Leif Sandsjö

Psychophysiological stress responses, muscle tension, and neck and shoulder pain among supermarket cashiers.

: This study examined psychological and physiological stress, as well as muscle tension and musculoskeletal symptoms, among 72 female supermarket cashiers. Stress levels were found to be significantly elevated at work, as reflected in the catecholamines, blood pressure, heart rate, electromyographic (EMG) activity, and self-reports. Fifty cashiers (70%) suffering from neck-shoulder pain (trapezius myalgia) were found to have higher EMG activity at work and reported more tension after work. Women who kept a diary for 1 week and reported more musculoskeletal pain (above the median) were older, had higher blood pressure, and reported more work stress and psychosomatic symptoms. The elevated stress levels at work are consistent with data from workers involved in other types of repetitive tasks and can be important for the high prevalence of neck and shoulder symptoms among the cashiers.

Subjective and objective evaluation of shoulder muscle fatigue.

In order to relate EMG signs of localized muscle fatigue to subjectively perceived muscle fatigue, a study was undertaken on 20 healthy volunteers exposing their right trapezius muscle by raising the arm to 90 degrees of abduction. Every person performed two contractions: 0 kg hand load during 5 min and 2 kg hand load during 2.5 min. Surface EMG was recorded and analysed with respect to RMS amplitude and mean power frequency (MPF). Subjective muscle fatigue was estimated with a psychophysical rating scale (Borgs CR-10 Scale). At high load level we found a significant correlation between MPF and the CR-scores (r = -0.46), but at low load level there was no correlation. At high load level there was a linear decrease of MPF with increasing load dose, but at low load level the MPF did not change, despite significant subjective fatigue. There was a linear rise of the CR-score with increasing load dose, more pronounced at high load level. It was concluded, that at low load levels common in working life, MPF and subjective scores seem to provide different fatigue information. Moreover, the MPF did not seem to work as a valid estimator of muscle fatigue at this low load level. Caution is recommended if it is to be used in static low-load situations.

Surface EMG and psychophysiological stress reactions in women during repetitive work

Abstract In order to understand the high prevalence of musculoskeletal disorders associated with stressful work, it is important to explore the relationship between muscle activity and psychophysiological stress responses. The present real-life study examines surface trapezius electromyographic (sEMG) activity, heart rate, blood pressure, and levels of urinary catecholamines and salivary cortisol among 31 female employees working at supermarkets, where the prevalence of neck and shoulder disorders is high (60–70%). As expected, the results show that psychophysiological arousal was high during work. Significant correlations were found between self-reports indicating negative stress (stressed, exhausted, tense) and sEMG activity during work. No significant correlations were found between self-reports of positive reactions (stimulated, concentrated, happy) and sEMG activity. No associations were found between sEMG activity and pain or between negative stress ratings and pain. Objectively measured workload and physiological stress responses did not correlate significantly with sEMG activity. Thus, our data indicate that perceived negative stress may have a specific influence on muscle activity, which may be of importance for musculoskeletal disorders in jobs with low-to-moderate physical load and negative psychosocial factors.

Trapezius muscle activity, neck and shoulder pain, and subjective experiences during monotonous work in women

Abstract The electromyographic (EMG) activity patterns of 18 female supermarket employees reporting neck and shoulder pain were compared with those of 6 of their female colleagues reporting no pain when doing cash-register work. It was found that the EMG activity of the trapezius muscle tended to show a lack of low and high levels among pain subjects, and that the time the trapezius muscle was at rest was longer in the group reporting no pain. In the non-dominant side, the muscle rest time was significantly longer (P < 0.05) in the group reporting no pain, and this group also showed a larger EMG activity difference between the dominant and non-dominant sides, indicating a less static bilateral muscle activation. Self-reports of negative experiences (stressed, exhausted and tense) were somewhat higher in the group reporting pain, while positive experiences during work (concentrated, stimulated and happy) appeared to be similar in the two groups of supermarket employees.

Electromyogram mean power frequency in non-fatigued trapezius muscle.

SummaryIn this study we have examined the variation of mean power frequency (MPF) in the electromyogram (EMG) from the non-fatigued trapezius muscle, with different external hand loads, in different shoulder joint positions, different torques and different planes of movement. The study was limited to the functional range of movement in the shoulder joint. It was performed on 19 healthy subjects. Surface EMG was recorded, analysed by means of a computer programme and examined by regression analysis. Normalized MPF values were calculated by dividing the MPF by the individual average MPF for all positions and loads. The results indicated no major variation in normalized MPF. The largest systematic variation of normalized MPF, ±8%, was related to joint angle. We have concluded that the MPF value obtained initially can be used within the functional range of movement to calculate the relative decrease in MPF as a result of muscle fatigue, and that the decrease is significant if it exceeds 8% of the initial value.

