Background and Purpose. Treatment of patients with impingement symptoms commonly includes exercises intended to restore “normal” movement patterns. Evidence that indicates the existence of abnormal patterns in people with shoulder pain is limited. The purpose of this investigation was to analyze glenohumeral and scapulothoracic kinematics and associated scapulothoracic muscle activity in a group of subjects with symptoms of shoulder impingement relative to a group of subjects without symptoms of shoulder impingement matched for occupational exposure to overhead work. Subjects. Fifty-two subjects were recruited from a population of construction workers with routine exposure to overhead work. Methods. Surface electromyographic data were collected from the upper and lower parts of the trapezius muscle and from the serratus anterior muscle. Electromagnetic sensors simultaneously tracked 3-dimensional motion of the trunk, scapula, and humerus during humeral elevation in the scapular plane in 3 hand-held load conditions: (1) no load, (2) 2.3-kg load, and (3) 4.6-kg load. An analysis of variance model was used to test for group and load effects for 3 phases of motion (31°–60°, 61°–90°, and 91°–120°). Results. Relative to the group without impingement, the group with impingement showed decreased scapular upward rotation at the end of the first of the 3 phases of interest, increased anterior tipping at the end of the third phase of interest, and increased scapular medial rotation under the load conditions. At the same time, upper and lower trapezius muscle electromyographic activity increased in the group with impingement as compared with the group without impingement in the final 2 phases, although the upper trapezius muscle changes were apparent only during the 4.6-kg load condition. The serratus anterior muscle demonstrated decreased activity in the group with impingement across all loads and phases. Conclusion and Discussion. Scapular tipping (rotation about a medial to lateral axis) and serratus anterior muscle function are important to consider in the rehabilitation of patients with symptoms of shoulder impingement related to occupational exposure to overhead work.

https://ir.uiowa.edu/cgi/viewcontent.cgi?article=1000&context=oeh_pubs

Alterations in Shoulder Kinematics and Associated Muscle Activity in People With Symptoms of Shoulder Impingement

This brief review examines some of the methods used to infer central control strategies from surface electromyogram (EMG) recordings. Among the many uses of the surface EMG in studying the neural control of movement, the review critically evaluates only some of the applications. The focus is on the relations between global features of the surface EMG and the underlying physiological processes. Because direct measurements of motor unit activation are not available and many factors can influence the signal, these relations are frequently misinterpreted. These errors are compounded by the counterintuitive effects that some system parameters can have on the EMG signal. The phenomenon of crosstalk is used as an example of these problems. The review describes the limitations of techniques used to infer the level of muscle activation, the type of motor unit recruited, the upper limit of motor unit recruitment, the average discharge rate, and the degree of synchronization between motor units. Although the global surface EMG is a useful measure of muscle activation and assessment, there are limits to the information that can be extracted from this signal.

The extraction of neural strategies from the surface EMG

Objective This systematic review was designed and conducted in an effort to evaluate the evidence currently available for the many suggested risk factors for work-related musculoskeletal disorders. Methods To identify pertinent literature we searched four electronic databases (Cinahl, Embase, Medline, and The Cochrane Library). The search strategies combined terms for musculoskeletal disorders, work, and risk factors. Only case–control or cohort studies were included. Results A total of 1,761 non-duplicated articles were identified and screened, and 63 studies were reviewed and integrated in this article. The risk factors identified for the development of work-related musculoskeletal disorders were divided and organized according to the affected body part, type of risk factor (biomechanical, psychosocial, or individual) and level of evidence (strong, reasonable, or insufficient evidence). Conclusions Risk factors with at least reasonable evidence of a causal relationship for the development of work-related musculoskeletal disorders include: heavy physical work, smoking, high body mass index, high psychosocial work demands, and the presence of co-morbidities. The most commonly reported biomechanical risk factors with at least reasonable evidence for causing WMSD include excessive repetition, awkward postures, and heavy lifting. Additional high methodological quality studies are needed to further understand and provide stronger evidence of the causal relationship between risk factors and work-related musculoskeletal disorders. The information provided in this article may be useful to healthcare providers, researchers, and ergonomists interested on risk identification and design of interventions to reduce the rates of work-related musculoskeletal disorders. Am. J. Ind. Med. 2009. 2009 Wiley-Liss, Inc.

