Work environment and neck and shoulder pain: the influence of exposure time. Results from a population based case-control study.

OBJECTIVES: To study associations between long term and short term exposure to different work environmental conditions and the incidence of neck or shoulder pain. The results were obtained as part of the MUSIC-Norrtälje study, which is a population based case-control study conducted in Sweden in 1993-7. METHODS: The cases were people from the study base who sought medical care or treatment for neck or shoulder pain. Information on physical and psychosocial conditions in the work environment, currently and 5 years ago, and lifestyle factors, was obtained by self administered questionnaires from 310 cases and 1277 randomly selected referents. RESULTS: Associations between both physical and psychosocial exposures in the work environment and seeking care for neck or shoulder pain were found. The risk patterns differed for the sexes, and risk ratios exceeding 1.5 were more often found among women than among men. Generally, subjects who had experienced a recent increase of exposure were more likely (relative risk (RR) 2.1-3.7) to seek care than those who had been exposed long term (RR 1.5-1.8). Among women, an increased amount of visual display terminal (VDT) work, work above shoulder level, and reduced opportunities to acquire new knowledge, and among men, an increased amount of seated work were associated with neck or shoulder pain. This might indicate short induction periods for neck or shoulder pain for these exposures. However, for repetitive work with the hands and hindrance at work among women, and possibly also local vibrations among men, the induction periods seem to be longer. Interactive effects between factors, both at work and in the family, were found, but only among women. CONCLUSIONS: Associations between some exposures in the work environment and seeking care for neck or shoulder pain were found. The high RRs for short term exposure might indicate that for many factors the induction period for neck or shoulder pain is short.

Exposure assessment of upper limb repetitive movements: a consensus document developed by the Technical Committee on Musculoskeletal Disorders of International Ergonomics Association (IEA) endorsed by International Commission on Occupational Health (ICOH).

This consensus document intends to supply a set of definitions, criteria and procedures useful to describe and, wherever possible, to assess the work conditions that can represent a physical overload for the upper limbs. The document is aimed at all the operators, i.e. occupational doctors but mainly technicians, who are, involved in risk exposure assessment and management. The document intends to provide methods and procedures easily applicable in the field, possibly not requiring sophisticated instrumentation and when possible based on observation procedures. The proposed methods shall be based as far as possible on knowledge and data from scientific literature: should they be contradictory or deficient, reference will be made to standards or pre-standards issued by national and international agencies and bodies, with the experience of researchers involved and common sense. In this regard, it is to be emphasized that the potential users increasingly demand an easily applicable method for description and assessment of work with repetitive movements. The group intends to give a response even if there are still uncertainties from a strictly scientific standpoint: however the group commits itself to perform subsequent validations especially of as yet unconsolidated issues. This document focuses specifically on identification of risk factors and describes some of the methods that have been developed for evaluating them. There is a rapidly developing body of literature on job analysis and not yet agreement on a single best way to analyze jobs. Professional judgement is required to select the appropriate methods. Analysis and design of jobs should to be integrated into an ongoing ergonomics program that includes management commitment, training, health surveillance, and medical case management. In summing up this report, space must be given to the check lists that are so often seen in the medical press, although this is not the occasion to propose a detailed analytical review.

Standing and very slow walking: foot pain-pressure threshold, subjective pain experience and work activity.

Prolonged standing is described as uncomfortable by exposed workers, but the discomfort has not been linked to precise descriptions of workplace activity. We observed 10 sales and kitchen workers ("group 1") who worked standing. We compared the plantar pain-pressure threshold (PPT) of "group 1" (10 standing workers) to that of "group 2" (11 researchers who could choose their posture freely). Group 1 spent an average time of 62% standing still compared to 5% for group 2. Despite the fact that group 1 were primarily confined to defined areas and stood for 62% of the time, their mean time standing still was only 7 s. They walked 35% of the time, but 57% of walking sequences were only one or two steps. Group 1 PPT declined by 23% over the work day compared to 5% among group 2 (p < 0.05, ANOVA). Foot PPT is a promising quantitative indicator of effects of standing work.

Gender differences in upper extremity musculoskeletal complaints in the working population.

