Validity of heart-rate based measurements of oxygen consumption during work with light and moderate physical activity.

For ergonomic purposes it is useful to quantify the energy expenditure and the level of physical activity imposed on workers. Oxygen consumption (VO2) is often used to calculate energy expenditure and can be used as an indication of physical activity. Twenty-five subjects participated in the study. Oxygen consumption (VO2) in L O2/min and heart-rate (HR) in beats per minute (bpm) were simultaneously measured during different work tasks at each individual's workplace. Ninety-one different work tasks with light or moderate physical activity were included (physical activity was classified by the VO2 measurements). Estimated oxygen consumption (L O2/min) was then calculated by using the HR measurements in bpm combined with individual HR-VO2 equations established in a laboratory. Although heart-rate based estimations of individual oxygen consumption showed relatively low precision, heart-rate measurements in combination with individual exponential HR-VO2 equations can be used to discriminate between work involving light physical activity and work involving moderate physical activity.

High heritability for concurrent low back and neck-shoulder pain: a study of twins.

STUDY DESIGN: A cross-sectional study on 21,225 twins based on a Web-based questionnaire was performed in 2005-2006 and administered by the Swedish Twin Registry. OBJECTIVE: To investigate the importance of genetic factors for the occurrence of "Concurrent low back (LBP) and neck-shoulder pain (NSP)" as well as of "Solely LBP," and "Solely NSP" in an adult population of women and men. SUMMARY OF BACKGROUND DATA: Many individuals suffering from LBP also have concurrent NSP, and little is known about the factors influencing the occurrence of this spinal comorbidity. METHODS: Heritability of Concurrent LBP and NSP, solely LBP, and solely NSP was analyzed in 2934 monozygotic twin pairs, 2009 same-sex dizygotic (DZ) twin pairs, and 1960 opposite-sex DZ twin pairs without any known rheumatic disorders using structural equation modeling (SEM). RESULTS: The SEM showed that 60% of the total variance for concurrent LBP and NSP can be explained by additive genetic effects, which was twice as large as for solely LBP (30%) and more than twice as large as for solely NSP (24%). CONCLUSION: Genetic factors had a considerably greater importance for the occurrence of concurrent LBP and NSP compared with solely LBP or solely NSP. The influence of genetic factors was similar for solely LBP and solely NSP.

Head movements during two computer work tasks assessed by accelerometry.

We investigated whether potential differences in head inclinations and accelerations for two highly similar computer work tasks could be detected using (1) a triaxial accelerometer and (2) a simulated uniaxial accelerometer. Ten subjects' head movements were registered with a triaxial accelerometer system for two similar document-management tasks at their work place: a fully electronic document-management task and one also involving paper documents. In situations where head movements were small, a triaxial accelerometer was able to discriminate between the different degrees of static work of the neck in terms of range of head inclinations and accelerations. A difference in head acceleration was also found by using a simulated uniaxial accelerometer. Thus, in terms of head movement and for work similar to this office work, potential dynamic differences in observationally similar work tasks can be investigated by using a triaxial accelerometer. For acceleration alone, a uniaxial accelerometer can also be used.

The influence of work-related exposures on the prognosis of neck/shoulder pain.

To determine associations between work-related exposures and the prognosis of self-reported neck/shoulder pain. This prospective cohort study was based on 803 working subjects who reported neck/shoulder pain at baseline. The proportion of subjects who 5-6 years later were symptom-free was calculated. Data concerning work-related biomechanical, psychosocial, and organizational exposures were collected at baseline. The Cox regression analyses were used to calculate the relative chances (RC) of being symptom-free at the end of the study for single exposures, and also for up to three simultaneous work-related exposures. Adjustments were made for sex and age. Only 36% of the subjects were symptom-free 5-6 years later. The relative chance for being symptom-free at the end of the study was 1.32 (95% CI = 0.99-1.74) for subjects who were exposed to sitting > or =75% of the working time and 1.53 (95% CI = 1.02-2.29) for subjects who were exposed to job strain, i.e., the combination of high demands and low decision latitude. The relative chance of being symptom-free at the end of the study was 0.61 (95% CI = 0.40-0.94) for subjects with at least two out of three simultaneous biomechanical exposures at work; manual handling, working with the hands above shoulder level, and working with vibrating tools. In a heterogeneous population with moderate nonspecific neck/shoulder pain, sedentary work enhanced the chance of being symptom-free 5-6 years later, whereas simultaneous exposures to at least two of manual handling, working with hands above shoulder level and working with vibrating tools were associated with a lower chance of being symptom-free at the end of the study. This could imply that subjects with neck/shoulder pain should avoid such simultaneous exposures.

The effect of ergonomic intervention on neck/shoulder and low back pain.

