Search PubMed⌕ Search

Biomedical subjects

M Nordin

Publications and source records attributed to M Nordin.

86 records · Page 5Linked to original sources
PubMed1987

Motor-unit responses in human wrist flexor and extensor muscles to transcranial cortical stimuli.

1. Transcranial cortical stimuli (TCCS) were used to elicit motor responses in contralateral wrist flexor and extensor muscles of healthy adult subjects. The motor responses were assessed by surface EMG recordings, by needle recordings of single motor-unit discharges, and by measurements of wrist twitch force. Our main aim was to analyze the single-unit events underlying those changes in latency, amplitude, and duration of the compound EMG responses, which could be induced by voluntary preactivation of target muscles and by changes in stimulation strength. 2. Different stimulus strengths were tested with and without background contractions in the flexor or extensor muscles. For each test (consisting of a series of 20 stimuli) the compound EMG responses were averaged and displayed together with the averaged wrist force signals. Responses of individual flexor and extensor motor units were displayed in raster diagrams and peristimulus time histograms. For units exhibiting a background firing, the mean background interdischarge interval was calculated and compared with the subsequent poststimulus intervals. 3. In relaxed muscles, a shortening of onset latency of evoked compound EMG responses was observed when raising stimulation strength. A similar latency reduction was not seen in any of the single-unit recordings. This would be consistent with the size principle of motoneuron recruitment. 4. A shortening of onset latency of evoked EMG potentials was observed also as a result of a voluntary preactivation. Such latency shifts, which were seen also in single-unit recordings, might be attributed to variations in the time required for D and I wave temporal summation at the anterior horn cell. 5. When raising stimulation strength or when adding voluntary background contraction, the evoked compound EMG potential grew not only in amplitude but also in duration, as later peaks of activity were added to the initial ones. Under optimal conditions (strong stimulus + background contraction), the period of excitation (termed E1) had an onset latency of approximately 15 ms and a duration of approximately 35 ms and was similar for wrist flexor and extensor muscles. 6. We never saw the same flexor or extensor unit fire more than once during the E1 period. For units preactivated by a background contraction, the stimulus-triggered impulse exhibited latency shifts, which, to a large extent, depended on the timing of the stimulus in relation to a preceding background discharge and which could be influenced by a change in stimulation strength.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1987

Evaluation of the workplace. An introduction.

To reduce and optimize the work load imposed on the musculoskeletal system in a given situation, three main areas of interest are work technique, workplace design, and the produced work itself. Ergonomically sound work techniques should be taught early and should be repeatedly evaluated and encouraged. Workplace and tool design must be adapted and modified according to the task performed at the workplace. The work produced has to be evaluated in terms of handling comfort and discomfort by the employee: the greater the comfort, the greater the productivity will be. Especially in the rehabilitation of patients with back injuries, these factors must always be considered to avoid recurrent episodes of pain and disability.

Back Pain↗
PubMed1986

Microelectrode recordings from the facial nerve in man.

Microneurographic recordings have for the first time been obtained from the human facial nerve trunk, close to its exit from the stylomastoid foramen. The aim was to search for evidence of an afferent or sympathetic component of the facial nerve at this level and to study the fascicular organization of motor fibres. Single unit discharges of motor axons were occasionally discerned, and all recordings showed multiunit motor impulses preceding the EMG activity of the appropriate facial muscles by about 5 ms during both blink reflexes and voluntary contractions. No evidence of low-threshold mechanoreceptive afferents was found. Electron microscopic studies at the level of recording showed unmyelinated axons but attempts to record nociceptive and sympathetic activity failed. However, deep facial pain evoked by intraneural stimulation suggested the presence of nociceptive afferents of non-cutaneous origin. Intrafascicular recording and stimulation showed that most fascicles were composed of motor axons innervating muscles within the whole ipsilateral half of the face.

Adult↗
PubMed1986

Gamma loop contributing to maximal voluntary contractions in man.