OBJECTIVES: This study analysed the association between gender and upper extremity musculoskeletal complaints, among the general working population and in various occupational groups. The hypothesis was tested whether the higher risk for women in the general working population for these complaints could partly be explained by differences in the distribution of men and women in occupations with different risks for the onset of upper extremity musculoskeletal complaints. METHODS: The data for this study came from cross-sectional questionnaire data from 16,874 employees categorised in 21 different occupational classes. Associations between gender and complaints of the upper extremities were analysed for the total study sample and for each occupational class separately. An adjustment was made for the variable 'occupational class' in the final model in order to study the impact of occupational gender segregation on gender differences in upper extremity complaints in the working population. RESULTS: In the total study sample, significantly higher risks of complaints of the neck, shoulder, elbow, and wrist among the women were observed. Within many occupational classes, women reported significantly higher risks than did men, in particular for complaints of the neck and shoulder. Adjustment for occupational class showed increased risks for female workers for complaints of the neck, shoulder, elbow, and wrist, hence, rejecting our hypothesis on occupational gender segregation as an explanation for the higher risks for upper extremity complaints among women in the general working population. CONCLUSIONS: This study confirmed the presence of gender differences in upper extremity musculoskeletal complaints among the working population and in many occupational classes, with female workers having the higher risk. The results, however, do not lend support to a differential occupational exposure theory as an explanation for the higher risks for these complaints among women in the general working population. Careful consideration of gender influence in ergonomic epidemiological studies is recommended.

Risk factors for neck and shoulder disorders: a nested case-control study covering a 24-year period.

BACKGROUND: In 1969 a population-based study was conducted in the Stockholm region. From the 2,579 randomly selected participants (18-65 years of age in 1969), the youngest subset were asked to participate in a reexamination in 1993. Information regarding working conditions, conditions outside work, and neck and shoulder disorders was collected retrospectively for the period 1970-1993. METHODS: Of 783 eligible subjects (42-59 years of age in 1993), 484 responded. Cases of neck/shoulder disorders were defined by past sick leave or medical attention or recent symptoms, depending on available information. For each case (n = 271) two controls were randomly selected, matched by age and gender. Variables regarding both physical and psychosocial conditions were included in the matched analyses. RESULTS: Among women mainly psychosocial factors and among men mainly physical factors were associated with neck/shoulder disorders. The only gender common risk indicator found was repetitive hand work (OR approximately 1.5). Interactive effects were also observed. CONCLUSIONS: The impact on neck/shoulder disorders from separate factors was moderate but combinations of physical and psychosocial factors, as well as of work-related and non-work-related factors, produced relative risks above 2.

Physical work load between 1970 and 1993--did it change?

OBJECTIVES: This study investigates changes in self-reported and expert-evaluated physical work loads between 1970 and 1993 in relation to calendar year, birth cohort, and gender in an urban and suburban population sample (232 men and 252 women) born between 1935 and 1952. METHODS: A self-administered questionnaire was answered in 1993 concerning different aspects of physical work loads between 1970 and 1993. With the use of a classification matrix, the objective physical work load on different body regions was also assessed. RESULTS: Between 1970 and 1993 the fraction of subjects in blue-collar occupations and the physical work loads decreased among the men, but they both increased among the women. Physical work loads were, in general, higher among the men than among the women at younger ages (below 30 years), but less so at higher ages. Expert evaluations of the musculoskeletal load showed a pattern similar to that of self-reported work loads. CONCLUSIONS: The gender difference in work load development with age may have implications for the development of musculoskeletal disorders.

To what extent do current and past physical and psychosocial occupational factors explain care-seeking for low back pain in a working population? Results from the Musculoskeletal Intervention Center-Norrtälje Study.

STUDY DESIGN: A population-based case referent study. OBJECTIVES: To determine whether current and past physical and psychosocial occupational factors are associated with care-seeking for low back pain in working men and women. SUMMARY OF BACKGROUND DATA: The importance of physical and psychosocial workloads as causal factors of low back pain has mostly been investigated in special occupational groups and with a cross-sectional design, which makes generalizability and interpretations more difficult. METHODS: The study comprised 2118 working men and women 20 to 59 years old (695 cases, and 1423 referents). Cases were defined as persons seeking care by any caregiver for low back pain. The exposure assessments were made through questionnaires and interviews about current and past physical and psychosocial loads during work and leisure time. RESULTS: In a logistic regression analysis, physical load from forward bending in men (RR = 1.8) and high physical load, in general, in women (RR = 2.0) showed increased relative risks. Psychosocial factors alone seemed to be of less importance in women, but "poor job satisfaction" and "mostly routine work without possibilities of learning" increased the risk in men. Combined current and past exposures further increased the risks. A combination of high physical and psychosocial loads increased the risk substantially, but few were exposed to such loads. Adjustment for lifestyle and other loads outside work did not change the results. CONCLUSION: Current and past physical and psychosocial occupational factors, both separately and combined, seem to be gender-specific, and to have a moderate impact on care-seeking for low back pain in a general working population.

Physical and psychosocial factors related to low back pain during a 24-year period. A nested case-control analysis.

STUDY DESIGN: A retrospective nested case-control study. OBJECTIVES: To identify occupational factors related to low back pain, and to study how interactions between psychosocial and physical factors, and between work-related and leisure-related factors affect low back pain in women and men. SUMMARY OF BACKGROUND DATA: A cohort of 484 subjects drawn from the general population was examined in 1969 and 1993, with a focus on occupational working conditions and musculoskeletal disorders. METHODS: Information about the physical and psychosocial working conditions and low back pain during the period 1970 to 1993 was collected retrospectively. Odds ratios and confidence intervals were calculated for different potential risk factors. RESULTS: During the 24-year period, 46% of the subjects became patients with low back pain. Among women, heavy physical workload, sedentary work, smoking, and the combination of whole-body vibrations and low influence over work conditions were associated with an excess risk of low back pain. Among men, excess risk for low back pain was seen in heavy physical workload, sedentary work, high perceived load outside work, and the combination of poor social relations and overtime. CONCLUSIONS: Factors at work were seen to be risk indicators for low back pain among both genders. Low influence over work conditions among women and poor social relations at work among men, in combination with other factors, seem to be of high relevance for the occurrence of low back pain.

Perception of surface pressure applied to the hand.

The study aimed to determine the relationship between the physical magnitude and the subjective perception of applied pressure, and to determine discomfort and pain thresholds. Free modulus magnitude estimation of the subjective pressure level was made on three points: on the finger, the palm and the thenar area. The pressure was judged to be higher at the thenar point than at the finger and palm points. The slopes of the linear functions (log magnitude estimates as a function of log pressure) were 0.66, 0.78 and 0.76 for the finger, palm and thenar points respectively. The discomfort threshold was 38% of the pain pressure threshold at the finger point, 40% at the palm and 22% at the thenar point. The results are probably of importance in the performance of hand-intensive work, in particular in the design of hand tools.

Evidence-based programs for the prevention of early exit from work.

Aging of the population and lowered average age of retirement imply greatly increased public costs for pensions and health care in western societies. Prolongation of working life is necessary to counteract large budget deficits, and most western countries are now in the process of changing public retirement benefits. However, a prolongation must be accomplished without threatening the well-being of elderly persons, and therefore working life needs changes that accommodate the capacity and demands of an aging work force are needed. No scientific intervention studies have as yet demonstrated that early exits from working life can be prevented while work ability, health, productivity, and a high quality of life are maintained. However, several studies on return-to-work after prolonged sick leave, re-entry to work after lay-offs, risk factors for early retirement, risk/health factors for maintained work ability, and case studies provide indirect support for the feasibility of preventing early exits, Scientific studies comparing different approaches, and performed in varying cultural and environmental conditions, are needed.

Retrospective versus original information on physical and psychosocial exposure at work.

OBJECTIVES: Retrospective exposure assessments are often performed in epidemiologic studies. The presence of an eventual misclassification, both nondifferential and differential, is debated but can rarely be investigated. The aim of this study was to compare self-reported information on the same physical and psychosocial work exposures with 25 years' difference. METHODS: In 1969-1970 a survey of randomly chosen men and women in Stockholm county, concerning, among other things, work exposures, was undertaken. During 1993-1994, 280 subjects participated in a reexamination, regarding psychosocial and physical factors at work and musculoskeletal disorders. The questions were all formulated in the same way as in 1969-1970. RESULTS: When self-reported information on work exposures, collected with a 25-year interval, was compared, acceptable, although not high, agreement was found for 3 out of 4 physical factors and for 4 out of 10 physical environmental factors. Questions measuring psychosocial load had somewhat lower agreement. Current exposure status influenced the memory of past exposures. Study subjects who reported low-back disorders at the reexamination tended to show a better agreement in their assessments of retrospective exposures than those without current symptoms. When relative risks from original and retrospective data were calculated, hardly any influence on the estimates due to that differential misclassification could be found. For persons with and without neck or shoulder symptoms no apparent differences in assessments were found. CONCLUSIONS: Retrospective assessments of exposures at the workplace showed misclassifications to a certain degree. However, the influence of the misclassifications on the risk estimates was limited.

