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Biomedical subjects

R Kadefors

Publications and source records attributed to R Kadefors.

At least 19 recordsLinked to original sources
PubMed2006

Trapezius muscle rest time during standardised computer work--a comparison of female computer users with and without self-reported neck/shoulder complaints.

Work related musculoskeletal disorders (WMSDs) in the shoulder/neck area are a common and increasing problem among European computer workers, especially women. Long-term low-level workloads with low degree of muscle rest are a potential risk factor for developing WMSDs. The purpose of the present study of female computer users (age 45-65 years) in Denmark and Sweden was to investigate if subjects with self-reported neck/shoulder complaints (cases, N=35) show less trapezius muscle relative rest time (RRT) than controls (N=44) when performing standardised short-term computer work tasks in controlled laboratory conditions. Surface electromyography (EMG) signals were recorded bilaterally from the upper trapezius muscles during a type, edit, precision and colour word stress task. Besides RRT, 10th percentile RMS values were calculated. On the average, 15 of the cases and 18 of the controls showed analysable EMG files per task. For the colour word stress task, the results showed lower RRT values and higher 10th percentile RMS amplitude levels among cases compared to controls. No such signs could be found for the other tasks performed. The present results indicate an increased motor response to a psychological stressor among subjects with self-reported neck/shoulder complaints.

Aged↗
PubMed2005

Neuromuscular assessment in elderly workers with and without work related shoulder/neck trouble: the NEW-study design and physiological findings.

Musculoskeletal disorders in the neck and shoulder area are a major occupational concern in the European countries especially among elderly females. The aim was to assess these disorders based on quantitative EMG indicators and functional tests. 252 female computer users (45-68 years) were recruited from four European countries in two contrast groups: (1) 88 neck/shoulder (NS) cases reporting trouble in the neck and/or shoulder region for more than 30 days during the last year, and (2) 164 NS-controls reporting such trouble for no more than 7 days. Questionnaires, functional/clinical tests, and physiological recordings were performed in workplace related field studies. The results showed no differences in anthropometrics but NS-cases reported more strained head positions and more eye problems than controls. The psychosocial working factors were similar, although, NS-controls had slightly better scores on working conditions, general health, and vitality compared to cases. The NS-cases had lower maximal voluntary contraction (MVC) during shoulder elevation (mean (SD) 310 (122) N) compared to the controls (364 (122) N). During 30% MVC electromyography (EMGrms) in the trapezius muscle was lower in NS-cases (194 (105) muV) than in controls (256 (169) muV), while no differences were found regarding endurance time. Estimated conduction velocity was not different between NS-cases and -controls. Four functional computer tests were performed equally well by NS-cases and -controls, and the corresponding EMG variables also did not differ. A major finding in this large-scale epidemiological study is the significantly lower MVC in NS-cases compared with NS-controls together with lower EMGrms value at 30% MVC, while computer tasks were performed at similar relative muscle activation. The study was unable to reveal quantitative EMG indicators and functional tests that could objectively assess disorders in NS-cases.

Adult↗
PubMed2004

Clinical signs and physical function in neck and upper extremities among elderly female computer users: the NEW study.

The aim of the study was to present the prevalence of clinical signs and symptoms among female computer users above 45 years, both in a group with self-reported neck/shoulder trouble (NS cases) and in a group without such trouble (NS controls). The hypothesis was that computer users with self-reported neck/shoulder trouble have more clinical findings than those not reporting trouble, and that a corresponding pattern holds true for physical function. In total 42 and 61 questionnaire-defined NS cases and NS controls participated and went through a clinical examination of the neck and upper extremities and five physical function tests: maximal voluntary contraction (MVC) of shoulder elevation, abduction, and handgrip, as well as endurance at 30% MVC shoulder elevation and a physical performance test. Based on clinical signs and symptoms, trapezius myalgia (38%), tension neck syndrome (17%) and cervicalgia (17%) were the most frequent diagnoses among NS cases, and were significantly more frequent among NS cases than NS controls. A total of 60% of the subjects with reported trouble had one or several of the diagnoses located in the neck/shoulder. Physical function of the shoulder was lower in subjects with self-reported trouble as well as in the subgroup of NS cases with clinical diagnoses. In conclusion, the present clinical diagnoses and physical function tests differed between NS cases and NS controls, and are therefore recommended to be included as quantitative objective measures in assessing musculoskeletal health. Physical function tests should be further developed in order to be able to detect pre-stages of work-related disorders for preventive strategies.

Case-Control Studies↗
PubMed2001

A non-invasive measure of changes in blood flow in the human anterior tibial muscle.