The aim of this study was to examine the effect of two types of ergonomic intervention on pain and pain-related disability in the neck/shoulder and low back regions. A cohort of 492 subjects of various occupations with non-specific neck/shoulder or low back pain was followed over a five to six year period. The study subjects were classified into four intervention groups: no ergonomic intervention, educational worksite intervention, workplace intervention, and combined workplace and educational worksite intervention. The group with no ergonomic intervention was used as the reference group. The changes in pain intensity and pain-related disability from baseline to follow-up in each of the three groups with intervention were compared to the changes in the reference group. During the follow-up, 39% of the subjects had received ergonomic intervention. The average change in pain intensity and pain-related disability was smaller in the educational worksite intervention group than in the reference group. The average reduction of pain intensity and pain-related disability did not differ between the two other intervention groups and the reference group. Thus, for subjects still at work, ergonomic intervention seemed to be ineffective for reducing neck/shoulder and low back pain and pain-related disability.

Work postures and neck-shoulder pain among orchestra musicians.

BACKGROUND: The purpose of the present study was to identify associations between a work posture with elevated arm position, duration of active playing time, and neck-shoulder pain among orchestra musicians. METHODS: In this study, with a cross-sectional study design, a total of 235 subjects from 12 Swedish orchestras were categorized into four exposure groups according to arm position and duration of active playing time. Logistic regression analysis was used to calculate odds ratios (OR) for neck-shoulder pain in the four exposure groups. RESULTS: A higher prevalence of neck-shoulder pain were found in the groups "elevated arm position, <2 hr per workday" [OR 4.15 (1.30-13.22)], and "elevated arm position, >3 hr per workday" [OR 5.35 (1.96-14.62)] compared to the group "neutral arm position, <2 hr per workday". CONCLUSIONS: Musicians working in an elevated arm position (e.g., violinists, violists, flutists, and trumpet players) had a higher prevalence of neck-shoulder pain than those working in a more neutral position.

Different working and living conditions and their associations with persistent neck/shoulder and/or low back disorders.

OBJECTIVES: To investigate whether different combinations of working and living conditions are associated with the risk for persistent neck/shoulder and/or low back disorders. The underlying purpose of this contextual approach was to identify target groups for primary/secondary prevention. METHODS: In a baseline study, 11 groups with different working and living conditions were identified by cluster analysis. In this study, these 11 groups were followed up by a postal questionnaire 5 years after baseline (response rate 82%, n = 1095). RESULTS: Five of the groups--the onerous human services job, the free agent, the family burden, the mentally stretched and the physically strained groups--had an increased risk for persistent disorders (OR 2.38-2.70). Four of these groups had rather sex-specific working and living conditions. CONCLUSIONS: The results support the hypothesis that different combinations of working and living conditions may increase the risk for persistent neck/shoulder and/or low back disorders to different degrees. Sex-specific working and living conditions increased the risk for women as well as for men, irrespective of whether the conditions were specific to women or men.

Sickness absence and concurrent low back and neck-shoulder pain: results from the MUSIC-Norrtälje study.

In Sweden, musculoskeletal disorders, in particular low back disorders (LBD) and neck-shoulder disorders (NSD) constitute by far the most common disorders, causing sick leave and early retirement. Studies that compare sickness absence in individuals with LBD and individuals with NSD are lacking. Moreover, it is likely that having concurrent complaints from the low back region and the neck-shoulder region could influence sickness absence. The purpose of the present study was to explore potential differences in sickness absence and in long-term sickness absence during a 5-year period, 1995-2001, among individuals with (1) solely LBD, (2) solely NSD, and (3) concurrent LBD and NSD. The present study was based on 817 subjects from the MUSIC-Norrtälje study, whom were working at baseline and whom at both baseline and follow-up reported LBD and/or NSD. Three groups were identified based on pain and pain-related disability at both baseline and follow-up: (1) solely LBD, (2) solely NSD, and (3) concurrent LBD and NSD. Subjects who did not give consistent answers at both the baseline and follow-up occasions were assigned a fourth group: (4) migrating LBD/NSD. Two outcomes were analysed: (1) prevalence of sickness absence, and (2) long-term sickness absence among those with sickness absence days. Logistic regression analysis was used to calculate odds ratios (OR) for sickness absence in the different disorder groups, taking into account confounding factors such as gender, age and other non-musculoskeletal-related disorders. In the group concurrent LBD and NSD, 59% had been sickness absent between baseline and follow up, compared to 42% in the group solely LBD, 41% in the group solely NSD, and 46% in the group migrating LBD/NSD. No difference in sickness absence was found between the group solely LBD compared to the group solely NSD [OR 0.65 (0.36-1.17)]. The adjusted OR for sickness absence in the group concurrent LBD and NSD compared to subjects with solely LBD or solely NSD was [OR 1.69 (1.14-2.51)]. The adjusted OR for having long-term sickness absence was 2.48 (95% CI = 1.32-4.66) for the group concurrent LBD and NSD. In the present study, having concurrent LBD and NSD were associated with a higher risk for sickness absence and also long-term sickness absence. This suggests that, when research on sickness absence and return to work after a period of LBD or NSD is performed, it is important to take into consideration any concurrent pain from the other spinal region. The study also implies that spinal co-morbidity is an important factor to be considered by clinicians and occupational health providers in planning treatment, or in prevention of these disorders.

