Showing papers by "Mohamad Parnianpour published in 1997"

The Effect of Fatigue on Multijoint Kinematics, Coordination, and Postural Stability During a Repetitive Lifting Test

Abstract: 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.

The effect of fatigue on multijoint kinematics and load sharing during a repetitive lifting test.

Abstract: Study design A repetitive lifting test in the sagittal plane was performed with a submaximal load at a maximal lifting rate to understand the effects of fatigue on kinematic and kinetic measures of performance. Objectives To quantify the effect of fatigue during a highly repetitive lifting task, in terms of lifting force transmitted to the load, joint motion patterns, and internal joint load sharing. Summary of background data Industrial surveillance and epidemiologic data suggest that repetitive lifting is a risk factor for low back pain. Previous studies examining the effect of fatigue have either been constrained to isolated trunk movement, or have not explored the internal load distribution and potential alteration in the loading patterns. Methods Sixteen healthy male subjects performed repetitive lifting in the sagittal plane with a load equal to 25% of their maximal lifting capacity, at a maximal lifting rate. Changes in lifting performance were determined from the power transferred to the box, joint kinematics, and joint kinetics. Data from three cycles at the start and end of the exercise were tested for the effect of fatigue using repeated-measures analysis of variance. Results Fatigue was documented by a reduction in average lifting force and hip and spine torque generation, whereas internal joint load sharing was relatively unchanged. The fatigue was associated with decreased knee and hip motion, and increased lumbar flexion. Decreased postural stability also was evident. Conclusions The significant decrease in postural stability and force generation capability because of the repetitive lifting task indicated a higher risk of injury in the presence of unexpected perturbation. Multijoint coordinated lifting tasks provide a more realistic protocol to study neuromuscular fatigue.

Stability of the human spine in neutral postures

Abstract: 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.

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

Abstract: 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.

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

Abstract: 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.

The effect of variations in trunk models in predicting muscle strength and spinal loading

Abstract: A unified modeling technique is proposed to predict the strength contour of trunk muscles during isometric exertions, which can identify the feasibility of task performance and quantify the utilization ratio for assessment of risk of development of muscular fatigue and over-exertion injury. In addition, the proposed model can estimate the joint reaction forces during performance of the feasible complex loading task in upright standing. Six anatomical models and six cost functions suggested by various research groups were considered in determining their effects on the predicted three-dimensional strength and lumbar intervertebral joint reaction forces obtained using linear and nonlinear optimizations. The present investigation has shown the importance of the fidelity of anatomical models used in estimation of spinal loading and trunk strength. The effect of cost functions on estimated compression and anterior-posterior shear forces was statistically significant. These models can assist in identifying the injurious tasks that must be ergonomically modified to prevent the risk of occupationally related low back injuries.

Effect of aging on human postural control during cognitive tasks.

Abstract: 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.

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

Abstract: 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.

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

Abstract: 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.

The effect of complex dynamic lifting and lowering characteristics on trunk muscles recruitment

Abstract: A better understanding of how the neuromuscular spinal system behaves during lifting and lowering could provide more insight about potential causes of occupational low back disorders (LBDs), and could help in the prevention and rehabilitation process of these disorders. The purpose of this study was to quantify trunk muscle activities under various whole-body free-dynamic symmetric and asymmetric complex lifting and lowering tasks. Eleven male subjects with no prior history of LBDs participated in the study. Electromyographic activities of ten trunk muscles were monitored while subjects either symmetrically or asymmetrically lifted and lowered a box under three different speeds and three weights. The results showed that all ten muscles were responsive to various experimental conditions with the erector spinae and internal oblique muscles showing the greatest response. Substantial electromyographic activities were observed in muscles that were on the contralateral side of the load. Lowering conditions yielded consistently lower muscular activities than their corresponding lifting conditions. These results show that it is essential to consider multiple trunk muscles in modeling efforts of quantifying spinal loading, as well as for back rehabilitation research purposes.

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

Abstract: 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.

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

Abstract: 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.

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

Abstract: 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. Language: en

Development Of A Cai For Use In An Industrial Biomechanics And Ergonomics Course

Abstract: 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, 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 handle 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, development stages, and key examples of the tutorial will be presented.