Individual and work-related risk factors associated with symptoms of musculoskeletal complaints

The relationship between the development of musculoskeletal disorders, body mass index, and academic stress in Bahraini University students

Background

There are many mechanisms in which stress can lead to weight gain thus high a BMI. The endocrine and inflammatory pathway can directly increase abdominal adiposity. Another way in which stress leads to weight gain is through changes in health behaviors. The study aimed to investigate the prevalence of musculoskeletal disorders (MSDs) among healthy students of Ahlia University, and to determine the relationship between the development of MSDs and academic stressors and body mass index.

Methods

Self-administered questionnaires were distributed to 94 students aged 18-26 years who were enrolled at various Ahlia University colleges and met other inclusion criteria. The students responded to the standardized Nordic musculoskeletal questionnaire and the modified College Student Stress Inventory regarding musculoskeletal symptoms and academic stressors. Height and weight measurements were also obtained to determine body mass index.

Results

A total of 77.66% reported MSDs in one or more body part, with the prevalence being higher among women than among men. The 7-day prevalence of MSDs severe enough to interfere with activities of daily living was 60.64%, and 44.68% by female and male students, respectively. There was a significant relationship between academic stress and MSDs in the neck, shoulders, lower back, and hips, while the relationship between MSDs, and body mass index, academic stress, and grade point average was not significant.

Conclusions

The prevalence of MSDs among Ahlia University students was found to be high. Apart from the positive correlation between academic stress and MSDs in certain body parts, other correlations were not significant.

Occupational rehabilitation programs for musculoskeletal pain and common mental health disorders: study protocol of a randomized controlled trial

BACKGROUND

Long-term sick leave has considerably negative impact on the individual and society. Hence, the need to identify effective occupational rehabilitation programs is pressing. In Norway, group based occupational rehabilitation programs merging patients with different diagnoses have existed for many years, but no rigorous evaluation has been performed. The described randomized controlled trial aims primarily to compare two structured multicomponent inpatient rehabilitation programs, differing in length and content, with a comparative cognitive intervention. Secondarily the two inpatient programs will be compared with each other, and with a usual care reference group.

METHODS/DESIGN

The study is designed as a randomized controlled trial with parallel groups. The Social Security Office performs monthly extractions of sick listed individuals aged 18-60 years, on sick leave 2-12 months, with sick leave status 50% - 100% due to musculoskeletal, mental or unspecific disorders. Sick-listed persons are randomized twice: 1) to receive one of two invitations to participate in the study or not receive an invitation, where the latter "untouched" control group will be monitored for future sick leave in the National Social Security Register, and 2) after inclusion, to a Long or Short inpatient multicomponent rehabilitation program (depending on which invitation was sent) or an outpatient cognitive behavioral therapy group comparative program. The Long program consists of 3 ½ weeks with full rehabilitation days. The Short program consists of 4 + 4 full days, separated by two weeks, in which a workplace visit will be performed if desirable. Three areas of rehabilitation are targeted: mental training, physical training and work-related problem solving. The primary outcome is number of sick leave days. Secondary outcomes include time until full sustainable return to work, health related quality of life, health related behavior, functional status, somatic and mental health, and perceptions of work. In addition, health economic evaluation will be performed, and the implementation of the interventions, expectations and experiences of users and service providers will be investigated with different qualitative methods.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01926574.

Motor variability in occupational health and performance

Several recent reviews have reported that 'repetitive movements' constitute a risk factor for occupational musculoskeletal disorders in the neck, shoulder and arm regions. More variation in biomechanical exposure is often suggested as an effective intervention in such settings. Since increasing variation using extrinsic methods like job rotation may not always be possible in an industrial context, the intrinsic variability of the motor system may offer an alternative opportunity to increase variation. Motor variability refers to the natural variation in postures, movements and muscle activity observed to different extents in all tasks. The current review discusses research appearing in motor control, sports sciences and occupational biomechanics literature to answer whether motor variability is important to consider in an occupational context, and if yes, whether it can be manipulated by training the worker or changing the working conditions so as to increase biomechanical variation without jeopardizing production. The review concludes that motor variability is, indeed, a relevant issue in occupational health and performance and suggests a number of key issues for further research.

Validation of a novel sham cervical manipulation procedure

BACKGROUND CONTEXT

No clinical trial of spinal manipulation for chronic neck pain (NP), for either single or multiple intervention session(s), has used an effective manual sham-manipulation control group.

PURPOSE

Validate a practical sham cervical high-velocity low-amplitude spinal manipulation.

STUDY DESIGN/SETTING

Randomized experimental validation study in an institutional clinical research laboratory.

PATIENT SAMPLE

Eligible subjects were males and females, 18 to 60 years of age with mechanical NP (as defined by the International Association for the Study of Pain Classification) of at least 3 months' duration. Subjects with arm pain, any pathologic cause of NP, or any contraindication to spinal manipulation were excluded.

OUTCOME MEASURES

The primary outcome was the patient's self-report or registration of group allocation after treatment. Secondary outcomes were numerical rating scale-101 for NP, range of motion (ROM; by goniometer), and tenderness (by pressure algometry).

METHODS

Eligible subjects were randomly allocated to one of two groups: real cervical manipulation (RM) or sham cervical manipulation (SM). All subjects were given two procedures in sequence, either RM+SM or SM+SM. Immediately after the two procedures, subjects were asked to register any pain experienced during the procedures and to identify their treatment group allocation. Force-time profiles were recorded during all procedures. Secondary clinical outcome measures were obtained at baseline, 5 and 15 minutes after the intervention, including ROM, self-report of pain, and local spinous process tenderness. Data for each variable were summarized and tested for normality in distribution. Summary statistics were obtained for each variable and statistically tested.

RESULTS

Sixty-seven subjects were randomized. Data from 64 subjects (32 per group) were available for analysis. There were no significant differences between the groups at baseline. One adverse event occurred in the "real" group, which was a mild posttreatment pain reaction lasting less than 24 hours. In the RM group, 50% of subjects incorrectly registered their treatment allocation; in the sham group, 53% did so. For the SM group, none of the procedures resulted in cavitation, whereas in the RM group, 87% of procedures resulted in cavitation. There were no significant changes between groups on pain, tenderness, or ROM. Force-time profiles of the RM and SM procedures demonstrated fidelity with significant differences between components as intended.

CONCLUSIONS

The novel sham procedure has been shown to be effective in masking subjects to group allocation and to be clinically inert with respect to common outcomes in the immediate posttreatment stage. Further research on serial applications and for multiple operators is warranted.

