Physical job demands in pregnancy and associated musculoskeletal health and employment outcomes: a systematic review.

OBJECTIVE: A decline in musculoskeletal health during pregnancy is an underappreciated adverse outcome of pregnancy that can have immediate and long-term health consequences. High physical job demands are known risk factors for nontraumatic musculoskeletal disorders in the general working population. Evidence from meta-analyses suggest that occupational lifting and prolonged standing during pregnancy may increase risk of adverse pregnancy outcomes. This systematic review examined associations between occupational lifting or postural load in pregnancy and associated musculoskeletal disorders and related sequalae. DATA SOURCES: Five electronic databases (Medline, Embase, CINAHL, NIOSHTIC-2, and Ergonomic Abstracts) were searched from 1990 to July 2022 for studies in any language. A Web of Science snowball search was performed in December 2022. Reference lists were manually reviewed. STUDY ELIGIBILITY CRITERIA: Eligible studies reported associations between occupational lifting or postural load and musculoskeletal health or sequelae (eg, employment outcomes) among pregnant and postpartum workers. METHODS: Data were extracted using a customized form to document study and sample characteristics; and details of exposures, outcomes, covariates, and analyses. Investigators independently assessed study quality for 7 risk-of-bias domains and overall utility, with discrepant ratings resolved through discussion. A narrative synthesis was conducted due to heterogeneity. RESULTS: Sixteen studies (11 cohort studies, 2 nested case-control studies, and 3 cross-sectional studies) from 8 countries were included (N=142,320 pregnant and N=1744 postpartum workers). Limited but consistent evidence with variable quality ratings, ranging from critical concern to high, suggests that pregnant workers exposed to heavy lifting (usually defined as ≥22 lbs or ≥10 kg) may be at increased risk of functionally limiting pelvic girdle pain and antenatal leave. Moreover, reports of dose-response relationships suggest graded risk levels according to lifting frequency, ranging from 21% to 45% for pelvic girdle pain and 58% to 202% for antenatal leave. Limited but consistent evidence also suggests that postural load increases the risk of employment cessation. CONCLUSION: Limited but consistent evidence suggests that pregnant workers exposed to heavy lifting and postural load are at increased risk of pelvic girdle pain and employment cessation. Job accommodations to reduce exposure levels may promote safe sustainable employment for pregnant workers.

Psychosocial risk factors for low back pain in US workers: Data from the 2002-2018 quality of work life survey.

BACKGROUND: Examining workplace psychosocial risk factors for back pain becomes increasingly important because of the changing nature of work and rising healthcare costs. Some psychosocial risk factors for back pain, such as work and family imbalance, exposure to a hostile work environment, and job insecurity, are understudied for the working population in the United States. METHODS: Data used in this study came from the Quality of Work Life Survey (QWL), a supplementary module of the General Social Survey conducted in the United States. Data from the 2002, 2006, 2010, 2014, and 2018 QWL surveys were used in these analyses, giving a total sample size of 6661. Five domains of workplace psychosocial risk factors for back pain were examined, including job strain, low social support, work-family imbalance, exposure to a hostile work environment (harassment and discrimination), and job insecurity. The adjusted odds ratio (aOR) of each psychosocial risk factor for back pain with 95% confidence intervals (CI) was estimated using a multivariable logistic regression model after controlling for job physical factors, occupation, and demographic and socioeconomic characteristics. RESULTS: Significant associations were found between back pain and several psychosocial factors including job strain (aOR 1.19; CI 1.00,1.41), work-family imbalance (aOR,1.42; CI 1.22,1.64), harassment (aOR 1.40; CI 1.15,1.71), and discrimination (aOR 1.20 CI 1.00,1.44). CONCLUSION: This study contributes to the understanding of the relationship between a variety of workplace psychosocial factors and back pain. Our findings suggest directions in future longitudinal research to examine emerging workplace psychosocial factors for back pain.

Estimating Trunk Angle Kinematics During Lifting Using a Computationally Efficient Computer Vision Method.

