Physical workload, low back pain and neck-shoulder pain: a Swedish twin study.

OBJECTIVES: To investigate if high physical workload is associated with low back pain (LBP) and/or neck-shoulder pain (NSP) when taking into account the influence of genetic and shared environmental factors. Further, the study aims to explore the potential influence of genetic and shared environmental factors in the associations between high physical workload and the three disorder subgroups: solely LBP, solely NSP, and concurrent LBP and NSP. METHODS: Data on 16,107 monozygotic and dizygotic twins, born during 1959-1985, were obtained from a cross-sectional study, performed in 2005-2006 by the Swedish Twin Registry. Odds ratios (ORs) calculated in cohort analyses and co-twin control analyses were used to assess the associations between high physical workload and LBP and NSP when controlling for genetic and shared environmental factors. RESULTS: In the cohort analysis, the association between high physical workload and the group with any one symptom (LBP and/or NSP) was OR 1.47 (95% CI 1.37 to 1.57). The co-twin control analyses indicated that the association was not confounded by genetic and shared environmental factors with OR 1.34 (95% CI 1.02 to 1.75) for dizygotic twins and OR 1.44 (95% CI 1.06 to 1.95) for monozygotic twins. In the cohort analyses the association with high physical workload was higher for concurrent LBP and NSP (OR 1.80 (95% CI 1.62 to 1.99)) than for solely LBP (OR 1.41 (95% CI 1.27 to 1.57)) and solely NSP (OR 1.31 (95% CI 1.20 to 1.43)). Concurrent LBP and NSP was the only group that showed a stepwise decrease of the point estimates between the cohort analysis and the co-twin control analyses, OR 1.71 (95% CI 1.00 to 2.94) for dizygotic twins, and OR 1.29 (95% CI 0.64 to 2.59) for monozygotic twins indicating confounding by genetic and shared environmental factors. CONCLUSIONS: High physical workload was associated with LBP and/or NSP even after adjusting for genetic or shared environmental factors. Only for concurrent LBP and NSP, genetic and shared environmental factors seemed to have an influence on the association with high physical workload.

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.

The influence on seeking care because of neck and shoulder disorders from work-related exposures.

The aim of this study was to assess the influence of work-related physical and psychosocial factors on seeking care for neck or shoulder disorders among men and women in a general working population. The study population comprised gainfully employed (>17 hours per week) men and women in the municipality of Norrtälje, altogether 392 cases and 1,511 controls. Cases were defined as persons seeking care because of neck or shoulder disorders by any caregiver in the region. The study began in 1994 and continued to 1997. We assessed physical and psychosocial exposures by questionnaires and interviews. The pattern of seeking care for neck or shoulder disorders differed between men and women. Among men, work with vibrating tools [relative risk (RR) = 1.6], not having a fixed salary (RR = 1.9), and low demands in relation to competence (RR = 1.5) were the strongest risk indicators obtained in analyses stratified for age and previous symptoms. Among women, repetitive hand or finger movements (RR = 1.6), constrained sitting (RR = 1.6), not having a fixed salary (RR = 2.0), and solitary work (RR = 1.8) were the strongest risk indicators. A large proportion of the general population was exposed to several of these moderately harmful conditions, and their concomitant effect may explain the high incidence of neck and shoulder disorders in the general working population.

Sports activities, body weight and smoking in relation to low-back pain: a population-based case-referent study.

The study aims to describe the influence of sports activities, high body weight and smoking on low-back pain. The results were obtained from a population-based case-referent study, the Musculoskeletal Intervention Center (MUSIC)-Norrtälje study. In all, 342 male and 449 female cases, and 662 male and 948 female referents participated. Neither low-intensity training many hours/week (> or = 5 h) nor high-intensity training few (1-2 h), intermediate (3-4 h) or many hours (> or = 5 h) per week affected the risk of low-back pain among men. Few (1-2) hours with high-intensity training increased the relative risk of low-back pain among women, RR 1.6 (1.1-2.4). An increased risk of low-back pain was found for men with high body weight, RR 2.2 (CI 1.2-3.9) but not for women. Smoking did not influence the risk of low-back pain.

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 work load in physical education teachers.

The main objective was to measure and quantify exposure to physical work load in physical education teachers. A further aim was to establish the reproducibility of a three-week test-retest interval of self-reported physical load and to evaluate the agreement between registered and self-rated physical load. Thirty teachers, both female and male, volunteered to participate in the study. The physical load on the lower extremities, as well as the back and the cardio-vascular strain was recorded during one working day. The results indicate that the physical work load in this occupational group is considerable due to the load on the lower extremities. The demands of the cardio-vascular system are also relatively high in comparison to other occupational groups. The teachers could assess their activity quite well regarding heavy lifting and time spent sitting.

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."

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.

Reproducibility of a questionnaire for assessment of present and past physical activities.

