Review
Use of surface electromyography to estimate neck muscle activity

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Abstract

This paper reviews the literature concerning the use of surface electromyography (sEMG) for the study of the neck musculature in response to work and workplace design during light work and semi-static tasks. The paper also draws upon basic research and biomechanical modeling in order to provide methodological recommendations for the use of surface electromyography in this region of the body and to identify areas which require further investigation. The paper includes review and discussion of electrode site location, methods of normalization, data reliability, and factors that can affect sEMG signals from this region, including noise, physiologic artifact, stress, visual deficiencies, and pain. General guidance for maximum exertions with the neck musculature, for sEMG normalization or other purposes, is also included.

Introduction

The recognition of the need for a review of the use of surface electromyography (sEMG) in the study of the neck musculature was an outcome of the 1998 Marconi Research Conference. One of the goals of the conference was to develop consensus papers on the use of sEMG in the study of the neck and upper extremity regions during precision tasks. The papers were to specifically address circumstances under which sEMG amplitude could be used to estimate loads of the neck and upper extremity muscles during static or semi-static occupational tasks. Limited consensus emerged during the conference regarding sEMG of the neck musculature, because relatively few studies have employed sEMG specifically to the neck musculature, there are inconsistencies among methods used in published studies, and there have been few investigations of methodological considerations specific to application of sEMG in that region of the body, including reliability assessments. As such, the objectives of this paper are to review the limited research in the area and identify questions for future research. The paper addresses muscle selection, electrode placement, data normalization, and data reduction methods for investigation of precision, static, or semi-static tasks where muscle fatigue is not the focal point of interest. Organization of the paper is depicted in Fig. 1.

Musculoskeletal discomfort in the neck has been associated with a variety of occupations and types of work, from those categorized as physically demanding, such as farm work [57], [66] and patient care [7], [33] to those that are considered fairly static, such as dental work [17], [47], [51], work at video display terminals [5], [36], and sewing machine operation [1], [67]. In a group of Danish CAD operators, Jensen et al. [28] found a 70% 12-month prevalence of musculoskeletal symptoms in the neck, higher than any other body region, including low back (54%), shoulders (54%), and hands/wrists (52%). Many types of tissue in the cervical region can be sites of pain, including the neck muscles, intervertebral discs, the posterior longitudinal ligament, and the facet joints [8]. Whereas heavy or more physical work has been associated with diagnoses of cervical spondylosis [22] and degenerative changes [78], static work is more often associated with tension neck syndrome (myofascial pain) or myalgia [20], [21], [22]. Static work concentrates the workload on fewer, smaller muscle groups [71], which may be selectively overloaded through prolonged activation of some of the fibers in those muscles.

Muscle activity in occupational tasks is often investigated using surface electromyographic recordings. Assessing activity in the muscles through electromyography provides insight into patterns of activation or tension developed in the muscles, which may be of interest in and of itself, because sustained muscle activity is known to cause ischemic muscular pain [8]. Even at joint loads as low as 5% of maximum capacity, localized muscle fatigue has been shown to develop during sustained contractions [68]. Thus the relevance of studying muscle activity that is expected to be relatively low, such as when working with computers or performing light assembly work. Additionally, muscle activation patterns can be used to test assumptions of biomechanical models [16], [49], or can be used as input to models in order to develop estimates of muscle tension and loads in other tissues that are specific to an individual [9]. In many studies of semi-static work, often also entailing repetitive movements of the upper extremities, attention has been routinely focused on the descending (or upper) trapezius muscle. This muscle is a prevalent site of pain. That pain is sometimes referred to as chronic trapezius myalgia or tension-neck syndrome, and may be associated with work [41]. It has been studied extensively and several recommendations have previously been made regarding normalization of the EMG signal [42] and the placement of electrodes over this muscle [29]. As such, and since the actions of this muscle are directed mainly towards the scapula and clavicle [31], [35], [86], and it does not appear to function primarily as a head or neck stabilizer, the trapezius muscle is of secondary importance to this review. The primary goal of the paper is to focus on those muscles whose main functions are stabilization or movement of the head or neck.

Section snippets

Muscle selection

The goals of any particular electromyographic investigation will dictate which muscles are selected for study, but consideration may be given to muscles that are sensitive to changes in experimental conditions, muscles that are relevant in a particular occupational setting (site of pain; subject to loading), or muscles that will provide input to a specific biomechanical model. Based on extensive anatomical dissections, Kamibayashi and Richmond [34] identified more than 20 pairs of muscles that

Locating electrodes

It may be clear by now that there are basically two approaches which researchers seem to take in locating surface electrodes to study the neck musculature: muscle-specific sites (such as in Keshner et al. [35] and Queisser et al. [54]) and location-specific sites (such as in Choi and Vanderby Jr. [9] and Moroney et al. [49]). Data from location-specific sites may be appropriate when interest is in levels of activity in a muscle group, such as the dorsal muscle group (also referred to as the

Normalization

Normalization of EMG data has been proposed to address variation introduced in the measurement process by differences in electrode spacing, anatomical factors, and variation in electrode placement in multi-day experiments in order to facilitate comparisons between different muscles and individual subjects. According to Basmajian and De Luca [3], “The absence of normalization often constitutes a deficiency in many reported investigations which have compared or averaged groups of subjects”.