Low back pain in a general population. Natural course and influence of physical exercise--a 5-year follow-up of the Musculoskeletal Intervention Center-Norrtälje Study.

STUDY DESIGN: A 5-year prospective cohort study was conducted of men and women seeking care for a new period of low back pain (LBP). OBJECTIVES: To study the natural course of pain and disability due to LBP during a 5-year follow-up period, and to investigate the possible influence of regular physical exercise on recovery. SUMMARY OF BACKGROUND DATA: LBP is major health problem, but its natural course is not very well studied. Several studies have investigated the role of physical exercise on LBP disorders, with inconsistent results. METHODS: At baseline, a total of 790 subjects seeking care for LBP were interviewed about physical exercise during leisure time. Over 5 years, 3 follow-up assessments were made by postal questionnaire. At all measuring points, pain intensity ratings and disability scores were compared between men and women, and among 3 exercise categories. RESULTS: The pain intensity and disability scores were improved after 5 years for both men and women. The most prominent improvements occurred after 6 months, but less so thereafter. There were no significant differences between men and women with regard to individual changes at the 5-year follow-up concerning the pain intensity or disability scores. There were no significant differences, either for women or men, between low, median, or high intensity exercise groups regarding pain intensity or disability values for the individual change at the 5-year follow-up. CONCLUSIONS: Over a 5-year period, both men and women who had sought care for LBP reported a decrease in pain and disability; however, only a few were fully restored. In this study, we found no effect of nonspecific physical exercise on recovery from LBP in men and women.

Bicycle messengers: energy expenditure and exposure to air pollution.

The purpose of the study was to determine the level of energy expenditure and exposure to air pollution for bicycle messengers. Relationships between heart rate (HR) and oxygen uptake, and between HR and pulmonary ventilation (VE) for each participant were established in laboratory tests. Air pollution and HR were measured during one working day. The total oxygen uptake was then described as the total energy expenditure in Joule (J) and in multiples of the energy expenditure at rest (MET). The mean energy expenditure during a working day (8 h) was 12 MJ, (4.8 MET). The level of air pollution exposure when cycling seemed to be comparable with the levels of exposure when sitting inside a vehicle. The VE during cycling was four times higher than resting value. Increased VE led to increased exposure to air pollution.

Neck/shoulder disorders in a general population. Natural course and influence of physical exercise: a 5-year follow-up.

STUDY DESIGN: A 5-year follow-up study was conducted of men and women seeking care for new incidents of neck/shoulder disorders (NSD). OBJECTIVES: To study the natural course of pain and disability caused by NSD during a 5-year follow-up and to investigate the possible influence of regular physical exercise on recovery. SUMMARY OF BACKGROUND DATA: NSD are a major health problem, but their natural course is not very well studied. Several studies have investigated the role of physical exercise on NSD, with inconsistent results. METHODS: At baseline, a total of 439 subjects seeking care for NSD completed a questionnaire, and were interviewed about personal, medical, and occupational history, as well as physical exercise during leisure time. Over 5 years, 4 follow-up assessments were made by postal questionnaire. At all measuring points, pain intensity ratings and disability scores were compared between men and women, and between 3 exercise categories. RESULTS: The highest improvements in pain and disability, both in men and in women, were seen after 3 months. After that, only minor improvements were seen. In some cases, there was deterioration. However, after 5 years, both men and women had significant improvements, men more than women. Only the women were analyzed concerning physical exercise and were pooled into 3 categories according to intensity of exercise. There were no differences in changes in pain intensity and disability scores from baseline between the groups. CONCLUSIONS: A gender difference was seen in the change of pain and disability, with men having higher improvement than women over 5 years. Self-reported physical exercise of any intensity was not associated with higher recovery in women.

Seeking care for neck/shoulder pain: a prospective study of work-related risk factors in a healthy population.

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

Paid and unpaid work, and its relation to low back and neck/shoulder disorders among women.

