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Biomedical subjects

R Kadefors

Publications and source records attributed to R Kadefors.

At least 55 records · Page 3Linked to original sources
PubMed1984

Electromyographic analysis of shoulder muscle load.

The influence of hand tool weight and arm position on shoulder muscle load was studied by electromyography. The investigation was made to facilitate recommendations on work place design. The aim is to reduce the occurrence of occupational shoulder disorders in industry. Nine volunteers held 21 different arm positions with the hand over waist level. In each position, the hand was loaded with 0, 1, and 2 kg. Each load was maintained for 15 s. The myoelectric activity in six shoulder muscles was recorded and analyzed automatically with respect to the amplitude. The results indicate that the degree of upper arm elevation is the most important parameter influencing shoulder muscle load. Short rotator muscles stabilizing the shoulder joint were found to be more hand-load dependent than the deltoid muscle. The ergonomic implications of this study are that work situations should be designed so that the arm can be kept close to the body and the hand load minimized.

Adult↗
PubMed1984

Relation of intramuscular pressure to the force output and myoelectric signal of skeletal muscle.

The force output of the biceps brachii muscle during static isometric contractions was studied in 26 arms of 23 subjects in relation to the simultaneously recorded level of the electromyogram (EMG) and the intra-muscular pressure (IMP). The EMG was picked up with wire electrodes and the IMP recorded through wick catheters or by infusion technique. The load at the wrist was monitored using a force transducer. A near linear relationship with correlation coefficients exceeding 0.96 was shown between the load on the wrist on the one hand and IMP and EMG on the other. The regression coefficients of the relation between the load and IMP or EMG varied considerably between individuals and between different measuring points in the same individual. In cases where the correlation between the wrist load on one hand and the IMP and EMG on the other was poor because of varying synergistic interaction between the flexor muscles, the EMG and IMP were always well correlated. This means that they change in the same way when the mechanical output of the muscle varies. This was also the case in three experiments where the IMP and EMG from all three elbow flexors were recorded while the subjects changed from a supinated to a pronated position supporting a constant load on the wrist. Considering these observations we present indirect evidence that IMP and the level of the EMG signal both are good estimators of isolated muscular force under isometric static conditions and over limited time.

Adult↗
PubMed1984

The relation between spectral changes of the myoelectric signal and the intramuscular pressure of human skeletal muscle.

The purpose of the present study was to investigate if the intramuscular pressure generated during an isometric muscle contraction is important for the appearance of EMG spectral changes accompanying localized muscular fatigue. The EMG and intramuscular pressure of the left biceps brachii in eight volunteers were recorded during standardized isometric contractions by means of intramuscular wire electrodes and infusion catheters, respectively. Spectral changes were elicited by a submaximal contraction and the intramuscular pressure at which the induced spectral changes were able to recover was determined. It was found that significant recovery was possible only if the intramuscular pressure dropped below a level of about 2.7 kPa (20 mm Hg). It is concluded that the intramuscular pressure during a sustained isometric contraction is relevant for the generation of fatigue induced spectral changes, and that measurement of the intramuscular pressure makes possible predetermination of whether or not an isometric muscle contraction is liable to result in localized muscular fatigue.

Adult↗
PubMed1984

Shoulder pain and heavy manual labor.

The problem of the increasingly common shoulder pain syndromes in industry was investigated by biomechanic and epidemiologic methods. Rotator cuff tendinitis constitutes a major problem in people with arduous occupations, i.e., shipyard welders (prevalence ratio, 18.3%), and steel plateworkers (16.2%). Static work seems to induce symptoms at an earlier age. The clinical diagnosis was supraspinatus tendinitis. The biomechanic studies confirmed the view that the shoulder muscles are heavily loaded when the arm is elevated. Excessive hand tool mass increases the strain markedly in some muscles, particularly the supraspinatus and the infraspinatus. The hypovascularity of the supraspinatus tendon is then likely to be accentuated by high intramuscular pressure that reduces the blood flow through the muscle. The strain on the supraspinatus muscle in overhead work is an important factor contributing to prolonged shoulder disability. An analysis of the distribution of loads imposed on the shoulder in practical working situations can be based on observations of working postures and external forces.

Adult↗
PubMed1982

The influence of day and night work on the circadian variations of cardiovascular performance.

Circadian variations of the pre-ejection period, Q-T interval, heart rate and oral temperature at rest and in day and night shift work were investigated. At rest, pronounced circadian variation was found in heart rate, pre-ejection period and Q-T interval. The ratio between Q-T interval and heart rate also shows a distinct circadian variation. When working, the rest rhythms of the variables were obscured. The physiological implications for shift work are discussed.

Adolescent↗
PubMed1982

Ergonomics: a new frontier in medical engineering.

Ergonomics as a field for medical engineering activities is outlined, particularly from the point of view of physical workload. The demand for better methods to deal with ergonomics' problems is high, including areas such as data-base design, mathematical modelling, sensor development, information processing, and instrumentation for ambulatory monitoring purposes. The discussion is exemplified by a project dealing with shoulder load in industrial work.

Biomedical Engineering↗
PubMed1981

Shoulder pain in industry: an epidemiological study on welders.

The occurrence of supraspinatus tendinitis in a group of welders at a shipyard was investigated, and compared with the occurrence of this condition in a group of office clerks. The study showed a prevalence ratio of 18 per cent in the welders, significantly higher than in the clerks. The average age (39 year) in the group with pain did not differ significantly from the average age in the entire group of welders. It is concluded that supraspinatus tendinitis is not exclusively an aging phenomenon, but that welding as an occupation plays an etiological role.

Adult↗
PubMed1978

Application of electromyography in ergonomics: new vistas.

The application of electromyography in analysis of muscle strain in working situations is far from straight-forward. Muscle force, for instance, is not directly accessible using electromyography. New insight in electrophysiological phenomena of human muscle provides however a firm basis for analysis of localized muscle fatigue at work. Such applications entail information at the muscle fiber membrane level.

Electromyography↗