Relationship between trapezius muscle activity and typing speed: taping effect

Clinically, over-activation of upper trapezius (UT) muscular activity is a common cause of symptoms in computer users. The purpose of this study was to investigate the correlation between trapezius muscular activity and typing speed with and without taping. Twelve participants performed a typing task for 15 min with and without taping on the UT muscle. Electromyography (EMG) of the muscular activity of UT and lower trapezius (LT) was recorded. With or without taping, there was a significantly positive correlation (r = 0.40, p = 0.04) between typing speed and UT/LT. Additionally, UT and UT/LT ratios were lower with taping than without taping (difference = 5.2% and 26.9%). The LT ratio was higher with taping than without taping (difference = 5.8%). Taping can alter the muscular activity of the trapezius during typing and may have the potential to be applied in computer users to prevent over-activation of UT muscular activity. Practitioner Summary: The effect of taping was tested on typing speed and trapezius muscular activity. With or without taping, typing speed was correlated with trapezius activity. The muscle activity of the trapezius, however, was lower with taping than without taping. Thus, taping has the potential to prevent over-activation of UT muscular activity during typing.

Clinimetric properties of the Turkish translation of a modified neck disability index

Background

Neck pain is a common problem that can greatly affect a person's activities of daily living. Functional status questionnaires are important in assessing this effect, and are used to follow up neck pain management programs. The Neck Disability Index (NDI) is the first-created scale for neck pain-related disability and is widely translated and in common used in many countries. Our aim is investigate to clinometric properties of a Turkish version of modified NDI and to give a choice in daily practise of versions to be used.

Methods

The modified NDI was applied to 30 patients for reliability. 185 patients participated in the validity study. All patients were recruited from the outpatient clinic of our department. The scale was translated by the forward and backward translation procedure according to the COSMIN criteria. The test was repeated at 48 hours interval for reliability study. SPSS-10.0, software was used for statistical analyses. The Intraclass correlation coefficient was used for the test- retest reliability of the modified NDI. Cronbach α was used for internal consistency. Factor analysis was used for construct validity. The validity of the modified NDI with respect to the SF-36, HAD, VAS pain, VAS disability was assessed using Spearman correlations.

Results

The Intraclass correlation coefficient between first and second (within 48 hours) evaluation of test (rs) was 0.92. Questions 1,4,6,8,10 were shown to have excellent reliability. (rs > 0.9). Question 10 was the most frequently challenged question because "recreational and social activities" do not have not the same meanings in Turkey than in western countries. This required that detailed explanations be provided by the investigators. Cronbach's alpha for the total index was 0.88. A single factor accounting for 80.2% of the variance was obtained. Validity studies demonstrated good and moderate correlations (rs) among NDI, HAD, VAS, physical function subtitle of SF 36 (0.62, 0.76, 0.68).

Conclusions

The modified NDI-Turkish version is a reliable and valid test and is suitable for daily practise.

Environmental discomfort and musculoskeletal disorders

BACKGROUND

Musculoskeletal disorders (MSDs) are the most common occupational disease in Europe, with high prevalence among hospital workers. Both environmental and psychosocial work factors may impact significantly on the development and exacerbation of MSDs.

AIMS

To evaluate whether environmental factors at work are associated with MSDs in hospital workers and to investigate potential interactions between environmental and psychosocial risk factors in the workplace that are associated with MSDs.

METHODS

A cross-sectional investigation was performed using the Nordic questionnaire to assess MSDs, the IAQ/MM-040 indoor air questionnaire for environmental factors, the demand-control model for job strain and the Goldberg questionnaire for anxiety and depression. The association between environmental factors and MSDs was studied using logistic regression analysis. In addition, the interactions of environmental factors with strain, anxiety and depression for MSDs were examined.

RESULTS

Environmental complaints were associated with MSDs. The strongest associations were found between temperature complaints (OR 2.73), noise and light complaints (OR 2.22), other environmental complaints (OR 3.12) and upper limb disorders. A significant interaction between temperature complaints and strain for upper limb disorders (F = 9.52, P < 0.05) was found.

CONCLUSIONS

To prevent MSDs, a multi-level approach is needed, including environmental measures and interventions directed to both psychosocial and organizational factors.

Chronic mechanical neck pain in adults treated by manual therapy: a systematic review of change scores in randomized controlled trials of a single session

We report a systematic analysis of group change scores of subjects with chronic neck pain not due to whiplash and without headache or arm pain, in randomized clinical trials of a single session of manual therapy. A comprehensive literature search of clinical trials of chronic neck pain treated with manual therapies up to December 2006 was conducted. Trials that scored above 60% on the PEDro Scale were included. Change scores were analyzed for absolute, percentage change and effect size (ES) whenever possible. Nine trials were identified: 6 for spinal manipulation, 4 for spinal mobilization or non-manipulative manual therapy (2 overlapping trials), and 1 trial using ischemic compression. No trials were identified for massage therapy or manual traction. Four manipulation trials (five groups) reported mean immediate changes in 100-mm VAS of -18.94 (9.28) mm. ES for these changes ranged from .33 to 2.3. Two mobilization trials reported immediate VAS changes of -11.5 and -4 mm (ES of .36 and .22, respectively); one trial reported no difference in immediate pain scores versus sham mobilization. The ischemic compression study showed statistically significant immediate decreases in 100-mm pain VAS (average = -14.6 mm). There is moderate-to-high quality evidence that immediate clinically important improvements are obtained from a single session of spinal manipulation. The evidence for mobilization is less substantial, with fewer studies reporting smaller immediate changes. There is insufficient evidence for ischemic compression to draw conclusions. There is no evidence for a single session of massage or manual traction for chronic neck pain.

Electromyographic assessment of apple bucket intervention designed to reduce back strain

The authors previously developed an apple bucket that was modified by use of a hip belt to reduce muscle fatigue. The intervention of belt use was accepted by workers and shown not to interfere with productivity. However, use of this intervention did not appear to reduce muscle fatigue when measured by tests of voluntary muscle strength. The purpose of the present study was to evaluate the intervention's effect on muscle fatigue employing surface electromyographic (EMG) amplitude. Amplitude measurements on 15 muscles were taken from 10 laboratory volunteers who were carrying a full bucket of apples, once while wearing the intervention belt and once without the intervention. These measurements were taken for seven different postures (four angles of trunk flexion (0 degrees , 20 degrees , 45 degrees , 90 degrees ) and three raised-arm positions (both up, dominant up, non-dominant up)) common to apple harvest work. Participants were measured in these conditions both with the bucket carried in front and with the bucket carried to the side. Significant reductions in amplitude favouring the intervention were seen for 11 of the 15 muscles in models considering the four body flexion angles. Ten of these were of the middle and lower back. These control/intervention differences were seen with both bucket-carrying positions (front vs. side) and tended to increase with increasing flexion angle. In contrast, no significant intervention effects were observed in models considering treatment by arm-raised position. One significant main effect (upper trapezius, side bucket) showed an amplitude reduction in the treatment condition. Another main effect showing increased amplitude in the intervention condition use was observed in the dominant levator scapulae (side bucket). Thus, the use of the intervention belt reduces EMG amplitude among a number of mid- and lower-back muscles. This is suggestive of a protective effect against back strain.

