Applications of biomechanics for prevention of work-related musculoskeletal disorders

A generic approach to developing human factors-quality assessment tools exemplified by the warehouse error prevention tool

This study proposes a generic approach for creating human factors-based assessment tools to enhance operational system quality by reducing errors. The approach was driven by experiences and lessons learned in creating the warehouse error prevention (WEP) tool and other system engineering tools. The generic approach consists of 1) identifying tool objectives, 2) identifying system failure modes, 3) specifying design-related quality risk factors for each failure mode, 4) designing the tool, 5) conducting user evaluations, and 6) validating the tool. The WEP tool exemplifies this approach and identifies human factors related to design flaws associated with quality risk factors in warehouse operations. The WEP tool can be used at the initial stage of design or later for process improvement and training. While this process can be adapted for various contexts, further study is necessary to support the teams in creating tools to identify design-related human factors contributing to quality issues.

Biomechanical differences in experts' and novices' footstep patterns during a palletizing task

Very few studies have examined differences between experts' and novices' foot positioning and movements during manual materials handling tasks. The impact of footstep patterns on low back loading needs to be better understood. The goals of this study were to characterize foot placement and movements in novices and experts and to assess their impact on back loading considering the height of grasp. The task consisted in transferring 24 15 kg boxes from a pallet to another. Foot placement and movements were classified with a recently developed taxonomy. Results show that experts' feet remained static more often than novices' feet during the lifting phase. Positioning the feet towards the deposit site during lifting increased asymmetrical moments, especially for novices. Positioning one foot forward increased asymmetrical moments for novices. Overall, footstep strategies are an effective indicator of low back exposure and should be considered in ergonomic studies.

Effect of Expertise on Shoulder and Upper Limb Kinematics, Electromyography, and Estimated Muscle Forces During a Lifting Task

OBJECTIVE

To highlight the working strategies used by expert manual handlers compared with novice manual handlers, based on recordings of shoulder and upper limb kinematics, electromyography (EMG), and estimated muscle forces during a lifting task.

BACKGROUND

Novice workers involved in assembly, manual handling, and personal assistance tasks are at a higher risk of upper limb musculoskeletal disorders (MSDs). However, few studies have investigated the effect of expertise on upper limb exposure during workplace tasks.

METHOD

Sixteen experts in manual handling and sixteen novices were equipped with 10 electromyographic electrodes to record shoulder muscle activity during a manual handling task consisting of lifting a box (8 or 12 kg), instrumented with three six-axis force sensors, from hip to eye level. Three-dimensional trunk and upper limb kinematics, hand-to-box contact forces, and EMG were recorded. Then, joint contributions, activation levels, and muscle forces were calculated and compared between groups.

RESULTS

Sternoclavicular-acromioclavicular joint contributions were higher in experts at the beginning of the movement, and in novices at the end, whereas the opposite was observed for the glenohumeral joint. EMG activation levels were 37% higher for novices but predicted muscle forces were higher in experts.

CONCLUSION

This study highlights significant differences between experts and novices in shoulder kinematics, EMG, and muscle forces; hence, providing effective work guidelines to ensure the development of a safe handling strategy is important.

APPLICATION

Shoulder kinematics, EMG, and muscle forces could be used as ergonomic tools to identify inappropriate techniques that could increase the prevalence of shoulder injuries.

Adjustments in Shoulder and Back Kinematics during Repetitive Palletizing Tasks

Repetitive task performance is a leading cause of musculoskeletal injuries among order-picking workers in warehouses. The repetition of lifting tasks increases the risk of back and shoulder injuries among these workers. While lifting in this industry is composed of loaded and unloaded picking and placing, the existing literature does not address the separate analysis of the biomechanics of the back and shoulder for these events. To that end, we investigated the kinematics of the back and shoulder movements of nine healthy male participants who performed three sessions of a simulated de/palletization task. Their back and shoulder kinematics were sensed using an optical motion capture system to determine the back inclination and shoulder flexion. Comparison of the kinematics between the first and last sessions indicated statistically significant changes in the timings, angles, coordination between the back and shoulder, and moments around the shoulder (p<0.05). The majority of the significant changes were observed during the loaded events, which confirms the importance of the separation of these events for biomechanical analysis. This finding suggests that focusing worker evaluation on the loaded periods can provide important information to detect kinematic changes that may affect musculoskeletal injury risk.