We used photoplethysmography (PPG) to monitor blood flow changes in the human anterior tibial muscle during arterial occlusion and during isometric and concentric contractions. Single-fibre laser-Doppler flowmetry (LDF) was used as a reference in 12 healthy subjects (5 men, 7 women; mean age 24 years). Post-exercise hyperaemic muscle blood flow (MBF) was measured immediately after isometric dorsiflexion of the ankle joint at maximal contraction for 1 min and full range-of-motion dorsiflexion and plantar flexion of the ankle joint for 1 min. A thigh tourniquet was applied for the evaluation of post-occlusive reactive hyperaemia. The MBF (baseline = 100%) was [mean (SD)] 150 (31)% (P = 0.003) by PPG (880 nm) and 182 (66)% (P = 0.012) by LDF. After 1 min of maximal isometric contraction, MBF increased to 150 (51)% (P = 0.003) by PPG (880 nm) and to 169 (43)% (P = 0.005) by LDF. After 1 min of maximal concentric contractions, MBF increased to 158 (59)% (P = 0.003) by PPG (880 nm) and to 170 (99)% (P = 0.008) by LDF. Skin blood flow, PPG (560 nm), did not change significantly after isometric or concentric contractions. The results indicate that reactive hyperaemia after exercise and arterial occlusion can be assessed in the human anterior tibial muscle using PPG.

Adult↗
PubMed2001

Motor unit recruitment in the trapezius muscle with special reference to coarse arm movements.

Chronic shoulder pain is common in a variety of occupations. The "Cinderella hypothesis" suggests that the pain originates from damaged type I muscle fibres driven into degenerative processes as a result of too long activation and too short recovery time. The main purpose of this study was to investigate if the same motor units are active during all phases of coarse arm movements. Eight healthy volunteers participated in the study. Intramuscular electromyographic signals were picked up with a four-lead fine wire electrode, during a unilateral straight arm movement. The movement started with either (part 1) an abduction or a flexion, then (2) a movement in the horizontal plane from the sagittal to the frontal plane or vice versa, and finally (3) an adduction or an extension to the start position. The movement cycle was performed in three different speeds, slow, medium, and high, with one, two or five cycles per 20 s, respectively. On an average, the motor unit action potentials (MUAPs) of 6 motor units (range, 1-15) were identified per trail. In total 94% of the MUAP trains that were identified showed firings in all 3 parts of the movements. The findings support the Cinderella hypothesis, although there is a need to further investigate the temporal pattern of long-term motor unit activity.

Action Potentials↗
PubMed2000

Intramuscular pressure of the infra- and supraspinatus muscles in relation to hand load and arm posture.

In work engaging the upper extremities, the musculoskeletal system of the shoulder is sometimes exposed to prolonged excessive load, leading to musculoskeletal disorders of the shoulder. One way of reducing work-related shoulder disorders is to establish guidelines for working postures. The purpose of this study was to identify harmful working positions, by performing a comprehensive survey of the intramuscular pressure (IMP) in the infra- and supraspinatus muscles in relation to different arm positions and external loads. Ten healthy males participated, and the IMP in the infra- and supraspinatus muscles was studied in a total of 112 combinations of arm positions and hand loads at levels that occur frequently in industrial work. High-precision spatial recordings were accomplished with a three-dimensional motion-analysis system, and the IMP was measured using the microcapillary infusion technique. The mean IMP of the infraspinatus muscle as well as that of the supraspinatus muscle increased continuously from a resting pressure at 0 degrees of upper arm elevation to a maximal pressure at 90 degrees of upper arm elevation, for all elevation planes. The mean IMP of the supraspinatus muscle appeared to be more dependent upon the elevation plane and less dependent upon the hand load, compared to the infraspinatus muscle. Even during only moderate arm elevation, the mean IMP of the infra- and supraspinatus muscles, presented here in polar diagrams, had already exceeded the levels of reduced recovery from local muscle fatigue and blood flow impairment. The elevation angle and the hand load primarily influence the development of IMP in the infra- and supraspinatus muscles.

Adult↗
PubMed1999

Musculoskeletal symptoms due to technical preconditions in long cycle time work in an automobile assembly plant: a study of prevalence and relation to psychosocial factors and physical exposure.