The aim of the present study was to estimate the influence of total work hours, paid work in the labor market and unpaid work in the family domain, on care-seeking for low back and neck/shoulder disorders in the female population. The exposure assessments considered a typical working' day during the previous twelve months and were assessed by interviews and questionnaires; 704 cases and 984 referents were examined. The cases had sought professional care during the study period; the referents were randomly selected from the same source population. There was no increased relative risk for care-seeking for low back and neck/shoulder disorders for gainfully employed women compared to those not employed, or for full-time compared to part-time working women. At least 60 hours per week of paid work, or at least 40 hours per week of unpaid work, separately, indicated an increased relative risk for care-seeking. The present results did not strengthen the hypothesis that a high amount of hours of work is an independent risk factor for musculoskeletal disorders.

Seeking care for low back pain in the general population: a two-year follow-up study: results from the MUSIC-Norrtälje Study.

STUDY DESIGN: A 2-year follow-up study was conducted to investigate new patients who sought care for low back pain from all the caregivers in a specific region with a population of approximately 17,000 men and women ages 20 to 59 years. OBJECTIVES: To describe care-seeking behavior for low back pain in a general population; to characterize pain, disability, and sick leave among the patients; and to study predictors of recovery. An additional aim was to find a simple way of classifying low back pain in epidemiologic studies. SUMMARY OF BACKGROUND DATA: Low back pain is very common, but its natural history in a general population and predictors of recovery are not fully known. METHODS: All the patients went through a clinical examination, and data on personal, medical, and occupational history were collected. Follow-up assessments were made during a 2-year period. RESULTS: Whereas 50% of the patients went to physicians and physiotherapists for treatment, 50% went to other caregivers. Some improvements in pain and disability were reported after 3 months, but not many after that. Approximately 70% of the care seekers had not been on sick leave during the follow-up period. Care seeking during the follow-up period was not associated with reduced pain and disability. No predictive factors for recovery were found. A simple pain drawing made by the patient gave information about pain distribution similar to that found by clinical examination. CONCLUSIONS: In a general working population in Sweden ages 20-59 years, approximately 5% sought care because of a new low back pain episode during a 3-year period. Few of the care seekers became pain-free during the follow-up period. This study strengthens the hypothesis that low back pain often becomes chronic even when sick leave is rare.

Validity of a self-administered questionnaire for assessing physical work loads in a general population.

The aim of the study was to evaluate eight questions concerning physical loads, used in public health questionnaires. Working women and men (203) completed a self-administered questionnaire twice, following a test-retest method. The questions were also validated with a structured interview. Response agreement was calculated with Cohen's kappa statistics with quadratic weights (kappa w). Test-retest agreement varied from 0.74 to 0.92, and inter-method agreement from 0.38 to 0.81. The lowest coefficients were for the questions concerning bent/twisted work postures (kappa w 0.38) and repetitive movements (kappa w 0.39). The results did not indicate any substantial influence of gender, type of work or musculoskeletal complaint. The questions concerning general physical activity and sitting work postures, and physical exercise/sports during leisure times, had good validity. The questions concerning bent/twisted work posture and repetitive movements need to be re-designed.

Validity of occupational energy expenditure assessed by interview.

Measuring physical activity at work has been a field of growing interest in recent decades, and there is a need for reliable, standardized assessment instruments for application in large population studies. The present study examined the validity of a task-oriented interview for assessing energy expenditure in occupational work. The interview was developed for use in the MUSIC-Norrtälje study, a population study with the overall aim of identifying risk and preventive factors for musculoskeletal disorders. Twenty-seven persons were included in the study. Each respondent defined all tasks performed during a typical workday and estimated their durations. For each task the interviewer then assessed the level of energy expenditure in multiples of the resting metabolic rate (MET) and calculated a time-weighted average MET (TWA-MET) for a typical workday. Measurements of oxygen consumption and observations of duration of each work task were performed during 2 workdays in all the interviewed subjects. The validity was tested by comparing TWA-MET derived from the interviews with those derived from measurements; the product moment correlation coefficient was 0.70. The interview may offer sufficient validity for assessment of energy expenditure in large population studies.

A triaxial accelerometer for measuring arm movements.

A triaxial accelerometer used as an inclinometer (INC) (Logger Technology, Sweden) needed to be evaluated for field measurements of arm postures and movements. INC consists of one portable data logger and up to four sensors. Each sensor measures the inclination to the vertical line. The sampling frequency is 20 Hz and, the logger can collect data for up to 12 h. The aim of the present study was to compare INC measurements with those from an optoelectronic measuring system- the Mac Reflex system (OPT) (Qualisys AB, Sweden). For all movements with normal to high velocities INC measured the degree of arm elevation with very high precision. At very high velocities and, especially when the direction of the velocity was perpendicular to the vertical line the largest differences between INC and OPT were found. In field studies INC has proved to be very safe and useful in assessment of arm movements. INC was easy to handle and easy to wear for the researcher and the subject, respectively.