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Biomedical subjects

M Parnianpour

Publications and source records attributed to M Parnianpour.

70 records · Page 4Linked to original sources
PubMed1993

The effects of resistance level on muscle coordination patterns and movement profile during trunk extension.

The objective of this research was to investigate the effects of varying resistance level on patterns of muscle activity and trunk motion during the performance of dynamic trunk extension. Twenty-five female subjects were tested at four resistance levels: nominal resistance, and 30%, 50%, and 70% of maximum isometric extension strength. Peak truncal velocity, acceleration, and deceleration decreased with increased resistance, although no difference existed between the nominal and 30% maximum voluntary contraction (MVC) conditions. Coactivation of abdominal muscles was present at all resistance levels, although it was greater for the nominal resistance condition than the other conditions. The timing of EMG activity of the extensor and abdominal muscles was significantly affected by resistance. The amplitude and time course of peak muscle activity are discussed in terms of the implications for spinal loading.

Abdominal Muscles↗
PubMed1993

Nonlinear response analysis of the human ligamentous lumbar spine in compression. On mechanisms affecting the postural stability.

Basic questions regarding how extreme compressive loads can be tolerated by the spine without experiencing abnormal motions or instabilities remain unresolved. Two finite element models of the human lumbar spine were generated. The detailed model accounted for the three-dimensional irregular geometry, material and geometric nonlinearities, nonhomogeneous fiber-matrix nature of the discs, ligaments, and articulation at the facet joints. The nonlinear stability response of the model was predicted under an axial compression force (200 N to 700 N) applied at the L1 while the S1 was fixed. The effect of the presence of a combined flexion moment and a horizontal support on the response was investigated. Another nonlinear model using rigid bodies interconnected by deformable beam elements was also considered. The computed results under the axial compression loads indicated that the response is highly nonlinear with no bifurcation or limit point (critical load). The unconstrained lumbar spine is most flexible in the sagittal plane (least stiff plane). The existence of the horizontal support and the combined flexion moment significantly increased the load-bearing capacity of the lumbar spine; the lumbar spine resisted the axial compression force of 400 N with minimal displacements. Under axial compression force, the flexion moment tends to restrict the posterior translational movement of the lordotic lumbar spine, whereas the horizontal support constrains the coupled lateral motion. A slight decrease in the lordosis was predicted for the compression load of 400 N. It is postulated that the anterior location of the line of gravity of the upper-body weight is regulated to provide the required combined loads on the lumbar spine so higher compression can be tolerated by the spine at minimal energetic cost. In vivo experimental results support the validity of the model predictions.

Aged↗
PubMed1993

Cross-sectional study of the isokinetic muscle trunk strength among school children.

Our surveys have shown lifetime prevalence of L.BP. over 30% among schoolchildren. The purpose of this study was to evaluate the relationship between back and isokinetic trunk strength, anthropometric parameters, and sports activities. One hundred and seventeen healthy children aged 10-16 years were included. All these volunteers had semi-structured interview, anthropometric and dynamic strength measurements. Lifetime prevalence of back pain was 44.5% and point prevalence was 13%. In this cross-sectional study, anthropometric and strength profiles were significantly related to age and gender. Non specific low back pain was not correlated to trunk muscle strength and/or sports activities.

Adolescent↗
PubMed1993

Isometric maximal and submaximal trunk extension at different flexed positions in standing. Triaxial torque output and EMG.

Thirty-one healthy men were tested for the effects of trunk-flexion positions (0 degrees, 15 degrees, and 35 degrees) in standing on triaxial torques and electromyogram of 10 trunk muscles during voluntary maximal and submaximal isometric trunk extension. At a more flexed position, both erector spinae and latissimus dorsi showed significantly higher RMS-EMG. The abdominal obliques were coactivated only during 100% maximum voluntary exertion at each posture. In all tests, the rectus abdomini were quiet. Mean maximum extension torque increased significantly at 15 degrees and 35 degrees of trunk flexion. The ratio of extension torque over RMS-EMG of the trunk extensor muscles, called the neuromuscular efficiency ratio (NMER), also increased in the more flexed posture. However, NMER has to be interpreted with caution because it is affected both by posture and exertion levels. The effects of posture on the torque generation capability of the trunk question the validity of the current lifting recommendations.

Abdominal Muscles↗
PubMed1991

Effects of spinal flexion and extension exercises on low-back pain and spinal mobility in chronic mechanical low-back pain patients.