Risk factors for work-related musculoskeletal disorders: a systematic review of recent longitudinal studies

Aims: The aim of the present paper is to present the development of the second version of the Copenhagen Psychosocial Questionnaire (COPSOQ II). Methods: The development of COPSOQ II took place in five main steps: (1) We considered practical experience from the use of COPSOQ I, in particular feedback from workplace studies where the questionnaire had been used; (2) All scales concerning workplace factors in COPSOQ I were analyzed for differential item functioning (DIF) with regard to gender, age and occupational status; (3) A test version of COPSOQ II including new scales and items was developed and tested in a representative sample of working Danes between 20 and 59 years of age. In all, 3,517 Danish employees participated in the study. The overall response rate was 60.4%; (4) Based on psychometric analyses, the final questionnaire was developed; and (5) Criteria-related validity of the new scales was tested. Results: The development of COPSOQ II resulted in a questionnaire with 41 scales and 127 items. New scales on values at the workplace were introduced including scales on Trust, Justice and Social inclusiveness. Scales on Variation, Work pace, Recognition, Work-family conflicts and items on offensive behaviour were also added. New scales regarding health symptoms included: Burnout, Stress, Sleeping troubles and Depressive symptoms. In general, the new scales showed good criteria validity. All in all, 57% of the items of COPSOQ I were retained in COPSOQ II. Conclusions: The COPSOQ I concept has been further developed and new validated scales have been included.

https://journals.sagepub.com/doi/pdf/10.1177/1403494809349858

The second version of the Copenhagen Psychosocial Questionnaire.

This study among 477 employees working in the call centre of a Dutch telecom company (response 88%) examined the predictive validity of the job demands – resources (JD – R) model for self-reported absenteeism and turnover intentions. The central hypothesis was that job demands would be the most important predictors of absenteeism, through their relationship with health problems (i.e., exhaustion and Repetitive Strain Injury—RSI), whereas job resources would be the most important predictors of turnover intentions, through their relationship with involvement (i.e., organizational commitment and dedication). Results of a series of SEM analyses largely supported these dual processes. In the first energy-driven process, job demands (i.e., work pressure, computer problems, emotional demands, and changes in tasks) were the most important predictors of health problems, which, in turn, were related to sickness absence (duration and long-term absence). In the second motivation-driven process, job resources (i.e., s...

/pdf/dual-processes-at-work-in-a-call-centre-an-application-of-g0ae37gboc.pdf

Dual processes at work in a call centre: An application of the job demands – resources model

The effect of electrode position on the upper trapezius muscle on the myo-electric signal amplitude was investigated with special reference to arm position and estimate of force output. Previously, a depression of the electromyogram (EMG) signal has been reported midway between the seventh cervical vertebrae (C7) and acromion (Veiersted 1991, Eur J Appl Physiol 62:91–98) although this electrode position has been recommended (Zipp 1982, Eur J Appl Physiol 50:41–54). Ten healthy subjects performed maximal shoulder elevations with the arm in vertical, abducted and flexed positions and they performed a dynamic movement test. The myo-electric signal was recorded along the length of the right upper trapezius muscle by a 16-channel bipolar array electrode and was integrated with a 0.2-s time resolution. A region just lateral to the midpoint between C7 and the lateral edge of acromion was found with high and stable amplitudes (% coefficient of variation equalled 5.6). At the midpoint a dip in the amplitude profile appeared which was slightly displaced by arm abduction or flexion probably due to sliding, of the skin relative to the muscle. A linear EMG-force relationship was found in the region with high signal amplitudes, whereas the more lateral and the dip region showed highly variable EMG-force relationships. Thus, it was found that when using bipolar surface electrodes with an interelectrode distance of 2 cm a centre position 2 cm lateral to the midpoint between C7 and acromion provided good repeatability and high signal yield.