Association between cervicocephalic kinesthetic sensibility and frequency of subclinical neck pain

Although impaired neck proprioception has been demonstrated in patients with chronic neck pain, previous studies have not consistently shown any association between pain intensity and proprioceptive performance. We therefore investigated whether temporal aspects of pain are associated with cervicocephalic kinesthetic sensibility. One hundred and twenty-seven adults with or without subclinical neck pain undertook two tasks, repositioning their heads to the neutral head position (head-to-NHP) and target position (head-to-target) in sagittal and transverse plane. Absolute error was calculated from position data recorded by an ultrasound-based motion analysis system. Pain frequency, duration, and intensity were evaluated using a questionnaire. A mixed effects model was constructed to test the effect on reposition error by different pain factors, with age, gender and maximal cervical range of motion as covariates. A higher pain frequency was associated with greater reposition errors for all movement directions in the head-to-NHP task. No consistent effect was observed for pain intensity or duration. In the case of the head-to-target task, no consistent effect was observed for any of the three pain factors. The findings reveal that pain frequency, not the intensity or duration of pain, is associated with neck proprioception in individuals with subclinical neck pain.

Chronic mechanical neck pain in adults treated by manual therapy: a systematic review of change scores in randomized clinical trials

OBJECTIVE

This study provides a systematic analysis of group change scores in randomized clinical trials of chronic neck pain not due to whiplash and not including headache or arm pain treated with manual therapy.

METHODS

A comprehensive literature search of clinical trials of chronic neck pain treated with manual therapies up to December 2005. Only clinical trials scoring above 11.5 (Amsterdam-Maastricht Scale) were included in the analysis.

RESULTS

From 1980 citations, 19 publications were selected. Of the 16 trials analyzed (3 were rejected for poor quality), 9 involved spinal manipulation (12 groups), 5 trials (5 groups) were for spinal mobilization or nonmanipulative manual therapy (1 trial overlapped), and 2 trials (2 groups) involved massage therapy. No trials included trigger point therapy or manual traction of the neck. For manipulation studies, the mean effect size (ES) at 6 weeks for 7 trials (10 groups) was 1.63 (95% confidence interval [CI], 1.13-2.13); 1.56 (95% CI, 0.73-2.39) at 12 weeks for 4 trials (5 groups); 1.22 (95% CI, 0.38-2.06) from 52 to 104 weeks for 2 trials (2 groups). For mobilization studies, 1 trial reported an ES of 2.5 at 6 weeks, 2 trials reported full recovery in 63.8% to 71.7% of subjects at 7 to 52 weeks, and 1 trial reported greater than 2/10 point pain score reduction in 78.3% of subjects at 4 weeks. For massage studies, 1 reported an ES of 0.03 at 6 weeks, whereas the other reported mean change scores of 7.89/100 and 14.4/100 at 1 and 12 weeks of, respectively.

CONCLUSIONS

There is moderate- to high-quality evidence that subjects with chronic neck pain not due to whiplash and without arm pain and headaches show clinically important improvements from a course of spinal manipulation or mobilization at 6, 12, and up to 104 weeks posttreatment. The current evidence does not support a similar level of benefit from massage.

The outcome of control groups in clinical trials of conservative treatments for chronic mechanical neck pain: a systematic review

Background

Chronic neck pain is highly prevalent in Western societies, with about 15% of females and 10% of males suffering with it at any time. The course of untreated chronic neck pain patients in clinical trials has not been well-defined and the placebo effect has not been clarified.

Methods

A systematic review of RCT's of conservative treatments for chronic mechanical neck pain was conducted. Studies were excluded if they did not include a control group, if they involved subjects with whiplash injuries, a predominance of headache or arm pain associated with chronic neck pain and if only one treatment was reported. Only studies scoring 3–5 out of 5 on the Jadad Scale for quality were included in the final analysis. Data on change in pain scores of subjects in both placebo (PL) as well as no-treatment (NT) control groups were analyzed. Mean changes in pain scores as well as effect sizes were calculated, summarized and compared between these groups.

Results

Twenty (20) studies, 5 in the NT group and 15 in the PL group, with outcome intervals ranging from 1–52 weeks were included in the final analysis. The mean [95% CI] effect size of change in pain ratings in the no-treatment control studies at outcome points up to 10 weeks was 0.18 [-0.05, 0.41] and for outcomes from 12–52 weeks it was 0.4 [0.12, 0.68]. In the placebo control groups it was 0.50 [0.10, 0.90] at up to 10 weeks and 0.33. [-1.97, 2.66] at 12–24 weeks. None of the comparisons between the no-treatment and placebo groups were statistically significant.

Conclusion

It appears that the changes in pain scores in subjects with chronic neck pain not due to whiplash who are enrolled in no-treatment and placebo control groups were similarly small and not significantly different. As well, they do not appear to increase over longer-term follow-up.

Using myoelectric signal parameters to distinguish between computer workers with and without trapezius myalgia

Complaints of chronic trapezius muscle pain among computer workers have increased in prevalence during the last decade. Currently there is no clear understanding of the pathophysiological mechanisms involved in affected muscles. The major objective of this work was to determine if measurable electrophysiological differences exist between the trapezius muscles in individuals suffering from trapezius myalgia (TM) and occupation-matched pain-free control subjects. Myoelectric signal (MES) data were recorded from the upper trapezius muscle while subjects with and without myalgia performed a standardized series of postural and arm-holding tasks. MES variables reflecting muscle fatigue, muscle tension and motor control strategies were analyzed to determine their potential ability to distinguish between the two groups. One variable, RestTime, was found to be significantly different between the groups but it was not specific enough to predict group association. A multivariate logistic regression analysis yielded a model that separated the two groups with better than 70% sensitivity and 70% specificity. The variables included in the model reflect differences in trapezius muscle activity between the groups, particularly related to motor control and/or active muscle tension, but not fatigue. The model was tested using a small sample of new data, which again produced a good sensitivity (85.7%) but not specificity (42.9%). To the authors' knowledge, this is the first objective MES-based model that has successfully classified subjects with or without TM based on a simple clinical test. Further work with this model might result in understanding the pathophysiology of TM, assisting with clinical diagnosis, and testing the effect of various treatment interventions.

