Biomechanical factors during common agricultural activities: Results of on-farm exposure assessments using direct measurement methods.

Agricultural work is associated with increased risk of adverse musculoskeletal health outcomes. The purpose of this study was to quantify exposure to biomechanical factors among a sample (n = 55) of farmers in the Midwest region of the U.S. while they performed a variety of routine agricultural activities, and to compare exposure levels between these activities. Surface electromyography was used to estimate activity levels of the erector spinae, upper trapezius, forearm flexor, and forearm extensor muscle groups. Simultaneously, inertial sensors were used to measure kinematics of the trunk, upper arm, and wrist. In general, lower muscle activity levels, less extreme postures, and slower movement speeds were observed during activities that involved primarily the use of agricultural machinery in comparison to manual activities, suggesting a potential advantage of mechanization relative to musculoskeletal health. Median wrist movement speeds exceeding recently proposed exposure thresholds were also observed during many manual activities, such as milking animals and repairing equipment. Upper arm postures and movement speeds did not appear to confer excessive risk for shoulder-related outcomes (on the whole), but interpretation of the results is limited by a sampling approach that may not have captured the full extent of exposure variation. Not surprisingly, substantial variation in exposure levels were observed within each agricultural activity, which is related to substantial variation in the equipment, tools, and work practices used by participants. Ultimately, the results of this study contribute to an emerging literature in which the physical demands of routine agricultural work have been described on the basis of sensor-based measurements rather than more common self-report or observation-based approaches.

Whole-Body Vibration and Trunk Posture During Operation of Agricultural Machinery.

Exposure to whole-body vibration (WBV) is common among agricultural workers and is associated with musculoskeletal health outcomes such as low back pain. Little is known, however, about the characteristics of exposure experienced during actual production practices. We measured WBV levels during agricultural machinery use among a sample of farmers (n = 55) performing routine agricultural activities and explored machinery attributes that may explain WBV summary measures. We also measured trunk posture to provide additional information about physical exposures during machinery operation. Measurements were made on-farm and during actual work conditions of a sample of agricultural machines (n = 112), including tractors, combines, heavy utility vehicles, and all-terrain vehicles (ATVs). Results indicated the presence of high levels of vibration (median frequency-weighted root-mean-square acceleration of approximately 0.8 m s-2) with time signatures that include high-amplitude mechanical shocks (median crest factor of nearly 23). Compared to other machinery types, combines exhibited the lowest WBV levels and among the most favorable trunk postures. Substantial variability was observed in both the WBV and trunk posture summary measures, suggesting for future studies that alternative sampling strategies are needed to fully capture temporal patterns of machinery use.

Musculoskeletal pain among Midwest farmers and associations with agricultural activities.

BACKGROUND: Although agricultural workers experience a high prevalence of musculoskeletal pain, associations between specific agricultural activities and musculoskeletal pain are not well characterized. METHODS: Among 518 regional farmers, responses to a mailed questionnaire were used to estimate (i) the 2-week prevalence of low back, neck/shoulder, and elbow/wrist/hand pain, and (ii) associations between the average hours per week performing common agricultural activities and musculoskeletal pain. RESULTS: The low back was the most common location of musculoskeletal pain (33.2%), followed by the neck/shoulder (30.8%) and elbow/wrist/hand (21.6%). Statistically significant adjusted associations were observed between performing equipment repair and maintenance and low back pain; milking animals and neck/shoulder pain; and manual material handling and elbow/wrist/hand pain, among others. CONCLUSIONS: The observed prevalence estimates are consistent with previous literature, and the associations between agricultural activities and musculoskeletal pain provide an initial basis for targeted intervention research.

Developing a pooled job physical exposure data set from multiple independent studies: an example of a consortium study of carpal tunnel syndrome.

