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Biomedical subjects

R Ortengren

Publications and source records attributed to R Ortengren.

At least 19 recordsLinked to original sources
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↗
PubMed1977

Quantitative electromyographic studies of back muscle activity relatated to posture and loading.

The myoelectric activity of some of the posterior muscles of the back was studied quantitatively using signal amplitude estimation and power spectrum analysis. Surface electrodes were placed on both sides of the trunk at T4, T8, L1, L3, and L5 levels. Four different angles of forward flexion were studied during external loading of the spine with 200 N. At 30 degrees of forward flexion studies were made when the load was increased from 0 to 300 N. Asymmetric loading was studied with the trunk erect, in lateral flexion, and in rotation. The myoelectric activity increased when the angle of flexion increased and when the external load was increaed at a fixed angle of flexion. During asymmetric loading, comparatively higher activity was found on the contralateral side in the lumbar region and on the ipsilateral side in the thoracic region. The magnitude of the power spectrum changes correlated well with the amplitude of the myoelectric signal. Spectral changes increased when the signal amplitude increased, indicating localized muscle fatigue.

Adult↗