Effect of using real motion versus predicted motion as input for digital human modeling of back and shoulder loads during manual material handling

Digital human modeling (DHM) technology is considered the state of the art in designing and evaluating workstations. Previous studies examined the differences between DHM's posture and motion prediction relative to human experimental data. Yet, the effect the two different inputs on biomechanical loads was not assessed. Therefore, this study evaluates the differences in L4/L5 compression force and shoulder torques during a work process calculated using DHM with motion prediction (Jack by Siemens) and DHM with experimental data. The work process is a sequential removing, carrying, and depositing task performed by nine females and nine males and recorded using a motion capture system. The analysis shows that using experimental data results in larger back compression force during the removing task (average 15.4%), similar force during the depositing task (average 0.68%), and less force during the carrying task (19.875%). Using experimental data resulted in larger shoulder torque during all tasks (average 24.97%).

Added value of motion capture technology for occupational health and safety innovations

Ergonomic principles in production assembly and manufacturing operations have become an essential part of comprehensive health and safety innovations. We aim to provide new insights into occupational health and safety innovations and how they utilise biomechanical methods and cutting-edge motion capture technology by assessing movements at a workplace. The practical goal is to quantify a connection between work exposure and ergonomic risk measures to determine biomechanical risk factors of diseases or health-related disorders objectively. The target group consisted of 62 factory employees working in manufacturing (26 participants on 12 devices) or assembly areas (36 participants on 9 devices). Body posture, body parts position, movements, energy cost and workloads were assessed using an inertial motion capture (MC) system. MC technology accurately assesses the operator’s movements. The proposed methodology could complement ergonomic procedures in the design of workstations, which is the added value of the motion capture technology for occupational health and safety innovations.

Effects of load mass and position on the dynamic loading of the knees, shoulders and lumbar spine during lifting: a musculoskeletal modelling approach

Musculoskeletal models may enhance our understanding of the dynamic loading of the joints during manual material handling. This study used state-of-the-art musculoskeletal models to determine the effects of load mass, asymmetry angle, horizontal location and deposit height on the dynamic loading of the knees, shoulders and lumbar spine during lifting. Recommended weight limits and lifting indices were also calculated using the NIOSH lifting equation. Based on 1832 lifts from 22 subjects, we found that load mass had the most substantial effect on L5-S1 compression. Increments in asymmetry led to large increases in mediolateral shear, while load mass and asymmetry had significant effects on anteroposterior shear. Increased deposit height led to higher shoulder forces, while the horizontal location mostly affected the forces in the knees and shoulders. These results generally support the findings of previous research, but notable differences in the trends and magnitudes of the estimated forces were observed.

Shoulder moments and angles during single and combined manual material handling tasks

Shoulder musculoskeletal disorders due to manual material handling tasks are common workplace injuries. Here we investigated the difference in shoulder biomechanics (moments and angles) between a single task of removing a box from a shelf (or depositing a box on a shelf) and the equivalent part of a combined task that consisted of removing, carrying and depositing boxes; that is, a single removing [depositing] task was compared with the removing [depositing] part of a combined task. We found that the peak and cumulative shoulder moments were larger during the single-task paradigm than during the equivalent part of the combined task by 26.3 and 25.5%, respectively. The two paradigms also differed in terms of shoulder angles. It is likely that the main contributors to this overestimation were differences between the single and combined tasks in terms of the lever arm (i.e. horizontal distance), the shoulder angle, and the task duration. Practitioners' Summary: We investigated shoulder moments during single and combined manual material handling tasks. Shoulder moments were found to be smaller during combined tasks. Practitioners should consider that analysing combined tasks using estimations based on single tasks could result in an overestimation of 26.3 and 25.5% in peak and cumulative shoulder moments, respectively.Abbrevaitions: MSDs: musculoskeletal disorders; MMH: manual material handling; LMM: linear mixed model.