Physical capacity in relation to present and past physical load at work: a study of 484 men and women aged 41 to 58 years.

BACKGROUND: A negative association has previously been reported between long-lasting physically heavy work and some measures of physical capacity. This relationship was further investigated in a 24-year follow-up study of 484 middle-aged men and women from the general population. METHODS: A questionnaire was administered in 1993 concerning retrospective recall of physical work loads and physical training in the time span between 1970 and 1993. Laboratory tests performed in 1993 included tests of muscle function (maximal isometric strength and dynamic endurance) and aerobic power (submaximal ergometer test). RESULTS: Consistent with the hypothesis, but mainly among the women, associations between long-lasting physically heavy demands and low trunk flexion strength, squatting endurance, and aerobic power were observed. In contrast, low isometric hand grip strength and low weight lifting endurance were seldom seen among those with high physical work loads, indicating a possible maintaining or training effect on the hand/arm/shoulder muscle groups. CONCLUSIONS: Physically heavy work seems to have a different impact on different parts of the musculoskeletal system, an effect that is also different between men and women.

Method for retrospective collection of work-related psychosocial risk factors for musculoskeletal disorders: reliability and aggregation.

Information on psychosocial work conditions during a 24-year period for 484 participants was collected retrospectively. Analyses were made of the interrater reliability, stability, specificity, and aggregation of data. The main finding was that it is possible to collect reliable information about psychosocial work conditions retrospectively for a long period of years when using a time ruler in a structured interview when earlier conditions are compared with the present. Interrater agreement was satisfactory for the larger part of the studied retrospective psychosocial risk factors and excellent for some of them. For most of the studied risk factors, the risk of overreporting exposure was low. The aggregation of data resulted in 2 indexes: poor social relations at work and low influence over work conditions. In conclusion, an individual time ruler works satisfactorily as a method of collecting retrospective information about psychosocial risk factors.

Evaluation of questionnaire-based information on previous physical work loads. Stockholm MUSIC 1 Study Group. Musculoskeletal Intervention Center.

OBJECTIVES: The principal aim of the present study was to evaluate questionnaire-based information on past physical work loads (6-year recall). METHODS: Effects of memory difficulties on reproducibility were evaluated for 82 subjects by comparing previously reported results on current work loads (test-retest procedure) with the same items recalled 6 years later. Validity was assessed by comparing self-reports in 1995, regarding work loads in 1989, with worksite measurements performed in 1989. RESULTS: Six-year reproducibility, calculated as weighted kappa coefficients (k(w)), varied between 0.36 and 0.86, with the highest values for proportion of the workday spent sitting and for perceived general exertion and the lowest values for trunk and neck flexion. The six-year reproducibility results were similar to previously reported test-retest results for these items; this finding indicates that memory difficulties was a minor problem. The validity of the questionnaire responses, expressed as rank correlations (r(s)) between the questionnaire responses and workplace measurements, varied between -0.16 and 0.78. The highest values were obtained for the items sitting and repetitive work, and the lowest and "unacceptable" values were for head rotation and neck flexion. Misclassification of exposure did not appear to be differential with regard to musculoskeletal symptom status, as judged by the calculated risk estimates. CONCLUSIONS: The validity of some of these self-administered questionnaire items appears sufficient for a crude assessment of physical work loads in the past in epidemiologic studies of the general population with predominantly low levels of exposure.

Risk factors for neck and upper limb disorders: results from 24 years of follow up.

OBJECTIVES: To investigate associations between different potential risk factors, related and not related to work, and disorders of the neck and upper extremities occurring up to 24 years later. METHODS: The study comprised 252 women and 232 men, Swedish citizens, 42-59 years of age and in a broad range of occupations. Information about potential risk factors was available from a former study conducted in 1969. Data on disorders of the neck, shoulder, and hand-wrist disorders were obtained retrospectively for the period 1970-93. RESULTS: Risk factors were found to differ between the sexes. Among women over-time work, high mental workload, and unsatisfactory leisure time were associated with disorders in the neck-shoulder region. Interaction was found between high mental workload and unsatisfactory leisure time. Neck symptoms earlier in life were associated with recurrent disorders. Hand and wrist disorders were associated mainly with physical demands at work. Among men blue collar work and a simultaneous presence of high mental workload and additional domestic workload predicted disorders in the neck-shoulder region. CONCLUSIONS: Factors related and not related to work were associated with disorders of the neck, shoulders, and hands and wrist up to 24 years later in life. These included factors related to working hours which previously have not been noted in this context. Interactions between risk factors both related and not related to work were commonly found.