BACKGROUND: Six research groups independently conducted prospective studies of carpal tunnel syndrome (CTS) incidence in 54 US workplaces in 10 US States. Physical exposure variables were collected by all research groups at the individual worker level. Data from these research groups were pooled to increase the exposure spectrum and statistical power. OBJECTIVE: This paper provides a detailed description of the characteristics of the pooled physical exposure variables and the source data information from the individual research studies. METHODS: Physical exposure data were inspected and prepared by each of the individual research studies according to detailed instructions provided by an exposure subcommittee of the research consortium. Descriptive analyses were performed on the pooled physical exposure data set. Correlation analyses were performed among exposure variables estimating similar exposure aspects. RESULTS: At baseline, there were a total of 3010 participants in the pooled physical exposure data set. Overall, the pooled data meaningfully increased the spectra of most exposure variables. The increased spectra were due to the wider range in exposure data of different jobs provided by the research studies. The correlations between variables estimating similar exposure aspects showed different patterns among data provided by the research studies. CONCLUSIONS: The increased spectra of the physical exposure variables among the data pooled likely improved the possibility of detecting potential associations between these physical exposure variables and CTS incidence. It is also recognised that methods need to be developed for general use by all researchers for standardisation of physical exposure variable definition, data collection, processing and reduction.

Pooling job physical exposure data from multiple independent studies in a consortium study of carpal tunnel syndrome.

Pooling data from different epidemiological studies of musculoskeletal disorders (MSDs) is necessary to improve statistical power and to more precisely quantify exposure-response relationships for MSDs. The pooling process is difficult and time-consuming, and small methodological differences could lead to different exposure-response relationships. A sub-committee of a six-study research consortium studying carpal tunnel syndrome: (i) visited each study site, (ii) documented methods used to collect physical exposure data and (iii) determined compatibility of exposure variables across studies. Certain measures of force, frequency of exertion and duty cycle were collected by all studies and were largely compatible. A portion of studies had detailed data to investigate simultaneous combinations of force, frequency and duration of exertions. Limited compatibility was found for hand/wrist posture. Only two studies could calculate compatible Strain Index scores, but Threshold Limit Value for Hand Activity Level could be determined for all studies. Challenges of pooling data, resources required and recommendations for future researchers are discussed. PRACTITIONER SUMMARY: There is a need for standardised measures and measurement protocols of physical exposure for the upper extremity. This study may provide guidance for those planning to conduct an epidemiological study on quantified job physical exposures, or planning to merge physical exposure data from similar studies with some methodologic differences.

Vitamin D intake is inversely associated with rheumatoid arthritis: results from the Iowa Women's Health Study.

OBJECTIVE: Vitamin D is a potent regulator of calcium homeostasis and may have immunomodulatory effects. The influence of vitamin D on human autoimmune disease has not been well defined. The purpose of this study was to evaluate the association of dietary and supplemental vitamin D intake with rheumatoid arthritis (RA) incidence. METHODS: We analyzed data from a prospective cohort study of 29,368 women of ages 55-69 years without a history of RA at study baseline in 1986. Diet was ascertained using a self-administered, 127-item validated food frequency questionnaire that included supplemental vitamin D use. Risk ratios (RRs) and 95% confidence intervals (95% CIs) were estimated using Cox proportional hazards regression, adjusting for potential confounders. RESULTS: Through 11 years of followup, 152 cases of RA were validated against medical records. Greater intake (highest versus lowest tertile) of vitamin D was inversely associated with risk of RA (RR 0.67, 95% CI 0.44-1.00, P for trend = 0.05). Inverse associations were apparent for both dietary (RR 0.72, 95% CI 0.46-1.14, P for trend = 0.16) and supplemental (RR 0.66, 95% CI 0.43-1.00, P for trend = 0.03) vitamin D. No individual food item high in vitamin D content and/or calcium was strongly associated with RA risk, but a composite measure of milk products was suggestive of an inverse association with risk of RA (RR 0.66, 95% CI 0.42-1.01, P for trend = 0.06). CONCLUSION: Greater intake of vitamin D may be associated with a lower risk of RA in older women, although this finding is hypothesis generating.