Sex differences in upper limb musculoskeletal biomechanics during a lifting task

Women experience higher prevalence of work-related upper limb musculoskeletal disorders compared to men. Previous studies have investigated the biological, kinematic and electromyographic sex-related differences during a lifting task but the actual differences in musculoskeletal loads remain unknown. We investigated the sex differences in three musculoskeletal indicators: the sum of muscle activations, the sum of muscle forces and the relative time spent beyond a shear-compression dislocation ratio. A musculoskeletal model was scaled on 20 women and 20 men lifting a 6 or 12kg box from hip to eye level. Women generated more muscle forces and activations than men, regardless of the lifted mass. Those differences occurred when the box was above shoulder level. In addition, women might spend more time beyond a shear-compression dislocation ratio. Our work suggests higher musculoskeletal loads among women compared to men during a lifting task, which could be the result of poor technique and strength difference.

Workers' biomechanical loads and kinematics during multiple-task manual material handling

This study investigated the biomechanical loads and kinematics of workers during multiple-task manual material handling (MMH) jobs, and developed prediction models for the moments acting on a worker's body and their peak joint angles. An experiment was conducted in which 20 subjects performed a total of 3780 repetitions of a box-conveying task. This task included continuous sequential removing, carrying and depositing of boxes weighing 2-12 kg. The subjects' motion was captured using motion-capture technology. The origin/destination height was the most influencing predictor of the spinal and shoulder moments and the peak trunk, shoulder and knee angles. The relationship between the origin/destination heights and the above parameters was nonlinear. The mass of the box, and the subject's height and mass, also influenced the spinal and shoulder moments. A tradeoff between the moments acting on the L5/S1 vertebrae and on the shoulder joint was found. Compared to the models developed in similar studies that focused on manual material handling (albeit under different conditions), the high-order prediction equation for peak spinal moment formulated in the present study was found to explain between 10% and 48% more variability in the moments. This suggests that using a high-order equation in future studies might improve the prediction.

Differences in spinal moments, kinematics and pace during single-task and combined manual material handling jobs

This study compared the spinal moments (i.e., peak and cumulative moments acting on the L5/S1 joint), kinematics (i.e., peak trunk and knee angles) and work pace of workers, when either removing a box from a shelf or depositing a box on a shelf, under two conditions: as a single task or as part of a combined task. An experiment was conducted, in which the subjects performed the tasks and were recorded using a motion capture system. An automated program was developed to process the motion capture data. The results showed that, when the removing and depositing tasks were performed as part of a combined task (rather than as single tasks), subjects experienced smaller peak and cumulative spinal moments and they performed the tasks faster. The results suggest that investigations into the separate tasks that comprise a combination have a limited ability to predict kinematics and kinetics during the combined job.

Evaluation and comparison of lift styles for an ideal lift among individuals with different levels of training

Training for safe lifting techniques is used by employers to lower their workers' exposure to risk of workplace injuries. To determine effectiveness of training, 266 attendees at two professional conferences were asked to identify and demonstrate their preferred lift technique with the demonstration being an ideal floor-to-waist height lift of a10-kg weighted crate. 'Bend your knees' was the most frequent preferred cue for each of the self-reported participant groups: untrained (n = 65), trained (n = 86), and trainers (n = 115) according to safe lifting techniques. The demonstrations showed that this cue was incorporated into the skill of lifting by all groups. Trained participants showed a stronger conformity for depth of squat; but, the overall variability suggested a lack of consensus on the ideal depth of squat. The trained group experienced less loading at L5/S1 (p = .021) compared to untrained that was countered by higher loading of the knee (p = .046). Trainers showed lower knee (p = .006) and shoulder (p = .03) loading with similar L5/S1 loading as the trained participants suggesting a broader set of criteria for safe lifting. While the study population was likely biased towards a common understanding of safe lifting techniques given the conferences were for ergonomists and safety professionals, the results provided valuable insight into potential knowledge gaps, and key messaging that is being delivered and integrated into one's knowledge; a program review of lift training is recommended.