OBJECTIVE: A computer vision method was developed for estimating the trunk flexion angle, angular speed, and angular acceleration by extracting simple features from the moving image during lifting. BACKGROUND: Trunk kinematics is an important risk factor for lower back pain, but is often difficult to measure by practitioners for lifting risk assessments. METHODS: Mannequins representing a wide range of hand locations for different lifting postures were systematically generated using the University of Michigan 3DSSPP software. A bounding box was drawn tightly around each mannequin and regression models estimated trunk angles. The estimates were validated against human posture data for 216 lifts collected using a laboratory-grade motion capture system and synchronized video recordings. Trunk kinematics, based on bounding box dimensions drawn around the subjects in the video recordings of the lifts, were modeled for consecutive video frames. RESULTS: The mean absolute difference between predicted and motion capture measured trunk angles was 14.7°, and there was a significant linear relationship between predicted and measured trunk angles (R2 = .80, p < .001). The training error for the kinematics model was 2.3°. CONCLUSION: Using simple computer vision-extracted features, the bounding box method indirectly estimated trunk angle and associated kinematics, albeit with limited precision. APPLICATION: This computer vision method may be implemented on handheld devices such as smartphones to facilitate automatic lifting risk assessments in the workplace.

Industrial exoskeletons: Need for intervention effectiveness research.

Exoskeleton devices are being introduced across several industry sectors to augment, amplify, or reinforce the performance of a worker's existing body components-primarily the lower back and the upper extremity. Industrial exoskeletons may play a role in reducing work-related musculoskeletal disorders arising from lifting and handling heavy materials or from supporting heavy tools in overhead work. However, wearing an exoskeleton may pose a number of risks that are currently not well-studied. There are only a few studies about the safety and health implications of wearable exoskeletons and most of those studies involve only a small number of participants. Before the widespread implementation of industrial exoskeletons occurs, there is need for prospective interventional studies to evaluate the safety and health effectiveness of exoskeletons across various industry sectors. Developing a research strategy to fill current safety and health knowledge gaps, understanding the benefits, risks, and barriers to adoption of industrial exoskeletons, determining whether exoskeleton can be considered a type of personal protective equipment, and advancing consensus standards that address exoskeleton safety, should be major interests of both the occupational safety and health research and practice communities.

Prevalence of low back pain, seeking medical care, and lost time due to low back pain among manual material handling workers in the United States.

BACKGROUND: Low back pain (LBP) is a common and costly problem throughout the United States. To achieve a greater understanding of the occupational risk factors, the National Institute for Occupational Safety and Health (NIOSH) funded a low back health effects consortium, which performed several surveillance studies throughout the United States. This study combines data from the consortium research groups resulting in a data set with nearly 2000 workers in various regions of the country. The purpose of this paper is to examine prevalence and personal risk factors of low back health effects among these workers. METHODS: There were three common questions regarding history of low back health effects in the past 12 months including 1) have you had LBP lasting 7 days, 2) have you sought medical care for LBP, and 3) have you taken time off work due to LBP. The questionnaire included demographic questions. There were five data collections institutions or sites including NIOSH, Ohio State University, University of Wisconsin-Milwaukee, Texas A&M University, and University of Utah. RESULTS: The 12-month period prevalence of low back pain lasting 7 days, seeking medical care, and lost time due to LBP were 25, 14 and 10%, respectively. There were no statistically significant differences in gender, age or weight between cases and non-cases for any prevalence measure. The height of workers was significantly greater in the cases compared to non-cases for all three prevalence definitions. There were significant differences among the sites on the prevalence of seeking medical care for LBP and lost time due to LBP. The Ohio State University had significantly higher prevalence rates for seeking medical care and lost time due to LBP than University of Wisconsin, University of Utah, or Texas A&M University. CONCLUSION: LBP, the least severe low back health effect studied, had the highest prevalence (25%) and lost time due to LBP, the most severe low back health effect studied, had the lowest prevalence (10%) among nearly 2000 US manual material handling workers. There was a significant site or regional influence in prevalence rates for seeking medical care and lost time due to LBP.

Predicting Sagittal Plane Lifting Postures From Image Bounding Box Dimensions.

