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Biomedical subjects

R Kadefors

Publications and source records attributed to R Kadefors.

At least 37 records · Page 2Linked to original sources
PubMed1994

Working on a moving surface--a biomechanical analysis of musculo-skeletal load due to ship motions in combination with work.

Ship motions are recognized by fishermen as a cause of high musculo-skeletal load. In the present study, the motions of a Swedish trawler at sea were registered over three degrees of freedom. Simultaneously, the working postures of a fisherman on board were registered in the sagittal plane during five different working situations: (1) standing erect in still conditions; (2) holding a load of 21 kg in still conditions; (3) standing erect during motion of the ship; (4) standing during motion of the ship, holding a load of 21 kg; and (5) repeatedly lifting and lowering a 21 kg load during motion of the ship. All registrations were sampled using a computer where data were processed in a two-dimensional, dynamic biomechanics model, developed for this particular purpose. Vertical and horizontal forces as well as moments were calculated for seven major joint systems of the body, as was compression at the L4/L5 vertebral level. In situation (3), ship motions were mainly counteracted by motions in the lower extremity and lumbar back, thus inducing increased strain in these parts of the body; other parts of the body were little affected. Holding a load considerably increased the load on most joints. Lifting the load further increased the musculo-skeletal strain and also increased the range of moments in each joint as well as the range of lumbar compression. Moment at the C7 vertebral level was relatively unaffected by ship motions and by handling external loads.

Biomechanical Phenomena↗
PubMed1994

Subjective and objective evaluation of shoulder muscle fatigue.

In order to relate EMG signs of localized muscle fatigue to subjectively perceived muscle fatigue, a study was undertaken on 20 healthy volunteers exposing their right trapezius muscle by raising the arm to 90 degrees of abduction. Every person performed two contractions: 0 kg hand load during 5 min and 2 kg hand load during 2.5 min. Surface EMG was recorded and analysed with respect to RMS amplitude and mean power frequency (MPF). Subjective muscle fatigue was estimated with a psychophysical rating scale (Borg's CR-10 Scale). At high load level we found a significant correlation between MPF and the CR-scores (r = -0.46), but at low load level there was no correlation. At high load level there was a linear decrease of MPF with increasing load dose, but at low load level the MPF did not change, despite significant subjective fatigue. There was a linear rise of the CR-score with increasing load dose, more pronounced at high load level. It was concluded, that at low load levels common in working life, MPF and subjective scores seem to provide different fatigue information. Moreover, the MPF did not seem to work as a valid estimator of muscle fatigue at this low load level. Caution is recommended if it is to be used in static low-load situations.

Adult↗
PubMed1994

Psychophysiological stress and EMG activity of the trapezius muscle.

Although it is generally assumed that mental stress induces muscular tension, the experimental data have, so far, been inconclusive. Likely explanations for these inconsistent findings are (a) too small subject samples in some experiments, (b) the use of only one type of stress stimulation, and (c) the lack of objective (physiological) measurements documenting the stress-inducing properties of the experimental treatment. Furthermore. the effect of mental stress and physical load separately, versus the combined influence of physical and mental load on muscular tension, has not been investigated earlier. Therefore, the aim o f the present experiment was lo examine the effects of mental stress as well as of physical load, separately and in combination, on perceived stress, physiological stress responses, and on muscular tension as reflected in electromyographical (EMG) activity of the trapezius muscle. Sixty two female subjects were individually exposed to mental arithmetic, the Stroop color word test (CWT), the cold pressor test, standardized test contractions (TCs), and the CWT combined with a TC. Compared to baseline, the stress session induced significant increases in systolic and diastolic blood pressure, heart rate, urinary catecholamines, salivary cortisol, and self-reported stress. Each of the two mental stress tests induced a significant increase in EMG activity. The CWT caused a rise in EMG activity also during the TC, which was significantly more pronounced than the increase induced by the CWT alone. Blood pressure responses and self-reported stress followed the same pattern as the EMG activity. The results are consistent with the assumption that psychological stress plays a role in musculoskeletal disorders by increasing muscular tension both in low-load work situations and in the absence of physical load. It is also indicated that the stress-induced increase in muscular tension is accentuated on top of a physical load.