Barriers to the Adoption of Wearable Sensors in the Workplace: A Survey of Occupational Safety and Health Professionals

OBJECTIVE

To gather information on the (a) types of wearable sensors, particularly personal activity monitors, currently used by occupational safety and health (OSH) professionals; (b) potential benefits of using such technologies in the workplace; and (c) perceived barriers preventing the widespread adoption of wearable sensors in industry.

BACKGROUND

Wearable sensors are increasingly being promoted as a means to improve employee health and well-being, and there is mounting evidence supporting their use as exposure assessment and personal health tools. Despite this, many workplaces have been hesitant to adopt these technologies.

METHODS

An electronic survey was emailed to 28,428 registered members of the American Society of Safety Engineers (ASSE) and 1,302 professionals certified by the Board of Certification in Professional Ergonomics (BCPE).

RESULTS

A total of 952 valid responses were returned. Over half of respondents described being in favor of using wearable sensors to track OSH-related risk factors and relevant exposure metrics at their respective workplaces. However, barriers including concerns regarding employee privacy/confidentiality of collected data, employee compliance, sensor durability, the cost/benefit ratio of using wearables, and good manufacturing practice requirements were described as challenges precluding adoption.

CONCLUSION

The broad adoption of wearable technologies appears to depend largely on the scientific community's ability to successfully address the identified barriers.

APPLICATION

Investigators may use the information provided to develop research studies that better address OSH practitioner concerns and help technology developers operationalize wearable sensors to improve employee health and well-being.

Factors determining workers' pace while conducting continuous sequential lifting, carrying, and lowering tasks

To plan a new manual material handling work process, it is necessary to predict the times required to complete each task. Current time prediction models lack validity when the handled object's mass exceeds 2 kg. In this study, we investigated the effect of workplace design parameters on continuous sequential lifting, carrying, and lowering of boxes weighing from 2 kg to 14 kg. Both laboratory and field experiments were conducted. Results revealed that the box's weight and the lifting and lowering heights influenced the tasks' times. Further, the time to perform a task was influenced by the performance of other tasks in the same work process. New time prediction models were developed using the laboratory experiment data. Our models were found to be more accurate on average than the Maynard Operation Sequence Technique (MOST) and Methods Time Measurement (MTM-1) by 42% and 20%, respectively, for predicting the times of real workers at an actual workplace.

Risk assessments using the Strain Index and the TLV for HAL, Part II: Multi-task jobs and prevalence of CTS

The Strain Index (SI) and the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value for hand activity level (TLV for HAL) have been shown to be associated with prevalence of distal upper-limb musculoskeletal disorders such as carpal tunnel syndrome (CTS). The SI and TLV for HAL disagree on more than half of task exposure classifications. Similarly, time-weighted average (TWA), peak, and typical exposure techniques used to quantity physical exposure from multi-task jobs have shown between-technique agreement ranging from 61% to 93%, depending upon whether the SI or TLV for HAL model was used. This study compared exposure-response relationships between each model-technique combination and prevalence of CTS. Physical exposure data from 1,834 workers (710 with multi-task jobs) were analyzed using the SI and TLV for HAL and the TWA, typical, and peak multi-task job exposure techniques. Additionally, exposure classifications from the SI and TLV for HAL were combined into a single measure and evaluated. Prevalent CTS cases were identified using symptoms and nerve-conduction studies. Mixed effects logistic regression was used to quantify exposure-response relationships between categorized (i.e., low, medium, and high) physical exposure and CTS prevalence for all model-technique combinations, and for multi-task workers, mono-task workers, and all workers combined. Except for TWA TLV for HAL, all model-technique combinations showed monotonic increases in risk of CTS with increased physical exposure. The combined-models approach showed stronger association than the SI or TLV for HAL for multi-task workers. Despite differences in exposure classifications, nearly all model-technique combinations showed exposure-response relationships with prevalence of CTS for the combined sample of mono-task and multi-task workers. Both the TLV for HAL and the SI, with the TWA or typical techniques, appear useful for epidemiological studies and surveillance. However, the utility of TWA, typical, and peak techniques for job design and intervention is dubious.

