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Biomedical subjects

R Ortengren

Publications and source records attributed to R Ortengren.

At least 19 recordsLinked to original sources
PubMed2001

Endurance, pain and resumption in fully flexed postures.

In this study effects of low loads in fully flexed postures were investigated. Thirteen men who were unused to the postures participated. Thirteen professional construction workers with long experience of suchlike postures were also studied. Pain reactions during and after loading were observed, as well as endurance time and the recovery process, here by studying the resumption time. Endurance and resumption times differed little from those given by models used for more common postures. Pain from the legs and not from the back limited the working ability in 86% of the endurance tests. Thirdly, the construction workers had significantly longer endurance time and shorter resumption time.

Adult↗
PubMed2001

Analysis and comparison of reflex times and electromyograms of cervical muscles under impact loading using surface and fine-wire electroces.

Myoelectric signals [electromyograms (EMGs)] can be collected using either surface or fine-wire electrodes. Application of the latter results in higher-frequency contents of EMG. In the field of impact biomechanics, surface electrodes are more often utilized than fine-wire ones. However, the removal of motion artefacts from EMG recorded under transient loads requires application of high-pass filters with relatively high cutoff frequencies, which may eliminate a significant part of the surface EMG power spectra. Therefore, in the current study, both surface and fine-wire electrodes were utilized to record the EMG of cervical muscles under conditions simulating a rear-end car collision at low speed. The results indicated that application of high-pass filtering at 50 Hz can be necessary to remove motion artefacts from the EMG collected under such conditions. Such filtering resulted in a higher decrease in amplitude of the surface EMG than that of the fine-wire one. However, the reflex times obtained here were not significantly affected by the type of the electrodes utilized to collect EMG.

Artifacts↗
PubMed2000

Endurance time, pain and resumption in passive loading of the elbow joint.

This study investigated reactions in passively loaded, fully extended elbow joints in 13 men. Pain reactions during and after loading were studied, as were endurance time, T(end), and resumption time, Tr. The loading moment on the elbow joint, Mn, varied between 7 and 100% of maximum elbow moment. Discomfort/ pain was estimated with Borg's CR-10 scale. T(end) decreased with increasing load level. The opposite was found for the resumption time: the higher the load, held until T(end), the shorter the Tr. The pain limiting the working capability originated mainly from muscle tissue and not from the joint itself. It is concluded that the relation between load and endurance time for passively loaded, fully extended elbow joints resembles that for muscular loading in more 'normal' postures. Equations for estimation of endurance and resumption times (in minutes) for fully extended joints are proposed: T(end) = 20.6e(-6.04Mn) and Tr = 0.0167e(8.84/(1.46+0.346Mn)), respectively.

Adolescent↗
PubMed1996

Reproducibility and stability of normalized EMG measurements on musculus trapezius.

The reliability of normalized EMGrms (root mean square value of the electromyographic signal) measurements from musculus trapezius were evaluated in a field study. The reproducibility and stability of the method as well as the reproducibility of the results for nine variables were examined. The variables were: static, median and peak values of the ADF (amplitude distribution function) and the total time and number of periods when the muscle's load was below 1, 2 and 5% of MVC (maximum voluntary contraction). Twelve data operators, performing entry work, were measured twice with an interval of a week. Coefficients of repeatability were calculated. The coefficient of repeatability for 5 of the variables showed that 95% of the differences between measurements 1 and 2 for each subject were less than two standard deviations from the group mean. The same was true for the other four variables if the result of one of the twelve measurements was removed. The agreement index, twice the standard deviation of the difference between the two measurements divided by the mean of the two measurements was low only for the static value of the ADF and the number of periods below 5% MVC. Six data operators performing entry work were examined six times at weekly intervals. The stability ratio SDmm/SDv was less than 1 for all variables except for time and number of periods when the muscle's load was below 5% MVC. SDmm is the standard deviation of the difference between minimum and maximum value for each of the subjects for the six measurements. SDv is the average of the standard deviations of the six measurements at each visit. Two groups, each consisting of 24 VDU operators doing similar work were compared using the results from one EMG measurement on the trapezius. No significant differences were found between the groups for any of the nine variables (0.07 < p < 0.87).

Adult↗
PubMed1984

A study of factors influencing muscle activity about the knee joint.

Several factors influencing the myoelectric activity of muscles surrounding the knee joint were studied using fine-wire monopolar electrodes. The muscles studied included the vastus lateralis, vastus intermedius, rectus femoris, vastus medialis, gracilis, sartorius, biceps femoris, semimembranosus, semitendinosus, tensor fasciae latae, medial head of the gastrocnemius, and lateral head of the gastrocnemius. Muscle activity was measured in response to unidirectional loads tending to flex and extend the knee, and to combined loads of flexion-adduction, flexion-abduction, extension-adduction, and extension-abduction. Results indicate that the individual muscle responses are dependent upon the direction, magnitude, and combination of external moments, as well as on the flexion angle of the knee joint. Muscle response appeared to be influenced by certain intrinsic mechanical characteristics of the knee joint that tend to change the moment arms of the muscles as the knee moves. For example, the substantial changes in quadriceps myoelectric activity with knee flexion, with constant load applied, can be related to the movement of the tibial-femoral contact changing the lever arm of the quadriceps mechanism. This study indicates that the mechanics of the knee joint must be taken into consideration while attempting to interpret or predict the load response of muscles crossing the knee joint.

Adult↗
PubMed1984

Electromyography of the paravertebral muscles in idiopathic scoliosis. Measurements of amplitude and spectral changes under load.