Long-term repeatability of force, endurance time and muscle activity during isometric contractions

We determined the repeatability and correlations between force, endurance and muscle activity during isometric contractions over three years. Twenty-six subjects, with and without complaints of the shoulder and neck, performed standardized maximal and submaximal shoulder-abduction contractions and wrist extension-contractions at yearly intervals from 1997 to 1999. Peak forces developed during maximal contraction and the endurance times of submaximal contractions during shoulder abduction and wrist extension were measured. Electromyography (EMG) of muscle activity was recorded bilaterally from the upper trapezius, middle deltoid, and forearm extensor muscles. Root mean square EMG amplitudes were calculated. We found statistically significant associations between peak forces developed during wrist extension and shoulder abduction, and between endurance times of submaximal wrist extension and shoulder abduction. No statistically significant changes in peak force and EMG(peak) were found over the measurement years. The responses were not statistically significantly influenced by gender, or neck and shoulder pain. However, we observed considerable intra-individual variation in the inter-year measurements particularly for the responses to submaximal contraction. Such large variations represent a challenge when attempting to use the responses to interpret the effects of therapies.

A comparison of symptomatic and asymptomatic office workers performing monotonous keyboard work—1: Neck and shoulder muscle recruitment patterns

Work-related neck and upper limb disorders (WRNULD) are common problems among office workers who use computers intensively and maintain prolonged static postures. These disorders have often been attributed to result from sustained muscle activity in the neck-shoulder musculature. The present study examined whether symptomatic subjects exhibited the same muscle activity patterns as asymptomatic controls when they performed a prolonged computer task under the same conditions. Surface electromyography (EMG) of four major neck-shoulder muscles were compared between a Case Group (n=23) and a Control Group (n=20) of female office workers. The Case Group had higher activity in the right upper trapezius (UT) while the Control Group had more symmetrical muscle activity between left and right UT. The Case subjects could also be differentiated into "High Discomfort" and "Low Discomfort" sub-groups based on their discomfort scores. The High Discomfort Group had significantly higher right UT activity compared to the Low Discomfort and Control Groups. Results suggested that symptomatic individuals had altered muscle recruitment patterns that persisted throughout the sustained occupational task, while discomfort increased with time-at-task. These findings indicate that altered muscle recruitment patterns observed in the symptomatic subjects preceded the onset of task discomfort, and this finding may have important implications for the etiology of WRNULD.

Physical Exposures in Work Commonly Done by Women

The North American workforce is still highly sex-segregated, with most members of each sex in jobs composed primarily of workers of the same sex. This division is accentuated when jobs involve physical demands. Women have traditionally been assigned to tasks whose physical demands are considered to be light. Nevertheless, these tasks can have biological effects, sometimes serious. Phenomena related to physical demands of women's work can be considered in three categories: (a) musculoskeletal and cardiovascular demands of tasks often assigned to women in factories and service work; (b) sex- and gender-specific effects of toxic substances found in the workplace; and (c) interactions between work and the domestic responsibilities of many women. These phenomena are described, using examples recently gathered from workplaces. Effects of biological sex are distinguished, as far as possible, from effects of gender (social roles). Keywords: ergonomics, gender, occupation, anthropometry, toxicity, repetitive movements, static effort

Upper quadrant postural changes of school children in response to interaction with different information technologies

The objective of this study was to quantitatively analyse the sitting posture of school children interacting with both old (book) and new (laptop and desktop computers) information technologies to test the hypothesis that posture is effected by the type of information technology (IT) used. A mixed model design was used to test the effect of IT type (within subjects) and age and gender (between subjects). The sitting posture of 32 children aged 4-17 years was measured whilst they read from a book, laptop, and desktop computer at a standard school chair and desk. Video images were captured and then digitized to calculate mean angles for head tilt, neck flexion, trunk flexion, and gaze angle. Posture was found to be influenced by IT type (p < 0.001), age (p < 0.001) and gender (p = 0.024) and significantly correlated to the stature of the participants. Measurement of resting posture and the maximal range of motion of the upper and lower cervical spines in the sagittal plane was also undertaken. The biophysical impact and the suitability of the three different information technologies are discussed.

Seeking Care for Neck/Shoulder Pain: A Prospective Study of Work-Related Risk Factors in a Healthy Population

This study estimated the 5-year cumulative incidence of neck/shoulder pain and identified work-related risk factors leading subjects to seek care for this problem. Four to six years after the case-referent MUSIC-Norrtälje Study, a postal questionnaire was sent to the referents of this study, and 81% responded. At baseline, 516 men and 697 women were assessed as to their work-related exposures. The 4- to 6-year cumulative incidence for seeking care for neck/shoulder pain was 29% for women and 18% for men. For men, moderately increased risks were found for manual handling, night work/shift work, hindrances at work, and solitary work. For men, the risk increased with an increasing number of risk indicators. No work-related risk factors were found for women, highlighting the difficulty of identifying risk factors in a general population.

Job enlargement and mechanical exposure variability in cyclic assembly work

Cyclic assembly work is known to imply a high risk for musculoskeletal disorders. To have operators rotate between work tasks is believed to be one way of decreasing this risk, since it is expected to increase variation in mechanical and psychological exposures (physical and mental loads). This assumption was investigated by assessing mechanical exposure variability in three assembly tasks in an electronics assembly plant, each on a separate workstation, as well as in a 'job enlargement' scenario combining all three stations. Five experienced operators worked for 1 h on each station. Data on upper trapezius and forearm extensor muscle activity were obtained by means of electromyography (EMG), and working postures of the head and upper arms were assessed by inclinometry. The cycle-to-cycle variance of parameters representing the three exposure dimensions: level, frequency and duration was estimated using ANOVA algorithms for each workstation separately as well as for a balanced combination of all three. For a particular station, the variability of trapezius EMG activity levels relative to the mean was higher than for extensor EMG: between-cycles coefficients of variation (CV) about 0.15 and 0.10, respectively. A similar relationship between CV applied to the parameter describing frequency of EMG activity. Except for head inclination levels, the between-cycles CV was larger for posture parameters than for EMG. The between-cycles variance increased up to six fold in the job enlargement scenario, as compared to working at only one station. The difference in mean exposure between workstations was larger for trapezius EMG parameters than for forearm extensor EMG and postures, and hence the effect of job enlargement on exposure variability was more pronounced for the trapezius. For some stations, job enlargement even implied less cycle-to-cycle variability in forearm extensor EMG parameters than working at that station only. Whether the changes in exposure variability associated with job enlargement were sufficient to imply a decreased risk for musculoskeletal disorders is not known.

Are psychosocial factors, risk factors for symptoms and signs of the shoulder, elbow, or hand/wrist?: A review of the epidemiological literature

BACKGROUND

In 1993, an extensive review on the role of psychosocial factors in the development of musculoskeletal problems was published by Bongers et al (1993). Since then, additional reviews on this topic have been published; however, none of these focussed on upper limb problems.

METHODS

In this systematic review, the methodological quality of all studies was assessed and levels of evidence were apriori defined.

