Precision of measurements of physical workload during standardised manual handling. Part I: surface electromyography of m. trapezius, m. infraspinatus and the forearm extensors.

Though surface electromyography (EMG) has been widely used in studies of occupational exposure, its precision in terms of the variance between-days and between-subjects has seldom been evaluated. This study aimed at such an evaluation. Six women performed three different work tasks: 'materials picking', 'light assembly', and 'heavy assembly', repeated on 3 different days. EMG was recorded from m. trapezius, m. infraspinatus and the forearm extensors. Normalisation was made to a maximal (MVE), and a submaximal (RVE), reference contraction. Variance components between days (within subjects) and between subjects were derived for the 10th, 50th and 90th percentiles, as well as for muscular rest parameters. For the task 'heavy assembly', the coefficient of variation between days (CV(BD)) was 8% for m. trapezius (right side, 50th percentile, MVE normalised values). Larger variabilities were found for m. infraspinatus (CV(BD) 15%), and the forearm extensors (CV(BD) 33%). Between-subjects variability (CV(BS)) was greater, 16% for m. trapezius and 57% for m. infraspinatus, 29% for the forearm extensors. RVE normalisation resulted in larger CV(BD), while reducing CV(BS). The between-days and between-subjects variability may be used to optimise sampling strategy, and to assess the bias in epidemiological studies. The bias caused by measurement procedures per se is acceptable.

[1]  P. Buckle,et al.  The nature of work-related neck and upper limb musculoskeletal disorders. , 2002, Applied ergonomics.

[2]  B G Armstrong,et al.  Effect of measurement error on epidemiological studies of environmental and occupational exposures. , 1998, Occupational and environmental medicine.

[3]  R Kadefors,et al.  Consequences of trapezius relaxation on the distribution of shoulder muscle forces: an electromyographic study. , 1998, Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology.

[4]  A Burdorf,et al.  Reducing random measurement error in assessing postural load on the back in epidemiologic surveys. , 1995, Scandinavian journal of work, environment & health.

[5]  L Finsen,et al.  Acute response to precision, time pressure and mental demand during simulated computer work. , 2000, Scandinavian journal of work, environment & health.

[6]  S. Skerfving,et al.  Quantifying work load in neck, shoulders and wrists in female dentists , 1997, International archives of occupational and environmental health.

[7]  L Finsen,et al.  Musculoskeletal disorders among dentists and variation in dental work. , 1998, Applied ergonomics.

[8]  G. Hansson,et al.  Validity and reliability of triaxial accelerometers for inclinometry in posture analysis , 2001, Medical and Biological Engineering and Computing.

[9]  K Ohlsson,et al.  Impact of physical exposure on neck and upper limb disorders in female workers. , 2000, Applied ergonomics.

[10]  J. Sluiter,et al.  Criteria document for evaluating the work-relatedness of upper-extremity musculoskeletal disorders. , 2001, Scandinavian journal of work, environment & health.

[11]  L. Kupper,et al.  Individual-based and group-based occupational exposure assessment: some equations to evaluate different strategies. , 1998, The Annals of occupational hygiene.

[12]  Svend Erik Mathiassen,et al.  Electromyographic activity in the shoulder-neck region according to arm position and glenohumeral torque , 2004, European Journal of Applied Physiology and Occupational Physiology.

[13]  R. Westgaard,et al.  Electromyographic evaluation of muscular work pattern as a predictor of trapezius myalgia. , 1993, Scandinavian journal of work, environment & health.

[14]  G M Hägg,et al.  Forearm muscular load and wrist angle among automobile assembly line workers in relation to symptoms. , 1997, Applied ergonomics.

[15]  K. B. Veiersted.  The reproducibility of test contractions for calibration of electromyographic measurements , 2004, European Journal of Applied Physiology and Occupational Physiology.

[16]  K Schüldt,et al.  Activity levels during isometric test contractions of neck and shoulder muscles. , 1988, Scandinavian journal of rehabilitation medicine.

[17]  D. Rempel,et al.  Sensitivity of trapezius electromyography to differences between work tasks - influence of gap definition and normalisation methods. , 2000, Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology.

[18]  R. H. Westgaard,et al.  Ergonomic intervention research for improved musculoskeletal health: A critical review , 1997 .

[19]  K Ohlsson,et al.  Goniometer measurement and computer analysis of wrist angles and movements applied to occupational repetitive work. , 1996, Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology.

[20]  Svend Erik Mathiassen,et al.  Job enlargement and mechanical exposure variability in cyclic assembly work , 2004, Ergonomics.

[21]  G-A Hansson,et al.  Modular data logger system for physical workload measurements , 2003, Ergonomics.

[22]  N. Özkaya,et al.  Testing apparatus and experimental procedure for position specific normalization of electromyographic measurements of distal upper extremity musculature. , 2001, Clinical biomechanics.

[23]  C. Jensen,et al.  The influence of electrode position on bipolar surface electromyogram recordings of the upper trapezius muscle , 2004, European Journal of Applied Physiology and Occupational Physiology.

[24]  K. B. Veiersted,et al.  Reliability of myoelectric trapezius muscle activity in repetitive light work. , 1996, Ergonomics.

[25]  B Jonsson,et al.  Measurement and evaluation of local muscular strain in the shoulder during constrained work. , 1982, Journal of human ergology.

[26]  K Ohlsson,et al.  Interindividual variation of physical load in a work task. , 1999, Scandinavian journal of work, environment & health.

[27]  G M Hägg,et al.  Normalization of surface EMG amplitude from the upper trapezius muscle in ergonomic studies - A review. , 1995, Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology.

[28]  R Ortengren,et al.  Reproducibility and stability of normalized EMG measurements on musculus trapezius. , 1996, Ergonomics.

[29]  P Asterland,et al.  Muscular rest and gap frequency as EMG measures of physical exposure: the impact of work tasks and individual related , 2000, Ergonomics.

[30]  G. Hansson,et al.  Influence of the subcutaneous fat layer, as measured by ultrasound, skinfold calipers and BMI, on the EMG amplitude , 2003, European Journal of Applied Physiology.

[31]  K. Hansen,et al.  Trapezius muscle load as a risk indicator for occupational shoulder-neck complaints , 1993, International archives of occupational and environmental health.

[32]  Benefits for Environmental Decisions,et al.  Commission On Behavioral and Social Sciences And Education , 1990 .

[33]  Svend Erik Mathiassen,et al.  Statistical power and measurement allocation in ergonomic intervention studies assessing upper trapezius EMG amplitude. A case study of assembly work. , 2002, Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology.

[34]  Carolyn M. Sommerich,et al.  Use of surface electromyography to estimate neck muscle activity. , 2000, Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology.