Working conditions, health and productivity among dentists in Swedish public dental care--a prospective study during a 5-year period of rationalisation.

In recent decades, comprehensive rationalisations have been implemented in public dentistry in Sweden. How rationalisations affect working conditions, health and production from a long-term perspective has been poorly investigated. This study aims to analyse changes and associations in dentists' working conditions, health and productivity during a 5-year period. In 2003 and 2008, 65 dentists responded to questionnaires measuring work conditions and health. Treatment times for patients and productivity were tracked in electronic registers. Paired t-tests showed that the number of treated adult patients per dentist increased, and perceived physical working conditions improved while perceived work control and leadership deteriorated. Structural equation modelling showed that physical factors were important for health and productivity. When assessing risks in the work environment, there is a need to understand the interaction of effects on working conditions and health due to rationalisations so as to increase the sustainability of production systems. PRACTITIONER SUMMARY: Dentistry in Sweden has undergone considerable change. Questionnaire surveys with dentists, undertaken in 2003 and 2008, found that the present rationalisations resulted in improved perceived physical working conditions. Aspects of the psychosocial working environment had deteriorated, however. This is a concern as health and workability are important for workplace efficiency.

Rationalisation in public dental care--impact on clinical work tasks and mechanical exposure for dentists--a prospective study.

Swedish dentistry has been exposed to frequent rationalisation initiatives during the last half century. Previous research has shown that rationalisation often results in increased risk of developing work-related musculoskeletal disorders, thus reducing sustainability in the production system. In this prospective study, we assessed mechanical exposures among Swedish dentists in relation to specific rationalisations of clinical dental work during a six-year period. Body postures and movements of 12 dentists were assessed by inclinometry synchronised to video recordings of their work. No rationalisation effects could be shown in terms of a reduction in non-value-adding work ('waste'), and at job level, no major differences in mechanical exposure could be shown between baseline and follow-up. CONCLUSION: The present rationalisation measures in dentistry do not seem to result in rationalisation at job level, but may potentially be more successful at the overall dental system level. PRACTITIONER SUMMARY: In contrast to many previous investigations of the mechanical exposure implications of rationalisation, the present rationalisation measures did not increase the level of risk for dentists. It is highlighted that all occupations involved in the production system should be investigated to assess production system sustainability.

Mechanical exposure among general practice dentists in Sweden and possible implications of rationalisation.

The present study investigates the dental work in terms of time distribution and mechanical exposure in value-adding work (VAW) and non-VAW. Further rationalisation of dental work would typically involve an increase in the proportion of VAW. Information on mechanical exposure within the classes of VAW and non-VAW may be used to predict possible implications of rationalisation. Sixteen dentists were investigated. Using a data logger, postures and movements were continuously recorded for each subject during the 4 h of work, which included the 45 min of video recording. Time distribution and mechanical exposure for the six different work activities identified were evaluated from the video recordings, using a loss analysis technique. VAW, which comprised 54% of the total working time, generally implied significantly more constrained mechanical exposures as compared with non-VAW. The results suggest that future rationalisation of dental work, involving a reduction of non-VAW, may increase the risk of developing musculoskeletal disorders. Statement of Relevance: The present study illustrates the potential effects of rationalisation on biomechanical exposures for dentists. The results highlight the significance of integrating ergonomic issues into the rationalisation process in dentistry in addition to ordinary workstation and tool design improvements performed by ergonomists.

Work related perceived stress and muscle activity during standardized computer work among female computer users.

The current study investigated the associations between work-related perceived stress and surface electromyographic (sEMG) parameters (muscle activity and muscle rest) during standardized simulated computer work (typing, editing, precision, and Stroop tasks). It was part of the European case-control study, NEW (Neuromuscular assessment in the Elderly Worker). The present cross-sectional study was based on a questionnaire survey and sEMG measurements among Danish and Swedish female computer users aged 45 or older (n=49). The results show associations between work-related perceived stress and trapezius muscle activity and rest during standardized simulated computer work, and provide partial empirical support for the hypothesized pathway of stress induced muscle activity in the association between an adverse psychosocial work environment and musculoskeletal symptoms in the neck and shoulder.

Trapezius muscle rest time during standardised computer work--a comparison of female computer users with and without self-reported neck/shoulder complaints.

Work related musculoskeletal disorders (WMSDs) in the shoulder/neck area are a common and increasing problem among European computer workers, especially women. Long-term low-level workloads with low degree of muscle rest are a potential risk factor for developing WMSDs. The purpose of the present study of female computer users (age 45-65 years) in Denmark and Sweden was to investigate if subjects with self-reported neck/shoulder complaints (cases, N=35) show less trapezius muscle relative rest time (RRT) than controls (N=44) when performing standardised short-term computer work tasks in controlled laboratory conditions. Surface electromyography (EMG) signals were recorded bilaterally from the upper trapezius muscles during a type, edit, precision and colour word stress task. Besides RRT, 10th percentile RMS values were calculated. On the average, 15 of the cases and 18 of the controls showed analysable EMG files per task. For the colour word stress task, the results showed lower RRT values and higher 10th percentile RMS amplitude levels among cases compared to controls. No such signs could be found for the other tasks performed. The present results indicate an increased motor response to a psychological stressor among subjects with self-reported neck/shoulder complaints.

Neuromuscular assessment in elderly workers with and without work related shoulder/neck trouble: the NEW-study design and physiological findings.

Musculoskeletal disorders in the neck and shoulder area are a major occupational concern in the European countries especially among elderly females. The aim was to assess these disorders based on quantitative EMG indicators and functional tests. 252 female computer users (45-68 years) were recruited from four European countries in two contrast groups: (1) 88 neck/shoulder (NS) cases reporting trouble in the neck and/or shoulder region for more than 30 days during the last year, and (2) 164 NS-controls reporting such trouble for no more than 7 days. Questionnaires, functional/clinical tests, and physiological recordings were performed in workplace related field studies. The results showed no differences in anthropometrics but NS-cases reported more strained head positions and more eye problems than controls. The psychosocial working factors were similar, although, NS-controls had slightly better scores on working conditions, general health, and vitality compared to cases. The NS-cases had lower maximal voluntary contraction (MVC) during shoulder elevation (mean (SD) 310 (122) N) compared to the controls (364 (122) N). During 30% MVC electromyography (EMGrms) in the trapezius muscle was lower in NS-cases (194 (105) muV) than in controls (256 (169) muV), while no differences were found regarding endurance time. Estimated conduction velocity was not different between NS-cases and -controls. Four functional computer tests were performed equally well by NS-cases and -controls, and the corresponding EMG variables also did not differ. A major finding in this large-scale epidemiological study is the significantly lower MVC in NS-cases compared with NS-controls together with lower EMGrms value at 30% MVC, while computer tasks were performed at similar relative muscle activation. The study was unable to reveal quantitative EMG indicators and functional tests that could objectively assess disorders in NS-cases.

Clinical signs and physical function in neck and upper extremities among elderly female computer users: the NEW study.

The aim of the study was to present the prevalence of clinical signs and symptoms among female computer users above 45 years, both in a group with self-reported neck/shoulder trouble (NS cases) and in a group without such trouble (NS controls). The hypothesis was that computer users with self-reported neck/shoulder trouble have more clinical findings than those not reporting trouble, and that a corresponding pattern holds true for physical function. In total 42 and 61 questionnaire-defined NS cases and NS controls participated and went through a clinical examination of the neck and upper extremities and five physical function tests: maximal voluntary contraction (MVC) of shoulder elevation, abduction, and handgrip, as well as endurance at 30% MVC shoulder elevation and a physical performance test. Based on clinical signs and symptoms, trapezius myalgia (38%), tension neck syndrome (17%) and cervicalgia (17%) were the most frequent diagnoses among NS cases, and were significantly more frequent among NS cases than NS controls. A total of 60% of the subjects with reported trouble had one or several of the diagnoses located in the neck/shoulder. Physical function of the shoulder was lower in subjects with self-reported trouble as well as in the subgroup of NS cases with clinical diagnoses. In conclusion, the present clinical diagnoses and physical function tests differed between NS cases and NS controls, and are therefore recommended to be included as quantitative objective measures in assessing musculoskeletal health. Physical function tests should be further developed in order to be able to detect pre-stages of work-related disorders for preventive strategies.