OBJECTIVE: The aim of this study was to evaluate the reproducibility of a self-administered questionnaire about present and past physical activities at work and during leisure time. METHODS AND DESIGN: The questionnaire, covering the period 1970-1993, comprised 12 questions on physical activities at work, and 12, with similar wording, for such activities in leisure time. There were also four questions on physical training. Two-week reproducibility (test-retest reliability) concerning the period 1970-1993 was analysed in a group of 44 subjects, and 1-year reproducibility, concerning current activities in 1993, was analysed in a second group of 123 subjects in relation to gender, age and low-back health. RESULTS: Test-retest reliability calculated as intraclass correlation coefficients (ri) for physical activities at work (ri 0.41-0.98) exceeded that for leisure time and physical training activities (ri 0.33-0.68). Calculated correlations did not differ markedly between past and present activities. No distinct influence of gender or low back health on 1-year reproducibility was found, in contrast to a slight tendency towards higher reproducibility among subjects of 50 years and older compared with younger subjects. CONCLUSIONS: Reproducibility of this questionnaire about physical activities at work showed no clear tendency to deteriorate regarding activities during the immediately preceding two decades. The questions about physical activities during leisure time have to be revised. Reliable retrospective information about physical activities in leisure time could perhaps not be collected by self-administered questionnaires and other methods, e.g. interview-based questionnaires, may be more suitable.

Evaluation of perceived and self-reported manual forces exerted in occupational materials handling.

The main objective of the study was to evaluate the ability of workers to reproduce simulated manual work forces correctly and to quantify these forces in Newtons (N) by means of self-reports. Fourteen male and 14 female workers participated in the study. Three experiments were carried out. In the first experiment, the ability to reproduce the magnitudes of simulated manual forces occurring in daily work and to estimate these forces in Newtons was tested. A specially designed force-measuring device was used for this purpose. In the second experiment, the subjects estimated the weights of five boxes ranging from 1 to 30 kg. In the third experiment, the subjects were asked to produce five predetermined push and pull forces ranging in magnitude from 10 to 300 N on to the handle of the force-measuring device. The ability to reproduce the magnitudes of manual forces when simulating four familiar work tasks was good (the intraclass correlation coefficients ranged from 0.75 to 0.95). The ability to quantify these forces in Newtons was not as good (the product moment correlation coefficients ranged from 0.21 to 0.69). When the subjects estimated the weights of boxes they underestimated the weights. When they produced predetermined push and pull forces they exerted higher forces than expected when low force levels were requested and lower forces when high force levels were requested. However, the forces were correctly ranked. In summary, simulation of the manual push/pull forces used in familiar work tasks seemed to offer sufficient reproducibility to be worth testing for validity. Self-reports, used without previous training or without known 'reference forces', seemed to be very rough when the aim was to estimate in kg or Newtons. However, the fact that individuals could rank the forces correctly opens a potential for refinement of self-reports as a method for quantifying manual forces in objective terms, e.g. kg or Newtons.

An interview technique for recording work postures in epidemiological studies. Music-Norrtälje Study Group.

BACKGROUND: The aim of the study was to present and evaluate a work-task-oriented interview technique focusing on the placement of the hands relative to the body and assessing per cent time spent in five standard work postures during a working day. METHODS: The reproducibility of estimated time spent in each work posture was tested by the test-retest method in 32 subjects; 16 were interviewed by the same interviewer and 16 were interviewed by another one at the retest. The validity concerning estimated time spent in th five standard work postures was tested in relation to observations in 58 male blue-collar workers. The mean registration (assessment) time was 6 hours and 15 minutes. RESULTS: No evident differences in the reproducibility depending on same or different interviewers at test and retest could be observed. The linear relationship between times estimated by the interview and by observations was high for four of the work postures: 'sitting' (r = 0.86), 'standing with hands above shoulder level' (r = 0.87), 'between shoulder and knuckle level' (r = 0.75), and 'below knuckle level' (r = 0.93). When the work posture 'standing with hands between shoulder and knuckle level' was divided into 'hands fixed' (r = 0.62) and 'hands not fixed' (r = 0.50) the correlations were weak. Current musculoskeletal complaints did not influence the accuracy of the estimations. CONCLUSIONS: The present task-oriented interview technique may be the best available method to estimate these work postures in a way that requires few resources compared to observations and technical measurements.

Reproducibility of a questionnaire for assessment of physical load during work and leisure time. Stockholm MUSIC I Study Group. MUSculoskeletal Intervention Center.

A self-administered questionnaire on physical load in lifetime occupational work, in present job, and in present leisure activities was tested for reproducibility with the test-retest method in 126 male and 217 female workers from 30 occupations. The questionnaire contained 92 questions and nine different response scales. The results indicated that questions concerning physical activity retrospectively and in the present job, vibrations in the present job, working postures involving the whole body, and questions concerning specific leisure activities (eg ball games, skiing, etc) seem to offer sufficient reproducibility to be worth testing for validity, at least at a 5-point ordinal level. Questions concerning working postures involving parts of the body, including awkward postures, and questions concerning manual materials handling seem to offer too poor reproducibility to be used in studies in which the aim is to quantify duration in proportions of a typical working day and frequencies in times per hour. Questions concerning level of physical activity and exertion in domestic work seem to offer too poor reproducibility to be used at a 5-point ordinal level. Gender, age, and musculoskeletal complaints did not influence the reproducibility to any great extent.

HARBO, a simple computer-aided observation method for recording work postures.

OBJECTIVES: The aim of the study was to present an observation method focusing on the positions of the hands relative to the body and to evaluate whether this simple observation technique gives a reliable estimate of the total time spent in each of five work postures during one workday. METHODS: In the first part of the study the interobserver reliability of the observation method was tested with eight blue-collar workers. In the second part the observed time spent with work above the shoulder level was tested in relation to an upper-arm position analyzer, and observed time spent in work below knuckle level was tested in relation to a trunk flexion analyzer, both with 72 blue-collar workers. RESULTS: The interobserver reliability for full-day registrations was high. The intraclass correlation coefficients ranged from 0.99 to 1.00. The observed duration of work with hands above shoulder level correlated well with the measured duration of pronounced arm elevation (> 75 degrees). The product moment correlation coefficient was 0.97. The observed duration of work with hands below knuckle level correlated well with the measured duration of pronounced trunk flexion angles (> 40 degrees). The product moment correlation coefficient was 0.98. CONCLUSION: The present observation method, designed to make postural observations continuously for several hours, is easy to learn and seems reliable.

Can cardiovascular load in ergonomic epidemiology be estimated by self-report? Stockholm MUSIC 1 Study Group.

In ergonomic epidemiology exposure to local loads as well as cardiovascular load may contribute to general and local fatigue and musculoskeletal disease. Self-reported exposure is often the only feasible method in large population studies. The aim of this study was to evaluate retrospectively self-reported physical activity and perceived exertion as estimates of cardiovascular load during occupational work. The study population consisted of 39 men, representing 25 different occupations, and 58 women, representing 28 occupations. Ratings of physical exertion (RPE scale) and physical activity (Edholm scale transferred to multiples of the basal metabolic rate, METs) at the end of a work shift were correlated with the average heart rate during the same work shift. In the male population, both RPE ratings and METs correlated significantly (P < .01) with the average heart rate. No such correlation was observed in the female population.

A portable ergonomic observation method (PEO) for computerized on-line recording of postures and manual handling.

A new portable ergonomic observation method (PEO) is presented. It is applicable to most professions and work tasks and requires only moderate human resources for data collection and analysis. Observations are made in real time directly at the workplace using a portable personal or hand-held computer, and data are accessible for immediate analysis and presentation. Duration and number of events are calculated for postures at four body regions (arms, neck, trunk and knee) as well as for manual handling. An evaluation of the PEO method, assessing some important aspects of internal validity as well as intra- and inter-observer reliability, was carried out using video recordings. It showed acceptable validity for some types of physical exposure, and high intra- and inter-observer reliability. Practical experiences from using the PEO method in a field study and further improvements of the method are discussed.

Direct measurements and systematic observations of physical workload among medical secretaries, furniture removers and male and female reference populations.

The aim of this investigation was to collect quantitative information about the occurrence of manual materials handling and working postures in working life. Direct technical recordings and systematic observations by trained ergonomists were used throughout a whole working day on 12 male furniture removers, 13 female medical secretaries, 27 males and 45 females randomly sampled from the working population in the Stockholm area. A quantitative job exposure profile was obtained by weighting together exposure data obtained by observation of tasks occurring during a normal working week. The results showed no major differences in physical exposures between the male and female reference populations. The medical secretaries spent less time than the female population kneeling/squatting and longer time than any other group with repetitive hand movements. Exposure data for task and job should be clearly distinguished.

Validity of self-reported exposures to work postures and manual materials handling. Stockholm MUSIC I Study Group.

Exposure data from self-administered questionnaires on manual materials handling and work postures were validated in relation to direct measurements and systematic observations on 39 men and 58 women representing 45 different occupations. The agreement was tested at a dichotomous level and, when possible, with quantification of duration or frequency. At the dichotomous level the agreement was "acceptable" for nine variables concerning work postures and the handling of loads weighing > 5 kg. No variable showed "acceptable" agreement when the duration or the frequency was quantified in more detail (4- to 6-point scales). Musculoskeletal complaints seemed to introduce a differential bias for some lifting variables. Thus some variables for postures or the handling loads of > 5 kg may, under certain conditions, be acceptable for use in epidemiologic studies when the relative risks are high. However, self-reported exposure seems to be too crude if more-detailed information is required.