The aim was to evaluate the prevailing ergonomic conditions in a parallelized flow, long cycle time, assembly system. The evaluation focused on physical exposure, psychosocial factors and work-related musculoskeletal symptoms. A random sample of 67 assembly operators was included in a cross-sectional study mainly based on questionnaires. Hand/wrist symptoms were common and related to work exposure with hand-held powered tools. In general, the self-reported physical exposure showed only a few significant associations with musculoskeletal symptoms. This may in part be explained by the ergonomic conditions generally being good, with a relatively low duration of 'combined' extreme work postures. Significant associations were found between the psychosocial work environment and musculoskeletal symptoms.

Adult↗
PubMed1999

Assessment of workload and arm position during different work sequences: a study with portable devices on construction workers.

It is recognised that work related shoulder pain is overrepresented among construction workers compared to other occupations. Studies have shown that working with hands above shoulder level increases the shoulder load. Most studies have been confined to the laboratory. The present project was carried out to map the muscular engagement and postures of construction workers undertaking ceiling fitting, and to compare the results to those of the laboratory studies. Two ambulatory devices were used, one allowing recording of electromyographic (EMG) signals bilaterally from the trapezius muscle, and the other to record the position of both arms and back by means of measuring the angles between the vertical line and the back and both upper arms. These recordings were performed during 1.5-2 h work sequences. The results show that the work was mostly performed in an upright position, that both arms were used to a similar amount and that the workers for a large proportion of their working time had their upper arms at levels that are considered harmful in view of shoulder load. The EMG data showed that nearly 50% of the work was spent with trapezius activity that exceeded that of the reference contraction used (about 15% of maximal voluntary contraction) and that the time spent in muscular relaxation was 10%. It was concluded that the exposure of construction workers undertaking ceiling fitting meets the criteria formulated on the basis of laboratory experiments with respect to a high risk of acquiring chronic shoulder pain, due to rotator cuff tendinitis.

Adult↗
PubMed1999

Psychophysiological stress responses, muscle tension, and neck and shoulder pain among supermarket cashiers.

This study examined psychological and physiological stress, as well as muscle tension and musculoskeletal symptoms, among 72 female supermarket cashiers. Stress levels were found to be significantly elevated at work, as reflected in the catecholamines, blood pressure, heart rate, electromyographic (EMG) activity, and self-reports. Fifty cashiers (70%) suffering from neck-shoulder pain (trapezius myalgia) were found to have higher EMG activity at work and reported more tension after work. Women who kept a diary for 1 week and reported more musculoskeletal pain (above the median) were older, had higher blood pressure, and reported more work stress and psychosomatic symptoms. The elevated stress levels at work are consistent with data from workers involved in other types of repetitive tasks and can be important for the high prevalence of neck and shoulder symptoms among the cashiers.

Adult↗
PubMed1999

Recruitment of low threshold motor-units in the trapezius muscle in different static arm positions.

A prevailing hypothesis for development of myalgia symptoms in the trapezius muscle is based on observations that in stereotypic activation of muscle the same low-threshold motor-units are the first ones to be recruited, and that these units are active throughout the contraction, until total relaxation. The theory suggests that these units are the first ones in monotonous repetitive work to be subject to degenerative processes, causing pain. The present project was undertaken to evaluate to what extent recruitment of motor-units in the trapezius muscle is position-specific, i.e. if there are motor-units that are recruited over a wide range of arm postures. Fine wire electrode pairs, inserted 2 cm lateral to the midpoint between the acromion and the C7 spinous processus, were used for signal acquisition. Methods for decomposition of the interference patterns were developed, allowing identification of single motor-units in signals registered in different arm positions. Voluntary recruitment of motor-units in the descending portion of the trapezius muscle was studied in 24 different arm positions (0-90 degrees shoulder flexion, 0-45 degrees humeral abduction, and 45-135 degrees elbow flexion) in three subjects. The results showed that the wire electrode technique and the signal processing algorithm employed allowed motor-unit identification in non-isometric conditions. It was found that low threshold motor-units in the trapezius muscle, active over a wide range of arm positions, could be identified in all three subjects. We refer to those as Cinderella, or C, units. These results support the research hypothesis addressed.

Adult↗
PubMed1998

The effect of light manual precision work on shoulder muscles--an EMG analysis.

In order to clarify if light manual precision work influences the activity of shoulder muscles, seven shoulder muscles were examined using electromyography (EMG) in five different arm positions in ten subjects. The subjects were asked to perform light precision work with the hand while maintaining the same arm position. The EMG activity in the shoulder muscles with the arm in specific positions was compared to the activity when manual precision work was added. The results were analysed statistically using a non-parametric method. We found an increased EMG activity in almost all arm positions and muscles. The increase was significant in four out of five arm positions regarding the infraspinatus and in three out of five positions concerning the levator scapulae. In the supraspinatus the increase was significant with the arm in its highest location. The average increase in shoulder muscle activity amounted to 22% of the resting activity.

