ReviewUse of surface electromyography to estimate neck muscle activity
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)
- et al.
Influence of screen and copy holder positions on head posture, muscle activity and user judgement
Appl. Ergon.
(1998) - et al.
Multiple muscle force simulation in axial rotation of the cervical spine
Clin. Biomech.
(1999) - et al.
Intramuscular and surface EMG power spectrum from dynamic and static contractions
J. Electromyogr. Kinesiol.
(1995) Biomechanical aspects of occupational neck postures during dental work
IJIE
(1999)- et al.
Musculoskeletal disorders among dentists and variation in dental work
Appl. Ergon.
(1998) - et al.
Estimating maximal EMG amplitude for the trapezius muscle: on the optimization of experimental procedure and electrode placement for improved reliability and increased signal amplitude
J. Electromyogr. Kinesiol.
(1996) - et al.
Anatomy and actions of the trapezius muscle
Clin. Biomech.
(1994) - et al.
Normalization of surface EMG amplitude from the upper trapezius muscle in ergonomic studies — a review
J. Electromyogr. Kinesiol.
(1995) - et al.
Influence of sitting postures on neck and shoulder e.m.g. during arm–hand work movements
Clin. Biomech.
(1987) - et al.
Cervical spine position versus e.m.g activity in neck muscles during maximum isometric neck extension
Clin. Biomech.
(1988)
E.m.g./moment relationships in neck muscles during isometric cervical spine extension
Clin. Biomech.
The effects of video display terminal height on the operator: a comparison of the 15 degree and 40 degree recommendations
Appl. Ergon.
Reproducibility of isometric strength: measurement of neck muscles
Clin. Biomech.
Prevalence of persistent neck and upper limb pain in a historical cohort of sewing machine operators
Am. J. Ind. Med.
Mental stress of long duration: EMG activity, perceived tension, fatigue, and pain development in pain-free subjects
Headache
Muscles alive, their functions revealed by electromyography
Job task and psychosocial risk factors for work-related musculoskeletal disorders among newspaper employees
Scand. J. Work Environ. Health
Work-related musculoskeletal disorders among physical therapists
Phys. Ther.
Neck and arm pain
Comparison of biomechanical human neck models: muscle forces and spinal loads at C4/5 level
J. Appl. Biomech.
Noninvasive analysis of human neck muscle function
Spine
Introduction to surface electromyography
Manual of surface electromyography
The use of surface electromyography in biomechanics
J. Appl. Biomech.
Electromyographic analysis of neck muscle fatigue in patients with osteoarthritis of the cervical spine
Spine
Role of muscle tension in personality theory
Psychol. Bull.
Epidemiology of musculoskeletal disorders due to biomechanical overload
Ergonomics
Prevalence rates and odds ratios of shoulder–neck diseases in different occupational groups
Br. J. Ind. Med.
Source document position as it affects head position and neck muscle tension
Ergonomics
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.
Load moments and myoelectric activity when the cervical spine is held in full flexion and extension
Ergonomics
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
Changes in isometric strength and range of motion of the idolated cervical spine after eight weeks of clinical rehabiliation
Spine
Job demands, muscle acitivity and musculoskeletal symptoms in relation to work with the computer mouse
Scand. J. Work Environ. Health
The influence of electrode position on bipolar surface electromyogram recordings of the upper trapezius muscle
Eur. J. Appl. Physiol.
Kinesiology, with special reference to electromyographic kinesiology
Musculoskeletal symptoms and job strain among nursing personnel: a study over a three year period
Occup. Environ. Med.
Morphometry of human neck muscles
Spine
Neck muscle activation patterns in humans during isometric stabilization
Exp. Brain Res.
Work with video display terminals among office employees. I. Subjective symptoms and discomfort
Scand. J. Work Environ. Health
A computer desk for bifocal lens wearers, with special emphasis on selected telecommunication tasks
Ergonomics
A precision task, posture, and strain
J. Safety Res.
Cited by (178)
Neck muscle fatigue due to sustained neck flexion during smartphone use
2024, International Journal of Industrial ErgonomicsAxial muscle activation provides stabilization against perturbations while running
2023, Human Movement ScienceEffects of a tongue training program in Parkinson's disease: Analysis of electrical activity and strength of suprahyoid muscles
2022, Journal of Electromyography and KinesiologySex and posture dependence of neck muscle size-strength relationships
2021, Journal of Biomechanics