Psychophysiological stress reactions, trapezius muscle activity, and neck and shoulder pain among female cashiers before and after introduction of job rotation

The aim of this study was to evaluate the effects of the introduction of a job rotation model on supermarket cashiers, with respect to psychophysiological stress reactions, muscle activity of the trapezius muscle (which covers the upper back, the neck and the shoulder), and musculoskeletal symptoms in the neck and shoulders. Thirty-one female cashiers were investigated before and after job rotation was introduced. Before the reorganization the participants were only performing cash register work at the checkout counters. After the reorganization they shifted between cash register work and work in different departments in the supermarket. At follow-up the participants, all right-handed, had a significantly lower diastolic blood pressure, and surface electromyography (EMG) showed a significantly decreased muscle activity in the trapezius muscle on the left side. Musculoskeletal symptoms of the neck and shoulders were only partly changed, and there was no change in prevalence of musculoskeletal pain, which was around 70%. From questionnaires, but not from self-ratings during work, it was found that the introduction of job rotation had been experienced as positive in several regards, although the perceptions of stress and hurry were the same at follow-up.

Effects of ambulant myofeedback training and ergonomic counselling in female computer workers with work-related neck-shoulder complaints: A randomized controlled trial

Objective: To investigate the effects of ambulant myofeedback training including ergonomic counselling (Mfb) and ergonomic counselling alone (EC), on work-related neck-shoulder pain and disability. Methods: Seventy-nine female computer workers reporting neck-shoulder complaints were randomly assigned to Mfb or EC and received four weeks of intervention. Pain intensity in neck, shoulders, and upper back, and pain disability, were measured at baseline, immediately after intervention, and at three and six months follow-up. Results: Pain intensity and disability had significantly decreased immediately after four weeks Mfb or EC, and the effects remained at follow up. No differences were observed between the Mfb and EC group for outcome and subjects in both intervention groups showed comparable chances for improvement in pain intensity and disability. Conclusions: Pain intensity and disability significantly reduced after both interventions and this effect remained at follow-up. No differences were observed between the two intervention groups.

Electromyographic changes in work-related myalgia of the trapezius muscle

SummaryIn 11 patients, all women, 21–55 years of age, with unilateral work-related myalgia of the trapezius muscle, the right and left trapezius muscles were examined simultaneously for electromyogram (EMG) signs of localized muscle fatigue. All patients were tested with 0-kg hand load for 5 min, holding the arms straight at 90° of elevation in the scapular plane. Only 4 of the patients tolerated exposure to higher load levels. They were tested with 1 kg hand load for 3 min and 2 kg hand load for 2 min, with a period of rest of 30 min between the trials. The EMG mean power frequency (MPF) and root mean square (rms) were calculated. Data were normalized with the initial value as a reference and regression analyses were performed. On both sides a decrease of MPF and an increase of rms were found with increasing time and load, i.e. classical EMG signs of localized muscle fatigue. Compared with the nonaffected side smaller changes were found on the affected side, possibly due to pain inhibition, impaired microcirculation and biochemical changes along the muscle fibres. At 0-kg hand load we found no change of MPF on either side despite subjective feelings of fatigue and pain. We interpreted these findings as an indication of reduced capacity of the affected trapezius muscle to sustain static load with early development of pain-associated local fatigue.

Assessment of workload and arm position during different work sequences: a study with portable devices on construction workers

It is recognised that work related shoulder pain is overrepresented among construction workers compared to other occupations. Studies have shown that working with hands above shoulder level increases the shoulder load. Most studies have been confined to the laboratory. The present project was carried out to map the muscular engagement and postures of construction workers undertaking ceiling fitting, and to compare the results to those of the laboratory studies. Two ambulatory devices were used, one allowing recording of electromyographic (EMG) signals bilaterally from the trapezius muscle, and the other to record the position of both arms and back by means of measuring the angles between the vertical line and the back and both upper arms. These recordings were performed during 1.5-2 h work sequences. The results show that the work was mostly performed in an upright position, that both arms were used to a similar amount and that the workers for a large proportion of their working time had their upper arms at levels that are considered harmful in view of shoulder load. The EMG data showed that nearly 50% of the work was spent with trapezius activity that exceeded that of the reference contraction used (about 15% of maximal voluntary contraction) and that the time spent in muscular relaxation was 10%. It was concluded that the exposure of construction workers undertaking ceiling fitting meets the criteria formulated on the basis of laboratory experiments with respect to a high risk of acquiring chronic shoulder pain, due to rotator cuff tendinitis.

Perceived work demands, felt stress, and musculoskeletal neck/shoulder symptoms among elderly female computer users. The NEW study

The aim of the present study was to test a structural model of the relationship between the perceived quantitative (time pressure and unevenly distributed workload) and emotional work demands and self-reported musculoskeletal symptoms from the neck and shoulder region with felt stress (rested, relaxed, calm, tense, stressed, and pressured at the end of a normal workday) as a mediating variable. As part of the NEW (Neuromuscular assessment in the Elderly Worker) study, a European case-control study, the present cross-sectional study was based on a questionnaire survey among Danish, Dutch, Swedish and Swiss female computer users aged 45 or older ( n =148). The hypothesized structural model was tested using structural equation modelling. The results indicate that perceived work demands influence neck/shoulder musculoskeletal symptoms through their effect on felt stress. The results further indicate complete mediation, which means that all of the effect of the perceived work demands on symptoms could be attributed to the stress mechanism. As regards the percentage of explained variance in the endogenous variables, 36% of the variation in felt stress was explained by the perceived work demands, and about 20% of the variation in musculoskeletal neck/shoulder symptoms was explained by the combination of the perceived work demands and the felt stress.