Estrogen and other female reproductive risk factors are not strongly associated with the development of rheumatoid arthritis in elderly women.

OBJECTIVE: Endogenous and exogenous reproductive hormones have been associated with rheumatoid arthritis (RA) in women, but data are inconsistent and no studies have assessed RA risk factors exclusively in elderly women. METHODS: The authors examined the association between reproductive factors, exogenous hormone exposure, and RA in a prospective cohort study of 31,336 Iowa women who were aged 55 to 69 years at cohort baseline in 1986. RESULTS: During 11 years of follow-up, 158 incident cases of RA were identified and validated. Age at last pregnancy (P trend =.01) and age at menopause (P trend =.03) were inversely associated with RA, whereas a history of polycystic ovary syndrome (relative risk [RR], 2.58; 95% confidence interval [CI], 1.06 to 6.30), endometriosis (RR, 1.72; 95% CI, 0.93 to 3.18), and former use of hormone replacement therapy (RR, 1.47; 95% CI, 1.04 to 2.06) were positively associated with RA. In multivariate analysis models, a history of polycystic ovary syndrome remained the most consistent predictor of RA, whereas the RRs for other factors attenuated. CONCLUSION: Few reproductive factors showed a strong or statistically significant association with RA in elderly women. The association of polycystic ovary syndrome may be indicative of perturbations of endocrine-immune activity that may influence the development of RA. This prospective cohort study adds to the understanding of the potential contribution of hormonal factors to the cause of RA in older women.

Method for quantitatively assessing physical risk factors during variable noncyclic work.

OBJECTIVES: Assessing exposure to physical risk factors during variable noncyclic work can be problematic. The purpose of this study was to modify an existing data reduction method for directly quantifying physical exposures during variable noncyclic work. METHODS: Myoelectric activity of the finger flexors of two groups of workers, heavy equipment operators (N=25) and mechanics (N=25), was sampled to determine the intensity and duration of forceful exertions during normal tasks. Data were reduced with a modification of the exposure variation analysis (EVA), called clustered EVA (CEVA), using three intensity and two duration categories. A two-way, mixed-effects, repeated-measures analysis of variance evaluated the percentage of sampled work time in each CEVA category. RESULTS: CEVA was able to quantify variable noncyclic work, and it contrasted the work of the two groups, with simple effects significantly different for all the exposure categories. The mechanics performed high-intensity short-duration contractions 9.1% of the time, whereas the operators had similar contractions only 1.8% of the time. Conversely, the operators used low-intensity contractions of prolonged duration over 81% of the time, compared with only 43% for the mechanics. CONCLUSIONS: CEVA is a useful modification of EVA for contrasting the noncyclic work typical of understudied industries like construction. A simplification of electromyography with summary measures such as CEVA provides a comprehensible, yet accurate measure of forceful exertions during worktasks.

Symptoms of musculoskeletal disorders among apprentice construction workers.

Musculoskeletal disorders (MSDs) are a major cause of work-related disability and lost-time illnesses for many occupational groups. This study determined the prevalence of musculoskeletal symptoms among young construction workers. A symptom and job factors survey was self-administered to 996 construction apprentices. Prevalence was determined by the percent of positive responses to musculoskeletal symptom questions. Odds ratios and 95 percent confidence intervals were the measures of association between prevalent musculoskeletal symptoms and demographic, leisure, and job factors and were determined by logistic regression. The low back was the site most commonly reported for job-related musculoskeletal symptoms (54.4%), which was also the most common reason for seeking care from a physician (16.8%) and missing work (7.3%). Number of years worked in the construction trade was significantly associated with knee (p-trend = 0.0009) and wrist/hand (p-trend < 0.04) MSD symptoms and was suggestive of an association with low back pain (p-trend = 0.05). "Working in the same position for long periods" was the job factor identified as most problematic, with 49.7 percent of all construction apprentices rating it as a moderate/major problem contributing to musculoskeletal symptoms. Musculoskeletal symptoms are a significant problem among young construction workers at the beginning of their careers. Prevention strategies are needed early in the apprentice training program to reduce the potential disability associated with work-related musculoskeletal symptom disorders.