Journal Article↗
PubMed1993

An approach to ergonomics evaluation of hand tools.

Based on current knowledge of cumulative trauma disorders in the hand and forearm, related to the use of hand tools, an analysis was undertaken of variables to be considered in ergonomics evaluation of hand tools. Measurement methods were developed and an evaluation station was implemented. Measurement methods are physical, physiological or psychophysical. They focus on the tool, and on the effect of typical use of the tool on the operator. The evaluation station serves as a resource in the development, selection, and testing of tools for a given purpose.

Journal Article↗
PubMed1993

A cube model for the classification of work with hand tools and the formulation of functional requirements.

In an interdisciplinary research project, a model, visualized as a cube, was developed for the classification and analysis of work with hand tools and for communication of different ways of solving problems related to manual handling. The dimensions of the cube are demands of force, precision and time. Each dimension is divided into three levels of low, moderate and high demands respectively. Preliminary limits are proposed for acceptable and non-acceptable use situations and for situations that have to be investigated further. Using a case study of plate shears as a starting point, various measures of improving the position in the cube are discussed. The hand tool, the workplace, the work organization as well as the user of the hand tool are included in the analysis.

Journal Article↗
PubMed1993

Tool design, user characteristics and performance: a case study on plate-shears.

Performance, grip forces and fatigue were studied in six male and six female subjects while cutting with plate-shears. Three types of plate-shears were used, one standard and two modified, either with a spring grip, or with a spring grip in combination with a reduced grip span. In addition, three types of plate - easy, moderately difficult and difficult to cut - were used. Male subjects used around 40% of their maximal grip force and female subjects around 60% with the moderately difficult plate; the male subjects produced more than twice as long a cutting distance as the females. Neither EMG analysis (frequency shifts) nor subjective exertion or reduction of handgrip MVC indicated a more pronounced fatigue in women than in men, probably because the female subjects used about a 50% lower cutting rate than the men. Productivity (in cm cut per min) was strongly related to measures of hand size and to the relative grip force used. Thus in a multiple regression analysis using metacarpal hand circumference and relative grip force as independent variables, R2 was 0.77. The two types of modified plate-shears were preferred by all and gave a roughly 30% higher productivity in the male subjects but did not improve productivity in the females. However, with a spring grip and reduced grip span, the female subjects reduced the relative grip forced used from around 65 to 50%. The total work (force-time integral) per cm cut was not influenced by type of plate-shear.

Journal Article↗
PubMed1992

Electromyographic changes in work-related myalgia of the trapezius muscle.

In 11 patients, all women, 21-55 years of age, with unilateral work-related myalgia of the trapezius muscle, the right and left trapezius muscles were examined simultaneously for electromyogram (EMG) signs of localized muscle fatigue. All patients were tested with 0-kg hand load for 5 min, holding the arms straight at 90 degrees of elevation in the scapular plane. Only 4 of the patients tolerated exposure to higher load levels. They were tested with 1 kg hand load for 3 min and 2 kg hand load for 2 min, with a period of rest of 30 min between the trials. The EMG mean power frequency (MPF) and root mean square (rms) were calculated. Data were normalized with the initial value as a reference and regression analyses were performed. On both sides a decrease of MPF and an increase of rms were found with increasing time and load, i.e. classical EMG signs of localized muscle fatigue. Compared with the nonaffected side smaller changes were found on the affected side, possibly due to pain inhibition, impaired microcirculation and biochemical changes along the muscle fibres. At 0-kg hand load we found no change of MPF on either side despite subjective feelings of fatigue and pain. We interpreted these findings as an indication of reduced capacity of the affected trapezius muscle to sustain static load with early development of pain-associated local fatigue.

Adult↗
PubMed1991

Intramuscular pressure and electromyography in four shoulder muscles.

