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R Kadefors

Publications and source records attributed to R Kadefors.

81 records · Page 5Linked to original sources
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[PROCID: a project of the European Community for the study and prevention of muscular disorders in computer terminal operators].

This paper presents an EC funded concerted action aimed at studying the prevention of muscle disorders in the operation of computer input devices. About 40% the today's working population use computers in their daily work. This percentage is expected to increase dramatically in the coming years. At the same time health statistics indicate an increased incidence of work related musculoskeletal disorders among computer users. A deeper knowledge in this field may improve the health risk assessment approach, the design of computer input devices and the revision process of existing standards, norms and guidelines concerning computer work. Specific research objectives include: the development of intramuscular techniques suitable for mapping motor unit recruitment under operation of computer input devices; the evaluation of muscle fatigue and motor unit recruitment in dynamic tasks in normal subjects and in patients with pain syndromes; the experimental evaluation of stress induced muscular tension at the motor unit level, in operation of computer input devices; the formulation of recommendations for work with computer input devices.

Computer Terminals↗
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Arm movement and EMG mean power frequency in the trapezius muscle: a comparison between surface and intramuscular recording techniques.

In a previous study it has been shown that there is a systematic variation of the EMG mean power frequency recorded under dynamic conditions with surface electrodes from non-fatigued trapezius muscle. The variation was most pronounced in relation to shoulder joint angle. The aim of the present study was to find out whether this variation was caused by geometric factors such as electrode displacement, or by neuromuscular factors within the muscle. A comparison has been made between surface and intramuscular recordings. EMG was recorded with standard surface electrodes and with a monopolar "hooked wire" intramuscular electrode. The recordings were analyzed for calculation of mean power frequency (MPF) and root mean squared (RMS) signal level. For MPF we found a low, but statistically significant correlation (r = 0.30) between surface and intramuscular recordings. For RMS the corresponding correlation was high (r = 0.92). Analysis of variance showed a high proportion of explained variance related to the shoulder joint angle for surface recordings, but not for intramuscular recordings. The results were confirmed in the regression analysis. The results indicate that the observed variation is largely caused by geometric displacement of the surface electrodes and not by intrinsic neuro-muscular factors.

Adult↗
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Work load, fatigue, and pause patterns in clinical dental hygiene.

PURPOSE: Previous studies have suggested that high frequencies of shoulder and neck complaints in dental hygienists mainly were due to longstanding, low-level static load of the neck and shoulder muscles. The purpose of the present study was to make continuous recordings of myoelectric signals from the shoulder muscles of dental hygienists in order to assess static load. METHODS: Myoelectric signals were recorded from the right trapezius muscle of 10 Swedish dental hygienists during half of a normal working day. A portable system for collection and on-line processing of myoelectric signals was used. Signal parameters were obtained, indicating muscular load, fatigue, pause frequency, and pause duration, respectively. All measurements were referred to a resting value and a reference contraction value established with the hand loaded with a 0.5 kg weight at the beginning of the recording session. RESULTS: A static load of 50 to 100% of the reference contraction (0.5 kg hand load with raised arm) was found in the trapezius muscle. The median load for the whole group was 57% of the reference level. Group data analyses of frequency EMG seldom showed significant fatigue. At individual levels, however, it was possible to identify localized muscle fatigue and relate it to a specific work task. There were many short pauses with a duration of 1 to 2 seconds, but an almost total lack of pauses of a duration longer than five seconds. CONCLUSIONS: Individual dental hygienists exhibited significant muscle fatigue that might be related to development of work related myalgias of the shoulder muscles. Future study of muscle patterns and dental hygiene tasks may lead to improved work designs and patterns for dental hygienists.

Adult↗