RESULTS

The large majority of the studies reported an association between at least one work-related psychosocial factor and adverse upper extremity symptoms or signs. High-perceived job stress was consistently associated with all upper extremity problems (UEP) in high and lower quality studies. Although not often studied, non-work-related stress was also consistently associated with UEP. In addition, there was some evidence for a relationship between high job demands and UEP, although the results did not meet the pre-set criterion for consistency.

CONCLUSIONS

High job stress and non-work-related stress reactions are consistently associated with UEP. In addition, high job demands is also in most studies associated with these disorders. Firm conclusions on the role of these factors in the etiology of UEP are not possible due to the cross-sectional nature of most studies.

Daytime trapezius muscle activity and shoulder-neck pain of service workers with work stress and low biomechanical exposure

AIM

The study aims to look for an association between trapezius muscle activity and shoulder-neck pain in work situations characterized by work stress and low biomechanical exposure.

METHODS

Female subjects (n = 93) were recruited from four occupational groups: health care, shop assistants, banking, and university secretaries. Thirty-eight workers were interviewed and classified as pain-afflicted by their shoulder-neck pain score in the last 6 months; 55 were pain-free. Shoulder-neck pain, bodily state of tension and fatigue, and subjective exposure assessments were monitored by repeated hourly measurements over 24 hr. Trapezius muscle activity was recorded bilaterally by surface EMG.

RESULTS

Shoulder-neck pain, perceived tension, work stress ("stressful environment"), and mental fatigue was augmented over the workday and reduced leisure time. Physical fatigue was low and stable. Thus, work stress appeared to be the dominant exposure associated with shoulder-neck pain. Muscle activity was low and similar for pain-afflicted and pain-free subjects during working hours. It was unchanged from work to leisure for the pain-afflicted workers and was significantly reduced for the pain-free group.

CONCLUSIONS

Stress-induced shoulder and neck pain is not necessarily associated with elevated trapezius muscle activity, but pain-free workers may benefit from better muscle relaxation in leisure.

The activation of mechanisms linking judgements of work design and management with musculoskeletal pain

The report of work-related musculoskeletal pain may be related to worker evaluations of the design and management of work through two mechanisms: one biomechanical and the other stress-related. This study of engineering workers (n = 204) explored the validity of these mechanisms using sequential logistic regression. Analyses suggested that workers' ratings of the adequacy of the design and management of their work were related to their report of work-related musculoskeletal pain. However, the mechanisms appeared to be activated in certain conditions. The reporting of pain in the upper body was both biomechanically- and stress-related, whereas that in the lower body was only biomechanically-related. It is argued that the mechanism activated appeared to be determined by the anatomical location of the pain, and probably the variance shared between the different aspects of work design and management, on the one hand, and the mechanical load of the job, on the other.

Perceived work stress, overcommitment, and self-reported musculoskeletal pain: a cross-sectional investigation

The objective of this study was to analyze associations of three indicators of perceived work stress (physical job demand, low control at work, and an imbalance between effort and reward), and of overcommitment, a personal pattern of coping with work demands, with musculoskeletal pain. A standardized questionnaire measuring these conditions in addition to self-reported musculoskeletal pain at different locations was administered to a group of 316 male and female employees of a public transport enterprise. After we adjusted for confounding effects of age, sex, socioeconomic status, shift work, and negative affectivity, we observed elevated prevalence odds ratios in employees who scored high on overcommitment, who were exposed to physical job demand, and, to a lesser extent, who reported psychosocial work stress. Results have implications for a more comprehensive approach to primary and secondary prevention of musculoskeletal pain.

Muscle activity and cardiovascular response during computer-mouse work with and without memory demands

Computer-mouse work is characterized by repetitive movements combined with mental demands. The present purpose was to study how the body responded to simulated Computer Aided Design (CAD) work without memory demand and when a high short-term memory demand was introduced. Nine female subjects repetitively performed a task which involved 15 s of elevation of the right index and middle fingers followed by 6 s of rest. Every second time the fingers rested, the left index finger was required to type a six-figure number, either '123456' (without memory demand) or a random number shown half a minute before (with memory demand). After 7 min of performing the task without memory demand, the memory demand was introduced and continued for 1 h. Introduction of memory demand resulted in increased heart rate (77-->84 beats/min), blood pressure (systolic 129-->140 mmHg; diastolic 72-->79 mmHg) and forearm extensor muscle activity (wrist, 2.7-->4.5% EMGmax; finger, 5.6-->7.5% EMGmax) and finger flexor muscle activity (0.7-->1.2% EMGmax) indicating increased co-contraction. Hereafter, muscle activity and cardiovascular response tended to decrease. Self-reported stress and rating of perceived exertion (RPE) for the right shoulder increased throughout the period. Two additional sub-studies were inlcuded, which focused on adaptation to the physical load, showing a decrease in muscle activity and arousal, and reintroduction of the memory load, showing a lower response as compared to the initial response. The practical consequences of the findings suggest that job content should have variable mental demands.

Shoulder and neck complaints in customer relations: individual risk factors and perceived exposures at work

Perceived psychosocial and biomechanical exposures, individual factors and pain in the shoulder and neck were recorded in two groups of female service workers (healthcare and shopping centre workers). The jobs investigated were characterized by 'much' direct human relations, 'little' sitting and 'much' standing, and were light work by physiological or biomechanical criteria but potentially psychosocially demanding. A screening survey (n = 400 females) was the basis for the selected sample (n = 66 females), which was the object of the main investigation of this study. Reliability of the questionnaires was tested in a separate group of female healthcare workers (n = 29). Heart rate recordings through the work day estimated workload. There was a high prevalence of shoulder and neck pain (> 50%) for both work groups. In the two populations it proved difficult to explain shoulder and neck pain by reported physical and psychosocial exposures or individual factors, except by the variable 'perceived general tension', which clearly differentiated workers with and without pain. The findings in this study indicated, first, that perceived general tension might be an independent risk factor for muscle pain and, second, that this might be related to personality factors. However, this putative relationship must be verified in a longitudinal study. As no variable describing exposures in the working environment was associated with shoulder and neck pain, the question is posed whether such complaints can be considered work-related. Alternatively, the variables used to describe mechanical and psychosocial exposures in this study may have low specificity in characterizing work-related risk factors for service workers with customer relations.

Psychosocial risk factors for neck pain: a systematic review

BACKGROUND

Neck pain, which is assumed to be a multifactorial disease, is a major problem in modern society.

METHODS

To identify the most important psychosocial risk factors for neck pain, a systematic review of the literature was carried out. The methodological quality of all studies in the review was assessed. Four levels of evidence were defined to assess the strength of evidence for potential risk factors for neck pain (strong, moderate, some or inconclusive evidence).