Additional methodological issues

Once sEMG data are collected, the primary interest of ergonomics researchers seems to be amplitude of the signal (mean, median, or static values). Only a few have attempted to make a connection between muscle force and muscle activity determined from sEMG, a connection that would seem to require an understanding of the relationship between sEMG level and external loads on the head and neck, as well as a biomechanical modeling component. An additional methodological issue that is related to

Special concerns

When using electromyography, it is important to be aware that factors in addition to those of interest to a specific experimental hypothesis may affect muscle activity. For example, muscle tension may reflect non-muscular sources of pain or dysfunction, such as the “splinting” mechanism which is commonly observed in transitory straightening of the cervical curvature following significant cervical extension injury. Other factors that may alter muscle activity include anxiety or stress [19],

Muscle selection and electrode placement

Electrode location is particularly critical in the cervical region because of the overlapping organization of the musculature. This should be explicitly described in the methods section of any paper in which electromyography is used, regardless of the muscles studied, though in a few of the papers examined for this review location descriptions were quite vague. Given that limited access sites seem to exist for sampling deeper muscles, additional studies are needed to more fully explore

Acknowledgements

The authors wish to thank Dr Chris Jensen of the National Institute of Occupational Health in Copenhagen Denmark, for his thoughtful review of the manuscript. Many of his suggestions were incorporated into the final version of the document. Thanks are also extended to Dr David Rempel and Dr Moshe Solomonow for providing the opportunity for a formal examination of the use of surface electromyography in the neck and upper extremities in workplace design research.

References (89)

  • K Schüldt et al.

    E.m.g./moment relationships in neck muscles during isometric cervical spine extension

    Clin. Biomech.

    (1988)
  • K.L Turville et al.

    The effects of video display terminal height on the operator: a comparison of the 15 degree and 40 degree recommendations

    Appl. Ergon.

    (1998)
  • J.J Ylinen et al.

    Reproducibility of isometric strength: measurement of neck muscles

    Clin. Biomech.

    (1999)
  • J.H Andersen et al.

    Prevalence of persistent neck and upper limb pain in a historical cohort of sewing machine operators

    Am. J. Ind. Med.

    (1993)
  • D Bansevicius et al.

    Mental stress of long duration: EMG activity, perceived tension, fatigue, and pain development in pain-free subjects

    Headache

    (1997)
  • J.V Basmajian et al.

    Muscles alive, their functions revealed by electromyography

    (1985)
  • B Bernard et al.

    Job task and psychosocial risk factors for work-related musculoskeletal disorders among newspaper employees

    Scand. J. Work Environ. Health

    (1994)
  • B.E Bork et al.

    Work-related musculoskeletal disorders among physical therapists

    Phys. Ther.

    (1996)
  • R Cailliet

    Neck and arm pain

    (1991)
  • H Choi et al.

    Comparison of biomechanical human neck models: muscle forces and spinal loads at C4/5 level

    J. Appl. Biomech.

    (1999)
  • M.S Conley et al.

    Noninvasive analysis of human neck muscle function

    Spine

    (1995)
  • J.R Cram et al.

    Introduction to surface electromyography

    (1998)
  • J Davis

    Manual of surface electromyography

    (1959)
  • C De Luca

    The use of surface electromyography in biomechanics

    J. Appl. Biomech.

    (1997)
  • Finsen L. Biomechanical analyses of occupational work loads in the neck and shoulder. PhD thesis, National Institute of...
  • P Gogia et al.

    Electromyographic analysis of neck muscle fatigue in patients with osteoarthritis of the cervical spine

    Spine

    (1994)
  • I.B Goldstein

    Role of muscle tension in personality theory

    Psychol. Bull.

    (1964)
  • A Grieco et al.

    Epidemiology of musculoskeletal disorders due to biomechanical overload

    Ergonomics

    (1998)
  • M Hagberg et al.
  • M Hagberg et al.

    Prevalence rates and odds ratios of shoulder–neck diseases in different occupational groups

    Br. J. Ind. Med.

    (1987)
  • N Hamilton

    Source document position as it affects head position and neck muscle tension

    Ergonomics

    (1996)
  • K Harms-Ringdahl et al.

    Intensity and character of pain and muscular activity levels elicited by maintained extreme flexion position of the lower-cervical-upper-thoracic spine

    Scand. J. Rehabil. Med.

    (1986)
  • K Harms-Ringdahl et al.

    Load moments and myoelectric activity when the cervical spine is held in full flexion and extension

    Ergonomics

    (1986)
  • M Hautekiet et al.

    The influences of the height of the VDU screen, and the position of the back rest on the neck muscle load and the position of the head

  • T Highland et al.

    Changes in isometric strength and range of motion of the idolated cervical spine after eight weeks of clinical rehabiliation

    Spine

    (1992)
  • C Jensen et al.

    Job demands, muscle acitivity and musculoskeletal symptoms in relation to work with the computer mouse

    Scand. J. Work Environ. Health

    (1998)
  • C Jensen et al.

    The influence of electrode position on bipolar surface electromyogram recordings of the upper trapezius muscle

    Eur. J. Appl. Physiol.

    (1993)
  • B Jonsson

    Kinesiology, with special reference to electromyographic kinesiology

  • M Josephson et al.

    Musculoskeletal symptoms and job strain among nursing personnel: a study over a three year period

    Occup. Environ. Med.

    (1997)
  • L Kamibayashi et al.

    Morphometry of human neck muscles

    Spine

    (1998)
  • E Keshner et al.

    Neck muscle activation patterns in humans during isometric stabilization

    Exp. Brain Res.

    (1989)
  • B.G Knave et al.

    Work with video display terminals among office employees. I. Subjective symptoms and discomfort

    Scand. J. Work Environ. Health

    (1985)
  • S Kumar

    A computer desk for bifocal lens wearers, with special emphasis on selected telecommunication tasks

    Ergonomics

    (1994)
  • S Kumar et al.

    A precision task, posture, and strain

    J. Safety Res.

    (1979)
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