A local anaesthetic drug was injected around the peroneal nerve in healthy subjects in order to investigate whether the resulting loss in foot dorsiflexion power in part depended on a gamma-fibre block preventing 'internal' activation of spindle end-organs and thereby depriving the alpha-motoneurones of an excitatory spindle inflow during contraction. The motor outcome of maximal dorsiflexion efforts was assessed by measuring firing rates of individual motor units in the anterior tibial (t.a.) muscle, mean voltage e.m.g. from the pretibial muscles, dorsiflexion force and range of voluntary foot dorsiflexion movements. The tests were performed with and without peripheral conditioning stimuli, such as agonist or antagonist muscle vibration or imposed stretch of the contracting muscles. As compared to control values of t.a. motor unit firing rates in maximal isometric voluntary contractions, the firing rates were lower and more irregular during maximal dorsiflexion efforts performed during subtotal peroneal nerve blocks. During the development of paresis a gradual reduction of motor unit firing rates was observed before the units ceased responding to the voluntary commands. This change in motor unit behaviour was accompanied by a reduction of the mean voltage e.m.g. activity in the pretibial muscles. At a given stage of anaesthesia the e.m.g. responses to maximal voluntary efforts were more affected than the responses evoked by electric nerve stimuli delivered proximal to the block, indicating that impaired impulse transmission in alpha motor fibres was not the sole cause of the paresis. The inability to generate high and regular motor unit firing rates during peroneal nerve blocks was accentuated by vibration applied over the antagonistic calf muscles. By contrast, in eight out of ten experiments agonist stretch or vibration caused an enhancement of motor unit firing during the maximal force tasks. The reverse effects of agonist and antagonist vibration on the ability to activate the paretic muscles were evidenced also by alterations induced in mean voltage e.m.g. activity, dorsiflexion force and range of dorsiflexion movements. The autogenetic excitatory and the reciprocal inhibitory effects of muscle vibration rose in strength as the vibration frequency was raised from 90 to 165 Hz. Reflex effects on maximal voluntary contraction strength similar to those observed during partial nerve blocks were not seen under normal conditions when the nerve supply was intact.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1986

Spinal configuration during lifting.

The change in spinal configuration of the cervical, thoracic, and lumbar regions in relation to an amount of weight lifted was determined using videophotogrammetry. Fifteen healthy male subjects, 20-38 years of age, with no previous history of back pain participated in the study. The subjects lifted a crate containing 0, 10, and 20 kg weights using the straight-legs, bent-over-back method of lifting. The results showed that cervical and thoracic spinal segment configurations were not significantly influenced by the amount of weight lifted and that the mobility of the lumbar spinal segment was significantly decreased with increasing load (p = .03).

Adult↗
PubMed1985

Thixotropic behaviour of human finger flexor muscles with accompanying changes in spindle and reflex responses to stretch.

Prompted by previous reports on muscle thixotropy, we have investigated changes in inherent and reflex stiffness of the finger flexor muscles of human subjects at rest, following transient conditioning manoeuvres involving contractions and/or length changes of the finger flexors. The stiffness measurements were combined with electromyographic recordings from forearm and hand muscles and with microneurographic recordings of afferent stretch responses in finger flexor nerve fascicles. Finger flexor stiffness was evaluated by measuring (a) the flexion angle of the metacarpo-phalangeal joints at which the system during rest balanced the force of gravity and (b) the speed and amplitude of angular finger extensions induced by recurrent extension torque pulses of constant strength delivered by a torque motor. In the latter case, extension drifts in the resting position of the fingers were prevented by a weak flexion bias torque holding the fingers in a pre-determined, semiflexed position against a stop-bar. Stiffness changes following passive large amplitude finger flexions and extensions were studied in subjects with nerve blocks or nerve lesions preventing neurally mediated contractions in the forearm and hand muscles. Inherent stiffness was enhanced following transient finger flexions and reduced following transient finger extensions. The after-effects gradually declined during observation periods of several minutes. Similar results were obtained in subjects with intact innervation who succeeded during the pre- and post-conditioning periods in keeping the arm and hand muscles relaxed (i.e. showed no electromyographic activity). In these subjects it was also found that the after-effects were similar for active and passive finger movements and that isometric voluntary finger flexor contractions loosened the system in a way similar to finger extensions. In some subjects electromyographic reflex discharges appeared in the finger flexors in response to the extension test pulses. When elicited by small ramp stretch stimuli of constant amplitude, the stretch reflex responses were found to vary in strength in parallel with the changes in inherent stiffness following the various conditioning manoeuvres. The strength of the multi-unit afferent stretch discharges in the muscle nerve, used as index of muscle spindle stretch sensitivity, varied in parallel with the changes in inherent stiffness. Post-manoeuvre changes in muscle spindle stretch sensitivity were seen also when the spindles were de-efferented by a nerve block proximal to the recording site. The results can be explained in terms of thixotropic behaviour of extra- and intrafusal muscle fibres.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1985

Surgical or conservative treatment of the acutely torn anterior cruciate ligament. A randomized study with short-term follow-up observations.

