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Biofeedback and optimization of muscle contraction mode as intervention strategy in the prevention of work-related musculoskeletal disorders

Pernille Vedsted  


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Accepted by: Faculty of Health Sciences University of Southern Denmark
Defended on: June 23, 2006
Official opponents: Professor, dr.ir. Hermie J. Hermens, Roessingh Research and Development, Enschede, The Netherlands , Lektor, ph.d. Bente Rona Jensen, Institut for Idræt, Panum Instituttet, Københavns Universitet , Klinisk lektor, Jesper Bælum
Tutors: Professor Gisela Sjøgaard, dr.med, ph.d., Arbejdsmiljøinstituttet, Kbh. , Lektor Klavs Madsen, ph.d., Institut for Idræt og Biomekanik, Syddansk Universitet

Published in the PhD Database: July 5, 2006


English abstract
The projects in this ph.d. thesis were conducted at the National Institute of Occupational Health, Copenhagen.

Continuous static muscle activity or highly repetitive muscle contractions have been identified as one of the major risk factors in the development of work-related musculoskeletal disorders (WRMD). The highest prevalence of musculoskeletal disorders is often seen in the upper extremities in subjects working with repetitive low-force work. WRMD account for 48% of all reported work-related diseases in 2003 (Årsopgørelse, Arbejdstilsynet, 2003) and comprise a significant problem in modern society. The need for intervention strategies is therefore believed to be substantial.

The aim of the thesis is to identify possible intervention strategies in the workplace that may prevent the development of WRMD due to repetitive low-force work. The specific aims were: 1) to minimize unnecessary muscle activity through biofeedback during standardized computer work under various working conditions; 2) to determine the optimal muscle activation mode (sustained or intermittent static or dynamic contractions) when performing low-force activities as they occur in the workplace based on minimal electrical, mechanical, and metabolic responses.

Biofeedback reduced muscle activity in m. trapezius by 30 ¿ 50% and in m. extensor digitorum communis by ~ 10%, which can have protective effect on work-related musculoskeletal disorders.

The evaluation of the optimal muscle activation mode was based on minimal electrical, mechanical, and metabolic responses. The results showed that no contraction mode for a given time-tension product could fulfil the criteria for lowest electrical muscle activity as well as the lowest metabolic load evaluated from oxygen tension and intramuscular pressure. Dynamic contractions resulted in relative higher electrical and mechanomyographic muscle activity, whereas static contractions caused relative higher metabolic load due to reduced blood flow and oxygen delivery to the muscle. A single optimal contraction mode for preventing muscle fatigue and WRMD cannot be recommended.

When formulating criteria and efficient intervention strategies for the prevention of work-related musculoskeletal disorders due to repetitive low-force work, biofeedback as well as a combination of various muscle contraction modes performed through different time and force exposure profiles is recommended



Danish abstract
Projekterne til denne ph.d.-afhandling blev udført på Arbejdsmiljøinstituttet, Kbh.

Vedvarende statiske eller gentagne intense muskelkontraktioner betragtes som den væsentligste risikofaktor for udvikling af arbejdsbetingede muskelskeletlidelser (AMSL). Forekomsten af AMSL ses ofte i overekstremiteter hos personer som har ensidig gentaget arbejde. AMSL udgjorde 48% af de anmeldte arbejdsskader i 2003 (Årsopgørelse, Arbejdstilsynet, 2003) og betragtes derfor som et stort problem i det moderne samfund. Behovet for interventionsstrategier er derfor stort.

Formålet med studiet var at fastlægge mulige interventionsstrategier på arbejdspladsen, der kan forebygge udviklingen af AMSL under ensidigt gentaget arbejde. Delmålene var: 1) ved hjælp af biofeedback at minimere unødig muskelaktivitet under et standardiseret computerarbejde, der udføres under to forskellige arbejdsforhold; 2) at bestemme den optimale muskelkontraktionstype (vedvarende eller intermittent statiske eller dynamiske kontraktioner) under standardiseret arbejde svarende til belastningsniveauer, som de forekommer på arbejdspladser.

Biofeedback nedsatte muskelaktiviteten i m. trapezius med 30 ¿ 50% og i m. extensor digitorum communis med ~ 10%, som kan nedsætte risikoen for udviklingen af AMSL.

Optimal muskelkontraktionstype blev evalueret på baggrund af minimal elektrisk, mekanisk og metabolisk respons. Resultaterne viste, at ingen kontraktionstype for en given kraftudvikling over tid kunne opfylde kriteriet for lavest elektrisk aktivitet samt laveste metaboliske belastning bedømt udfra ilttension og intramuskulært tryk. Dynamiske kontraktioner medførte relativt højere elektrisk aktivitet samt mekanomyografisk aktivitet, hvorimod statiske kontraktioner medførte relativt større metaboliske belastninger på grund af ringere blodgennemstrømning og ilttilførsel til musklen. Derudfra kan en ensidig kontraktionstype ikke anbefales.

Ved fastlæggelse af kriterier og effektive interventionsstrategier på arbejdspladsen, der kan forebygge udviklingen af AMSL under ensidigt gentaget arbejde, anbefales der biofeedback samt en kombination af varierende muskelkontraktionstype udført med forskellige tids- og kraftudviklingsprofiler.