OBJECTIVE: A method for automatically classifying lifting postures from simple features in video recordings was developed and tested. We explored if an "elastic" rectangular bounding box, drawn tightly around the subject, can be used for classifying standing, stooping, and squatting at the lift origin and destination. BACKGROUND: Current marker-less video tracking methods depend on a priori skeletal human models, which are prone to error from poor illumination, obstructions, and difficulty placing cameras in the field. Robust computer vision algorithms based on spatiotemporal features were previously applied for evaluating repetitive motion tasks, exertion frequency, and duty cycle. METHODS: Mannequin poses were systematically generated using the Michigan 3DSSPP software for a wide range of hand locations and lifting postures. The stature-normalized height and width of a bounding box were measured in the sagittal plane and when rotated horizontally by 30°. After randomly ordering the data, a classification and regression tree algorithm was trained to classify the lifting postures. RESULTS: The resulting tree had four levels and four splits, misclassifying 0.36% training-set cases. The algorithm was tested using 30 video clips of industrial lifting tasks, misclassifying 3.33% test-set cases. The sensitivity and specificity, respectively, were 100.0% and 100.0% for squatting, 90.0% and 100.0% for stooping, and 100.0% and 95.0% for standing. CONCLUSIONS: The tree classification algorithm is capable of classifying lifting postures based only on dimensions of bounding boxes. APPLICATIONS: It is anticipated that this practical algorithm can be implemented on handheld devices such as a smartphone, making it readily accessible to practitioners.

The accuracy of a 2D video-based lifting monitor.

A widely used risk prediction tool, the revised NIOSH lifting equation (RNLE), provides the recommended weight limit (RWL), but is limited by analyst subjectivity, experience, and resources. This paper describes a robust, non-intrusive, straightforward approach to automatically extract spatial and temporal factors necessary for the RNLE using a single video camera in the sagittal plane. The participant's silhouette is segmented by motion information and the novel use of a ghosting effect provides accurate detection of lifting instances, and hand and feet location prediction. Laboratory tests using 6 participants, each performing 36 lifts, showed that a nominal 640 pixel × 480 pixel 2D video, in comparison to 3D motion capture, provided RWL estimations within 0.2 kg (SD = 1.0 kg). The linear regression between the video and 3D tracking RWL was R2 = 0.96 (slope = 1.0, intercept = 0.2 kg). Since low definition video was used in order to synchronise with motion capture, better performance is anticipated using high definition video. Practitioner's summary: An algorithm for automatically calculating the revised NIOSH lifting equation using a single video camera was evaluated in comparison to laboratory 3D motion capture. The results indicate that this method has suitable accuracy for practical use and may be, particularly, useful when multiple lifts are evaluated. Abbreviations: 2D: Two-dimensional; 3D: Three-dimensional; ACGIH: American Conference of Governmental Industrial Hygienists; AM: asymmetric multiplier; BOL: beginning of lift; CM: coupling multiplier; DM: distance multiplier; EOL: end of lift; FIRWL: frequency independent recommended weight limit; FM: frequency multiplier; H: horizontal distance; HM: horizontal multiplier; IMU: inertial measurement unit; ISO: International Organization for Standardization; LC: load constant; NIOSH: National Institute for Occupational Safety and Health; RGB: red, green, blue; RGB-D: red, green, blue - depth; RNLE: revised NIOSH lifting equation; RWL: recommended weight limit; SD: standard deviation; TLV: threshold limit value; VM: vertical multiplier; V: vertical distance.

Frequent Exertion and Frequent Standing at Work, by Industry and Occupation Group - United States, 2015.

Repeated exposure to occupational ergonomic hazards, such as frequent exertion (repetitive bending or twisting) and frequent standing, can lead to injuries, most commonly musculoskeletal disorders (1). Work-related musculoskeletal disorders have been estimated to cost the United States approximately $2.6 billion in annual direct and indirect costs (2). A recent literature review provided evidence that prolonged standing at work also leads to adverse health outcomes, such as back pain, physical fatigue, and muscle pain (3). To determine which industry and occupation groups currently have the highest prevalence rates of frequent exertion at work and frequent standing at work, CDC analyzed data from the 2015 National Health Interview Survey (NHIS) Occupational Health Supplement (OHS) regarding currently employed adults in the United States. By industry, the highest prevalence of both frequent exertion and frequent standing at work was among those in the agriculture, forestry, fishing, and hunting industry group (70.9%); by occupation, the highest prevalence was among those in the construction and extraction occupation group (76.9%). Large differences among industry and occupation groups were found with regard to these ergonomic hazards, suggesting a need for targeted interventions designed to reduce workplace exposure.

Workplace psychosocial and organizational factors for neck pain in workers in the United States.

BACKGROUND: Neck pain is a prevalent musculoskeletal condition among workers in the United States. This study explores a set of workplace psychosocial and organization-related factors for neck pain. METHODS: Data used for this study come from the 2010 National Health Interview Survey which provides a representative sample of the US population. To account for the complex sampling design, the Taylor linearized variance estimation method was used. Logistic regression models were constructed to measure the associations. RESULTS: This study demonstrated significant associations between neck pain and a set of workplace risk factors, including work-family imbalance, exposure to a hostile work environment and job insecurity, non-standard work arrangements, multiple jobs, and long work hours. CONCLUSION: Workers with neck pain may benefit from intervention programs that address issues related to these workplace risk factors. Future studies exploring both psychosocial risk factors and physical risk factors with a longitudinal design will be important. Am. J. Ind. Med. 59:549-560, 2016. © 2016 Wiley Periodicals, Inc.

Evaluation of the Impact of the Revised National Institute for Occupational Safety and Health Lifting Equation.

OBJECTIVE: The objective of this article is to evaluate the impact of the Revised National Institute for Occupational Safety and Health Lifting Equation (RNLE). BACKGROUND: The RNLE has been used extensively as a risk assessment method for prevention of low back pain (LBP). However, the impact of the RNLE has not been documented. METHODS: A systematic review of the literature on the RNLE was conducted. The review consisted of three parts: characterization of the RNLE publications, assessment of the impact of the RNLE, and evaluation of the influences of the RNLE on ergonomic standards. The literature for assessing the impact was categorized into four research areas: methodology, laboratory, field, and risk assessment studies using the Lifting Index (LI) or Composite LI (CLI), both of which are the products of the RNLE. RESULTS: The impact of the RNLE has been both widespread and influential. We found 24 studies that examined the criteria used to define lifting capacity used by the RNLE, 28 studies that compared risk assessment methods for identifying LBP, 23 studies that found the RNLE useful in identifying the risk of LBP with different work populations, and 13 studies on the relationship between LI/CLI and LBP outcomes. We also found evidence on the adoption of the RNLE as an ergonomic standard for use by various local, state, and international entities. CONCLUSION: The review found 13 studies that link LI/CLI to adverse LBP outcomes. These studies showed a positive relationship between LI/CLI metrics and the severity of LBP outcomes.

Low Back Pain Prevalence and Related Workplace Psychosocial Risk Factors: A Study Using Data From the 2010 National Health Interview Survey.

OBJECTIVES: The objectives of this study were to estimate prevalence of low back pain, to investigate associations between low back pain and a set of emerging workplace risk factors, and to identify worker groups with an increased vulnerability for low back pain in the United States. METHODS: The data used for this cross-sectional study came from the 2010 National Health Interview Survey, which was designed to collect data on health conditions and related risk factors from the US civilian population. The variance estimation method was used to compute weighted data for prevalence of low back pain. Multivariable logistic regression analyses stratified by sex and age were performed to determine the odds ratios (ORs) and the 95% confidence interval (CI) for low back pain. The examined work-related psychosocial risk factors included work-family imbalance, exposure to a hostile work environment, and job insecurity. Work hours, occupation, and other work organizational factors (nonstandard work arrangements and alternative shifts) were also examined. RESULTS: The prevalence of self-reported low back pain in the previous 3 months among workers in the United States was 25.7% in 2010. Female or older workers were at increased risk of experiencing low back pain. We found significant associations between low back pain and a set of psychosocial factors, including work-family imbalance (OR 1.27, CI 1.15-1.41), exposure to hostile work (OR 1.39, CI 1.25-1.55), and job insecurity (OR 1.44, CI 1.24-1.67), while controlling for demographic characteristics and other health-related factors. Older workers who had nonstandard work arrangements were more likely to report low back pain. Women who worked 41 to 45 hours per week and younger workers who worked >60 hours per week had an increased risk for low back pain. Workers from several occupation groups, including male health care practitioners, female and younger health care support workers, and female farming, fishing, and forestry workers, had an increased risk of low back pain. CONCLUSIONS: This study linked low back pain to work-family imbalance, exposure to a hostile work environment, job insecurity, long work hours, and certain occupation groups. These factors should be considered by employers, policymakers, and health care practitioners who are concerned about the impact of low back pain in workers.

Muscular activity of lower limb muscles associated with working on inclined surfaces.

This study investigated the effects of visual cues, muscular fatigue, task performance and experience of working on inclined surfaces on activity of postural muscles in the lower limbs associated with maintaining balance on three inclined surfaces - 0°, 14° and 26°. Normalised electromyographic (NEMG) data were collected in 44 professional roofers bilaterally from the rectus femoris, biceps femoris, tibialii anterior and gastrocnemii medial muscle groups. The 50th and 95th percentile NEMG amplitudes were used as EMG variables. Results showed that inclination angle and task performance caused a significant increase in the NEMG amplitudes of all postural muscles. Visual cues were significantly associated with a decrease in the 95th percentile EMG amplitude for the right gastrocnemius medial and tibialis anterior. Fatigue was related to a significant decrease in the NEMG amplitude for the rectus femoris. Experience of working on inclined surfaces did not have a significant effect on the NEMG amplitude.

Workplace psychosocial factors associated with work-related injury absence: a study from a nationally representative sample of Korean workers.

BACKGROUND: Little is known about the association between psychosocial factors and injury absence in the workplace. PURPOSE: This study aims to assess the association of comprehensive workplace psychosocial factors with work-related injury absence among Korean workers. METHODS: The data (n = 7,856) were derived from the First Korean Working Conditions Survey conducted in 2006 with a representative sample (n = 10,043) of the Korean working population. The survey instrument contained questions about hours of work, physical risk factors, work organization, and the effect of work on health/injury. Work-related injury absence was indicated by a dichotomous variable with at least 1 day absence during the preceding 12 months. Logistic regression models were used to calculate odds ratio and confidence interval (CI). Incremental adjustments for sociodemographic, health behavior, and occupational confounding variables were employed in the models. RESULTS: The overall 1-year prevalence of work-related injury absence in this study was 1.37 % (95 % CI, 1.11-1.63 %). Those who experienced violence at work (adjusted odds ratio (aOR), 7.05 (95 % CI, 2.69-18.5)), threat of violence at work (aOR, 4.25 (95 % CI, 1.32-13.64)), low job autonomy (aOR, 1.79 (95 % CI, 1.17-2.74)), and high job strain (aOR, 2.38 (95 % CI, 1.29-4.42) had an increased risk of injury absence, compared with their respective counterparts (p < 0.05). Among all job types, skilled workers in Korea were at a near fourfold risk of work absence due to occupational injuries, compared with managers in low-risk jobs. CONCLUSION: Workplace violence and increased job strain were two key workplace psychosocial factors associated with work-related injury absence.

Workplace Psychosocial Factors, Work Organization, and Physical Exertion as Risk Factors for Low Back Pain Among US Workers: Data From the 2015 National Health Interview Survey.

OBJECTIVE: To evaluate the association between workplace psychosocial, organization, and physical risk factors with low back pain (LBP) among US workers. METHODS: 2015 National Health Interview Survey data were analyzed to calculate the prevalence rates and prevalence ratios for LBP across levels of workplace psychosocial and organizational risk factors among 17,464 US adult workers who worked ≥20 hours per week. Results were also stratified by workplace physical exertion. RESULTS: The adjusted prevalence rates of LBP were significantly elevated for workers reporting high job demand, low job control, work-family imbalance, bullying, job insecurity, working alternate shifts, and physical exertion. Job control and nonstandard shifts were significantly associated with LBP only among those who reported low/no physical exertion. CONCLUSIONS: LBP prevalence was associated with select workplace psychosocial and organization risk factors. Stratification by physical exertion modified multiple associations.

Investigating gripping force during lifting tasks using a pressure sensing glove system.