In a prospective study, 90 consecutive patients with total midstructural tears of the anterior cruciate ligament (ACL) were assigned at random to surgical (Group I) or conservative (Group II) treatment. Within 18.2 months of operation, 95% of the patients in Group I and 11% of those in Group II had a stable knee. The mean knee function score in Group I was 89 points, and 75% achieved more than 84 points (good or excellent). In Group II the mean score was 85; only 53% achieved more than 84 points (p less than .05). Group II patients showed greater mean quadriceps strength than those in Group I. The ability to perform a one-leg jump and to run a figure eight was similar in both groups. Early primary suture of the acutely torn ACL usually resulted in a stable knee, whereas conservatively treated patients showed knee instability. At the 18-month interval, however, the patients' functional performance seemed to be comparable in the two groups.

Adolescent↗
PubMed1984

The influence of a preventive educational programme on trunk flexion in janitors.

The influence of a preventive educational back care programme on the movement patterns of the spine during work was assessed objectively and subjectively in six janitors. Trunk flexion was measured in the subjects using a flexion analyser before they attended a preventive educational back care programme and twice afterwards. The results show that the subjects increased the amount of time spent in an upright position by about a third after the educational programme and maintained this change two and a half to three months later. They also decreased the time spent in moderate and deep forward flexion (37-72 degrees ) by about half and also maintained this decrease at three months. These changes are consistent with a decrease of the mechanical load on the spine. The study emphasises that it is possible to alter movement patterns of the spine, and thereby decrease the load during janitorial work, by a suitably designed educational programme.

Journal Article↗
PubMed1984

Intra-abdominal pressure measurements using a wireless radio pressure pill and two wire connected pressure transducers: a comparison.

Intra-abdominal pressures were measured simultaneously with a wireless radio pill and two wire-connected pressure transducers introduced orally and rectally respectively. Measurements were made on 8 men during common postures, simple activities and static and dynamic lifting. An acceptable correspondence was found in wave forms of the generated pressure curves in time and shape. The three systems showed, however, a less good agreement in recorded peak differences, i.e. highest and lowest pressure responses to each task. The radio pill is simple to use, but more difficult to calibrate and expensive, compared to the wire-connected methods, which however are less attractive for use in the work environment.

Abdomen↗
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↗
PubMedDate not supplied

Analysis and quantitative myoelectric measurements of loads on the lumbar spine when holding weights in standing postures.

Ten subjects executed a number of weight-holding and force-resisting work tasks while standing either upright or with their trunks in 30 degrees of forward flexion. All tasks involved sagitally symmetric body configurations and were performed isometrically. A simple calculation scheme was devised to predict the lumbar trunk muscle contraction forces and the lumbar spine compression forces required for execution of each task. The myoelectric activity was recorded quantitatively at eight sites over the lumbar trunk muscles and at four sites over the abdominal muscles. Good correlation was found between the predicted muscle contraction forces and the myoelectric activities.

Adult↗
PubMedDate not supplied

Measurements of trunk movements during work.

To study spinal movements during work, an instrument that measured angles and angle changes in relation to a vertical plane was adapted to continuously measure forward flexion of the trunk. The instrument, which is battery-powered and worn on the back, registers the amount of flexion and its distribution over time during a work cycle by recording the time spent in each of five 18 degrees intervals between 0 degrees and 90 degrees. Also the number of times that the angle of flexion changed from one interval to another is recorded. A total of 43 subjects from three occupations--dentistry, nurses' aide work, and warehouse work--were each tested during a 60 minute work cycle. On the average, the dentists spent most of the time (52.2 minutes) in a semi-flexed position not exceeding 36 degrees and performed eight deep forward flexions (greater than 73 degrees). The nurses' aides spent one-half of the work cycle (34.4 minutes) in an upright position (0-18 degrees) and performed 70 deep forward flexions. The warehouse workers spent less than one-half of the work cycle in an upright position (27.5 minutes) and performed 153 deep forward flexions that nearly always were associated with lifting.

Adult↗
PubMedDate not supplied

The effect of a patella brace on performance in a knee extension strength test in patients with patellar pain.

The object of this study was to analyze the quadriceps muscle peak strength with the Cybex-II isokinetic dynamometer in patients with patellofemoral arthralgia with and without a patella brace. Twenty-four patients, 18 women and 6 men, were studied. All had patellofemoral arthralgia. The diagnosis was made on typical clinical findings, but was supplemented with arthroscopy in seven patients with pain also over the medial joint line. After a 2 week adaptation period with the brace, a Cybex-II test was done with and without the brace. The other leg was tested as control. Twenty-one patients (88%) improved their performance in the strength test with the brace (mean difference 13.7 +/- 9.1%). With the brace, 14 patients (58%) performed at 95% of their control leg or more compared to 6 (25%) without the brace. Patients under the age of 30 years had a better effect than patients over that age.

Adolescent↗