Adult↗
PubMed1998

Consequences of trapezius relaxation on the distribution of shoulder muscle forces: an electromyographic study.

This study was focused on the ability to reduce voluntarily the muscle activity in the descending part of the trapezius muscle without changing the arm position or hand load, and its consequences on the distribution of shoulder muscle forces. Visual feedback techniques were used. Six different arm positions were investigated in 11 subjects. Electromyography was used for monitoring the muscle involvement. The selection of relevant muscles was performed by a model simulation of the shoulder using a newly developed biomechanical model of the human shoulder. The ability to reduce the muscle activity of the descending part of the trapezius was confirmed and the reduction ranged from 60 to 76% depending on the arm position. Among the muscles studied the rhomboid major and minor and the transverse part of the trapezius were affected the most, increasing their activity on the average to 232, 175 and 201% respectively, compared to the initial activity. The anterior part of the deltoid and the medial part of the serratus anterior also intensified their activity. The influence on the levator scapulae was, contrary to simulation results and to empirical knowledge, a decrease of the muscle activity. It is suggested that attention is given to the rhomboids and the transverse part of the trapezius when muscle activity is reduced in the descending part of the trapezius, for instance in biofeedback-based therapy. In conclusion, the study showed that reducing the trapezius activity caused a redistribution of muscle forces in the shoulder.

Adult↗
PubMed1996

Ergonomics in parallelized car assembly: a case study, with reference also to productivity aspects.

In 1985 Volvo started the development of a new plant for the assembling of cars. This plant was situated in the town of Uddevalla in Sweden. One deliberate aim with this plant was to combine an enhanced productivity and product quality with good ergonomics conditions and improved work organization. The plant was designed with a production system where parallel work-teams of about five persons could assemble from 1/4 up to complete cars. A newly developed tilting device, a piece of equipment that could rotate, rise and lower the car body in order to facilitate assembly work, was introduced. Ergonomic analyses of postural and musculoskeletal strain showed that parallelized flow production, according to the production principles of the Uddevalla plant, was superior to traditional car assembly according to the serial flow production concept, i.e. the traditional assembly line. It was noted that this ergonomic standard was implemented without compromising productivity. In conclusion, increased knowledge and experience of parallelized production systems has been gained which should be considered in the development of future assembly plants, even though the Uddevalla factory itself was closed down in 1993.

Journal Article↗
PubMed1995

Voluntary redistribution of muscle activity in human shoulder muscles.

Four shoulder muscles (the supraspinatus, the infraspinatus, the anterior and middle portion of the deltoid, and the descending part of the trapezius) were examined with electromyography in abducted arm positions. By using feedback techniques, we found that the subjects could reduce the EMG activity voluntarily by 22-47% in the trapezius muscle while keeping different static postures. This was not true for any other muscle investigated. When the trapezius activity was reduced there was a tendency towards an increase of EMG activity in some other shoulder muscles, particularly the infraspinatus. The findings may be related to relaxation from an initial overstabilization of the shoulder, or redistribution of load among synergists. It is suggested that the possibility of reducing trapezius activity may be of ergonomic significance. It is also noted that EMG trapezius activity may not serve as a universal descriptor of total muscular load in the shoulder.

Adult↗
PubMed1995

Comparison of lung radiography and counting of exposure time to magnetopneumography for estimation of total lung dust retention in arc welders.

Magnetopneumography (MPG) is a non-invasive technique to measure the amount of magnetizable dust retained in the lung. This study concerns the relation between MPG measurements of welding fume dust retention in the human lung on the one hand and chest radiography and crude counting of exposure time on the other. Precision and accuracy of the MPG instrument was found to be high. A weak but statistically significant correlation (r = 0.45, P < 0.05) was found between exposure time and retention of magnetizable material in a group of 112 full time manual metal arc welders. The variability was high. Retention rate was estimated on a group level. Chest radiographs of 23 arc welders were reviewed separately in random order by two independent readers who were not aware of MPG findings, occupational anamnesis or the subject's identity and age. No statistically significant correlation was found between MPG and the observer's grading. A weak but statistically significant correlation was found between the readers. We conclude that MPG is highly sensitive to retention of magnetizable material retained in the lung and that the correlation between radiography and MPG reported by previous workers could not be verified in this study. The divergent results may well be due to methodological differences. Investigations using more specific roentgenological methods, such as high resolution computed tomography (HRCT), should be performed.

Adult↗