The myoelectric activity of the paraspinal muscles was recorded in girls with idiopathic scoliosis and in healthy controls. The muscles of the back were loaded isometrically and the signals recorded at the T8 and L3 levels were analysed as regards amplitude and frequency. A comparatively higher signal amplitude was found on the convex side of the scoliosis curve. This was found to be due to a lower amplitude on the concave side when the scoliosis group was compared to the controls. The amplitude difference was correlated to the degree of scoliosis. A shift in the myoelectric spectrum toward lower frequencies occurred during the loading period. There were no differences in this respect between the sides of the scoliosis, nor were there differences between the scoliosis patients and the controls. Secondary adaptation to the higher load demand by the muscles on the convex side in scoliosis is the most probable explanation for our observations.

Adolescent↗
PubMed1982

Analysis and measurement of lumbar trunk loads in tasks involving bends and twists.

Ten subjects performed isometric weight-holding and force-resisting work tasks while standing upright, both with and without a twist of the trunk; with the trunk bent laterally; and in postures involving combinations of bending and twisting. The lumbar trunk muscle contraction forces and the lumbar spine compression and shear forces imposed by these tasks were predicted using a biomechanical model. Myoelectric activity was recorded quantitatively at eight locations over the back muscles and at four locations over the abdominal wall muscles. Correlation coefficients from 0.67 to 0.88 were found between the predicted muscle contraction forces and the measured myoelectric activities when the predictions were made so as to minimize muscle contraction force per unit area. Trunk twisting and lateral bending were found to load the spine and trunk muscles less than trunk flexion or holding of weights in front of the body.

Adult↗
PubMed1982

Loads on the lumbar spine. Validation of a biomechanical analysis by measurements of intradiscal pressures and myoelectric signals.

UNLABELLED: We studied the validity of predictions of compressive loads on the lumbar spine and contraction forces in lumbar trunk muscles based on a biomechanical model. The predictions were validated by quantitative measurements of myoelectric activities at twelve locations on the trunk and of the pressure in the third lumbar disc. Twenty-five tasks were performed isometrically by four healthy volunteers. The model predicted that the tasks imposed mean compressive loads on the spine of as much as 2400 newtons and required contraction forces of the posterior muscles of the back of as much as 1800 newtons. Intradiscal pressures of as much as 1600 kilopascals were measured. The predicted and measured quantities were well correlated. It appears that the model adequately predicted the compressive loads on the lumbar spine and the tensions in the back muscles. CLINICAL RELEVANCE: Patients with low-back disorders limit their physical activities, which indicates that loading on the spine must be a factor in those disorders. This study shows that the loads imposed on the spine by physical activities need not be measured. They can easily be calculated. This will significantly accelerate biomechanics research on low-back disorders. The calculation techniques that we validated for predicting loads on the spine can be used to calculate the loads on any skeletal structure. Those loads are largely determined not by the externally applied loads, but by the moments of those applied loads and by the moments of the weights of the body segments that the structure must support.

Abdomen↗
PubMed1981

Isolated finger flexion force--a methodological study.

A method is presented for measuring isolated finger flexion force in a transverse volar grip in a standardized manner. Normal values for forty healthy subjects are given. The mean force of the digits varied from 5.9 to 10.6kp, the middle finger being the strongest, followed by the index, ring and little finger. Large individual variations were observed, especially among men. Men were significantly stronger than woman in corresponding digits. The symmetry between the hands, judged by the order of strength of the fingers, was good in both sexes but especially in women. It is suggested that the strength ratio between dominant and non-dominant might be used to assess the recovery of finger flexion force after, for instance, tendon surgery. Although a correlation exists between isolated finger flexion force and vigorimetric values of the hand grip strength, it is of little value in evaluation of an individual patient.

Adult↗
PubMed1979

Vestibulospinal reflex activity in patients with adolescent idiopathic scoliosis. Postural effects during caloric labyrinthine stimulation recorded by stabilometry.

Postural sway has been quantified with stabilometry during caloric labyrinthine stimulation in an erect posture in 49 patients, aged 10--16 years, with adolescent idiopathic scoliosis. Thirty-two healthy children of the same age constituted a control group. The scoliotic patients tended to have an increased postural sway during labyrinthine stimulation on the convex side compared to the effects on the concave side. Significant differences were observed when left and right scoliotic patients were compared with the controls. The results can be explained by an asymmetric sensitivity in the labyrinth or by a dysfunction in the postural control mechanisms at the brain stem level.

Adolescent↗
PubMed1978

Postural equilibrium in adolescent idiopathic scoliosis.

Postural equilibrium has been quantified by stabilometry in 57 patients with adolescent idiopathic scoliosis aged 10-16 years. Treatment was required in 39 cases whereof 18 were placed under observation only. The control group comprised 32 healthy children of the same age. An experimental design was made to vary the degree of difficulty of upright standing in four different test situations. The postural sway was analysed in the sagittal and lateral direction as well as in the area of total sway. The scoliotic patients had a significantly poorer postural control compared with the healthy children in all the tests. The difference was most pronounced in tests in which the proprioceptive functions were most important for maintaining the postural equilibrium. The left convex patients had quantitatively more pronounced reactions than the right convex patients. Patients with small curvatures, i.e., patients placed under observation only, had significantly increased postural sway compared with patients with more severe deformity. This fact, together with findings in patients with double primary curvatures, and the results of the study of brace effects, indirectly indicate the possibility of a postural disequilibrium as a contributory causative factor in adolescent idiopathic scoliosis.

Adolescent↗