A data-driven approach to modeling physical fatigue in the workplace using wearable sensors

Wearable sensors are currently being used to manage fatigue in professional athletics, transportation and mining industries. In manufacturing, physical fatigue is a challenging ergonomic/safety "issue" since it lowers productivity and increases the incidence of accidents. Therefore, physical fatigue must be managed. There are two main goals for this study. First, we examine the use of wearable sensors to detect physical fatigue occurrence in simulated manufacturing tasks. The second goal is to estimate the physical fatigue level over time. In order to achieve these goals, sensory data were recorded for eight healthy participants. Penalized logistic and multiple linear regression models were used for physical fatigue detection and level estimation, respectively. Important features from the five sensors locations were selected using Least Absolute Shrinkage and Selection Operator (LASSO), a popular variable selection methodology. The results show that the LASSO model performed well for both physical fatigue detection and modeling. The modeling approach is not participant and/or workload regime specific and thus can be adopted for other applications.

The Composite Strain Index (COSI) and Cumulative Strain Index (CUSI): methodologies for quantifying biomechanical stressors for complex tasks and job rotation using the Revised Strain Index

The Composite Strain Index (COSI) quantifies biomechanical stressors for complex tasks consisting of exertions at different force levels and/or with different exertion times. The Cumulative Strain Index (CUSI) further integrates biomechanical stressors from different tasks to quantify exposure for the entire work shift. The paper provides methodologies to compute COSI and CUSI along with examples. Complex task simulation produced 169,214 distinct tasks. Use of average, time-weighted average (TWA) and peak force and COSI classified 66.9, 28.2, 100 and 38.9% of tasks as hazardous, respectively. For job rotation the simulation produced 10,920 distinct jobs. TWA COSI, peak task COSI and CUSI classified 36.5, 78.1 and 66.6% jobs as hazardous, respectively. The results suggest that the TWA approach systematically underestimates the biomechanical stressors and peak approach overestimates biomechanical stressors, both at the task and job level. It is believed that the COSI and CUSI partially address these underestimations and overestimations of biomechanical stressors. Practitioner Summary: COSI quantifies exposure when applied hand force and/or duration of that force changes during a task cycle. CUSI integrates physical exposures from job rotation. These should be valuable tools for designing and analysing tasks and job rotation to determine risk of musculoskeletal injuries.

Toward Unobtrusive Patient Handling Activity Recognition for Injury Reduction Among At-Risk Caregivers

Nurses regularly perform patient handling activities. These activities with awkward postures expose healthcare providers to a high risk of overexertion injury. The recognition of patient handling activities is the first step to reduce injury risk for caregivers. The current practice on workplace activity recognition is based on human observational approach, which is neither accurate nor projectable to a large population. In this paper, we aim at addressing these challenges. Our solution comprises a smart wearable device and a novel spatio-temporal warping (STW) pattern recognition framework. The wearable device, named Smart Insole 2.0, is equipped with a rich set of sensors and can provide an unobtrusive way to automatically capture the information of patient handling activities. The STW pattern recognition framework fully exploits the spatial and temporal characteristics of plantar pressure by calculating a novel warped spatio-temporal distance, to quantify the similarity for the purpose of activity recognition. To validate the effectiveness of our framework, we perform a pilot study with eight subjects, including eight common activities in a nursing room. The experimental results show the overall classification accuracy achieves 91.7%. Meanwhile, the qualitative profile and load level can also be classified with accuracies of 98.3% and 92.5%, respectively.

Effect of uphill walking with varying grade and speed during load carriage on muscle activity

Indian soldiers, while guarding the mountainous border areas, often carry loads in steep uphill gradients. This activity may predispose the risk of muscle injury. The present study aimed to examine the effects of an increasing load, speed and gradient during incremental uphill treadmill walking on different muscles. Twelve infantry soldiers walked on a treadmill at two speeds (2.5 and 4 km/h) with no load, and carrying 10.7, 17 and 21.4 kg loads at 0, 5, 10, 15, 20, 25% gradients. Electromyographic responses of erector spinae (>240%) and vastus medialis (>240%) were mostly affected, followed by soleus (>125%) and gastrocnemius medialis (>100%) at maximum speed, load and gradient combination compared to 0% gradient. Carrying 10.7 kg at 15% gradient and above was found to be highly strenuous and fatiguing with the risk of muscle injury. Uphill load carriage in slower speed is recommended for the maintenance of combat fitness of the individual at higher gradients. Practitioner Summary: The present article has evaluated the stress encountered by soldiers during load carriage at incremental uphill gradients while walking at different speeds by recording the muscular activities. Load carriage in steep uphill gradients is highly strenuous and may lead to muscle injury thus compromising the combat fitness.