Interview versus questionnaire for assessing physical loads in the population-based MUSIC-Norrtälje Study.

BACKGROUND: MUSIC-Norrtälje study is a case-referent study, the aim of which is to find risk and health factors for low back and neck/shoulder disorders. In this part of the study, the interview technique and the self-administered questionnaire used for assessment of physical loads are described and the inter-method reliability of parts of the self-administered questionnaire is estimated. The distribution of exposure levels in a general population is also described. METHODS: The study period was three years from November 1993 to November 1996, and the study subjects totaled 2,480 persons (813 female and 610 male referents, 380 female and 315 male low back cases, 252 female and 106 male neck/shoulder cases). The interview concerned "a typical working day" during the preceding 12 months and comprised assessment of energy expenditure, work postures, and manual materials handling for work and leisure time, including regular sport activities. The self-administered questionnaire comprised 18 questions, each covering 5 different points of time: right now, 5, 10, 15, 20 years ago. The answers to eight of the questions about current conditions were compared to corresponding interview responses. The interview was considered as the "gold standard." RESULTS: Ninety-eight percent of the subjects completed the interview without any great difficulties. According to the interview, the distributions of different exposure levels were generally positively skewed, i.e., the frequency of highly exposed subjects was low in the study base. The correlation between interview and questionnaire responses among the referents was high for time spent "sitting at work" (r = 0.82), "VDU work" (r = 0.87), and work related "motor vehicle driving" (r = 0.80). The correlation was moderate for work-related "hands above shoulder level" (rs = 0.63), and "hands below knee level (trunk flexion)" (rs = 0.66). The correlation was lower for leisure time activities such as "domestic work" (r = 0.55), "time for own activities" (r = 0.39), and "sitting during leisure time" (r = 0.38). Subjects seeking care for low back or neck/shoulder disorder estimated equally correctly or not, as had the referents. However, non-differential misclassification was present in all questions, which will attenuate observed estimates of the relative risk. CONCLUSIONS: Even though interview data are preferable, questionnaire data may be useful for assessing well-defined work tasks and for "sitting at work."

Possibilities for regulatory actions in the prevention of musculoskeletal disorders.

This review argues that there is a need for regulatory action against work-related musculoskeletal disorders. Designing such regulation is fraught with problems, such as insufficient knowledge about mechanisms and exposure-dose-response relationships, and lack of consensus on definitions. The multifactorial character of the disorders, especially risks involving work organization, further increases the problems. Nevertheless, regulation is necessary because of the poor results of voluntary prevention and the large costs of these disorders. Some major regulations are reviewed, and it is argued that there is insufficient scientific support for quantitative regulations proposed for some European norms. The recent Nordic ergonomic regulations for the prevention of work-related musculoskeletal disorders is a step forward, since they succeed in providing guidance, including some on work organizational issues, with only few quantitative measures. Researchers should become more involved in these activities, and priorities in future research that would benefit a more scientific approach to ergonomic regulation are indicated.

Validity of self-reported duration of work postures obtained by interview. MUSIC-Norrtälje Study Group.

The aim of the study was to validate interview data concerning the duration of four work postures (1) sitting, (2) standing/walking with hands above shoulder level, (3) standing/walking with hands between shoulder and knuckle level, and (4) standing/walking with hands below knuckle level. The self-reported time spent in each posture was tested in relation to observations and technical measurements in 20 subjects during two full working days. The linear relationships between self-reports and observations were strong for the three postures; sitting (r2 = 0.55), hands above shoulder level (r2 = 0.58) and hands below knuckle level (r2 = 0.69). Thus, using this interview technique, self-reports concerning time spent in (1) sitting, (2) standing/walking with hands above shoulder level and, (3) standing/walking with hands below knuckle level may be accurate enough for studying these work postures in epidemiological studies.