Antioxidant micronutrients and risk of rheumatoid arthritis in a cohort of older women.

The association of antioxidant vitamins and trace elements from foods and supplements with risk of rheumatoid arthritis was evaluated in a prospective cohort study of 29,368 women who were aged 55-69 years at baseline in 1986. Through 1997, 152 cases of rheumatoid arthritis were identified. After controlling for other risk factors, greater intakes (highest tertile vs. lowest) of supplemental vitamin C (relative risk (RR) = 0.70, 95% confidence interval (CI): 0.48, 1.09; p-trend = 0.08) and supplemental vitamin E (RR = 0.72, 95% CI: 0.47, 1.12; p-trend = 0.06) were inversely associated with rheumatoid arthritis. There was no association with total carotenoids, alpha- or beta-carotene, lycopene, or lutein/zeaxanthin, while there was an inverse association with beta-cryptoxanthin (RR = 0.59, 95% CI: 0.39, 0.90; p-trend = 0.01). Greater use of supplemental zinc (RR = 0.39, 95% CI: 0.17, 0.88; p-trend = 0.03) was inversely associated with rheumatoid arthritis, while any use of supplemental copper (RR = 0.54, 95% CI: 0.28, 1.03) and manganese (RR = 0.50, 95% CI: 0.23, 1.07) showed suggestive inverse associations with rheumatoid arthritis. Greater intakes of fruit (RR = 0.72, 95% CI: 0.46, 1.12; p-trend = 0.13) and cruciferous vegetables (RR = 0.65, 95% CI: 0.42, 1.01; p-trend = 0.07) also exhibited trends toward inverse associations with risk. When the antioxidants were modeled together, only beta-cryptoxanthin and supplemental zinc were statistically significant predictors. Intake of certain antioxidant micronutrients, particularly beta-cryptoxanthin and supplemental zinc, and possibly diets high in fruits and cruciferous vegetables, may be protective against the development of rheumatoid arthritis.

Test-retest reliability of a self-administered musculoskeletal symptoms and job factors questionnaire used in ergonomics research.

The purpose of this study was to investigate the test-retest reliability of questionnaire items related to musculoskeletal symptoms and the reliability of specific job factors. The type of questionnaire items described in the present study have been used by several investigators to assess symptoms of musculoskeletal disorders and problematic job factors among workers from a variety of occupations. Employees at a plastics molding facility were asked to complete an initial symptom and jobs factors questionnaire and then complete an identical questionnaire either two or four weeks later. Of the 216 employees participating in the initial round, 99 (45.8%) agreed to participate in the retest portion of the study. The kappa coefficient was used to determine repeatability for categorical outcomes. The majority of the kappa coefficients for the 58 questionnaire items were above 0.50 but ranged between 0.13 and 1.00. The section of the questionnaire having the highest kappa coefficients was the section related to hand symptoms. Interval lengths of two and four weeks between the initial test and retest were found to be equally sufficient in terms of reliability. The results indicated that the symptom and job factors questionnaire is reliable for use in epidemiologic studies. Like all measurement instruments, the reliability of musculoskeletal questionnaires must be established before drawing conclusions from studies that employ the instrument.

Carpal tunnel syndrome among apprentice construction workers.

