerometery sensing strategy.

Surface Responses of Maximum Isokinetic Ankle Torque Generation Capability

Abstract: The majority of existing normative torque generation capability (torque capability for short) databases are reported in the form of torque as a function of joint angle. although it is well recognized that torque capability is a function of both the joint angular position and angular velocity. The main objective of this study was to develop the methodology of 3-D dynamic representation of torque capability using the ankle joint as an example. The ankle torque capability of 20 males and females was assessed at 5 levels of ankle joint angular positions and velocities in each direction of plantar and dorsi flexion. The ANOVA results indicated significant main effects of joint angular position, angular velocity, direction, and gender, in addition to the interaction effect of angular position and velocity (p < .003) on the torque capability of the ankle joint. The regression analysis indicated that an individualized quadratic surface response performed significantly belter than the models developed for each gen...

A technique for quantifying the response of seated individuals to dynamic perturbations.

Abstract: A technique is presented for monitoring the seated postural stability and control of human subjects. Estimates are made of the locations of the subject's center of pressure (CP(S)) and projection of the center of mass (CM(NP)) from moment balance equations using measured force and acceleration data. The CP(S) and CM(NP) indices describe the stability of the subject, independent of the chair, even in the presence of perturbations. The measurement system was evaluated for both rigid objects and human subjects situated in a wheelchair undergoing displacement. Estimated CM(NP) was within +/-5 mm of the actual value for static loads. For human subjects, the average correlation coefficient between the estimated CM(NP) signal and that computed from video data was 0.90; however, transient overestimation of displacement was seen during subject acceleration. The technique could help to better assess seated stability in dynamic environments, such as those experienced by wheelchair users in motor vehicles.

Analysis and synthesis of human motion from external measurements

Abstract: The structures observed in humans are being progressively applied to the theoretical approaches developed in robotics. To gain insight to the intricate mechanism of human motion, researchers sometimes use imaging technology to record the trajectories of humans performing various tasks. From these observations, they are able to estimate the forces and moments at each joint by an inverse dynamics computation. This problem is conceptually simple; however, in practice, the inverse solution requires the calculation of higher order derivatives of experimental observations contaminated by noise. The errors due to differentiation results in erroneous joint force and moment calculations. This paper provide a control theoretic framework for analyzing human motion which avoids derivative computations. The method is also suitable for synthesis of stable controllers for robotic and 'biorobic' applications which require tracking a desired reference trajectory under different loading conditions.

Simulation of the Seated Postural Stability of Healthy and Spinal Cord-Injured Subjects Using Optimal Feedback Control Methods.

Abstract: A two-dimensional, biomechanical computer model was developed, using the software package Working Model1M, to simulate the postural control of seated individuals. Both able-bodied and spinal cord-injured subjects were represenied. The model incorporated active control of the upper body through full-state feedback. Specifically, a linear quadratic regulator scheme was implemented in the model. Nonlincaritics were included in the torque computations to mimic physiological constraints and disabiliiy. Interactions between the subject and the wheelchair were also included in the model. Simulation results were compared with those obtained from experiments in which the subjects had attempted to remain stable during the application of significant disturbance moments, similar to lhose experienced during braking in a vehicle. While subjects exhibited more complex control schemes, the model was able to simulate overall stability. Therefore, it is believed that the model could prove beneficial to future rese...

Combined Spinal Motion and Loading in Occupational Low Back Disorders

Abstract: Low back disorders (LBDs) are considered the most prevalent musculoskeletal disorders in occupational settings. There is significant epidemiological and biomechanical evidence that implicates combined motion and loading as important risk factors for LBDs. The purpose of this paper is to demonstrate a potential approach for quantifying 3-D combined motion, loading, and loading rates in ergonomic research. Data from a field study were used to quantify combined; three-dimensional (3-D) trunk velocities of low and high-risk groups, and data from lifting study were used to assess the 3-D combined spinal loading and loading rate. The results showed that evaluating the percent of time the magnitude of 3-D vectors was over defined limits (velocities, loads, or load rates) provides the important temporal aspect of risk factors, which is commonly ignored in LBD risk assessment. The results also showed that loading rate was a sensitive indicator of dynamic loading. In conclusion, the present approach allows the deta...

The effect of pure compression load on spine stabxlity : A test of muscular coactivation theory

Abstract: The purposes of this study were two folds: 1) to monitor the changes in the spinal configuration (its geometry), and to record the EMG activities of ten selected trunk muscles at three levels of hand held compressive loads, and 2) to simulate compressive loading on a three dimensional finite element model of ligamentous spine. A three-dimensional finite element model of the ligamentous spine, developed by Patwardhan et al [18] was used to simulate the spinal response to compressive loads at TL. The hypothesis that the spine is stabilized by coactivation of multi-segmental muscles could not be supported by this study due to the lack of trunk muscle activity and spinal postural changes, contrary to finite element analysis, observed during purely compressive loading. The resalts provide insight to optimal design of exercise programs to strengthen the trunk stabilizers. Exercising with weights close to the body may recruit the deeper stabiling muscles more than activities creating high moments about the lumbar spine that activate the more superficial muscles connecting the pelvic to the spine.