It has been estimated that one fourth to one half of all patients treated in physical therapy clinics suffer from low-back pain. The purpose of this study was to compare the effects of spinal flexion (Group I) and extension (Group II) exercises on low-back pain severity and thoracolumbar spinal mobility in chronic mechanical low-back pain patients. Both groups had significantly less low-back pain after treatment (P less than .10). There was no significant difference, however, between the spinal flexion and extension exercises in reduction of low-back pain severity. The results indicated a significant difference between the groups in increasing the sagittal mobility (P less than .10). The results did not indicate any significant difference between and within groups in increasing the coronal and transverse mobility of the thoracolumbar spine. Either the spinal flexion or extension exercises could be used to reduce chronic mechanical low-back pain severity, but the flexion exercises had an advantage in increasing the sagittal mobility within a short period of time.

Adult↗
PubMed1990

The relationship of torque, velocity, and power with constant resistive load during sagittal trunk movement.

Strength and fitness studies have been used to determine the predictability of back pain episodes. Tests have demonstrated that isometric strength displays little prognostic value in the development of low-back pain. Static isometric tests have achieved widespread usage due to the simplicity and safety of protocols, the readily available technology, and the low administrative costs. Dynamic lifting models have, however, predicted significantly higher spinal loads than those derived from static models. The objectives of this study were twofold: to investigate the relationship of the torque, velocity, and power to the resistive load during trunk flexion and extension, and to develop predictive models for these relationships for the subject's performance of the 10th, 50th, and 90th percentile distribution. The results of the study found that the flexion/extension torque had a positive linear correlation with the set resistance; the velocity displayed a negative linear correlation, while power had a quadratic relationship with the resistance.

Adult↗
PubMed1989

Histochemistry and morphology of erector spinae muscle in lumbar disc herniation.

The purpose of this study was to detect any changes in the erector spinae muscles in patients undergoing surgery for lumbar disc herniation (LDH) and to analyze which factors (sex, age, the level and site of disc protrusion, and duration of symptoms) would be related to these changes. The percentage of mean area of the type I fibers was significantly larger in males and in the older age group (P less than 0.05), due to the decreasing size of type IIa and IIb fibers. Patients with LDH have: 1) angulated and selective atrophy of type II fibers with a higher type IIb/IIa ratio; 2) with increasing age and duration of symptoms, more marked atrophy of type II fibers; and 3) other unspecific pathologic changes.

Adult↗
PubMed1989

A database of isoinertial trunk strength tests against three resistance levels in sagittal, frontal, and transverse planes in normal male subjects.

Spatial joint complexes, such as the spine, require multiaxial systems to adequately assess their functional capacity. The B200 Isostation (Isotechnologies, Inc., Carrboro, North Carolina) is a triaxial system that has three hydraulic pumps under control of an IBM-XT. The transducers measure the torque, angular position, and velocity for all axes simultaneously. There is no isoinertial data base available for strength at different resistances in the sagittal, coronal, and transverse planes. A normal data base for dynamic performance against resistances equal to 30%, 50%, and 70% of the maximum isometric strength of trunk muscles in all three planes was established.

Adult↗
PubMed1989

Reproducibility of trunk isoinertial performances in the sagittal, coronal, and transverse planes.

A new triaxial dynamometer to quantify the performance of trunk muscles has been developed, and a study was conducted to determine the best control parameters to use with this triaxial isodynamic mode of testing. Nine male subjects were tested at three resistance levels in the sagittal, coronal, and transverse planes. The purpose was to establish the reproducibility of the performance parameters in each plane at all resistance levels, and to identify those parameters which gave the most reliable information for objective assessment of the low back functional state. Measured torque had the highest reproducibility rate, and the most reliable assessments were obtained at the highest resistance level.

Adult↗
PubMed1988

1988 Volvo award in biomechanics. The triaxial coupling of torque generation of trunk muscles during isometric exertions and the effect of fatiguing isoinertial movements on the motor output and movement patterns.

Previous studies have shown that reduction of precise motor control accompanies local muscular fatigue. The effects of isodynamic fatiguing of flexion and extension trunk movements on the movement patterns and the motor output of the trunk were investigated. Twenty male subjects with no history of low-back pain for the past 6 months volunteered for the study. A triaxial dynamometer was used that simultaneously provided measurement of torque, angular position and velocity of each axis. Resistances were set independently for each axis by an interfaced computer. The subjects performed trunk flexion and extension movement against a sagittal plane resistance equal to 70% of their maximum isometric extension strength in the upright position. The minimum resistances in the coronal and transverse planes were set up at 7 Newton meters. The subjects were asked to perform trunk movement as quickly and as accurately as possible while exerting the maximum efforts until exhaustion. Analysis of variance, the MANOVA procedure with a repeated measure design, was performed among the selected parameters of the first, middle and last three repetition cycles. The selected parameters are the trunk motor output and movement patterns; the total angular excursion, range of motion, maximum and average torque and angular velocity of the trunk. All the selected parameters were significantly reduced in the sagittal plane. Subjects displayed significantly less motor control and greater range of motion in the coronal and transverse planes in performing the primary task of flexion and extension. The reduction in the functional capacity of the primary muscles performing the required task is compensated by secondary muscle groups and the spinal structure is loaded in a more injury prone pattern, as identified by finite element models. In addition it is suggested that the fatigued muscles would be less able to compensate any perturbation in the load or position of the trunk. The repetitive loading results in a weakening of the viscoelastic passive elements of the spineless structure. The loss of ability to protect these weakened passive elements makes the spine susceptible to industrial and recreational injuries.