BACKGROUND: In terms of lost-work time and restricted workdays, surgery, and rehabilitation, one of the most costly occupational musculoskeletal disorders is carpal tunnel syndrome (CTS). The purpose of this study was to determine the prevalence of CTS among apprentice construction workers. METHODS: This cross-sectional study included apprentices from four construction trades. Apprentices completed a self-administered questionnaire and received electrophysiologic studies assessing median nerve function across the carpal tunnel. A surveillance case definition for CTS was based on characteristic hand symptoms and the presence of median mononeuropathy across the carpal tunnel. RESULTS: Of the 1,325 eligible apprentices, 1,142 (86.2%) participated in the study. The prevalence of CTS among apprentices was 8.2%; sheet metal workers had the highest rate (9.2%). In operating engineers, the prevalence of CTS was significantly higher (OR = 6.9; 95% CI = 2.6-18.2) among the heavy equipment mechanics than the drivers of those vehicles. Body mass index, age, and self-reports of working overhead were associated with prevalent CTS. Less than 15% of the apprentices with CTS sought medical attention for their disorder. CONCLUSIONS: Many construction workers begin developing CTS before or during their apprenticeship. Few apprentices seek medical attention for hand symptoms characteristic of CTS. The results of this study indicate a public health need for the implementation of prevention strategies for CTS in the construction industry.

Cigarette smoking and the risk of rheumatoid arthritis among postmenopausal women: results from the Iowa Women's Health Study.

PURPOSE: To determine whether cigarette smoking increases the risk of rheumatoid arthritis among postmenopausal women. SUBJECTS AND METHODS: We followed a cohort of 31 336 women in Iowa who were aged 55 to 69 years in 1986 and who had no history of rheumatoid arthritis. Through 1997, 158 cases of rheumatoid arthritis were identified and validated based on review of medical records and supplementary information provided by physicians. Multivariable Cox proportional hazards regression was used to derive rate ratios (RRs) and 95% confidence intervals (CIs) for the association between cigarette smoking and rheumatoid arthritis. RESULTS: Compared with women who had never smoked, women who were current smokers (RR = 2.0; 95% CI: 1.3 to 2.9) or who had quit 10 years or less before study baseline (RR = 1.8; 95% CI: 1.1 to 3.1) were at increased risk of rheumatoid arthritis, but women who had quit more than 10 years before baseline were not at increased risk (RR = 0.9; 95% CI: 0.5 to 2.6). Both the duration and intensity of smoking were associated with rheumatoid arthritis. Multivariable adjustments for age, marital status, occupation, body mass index, age at menopause, oral contraceptive use, hormone replacement therapy, alcohol use, and coffee consumption did not alter these results. CONCLUSION: These results suggest that abstinence from smoking may reduce the risk of rheumatoid arthritis among postmenopausal women.

Blood transfusion, alcohol use, and anthropometric risk factors for rheumatoid arthritis in older women.

OBJECTIVE: To evaluate whether blood transfusion, alcohol use, or anthropometric characteristics are risk factors for rheumatoid arthritis (RA) in older women. METHODS: These factors were evaluated in a prospective cohort study that was initiated in 1986, and included 31,336 women aged 55-69 years without a history of RA. Risk factor data were self-reported using a mailed questionnaire. Through 1997, 158 cases of RA meeting at least 4 of 7 American College of Rheumatology criteria were identified and validated by medical record review. The relative risk (RR) and 95% confidence interval (CI) were used as the measure of association, and were adjusted for the potential confounding effects of age, marital status, smoking history, age at menopause, and use of estrogen replacement therapy. RESULTS: History of blood transfusion was inversely associated with RA (multivariate RR = 0.72; 95% CI 0.48-1.08), and this association was stronger for rheumatoid factor (RF) positive disease (RR = 0.59; 95% CI 0.35-1.00). There were no associations for use of medications for hyper- or hypothyroidism or adult onset diabetes. Anthropometric factors (height, weight, body mass index, body fat distribution), leisure time physical activity, and alcohol use were not associated with risk of RA. CONCLUSION: A history of blood transfusion was inversely associated with RA, particularly RF positive RA. Anthropometric factors, physical activity, and alcohol use did not influence the risk of RA in this cohort of older women.