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

screen, and men’s short time in the same job and good computer skills were associated with neck symptoms. Hand-wrist symptoms were predicted by previous symptoms and low influence at work for both the men and women and sensorial demands for the women only. The duration of computer use predicted hand-wrist symptoms [eg, odds ratio (OR) of 2.3, 95% confidence interval (95% CI) 1.2–4.3, for almost continual computer use], but not neck symptoms. For those with almost continual computer use, hand-wrist symptoms were associated with mouse use for at least half of the worktime (OR 4.0, 95% CI 1.0–15.5) and not using the mouse at all (OR 4.0, 95% CI 1.1–14.4), as compared with mouse use for one-fourth of the worktime. Conclusions Limiting computer use to less than three-fourths of the worktime would help to prevent handwrist symptoms. Furthermore, low influence at work predicts both neck and hand-wrist symptoms.

Development of neck and hand-wrist symptoms in relation to duration of computer use at work.

Objectives This prospective study concentrated on determining factors of computer work that predict musculoskeletal symptoms in the shoulder, elbow, and low-back regions.

Methods A questionnaire on ergonomics, work pauses, work techniques, and psychosocial and work factors was delivered to 5033 office workers at baseline in early 1999 (response rate 69%) and to 3361 respondents at the time of the follow-up in late 2000 (response rate 77%). An increased frequency or intensity of symptoms was the outcome variable, including only nonsymptomatic respondents from the baseline questionnaire (symptom frequency below 8 days within the last 12 months or intensity score below 4 within the last 3 months).

Results In the follow-up, 10%, 18%, and 23% had symptoms more often in the elbow, shoulder, and low back, respectively, and 14%, 20%, and 22% had more intense symptoms. Women were more likely to be afflicted than men in all regions. In the full-fit multivariate logistic regression analysis, little influence on the timing of a rest pause and being disturbed by glare or reflection were significant predictors of shoulder symptoms, screen below eye height was a significant predictor for elbow symptoms, and previous symptoms was a significant predictor for symptoms in all regions. Computer worktime and psychosocial dimensions were not significant predictors.

Conclusions Influence on work pauses, reduction of glare or reflection, and screen height are important factors in the design of future computer workstations. Since previous symptoms was a significant predictor of recurrent symptoms in all three regions under study, it can be concluded that musculoskeletal symptoms are persistent.

Computer users' risk factors for developing shoulder, elbow and back symptoms.

Musculoskeletal symptoms and duration of computer and mouse use

Objectives This study assessed work postures, movements, psychosocial job demands, and shoulder and wrist extensor muscle activity and registered the prevalence of musculoskeletal symptoms of computer-aided design (CAD) operators. Methods A questionnaire survey was used to study the use of the computer mouse, psychosocial work factors, and musculoskeletal symptoms among 149 CAD operators. A workplace study was performed using observations, electrogoniometers on the wrists, and electromyography to measure exposures and physiological responses during CAD work among a subgroup of the CAD operators. Results Musculoskeletal symptoms were far more prevalent for the arm or hand operating the mouse than for the other arm or hand, and women were more affected than men. The symptoms may be related to such risk factors as repetitive movements, static postures (eg, ulnar-deviated and extended wrist on the mouse side), and static muscular activation patterns. The risk factors were present due to continuous mouse use and possibly also due to high demands for mental attentiveness, precision, and information processing. Conclusion Exposure during work with a computer mouse may present a risk for developing musculoskeletal symptoms. Improvements should focus on introducing more variation.

Chris Jensen

Papers

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

Development of neck and hand-wrist symptoms in relation to duration of computer use at work.

Computer users' risk factors for developing shoulder, elbow and back symptoms.

Musculoskeletal symptoms and duration of computer and mouse use

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