Comparative assessment of study groups of elderly female computer users from four European countries: questionnaires used in the NEW study.

There is a lack of consistent and comprehensive questionnaire forms for the studies of factors associated with work-related musculoskeletal disorders at the European level. One of the results of the EU-funded project, neuromuscular assessment in the elderly worker (NEW), is a set of questionnaires for the screening of musculoskeletal status and the studies of factors that are believed to affect musculoskeletal health. The questionnaires have been used among elderly women (45+) in different occupations and organisations in Denmark, The Netherlands, Sweden and Switzerland. The aim of this short communication is to present the questionnaires used in the NEW study and to evaluate the appropriateness of pooling data gathered in each participating country into a common database. It is concluded that although differences exist among the study samples, these are not of such a magnitude or pattern that data from the four groups cannot be pooled. The questionnaires are available in Danish, Dutch, English, German and Swedish.

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.

The influence of different intermittent myofeedback training schedules on learning relaxation of the trapezius muscle while performing a gross-motor task.

The aim of this study was to investigate the influence of different intermittent myofeedback training schedules, as provided by a Cinderella-based myofeedback system, on learning relaxation and resistance to extinction of the trapezius muscle, in subjects performing a unilateral gross-motor task. Eighteen healthy subjects performed the task without and with feedback to study baseline and learning relaxation. Subsequently, resistance to extinction was investigated by performing the task without feedback. The gross-motor task consisted of continuously moving the dominant arm between three target areas at a constant pace. Subjects were randomly assigned into three groups, characterized by the sequence of feedback schedules with which the task was performed on 3 consecutive days. Auditory feedback was provided after a 5-, 10-, or 20-s interval when a pre-set level of 80% rest was not reached. Bipolar surface electromyography recordings performed at the dominant upper trapezius muscle were quantified using relative rest time (RRT) and root mean square (RMS) parameters. Learning relaxation was defined as an increase in RRT and a decrease in RMS values. Results showed the highest RRT levels as well as a decrease in RMS for the 10-s schedule. Additionally, the 10-s schedule was unique in its ability to elevate muscular rest above the 20% level, which may be considered relevant in preventing myalgia. None of the three schedules showed resistance to extinction. It was concluded that the 10-s interval was preferred over the 5- and 20-s schedules in learning trapezius relaxation in subjects performing a unilateral gross-motor task.

Surface EMG and psychophysiological stress reactions in women during repetitive work.

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.

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.

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.

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.

Work load, fatigue, and pause patterns in clinical dental hygiene.

PURPOSE: Previous studies have suggested that high frequencies of shoulder and neck complaints in dental hygienists mainly were due to longstanding, low-level static load of the neck and shoulder muscles. The purpose of the present study was to make continuous recordings of myoelectric signals from the shoulder muscles of dental hygienists in order to assess static load. METHODS: Myoelectric signals were recorded from the right trapezius muscle of 10 Swedish dental hygienists during half of a normal working day. A portable system for collection and on-line processing of myoelectric signals was used. Signal parameters were obtained, indicating muscular load, fatigue, pause frequency, and pause duration, respectively. All measurements were referred to a resting value and a reference contraction value established with the hand loaded with a 0.5 kg weight at the beginning of the recording session. RESULTS: A static load of 50 to 100% of the reference contraction (0.5 kg hand load with raised arm) was found in the trapezius muscle. The median load for the whole group was 57% of the reference level. Group data analyses of frequency EMG seldom showed significant fatigue. At individual levels, however, it was possible to identify localized muscle fatigue and relate it to a specific work task. There were many short pauses with a duration of 1 to 2 seconds, but an almost total lack of pauses of a duration longer than five seconds. CONCLUSIONS: Individual dental hygienists exhibited significant muscle fatigue that might be related to development of work related myalgias of the shoulder muscles. Future study of muscle patterns and dental hygiene tasks may lead to improved work designs and patterns for dental hygienists.

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 (Borg's 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.

EMG mean power frequency: Obtaining a reference value.

Normalization of the electromyographic mean power frequency is generally performed on the basis of single estimates. Random variation of reference values based on such single estimates can seriously impair data reported in normalized form. In the present study we have examined five procedures for calculation of an initial reference value: calibration contractions at 0-kg (repeated) and 2-kg hand load, and regression routines at 0-kg and 2-kg hand load. There was a large between-subject variation if all different routines were considered, a moderate between-routine variation, and a quite small within-subject variation. The correlation between the different routines was high. At the same load level calibration and regression routines gave equivalent results, but the variability was less at the higher load level. The variations found are of such a magnitude that it is necessary to reduce the influence of random variation. Procedure proposed for reduction of this variability is repeated calibration measurements. A preferred test position for the trapezius muscle is straight arm, 90° of abduction in the scapular plane, 2-kg hand load.

Arm movement and EMG mean power frequency in the trapezius muscle: a comparison between surface and intramuscular recording techniques.

In a previous study it has been shown that there is a systematic variation of the EMG mean power frequency recorded under dynamic conditions with surface electrodes from non-fatigued trapezius muscle. The variation was most pronounced in relation to shoulder joint angle. The aim of the present study was to find out whether this variation was caused by geometric factors such as electrode displacement, or by neuromuscular factors within the muscle. A comparison has been made between surface and intramuscular recordings. EMG was recorded with standard surface electrodes and with a monopolar "hooked wire" intramuscular electrode. The recordings were analyzed for calculation of mean power frequency (MPF) and root mean squared (RMS) signal level. For MPF we found a low, but statistically significant correlation (r = 0.30) between surface and intramuscular recordings. For RMS the corresponding correlation was high (r = 0.92). Analysis of variance showed a high proportion of explained variance related to the shoulder joint angle for surface recordings, but not for intramuscular recordings. The results were confirmed in the regression analysis. The results indicate that the observed variation is largely caused by geometric displacement of the surface electrodes and not by intrinsic neuro-muscular factors.

Electromyographic changes in work-related myalgia of the trapezius muscle.

In 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 degrees 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.

Variability of the EMG mean power frequency: A study on the trapezius muscle.

Calculation of the EMG mean power frequency (MPF) is a common procedure applied in evaluation of the frequency shift associated with local muscle fatigue. Variations of the MPF that are unrelated to muscle fatigue may jeopardize the estimation of the frequency shift. Different kinds of variation include random variation and systematic variation due to changes in posture or load. In a previous article we have evaluated the systematic linear variation of the MPF. The aim of the present study was to examine the random variation. Data sequences of 10 s, each obtained from nonfatigued trapezius muscle of 19 healthy subjects, were examined over a functional range of load and joint angles with multiple regression analysis. The random variation was evaluated with residual analysis. The residual standard deviation within the whole group was 10% for surface recordings and 13% for intramuscular recordings. If only within-subject variation was considered, the corresponding values were 5 and 8%. Based on this, confidence and prediction intervals for the regression models were calculated. Ninety-five percent confidence intervals were ±1-3% around the regression surfaces, whereas 95% prediction intervals for single measurements were as large as ±20-26% for the whole group, and ±11-20% if only within-subject variations were considered. Assessment of localized muscle fatigue using single MPF estimates should therefore be avoided. Multiple measurements and regression analysis are discussed as methods to minimize the effects of random variations.