Lifting tasks remain one of the leading causes of musculoskeletal disorders (MSDs), primarily in the low back region. Lifting analysis tools are, therefore, designed for assessing the risk of low back pain. Shoulder musculoskeletal problems have emerged as common MSDs associated with manual handling tasks. It is hypothesized that gripping force is related to lifting conditions and may be used as a supplementary risk metric for MSDs in the shoulder and low back regions, because it measures additional hand exertions for coupling the lifted object during lifting. We assessed the capability tactile gloves for measuring the gripping force during lifting as a means for assessing different task conditions (lifting weight, lifting height, lifting direction, body rotation, and handle). Thirty participants wore the tactile gloves and performed simulated lifting tasks. Regression models were used to analyze the effects of the task variables on estimating the measured gripping force. Results demonstrated that 58% and 70% of the lifting weight variance were explained by the measured gripping force without and with considering the individual difference, respectively. In addition to the lifting risk measures commonly used by practitioners, this study suggests a potential for using gripping force as a supplementary or additional risk metric for MSDs.

Musculoskeletal symptoms and associated risk factors in a large sample of Chinese workers in Henan province of China.

OBJECTIVE: To investigate the one-year prevalence of musculoskeletal symptoms and associated risk factors in a large sample of Chinese workers in various industrial settings. METHODS: A total of 5,338 (3,632 males and 1,706 females) workers from 13 companies participated in this study. Musculoskeletal symptoms in different body regions in the previous year and their risk factors were assessed by a self-reported questionnaire. Logistic regression analyses were performed to estimate the individual, work-related physical and psychosocial risk factors for the musculoskeletal symptoms. RESULTS: The most commonly affected body regions among the workers were lower back (59.7%), neck (48.6%), shoulders (38.8%), and wrists (33.5%). Female workers had greater prevalence of musculoskeletal symptoms in the neck, shoulders, and wrists than male workers. Results of multivariate analyses indicated that individual, work-related physical and psychosocial factors were associated with the musculoskeletal symptoms. CONCLUSION: The results suggest that interventions aimed at reducing musculoskeletal symptoms in the Chinese working population should take into account multiple risk areas including individual, physical job characteristics and work-related psychosocial factors.

Two linear regression models predicting cumulative dynamic L5/S1 joint moment during a range of lifting tasks based on static postures.

Previous studies have indicated that cumulative L5/S1 joint load is a potential risk factor for low back pain. The assessment of cumulative L5/S1 joint load during a field study is challenging due to the difficulty of continuously monitoring the dynamic joint load. This study proposes two regression models predicting cumulative dynamic L5/S1 joint moment based on the static L5/S1 joint moment of a lifting task at lift-off and set-down and the lift duration. Twelve men performed lifting tasks at varying lifting ranges and asymmetric angles in a laboratory environment. The cumulative L5/S1 joint moment was calculated from continuous dynamic L5/S1 moments as the reference for comparison. The static L5/S1 joint moments at lift-off and set-down were measured for the two regression models. The prediction error of the cumulative L5/S1 joint moment was 21 ± 14 Nm × s (12% of the measured cumulative L5/S1 joint moment) and 14 ± 9 Nm × s (8%) for the first and the second models, respectively. Practitioner Summary: The proposed regression models may provide a practical approach for predicting the cumulative dynamic L5/S1 joint loading of a lifting task for field studies since it requires only the lifting duration and the static moments at the lift-off and/or set-down instants of the lift.

Load Asymmetry Angle Estimation Using Multiple view Videos.

A robust computer vision-based approach is developed to estimate the load asymmetry angle defined in the revised NIOSH lifting equation (RNLE). The angle of asymmetry enables the computation of a recommended weight limit for repetitive lifting operations in a workplace to prevent lower back injuries. An open-source package OpenPose is applied to estimate the 2D locations of skeletal joints of the worker from two synchronous videos. Combining these joint location estimates, a computer vision correspondence and depth estimation method is developed to estimate the 3D coordinates of skeletal joints during lifting. The angle of asymmetry is then deduced from a subset of these 3D positions. Error analysis reveals unreliable angle estimates due to occlusions of upper limbs. A robust angle estimation method that mitigates this challenge is developed. We propose a method to flag unreliable angle estimates based on the average confidence level of 2D joint estimates provided by OpenPose. An optimal threshold is derived that balances the percentage variance reduction of the estimation error and the percentage of angle estimates flagged. Tested with 360 lifting instances in a NIOSH-provided dataset, the standard deviation of angle estimation error is reduced from 10.13° to 4.99°. To realize this error variance reduction, 34% of estimated angles are flagged and require further validation.