RESULTS

Some evidence was found for a positive relationship between neck pain and high quantitative job demands, low social (coworker) support, low job control, high and low skill discretion and low job satisfaction. Inconclusive evidence was found for high job strain, low supervisor support, conflicts at work, low job security, and limited rest break opportunities.

CONCLUSIONS

The procedure of the assessment of the methodological quality and the rating system applied to distinguish between high- and low-score studies, had a considerable influence on the level of evidence, indicating that changes in this procedure may have a major impact on the overall conclusions of this review.

Musculoskeletal disorders of the neck and shoulders in female sewing machine operators: prevalence, incidence, and prognosis

OBJECTIVES

To assess the occurrence and persistence of two restrictively defined neck-shoulder disorders among sewing machine operators. To assess factors associated with the development of neck-shoulder disorder and prognostic factors for remaining a case, when disorders were already present.

METHODS

In an initial group of 243 sewing machine operators, 178 were followed up for 2 years. At baseline and at 1 and 2 years follow up the participants underwent a clinical examination of the neck and arms and filled in a questionnaire about current musculoskeletal complaints. Clinical criteria for two main neck-shoulder disorders were defined: rotator cuff tendinitis and myofascial pain syndrome. A baseline control group consisted of 357 women with varied non-repetitive work.

RESULTS

At baseline the overall prevalence of myofascial pain syndrome and rotator cuff tendinitis was 15.2% and 5.8% among sewing machine operators compared with 9.0% and 2.2%, respectively, among controls. The presence of the disorders was strongly associated with a self perception of poor general health. Although myofascial pain syndrome showed a U shaped association with years as a sewing machine operator, rotator cuff tendinitis was absent among the newest recruits and present among 15% of the women with more than 20 years as a sewing machine operator. Besides years as a sewing machine operator, the risk of having a neck-shoulder disorder at baseline was significantly associated with high stress (prevalence ratio (PR)=2.54; 95% confidence interval (95% CI) 1.28 to 5.05) when adjusted for age, body mass index, smoking, living alone with children, job strain, and social support from colleagues and supervisors. Only one of 13 participants with rotator cuff tendinitis at baseline recovered during follow up. Myofascial pain syndrome showed a much more fluctuating tendency. Low social support (RR 3.72; 95% CI 1.22 to 11.30) and smoking (RR 3.93; 95% CI 1.33 to 11.58) were associated with the development of neck-shoulder disorders, which was also associated with neck-shoulder pain score and living alone with children.

CONCLUSION

Rotator cuff tendinitis showed a higher degree of persistence than myofascial pain syndrome. Both disorders highly influenced the perception of general health. Women who lived alone with children, were smokers, or experienced low support from colleagues and supervisors had a higher risk of contracting a neck-shoulder disorder.

The relationship between psychosocial work characteristics and low back pain: underlying methodological issues

OBJECTIVE

To evaluate the current epidemiological evidence linking psychosocial work characteristics with low back pain.

BACKGROUND

Psychosocial work characteristics have been widely evaluated as potential risk factors for low back injury. However, studies with different study populations and using various types of measures have had conflicting results.

METHODS

This review is the most extensive to date, reviewing 66 articles that have provided empirical evidence about the relationship between psychosocial work characteristics and initial reporting of lower back pain. The studies are reviewed with an emphasis on certain methodological issues: controlling for potential confounding; timing of the data collection; and measurement of the exposures and outcomes.

RESULTS

The results of this review suggest that controlling for potential confounding from occupational biomechanical demands had a large influence on the associations found between psychosocial work characteristics and lower back pain. In addition, the use of accurate and reliable measures for the occupational exposures (biomechanical and psychosocial) and the lower back pain outcomes appears to influence the strength of the associations found between psychosocial work characteristics and lower back pain.

CONCLUSION

Given the methodological concerns discussed in this review, it is difficult to draw strong causal inferences from this literature. However, it does appear that psychosocial characteristics are related to some lower back pain outcomes, and that employees' reactions to psychosocial work characteristics (e.g., job dissatisfaction and job stress) are more consistently related to lower back pain than are the psychosocial work characteristics themselves (e.g., work overload, lack of influence over work, quality of relationships with coworkers).

RELEVANCE

This review attempts to identify and address methodological issues in the literature evaluating the relationship between psychosocial work characteristics and lower back pain. Implications for future research are presented.

Muscle activity as a releasing factor for pain in the shoulder and neck

In this review, the evidence for trapezius muscle activity as a releasing factor for shoulder and neck pain is considered, mainly on the basis of studies in our laboratory. Two lines of evidence are produced, (i) vocational studies in an occupational setting, where muscle activity pattern is recorded by surface EMG and a clinical examination of the shoulder region of the subjects performed; and (ii) laboratory studies where muscle activity patterns and pain development are recorded in an experimental situation with mental stress and minimal physical activity. The vocational studies demonstrate pain development in the shoulder and neck despite very low muscle activity recorded, making it very difficult to assume muscular involvement for all cases with such complaints. However, the hypothesis of pain development through overexertion of a subpopulation of low-threshold motor units also makes it difficult to draw a firm negative conclusion. The laboratory experiments, on the other hand, show that trapezius activity patterns in response to stress have many features that would be expected if muscle activation induces pain symptoms. It is further noted that the trapezius is the only muscle with activity patterns that show these features. Possibly, we observe the effects of parallel physiological phenomena, e.g., a systemic autonomic activation that induces pain symptoms and also facilitates the motor response of some muscles. Evidence of autonomic activation of trapezius is presented by the observation of low-level, rhythmic EMG activity during sleep. However, this is not firm evidence for the above hypothesis, which at present best serves as a basis for further experimentation.

Hand and arm injuries associated with repetitive manual work in industry: a review of disorders, risk factors and preventive measures

Musculoskeletal disorders are the most common self-reported, work-related illness in the UK, with upper limb disorders ranking second only to back complaints. The rapid increase in disablement cases, the reduced productivity resulting from the disorders, and, perhaps, the threat of litigation which is on the increase, has led to an increased awareness of the problems and an increasing desire to reduce the incidence of such disorders. This paper reviews the problem of upper limb disorders and focuses on those disorders that could be associated with repetitive manual work in industry. The disorders are described and categorized, and potential occupational risk factors are discussed and related to the injuries. In addition, a number of preventive measures, in the form of ergonomics design changes and changes in workplace practice are reviewed. There are frequent calls for well-designed epidemiological studies, so that meaningful dose-response relationships can be drawn up. A significant part of good study design is associated with measurement and analysis of the user-tool interface and the working environment. With this in mind, a variety of measurement techniques are described. Furthermore, this paper highlights the need for study designs to be founded on a better understanding of the potential damage mechanisms, and points the way towards which areas should be investigated.