Estimations of shoulder muscle load are important in biomechanic and ergonomic research. We have studied shoulder muscle load in the trapezius (six subjects), deltoid (six subjects), infraspinatus (eight subjects), and supraspinatus (seven subjects) muscles with simultaneous intramuscular pressure (IMP) and intramuscular bipolar electromyography (EMG) recordings. For imposition of shoulder muscle load, the arm was positioned in abduction or flexion with different hand loads (0, 1, or 2 kg), or isometric force registrations were performed. The microcapillary infusion technique was used for IMP recordings. The IMP in the supra- and infraspinatus muscles were high compared with the trapezius and deltoid muscles in abducted arm positions. In all test situations, IMP and EMG gave a similar description of local muscle load. IMP at maximal voluntary contraction was highest in the supraspinatus and infraspinatus muscles. Both IMP and EMG in all four muscles showed an almost linear correlation to recorded isometric external force. The difference in IMP between shoulder muscles in the same arm position may be due to muscle anatomy, muscle function, and compliance of surrounding tissues. Because a high IMP may impede muscle blood flow, our findings may possibly explain the physiological stress on the rotator cuff muscles as compared with the deltoid and trapezius muscles in work with elevated arms.

Biomechanical Phenomena↗
PubMed1991

The effect of arm support on supraspinatus muscle load during simulated assembly work and welding.

The effect of arm support, by a suspension device, on muscle load in the supraspinatus muscle was evaluated with simultaneous intramuscular pressure measurement and electromyography (EMG) in nine healthy subjects. Two work situations, a low load assembly type of work, and welding with a higher shoulder muscle load, were simulated in the laboratory. Each subject performed three work-cycles of each type, with and without arm support. Arm suspension reduced supraspinatus muscle load in both work situations with reduction in pressure of 34% and 22% respectively, and reduction in normalized EMG of 20% and 17% respectively. The reduction of muscle load was significant, but in the welding situation with arm-suspension 10-15 N, average muscle pressure was still high enough to reduce muscle blood flow. The interpretation of the importance of this load reduction for the development of work-related shoulder pain is problematic.

Adult↗
PubMed1990

Electromyogram mean power frequency in non-fatigued trapezius muscle.

In this study we have examined the variation of mean power frequency (MPF) in the electromyogram (EMG) from the non-fatigued trapezius muscle, with different external hand loads, in different shoulder joint positions, different torques and different planes of movement. The study was limited to the functional range of movement in the shoulder joint. It was performed on 19 healthy subjects. Surface EMG was recorded, analysed by means of a computer programme and examined by regression analysis. Normalized MPF values were calculated by dividing the MPF by the individual average MPF for all positions and loads. The results indicated no major variation in normalized MPF. The largest systematic variation of normalized MPF, +/- 8%, was related to joint angle. We have concluded that the MPF value obtained initially can be used within the functional range of movement to calculate the relative decrease in MPF as a result of muscle fatigue, and that the decrease is significant if it exceeds 8% of the initial value.

Adult↗
PubMed1990

Musculo-skeletal symptoms and signs and isometric strength among fishermen.

Previous studies have shown that subjective symptoms from the musculo-skeletal system are common among fishermen. In the present study, physical signs of malfunction were also found to be common in this profession. The co-existence of physical signs and subjective symptoms differed greatly between different joint systems, and the correlation was in some locations very low. The prevalence of physical health problems other than orthopaedic problems was low. Isometric lifting strength was high compared to results reported on other vocational groups.

Adult↗
PubMed1990

The influence of musculo-skeletal load, and other factors, on staff turn-over in fishery: a post employment questionnaire study.