Adult↗
PubMed1988

Three-dimensional spinal motion measurements. Part 1: A technique for examining posture and functional spinal motion.

This study examines the application of a new noninvasive technology capable of accurately, reproducibly, and reliably measuring spinal motion, in real time, with 3 df. The mean values and SD of range of motion in the lumbar, thoracic, and cervical regions compares favorably with results reported by other authors. Pearson correlations yielded a statistically significant weak inverse relationship between age and range of motion in the sagittal and frontal planes (p less than .02). No correlation between sex, height, or weight and range of motion was found. There was no statistically significant evidence of organized coupling. However, a relationship between rotation and lateral motion in the thoracic region was noted.

Aging↗
PubMed1987

Normal trunk muscle strength and endurance in women and the effect of exercises and electrical stimulation. Part 1: Normal endurance and trunk muscle strength in 101 women.

The lack of trunk muscle strength and endurance has frequently been cited as a suspected factor in the etiology of low-back pain. Several investigators have suggested that asymptomatic patients have stronger trunk muscles than patients with low-back pain. People who are physically fit appear to have a decreased incidence of low-back pain. Increased trunk muscle endurance also have been observed to decrease the incidence of low-back pain. The objective evaluation of the strength and endurance of trunk musculature may, therefore, be significant. Part 1 of this study was designed to develop a reproducible strength-endurance screening procedure and to establish normal isometric-isokinetic trunk muscle strength and endurance parameters for women. This study showed that isometric trunk flexion varied from 19-109 Nm and trunk extension from 38-168 Nm. Peak values for isokinetic trunk flexion at two speeds (30 degrees per second and 60 degrees per second) varied from 17-191 Nm and isokinetic trunk extension from 14-208 Nm. The average endurance time for trunk extensors tested with the Sorensen test was 196 seconds.

Adolescent↗
PubMed1987

Normal trunk muscle strength and endurance in women and the effect of exercises and electrical stimulation. Part 2: Comparative analysis of electrical stimulation and exercises to increase trunk muscle strength and endurance.

Several studies have shown positive correlations between muscle strength, flexibility, and the frequency of low-back pain. Weak trunk musculature and decreased endurance have thereby come to be identified as significant risk factors in the development of occupational back problems. Because it is widely accepted that exercise plays an important role in the conservative treatment and prevention of low-back pain, the goals of most rehabilitative programs involves improving the strength and endurance of the low-back pain patient. Whereas electrical stimulation has been shown to increase the muscle strength of the lower extremities, this effect has not been demonstrated for the trunk muscles. Part 2 is a prospective controlled study designed to document and to compare objectively the effects of electrical stimulation and exercise on trunk muscle strength. A total of 117 healthy women were divided randomly into four groups. Two groups received electrical stimulation with different electrical parameters, one group received exercises, and one group acted as a control group. The results showed that low-frequency electrical stimulation and exercises significantly (P less than .05) increased isokinetic back-muscle strength compared to the control and medium-high-frequency electrical stimulation groups. Both types of electrical stimulation, however, significantly increased (P less than .05) the endurance in the back muscles compared with the control and the exercise groups. This study showed that electrical stimulation may be a valuable treatment in the early care of low-back pain patients in maintaining and increasing strength and endurance of back muscles when a more active exercise program is too painful to perform.

Adolescent↗
PubMedDate not supplied

Generalizability of trunk muscle EMG and spinal forces.

The generalizability of trunk muscle EMG and spinal loading estimates obtained from an EMG-assisted biomechanical model was assessed over three occasions and three repetitions. The greatest sources of variability consisted of the intersubject differences and the interaction between subject and occasion. The ID (reliability coefficient) was less for trunk muscle activity compared with estimates of anteroposterior shear force, compression force, and gain computed from the biomechanical model. In order to obtain an ID of 0.8, we recommend five testing occasions for submaximal EMG measurements and three testing occasions for biomechanical estimates. Reproducible estimates of maximal trunk extensor EMG could not be obtained within five testing occasions and five repetitions. Although many recruitment patterns could cause the same extension torque output, their net effect on internal loading seems to be less variable than the underlying measurements.

Abdominal Muscles↗
PubMedDate not supplied

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

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.

Algorithms↗