One-year reproducibility and stability of the signal amplitude ratio and other variables of the electromyogram: test-retest of a shoulder forward flexion test in female workers with neck and shoulder problems

We have studied 23 women with neck and shoulder problems in a car factory with a 1-year interval. Our main aim was to investigate the reproducibility and stability of the tension pattern. In addition, the mean frequency (MNF) of the power spectrum and the signal amplitude (RMS) of the surface electromyograph (EMG) of the trapezius, deltoid and infraspinatus muscles and mechanical output were determined throughout 100 maximal isokinetic shoulder forward flexions. The signal amplitude ratio (SAR) was calculated as the ratio between the signal amplitude of the EMG of the passive relaxation and the active flexion part of each contraction cycle. The SAR variable can be reproduced (r = 0.47-0.76) with a 1-year interval. There was a significantly lower SAR of the trapezius at the second test, which might have been due to lower work pace at the factory. The longitudinal patterns of SAR throughout the two tests were similar at both tests. There were significant correlations between tests for 18 out of 22 EMG variables, even though the correlations were generally lower than for SAR (initial MNF: r = 0.39-0.48; MNF endurance level: r = 0.55-0.83; RMS (%): r = 0.08-0.46). Peak torque had better reproducibility than work. In conclusion, SAR has a long-term reproducibility equal to or better than other EMG and biomechanical variables. The present results indicate that SAR has potential to measure unnecessary muscle tension in intervention studies and to identify individual movement patterns.

Effects of a multidisciplinary rehabilitation programme on health-related quality of life in patients with prolonged musculoskeletal disorders: a 6-month follow-up of a prospective controlled study

PURPOSE

The aim of this prospective, controlled, follow-up study (6 months) was to examine the effects of a multidisciplinary rehabilitation programme on perceived health-related quality of life (HRQL) in patients with prolonged musculoskeletal disorders (PMSD). The programme focused on body awareness therapy and cognitive and relaxation treatment.

METHOD

The rehabilitation group comprised 122 patients, and there were 114 patients in the matched control group (CG). Both groups of patients had access to primary health care. Baseline data were compared with 6-month follow-up data within and between the groups. The following measurements were employed: HRQL (Nottingham Health Profile), body awareness, postural control, pain (VAS), pain-related medicine consumption, isometric arm muscle endurance, aerobic capacity, psychosomatic symptoms, physical and psychosocial working environment and sick leave.

RESULTS

Variables that improved significantly as compared with the CG were: HRQL, anxiety, pain related to movements, psychosomatic symptoms and need for pain-related medicines.

CONCLUSIONS

The multidisciplinary rehabilitation programme used here improved HRQL in patients with PMSD to a greater extent than the standard treatment provided within primary heath care (p = 0.01) at least in the short term.

[Methodological issues in epidemiological studies of repetitive strain injuries]

Repetitive strain injuries (RSI) are a major public health problem with social and economic repercussions. This article presents a critical review of the published literature on RSI. The vast majority of the studies conducted in the last two decades were cross-sectional and exploratory. Results are difficult to interpret due to such methodological problems as lack of standardization and accuracy in identification of cases, inclusion of cases with potentially different diseases, varying levels of severity in the same study, lack of distinction between prevalent and incident cases, lack of precision in the definition and measurement of exposure, and confounding, besides the built-in constraint of cross-sectional studies for inferring causality. Some of these problems result from our insufficient knowledge of upper-limb soft tissue disorders and the absence of reliable diagnostic tests. Such problems could be addressed by studies whose design considered and stratified cases according to certainty and specificity of diagnosis.

Perceived work conditions and work-related symptoms among employed Finns

The aim of the study was to determine the number and nature of perceived harmful work conditions and perceived work-related symptoms among employed Finns by sex and socioeconomic group. The associations between perceived harmful work conditions and perceived symptoms were also investigated. Knowledge of perceived work-related ill health can serve as a basis for health promotion at work. In a computer-assisted telephone interview of 2744 salaried employees and wage-earners, the respondents were asked about perceived harmful work conditions as well as perceived health complaints, and their relatedness to work. At least one harmful factor at work was reported by 94% of the respondents, and half of them reported more than three such factors. The most commonly occurring harmful factors were increased work pace, mental demand, repetitive movements, and noise. Of the symptoms perceived as work-related, musculoskeletal symptoms were the most common. They were reported by 44% of the respondents, followed by mental symptoms (26%), psychosomatic symptoms (19%), and respiratory or sensory symptoms (15%). Both the reporting of perceived harmful work factors and perceived work-related symptoms varied by socioeconomic group and sex. Perceived work-related musculoskeletal symptoms were associated with perceived ergonomic harmful work factors among both the men and the women, with physical or chemical work factors among the men, and with psychosocial or work organizational factors among the women. Perceived work-related respiratory symptoms were associated with perceived harmful physical or chemical work factors among both the men and the women, and both groups also reported mental and psychosomatic symptoms in relation to harmful psychosocial or organizational work factors. Among the women psychosomatic symptoms and harmful ergonomic work factors were also related. Perceived harmful factors at work and work-related symptoms are common among the work force. Even though the degree of work-related ill health was related to socioeconomic group, the reporting of particular symptoms indicated the probability of a particular work factor being considered harmful independently of socioeconomic group, although there was some relationship to sex. The implications for occupational health services are evident; employees' work-related symptoms can serve as an indicator of (preventable) perceived problems at work.

Arm and trunk posture during work in relation to shoulder and neck pain and trapezius activity

OBJECTIVE: To investigate work technique in relation to work-related shoulder and neck pain (SNP) and upper trapezius muscle activity. DESIGN: A matched pair, case-control field study of female employees with and without SNP. BACKGROUND: It has proved difficult to distinguish subjects with SNP from those without by vocational electromyographic recordings from the upper trapezius muscle. Other potential risk indicators include psychosocial factors and work technique. This study focuses on the latter. METHODS: Manual (14 pairs) and office workers (24 pairs) were recorded during a 30-min work period. Simultaneous recordings of upper trapezius activity by surface electromyography and arm and upper back postures by inclinometers were analysed. RESULTS: Cases and controls were not differentiated on the basis of arm elevation or of trunk posture in the sagittal plane. No significant correlations were found between variables averaging the muscle activity and the arm elevation over the recording period. Statistically significant correlations were, however, found between these variables when analysing recordings at high time resolution (0.2 s) and adjusting for the delay in arm elevation relative to the upper trapezius muscle activity (r = 0.43, manual group; r = 0.32, office group). CONCLUSIONS: Factors other than arm elevation probably contribute more significantly to the load in the upper trapezius muscle, and to the development of work-related SNP in work situations with moderate arm elevation. RELEVANCE: The study suggests that arm and trunk posture recordings are not a sensitive indicator of risk of shoulder and neck complaints in work with low to moderate biomechanical demands.