Five hundred and seventy five out of 1642 fishermen from the Swedish west coast left the trade during the period 1982-1987 for reasons other than age retirement or death. A questionnaire study directed to all these fishermen showed that the majority of the fishermen leaving the trade were young and most of them left fishing within the first few years. The major reasons for leaving the job were low or uncertain earnings, long absence from home or musculo-skeletal symptoms. The major advantages with the work given by the ex-fishermen were working outdoors, good fellowship, personal influence on and excitement of the work. The frequency of subjective musculo-skeletal symptoms was lower among the ex-fishermen than among active fishermen in a previous investigation. However, the active fishermen had to a lower extent been unable to perform daily work due to their symptoms. Seasickness had been a problem for a portion of the ex-fishermen.

Adult↗
PubMed1989

Intramuscular pressure and electromyography in the supraspinatus muscle at shoulder abduction.

In ergonomic and biomechanic research, estimations of shoulder muscle load and evaluation of different measuring techniques are important. Intramuscular pressure (IMP), using the microcapillary infusion technique and bipolar intramuscular electromyography (EMG), was recorded from the same part of the supraspinatus muscle. In 12 subjects, IMP and EMG were recorded at shoulder abduction angles of 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 135 degrees with no or a 1- or 2-kg hand load in each position. The shoulder torque was calculated for each test position. A correlation was found for both mean IMP and mean EMG versus shoulder torque if the position with extreme muscle shortening (135 degrees abduction) was excluded. IMP was high (greater than 50 mmHg) in almost all test situations. In seven other subjects, isometric force in abduction was correlated with IMP and EMG. Both methods showed an equally good correlation with external shoulder force, IMP gives as good an estimation of relative muscle force as EMG, but any comparison between EMG and IMP must be done at the same muscle length.

Adult↗
PubMed1988

Intramuscular pressure in the supraspinatus muscle.

Shoulder pain correlated to manual labour is an increasing problem. The etiology is multifactorial and often unclear. High local muscle load and muscle ischemia in the supraspinatus muscle is present in elevated arm positions, as shown in several electromyographic studies. The purpose of this study was to evaluate intramuscular pressure (IMP) as a way to describe local muscle load in the supraspinatus muscle. Measurements were made in 15 arm positions, and with hand loads of 0, 1, or 2 kg weight, in 12 shoulders. The IMP was recorded with microcapillary infusion technique. The method was found to be suitable in recording IMP at rest and during exercise. High intramuscular pressures, i.e., above 50 mm Hg (6.7 kPa), were seen in moderate humeral abduction. The IMP increased further in abduction up to 90 degrees, where mean IMP was 122 mm Hg (16.2 kPa). Added hand load increased intramuscular pressure in all positions except in shoulder flexion of 135 degrees. The study thus demonstrated that intramuscular pressure offers important information about the load on the supraspinatus muscle in different positions of the arm. The results indicate that fatigue and shoulder pain related to elevated arm positions may be caused by muscle ischemia induced by the high intramuscular pressure present in these positions.

Adult↗
PubMed1988

Musculo-skeletal symptoms as related to working conditions among Swedish professional fisherman.

The present study has confirmed the concern of previous investigators that professional fishing is a strenuous occupation. We have been able to show that complaints of symptoms from the musculo-skeletal system are common, and that they follow a logical pattern in terms of the influence of a few key parameters, such as age, number of years in the fishing trade, type of fishing and type of working tasks on board. There is reason to believe that these findings provide a sound basis for action-oriented research and a development programme focusing on reducing the risk of fishermen acquiring chronic chronic disorders of the musculo-skeletal system. In a subsequent article we shall present such a programme, which has been carried out for the Swedish fishery.

Journal Article↗
PubMed1988

Workload and ergonomics measures in Swedish professional fishing.

The major types of professional coastal fishery in Sweden were studied. A questionnaire indicated that symptoms from the musculo-skeletal system were common and that certain symptoms related to certain types of fishing. Working tasks inducing severe workload were identified. They concerned handling the fishing gear as well as handling the catch. Ergonomics measures to decrease the workload were suggested and evaluated through ergonomics assessment, measurements of oxygen uptake and working posture analyses. It was found that ergonomics measures can be taken which are efficient in reducing the load on the musculo-skeletal system of the fishermen.

Journal Article↗