Older workers in the construction industry: results of a routine health examination and a five year follow up

OBJECTIVE

To describe the health status of older construction workers and the occurrence of early retirement due to disability or of mortality within a five year follow up.

METHODS

Firstly, a cross sectional study was performed among 4958 employees in the German construction industry, aged 40-64 years, who underwent standardised routine occupational health examinations in 1986-8. The study population included plumbers, carpenters, painters/varnishers, plasterers, unskilled workers, and white collar workers (control group). Job specific prevalence and age adjusted relative prevalence were calculated for hearing loss, abnormal findings at lung auscultation, reduced forced expiratory volume, increased diastolic blood pressure, abnormalities in the electrocardiogram, increased body mass index, hypercholesterolaemia, increased liver enzymes, abnormal findings in an examination of the musculoskeletal system, and abnormalities of the skin. Secondly, follow up for disability and all cause mortality was ascertained between 1992 and 1994 (mean follow up period = 4.5 y). Job specific crude rates were calculated for the occurrence of early retirement due to disability and for all cause mortality. With Cox's proportional hazards model, job specific relative risks, adjusted for age, nationality, and smoking were obtained.

RESULTS

Compared with the white collar workers, a higher prevalence of hearing deficiencies, signs of obstructive lung diseases, increased body mass index, and musculoskeletal abnormalities were found among the construction workers at the baseline exam. During the follow up period, 141 men died and 341 men left the labour market due to disability. Compared with white collar workers, the construction workers showed a 3.5 to 8.4-fold increased rate of disability (P < 0.05 for all occupational groups) and a 1.2 to 2.1-fold increased all cause mortality (NS).

CONCLUSIONS

This study shows the need and possibilities for further health promotion in workers employed in the construction industry, targeting both work related conditions and personal lifestyle factors. Rehabilitation measures should be enforced to limit the rate of disability among construction workers.

Attention-related muscle activity in different body regions during VDU work with minimal physical activity

The purpose of this study was to characterize regional variation in task-irrelevant muscle activity. Surface EMG was recorded at 20 different muscle sites during a complex choice-reaction task. Up to ten muscle sites were recorded in parallel and always including the upper trapezius muscles. The experimental setting was designed to minimize the physical activity while performing a VDU-based task demanding continuing attention. Consequently, the label 'attention-related muscle activity' has been adopted. The presence of this activity varied between subjects and between the different muscle sites. It tended to decrease in a caudal direction and to be low in the muscles of the extremities, with the exception of the extensor muscles of the hand and foot. Attention-related activity was prevalent in the frontalis and upper trapezius muscles. This result is discussed with respect to a potentially harmful health effect of task-irrelevant muscle activity.

Can stress-related shoulder and neck pain develop independently of muscle activity?

A case-control designed was used to investigate associations and interactions between muscle activity measured by surface electromyography (EMG) in the upper trapezius muscle and subjectively reported risk factors in workers with and without shoulder and neck pain. EMG data were collected both in the workplace (indicating vocational muscle activity) and in a laboratory setting (indicating non-specific muscle activity). Women in manual (15 pairs) and office (24 pairs) work were included. The pairs were matched on age, gender and on current and historical work load, such as working hours, type and length of employment. Previous reports of this study have indicated that shoulder and neck myalgia was associated with increased muscle activity for the manual workers, and with psychological and psychosocial factors for the office workers. These risk factors were in the present report used as the basis for studying associations and interactions between muscle activity (1), psychological and psychosocial factors (2), and shoulder and neck pain (3). Subjectively reported or perceived general tension, a stress symptom presumed related to psychosocial and psychological factors, was previously found to be the strongest and only variable separating cases and controls in both work groups. In this paper, no relationship was found between perceived general tension and EMG variables for the office workers. For the manual workers a strong interaction was found; perceived general tension correlated positively with EMG variables for the controls, and negatively with EMG variables for the cases. It is hypothesised that the feeling of general tension represents a physiological activation response that may or may not include muscle fibre activation. This implies that pain provoked by psychosocial stress factors may not be mediated through increased muscle activity.

A case-control study of psychological and psychosocial risk factors for shoulder and neck pain at the workplace

Risk factors associated with work-related shoulder and neck myalgia were investigated in a case-control study with pairs matched for age, gender, and physical exposure. Guided interviews with standardized and self-constructed questionnaires were performed among manual (n = 15 pairs) and office (n = 24 pairs) workers. Perceived general tension was the variable with the strongest association with shoulder and neck pain in both work groups. Otherwise, the results in the two groups were very different, indicating that different risk factors and mechanisms were associated with shoulder and neck pain in the two work groups. The study provides background information for future attempts to establish causal relationships between physical and psychosocial exposure and shoulder and neck pain, which can be more accurately investigated in a longitudinal rather than a cross-sectional experimental design.

Muscle coordination and choice-reaction time tests as indicators of occupational muscle load and shoulder-neck complaints

The use was explored of psychomotor tests as indicators of the risk of shoulder-neck disorders in workers with low-level static loads on the shoulder muscles. Two groups of workers performing office work and light production work were studied. A muscle coordination test with continuous movement of the arm and hand between three target areas and a psychogenic tension test, posing mental demands and with minimal requirement for body movements, aimed to quantify muscle activity in excess of that needed for biomechanical purposes. The electromyogram (EMG) recording of the active trapezius muscle in the muscle coordination test correlated with the median and static EMG values of the vocational (i.e. during the normal work task) trapezius recording both for the office and production workers, but showed no correlation with shoulder-neck complaints. The EMG responses in the psychogenic tension test and of the passive (contralateral) trapezius in the muscle coordination test correlated best with the parameters showing short, spontaneous pauses in the EMG recording of occupational load. For the office workers, but not for the production workers these parameters also correlated with shoulder-neck complaints and the presence of psychosocial problems. Psychomotor tests may thus be useful as indicators of the risk of shoulder-neck complaints in certain occupations, but further experimentation is needed to validate this conclusion.

Trapezius muscle load as a risk indicator for occupational shoulder-neck complaints

Upper trapezius muscle activity was quantified by electromyographic (EMG) recordings using surface electrodes to study occupational muscle load as a risk indicator for the development of shoulder-neck complaints. Thirty-nine female production workers and thirty-two female office workers showed much larger interindividual differences than the mean difference in muscle activity between the two groups. By comparison with the production workers, the muscle activity patterns of the office workers were characterized by more short pauses and a lower static load. The median load level was similar for the two groups. For the office workers, but not for the production workers, weak correlations were found between symptoms of pain in the shoulder-neck region and some of the EMG parameters (static level and frequency of micropauses > 0.6 s. Current techniques for measuring shoulder muscle load by EMG recordings seem inadequate as screening methods to predict future risk of development of muscle pain symptoms.