Modeling people with motor disabilities to empower the automatic accessibility and ergonomic assessment of new products

Virtual User Models (VUMs) can be a valuable tool for accessibility and ergonomic evaluation of designs in simulation environments. As increasing the accessibility of a design is usually translated into additional costs and increased development time, the need for specifying the percentage of population for which the design will be accessible is crucial. This paper addresses the development of VUMs representing specific groups of people with disabilities. In order to create such VUMs, we need to know the functional limitations, i.e. disability parameters, caused by each disability and their variability over the population. Measurements were obtained from 90 subjects with motor disabilities and were analyzed using both parametric and nonparametric regression methods as well as a proposed hybrid regression method able to handle small sample sizes. Validation results showed that in most cases the proposed regression analysis can produce valid estimations on the variability of each disability parameter.

Development of Human Posture Simulation Method for Assessing Posture Angles and Spinal Loads

Video-based posture analysis employing a biomechanical model is gaining a growing popularity for ergonomic assessments. A human posture simulation method of estimating multiple body postural angles and spinal loads from a video record was developed to expedite ergonomic assessments. The method was evaluated by a repeated measures study design with three trunk flexion levels, two lift asymmetry levels, three viewing angles and three trial repetitions as experimental factors. The study comprised two phases evaluating the accuracy of simulating self and other people's lifting posture via a proxy of a computer-generated humanoid. The mean values of the accuracy of simulating self and humanoid postures were 12° and 15°, respectively. The repeatability of the method for the same lifting condition was excellent (~2°). The least simulation error was associated with side viewing angle. The estimated back compressive force and moment, calculated by a three dimensional biomechanical model, exhibited a range of 5% underestimation. The posture simulation method enables researchers to simultaneously quantify body posture angles and spinal loading variables with accuracy and precision comparable to on-screen posture matching methods.

Exposure-response relationships for the ACGIH threshold limit value for hand-activity level: results from a pooled data study of carpal tunnel syndrome

OBJECTIVES

This paper aimed to quantify exposure-response relationships between the American Conference of Governmental Industrial Hygienists' (ACGIH) threshold limit value (TLV) for hand-activity level (HAL) and incidence of carpal tunnel syndrome (CTS).

METHODS

Manufacturing and service workers previously studied by six research institutions had their data combined and re-analyzed. CTS cases were defined by symptoms and abnormal nerve conduction. Hazard ratios (HR) were calculated using proportional hazards regression after adjusting for age, gender, body mass index, and CTS predisposing conditions.

RESULTS

The longitudinal study comprised 2751 incident-eligible workers, followed prospectively for up to 6.4 years and contributing 6243 person-years of data. Associations were found between CTS and TLV for HAL both as a continuous variable [HR 1.32 per unit, 95% confidence interval (95% CI) 1.11-1.57] and when categorized using the ACGIH action limit (AL) and TLV. Those between the AL and TLV and above the TLV had HR of 1.7 (95% CI 1.2-2.5) and 1.5 (95% CI 1.0-2.1), respectively. As independent variables (in the same adjusted model) the HR for peak force (PF) and HAL were 1.14 per unit (95% CI 1.05-1.25), and 1.04 per unit (95% CI 0.93-1.15), respectively.

CONCLUSION

Those with exposures above the AL were at increased risk of CTS, but there was no further increase in risk for workers above the TLV. This suggests that the current AL may not be sufficiently protective of workers. Combinations of PF and HAL are useful for predicting risk of CTS.

Strengths and limitations of a musculoskeletal model for an analysis of simulated meat cutting tasks

This study assessed the capacity of a musculoskeletal model to predict the relative muscle activation changes as a function of the workbench height and the movement direction during a simulated meat cutting task. Seven subjects performed a cutting task alternating two cutting directions for 20 s at four different workbench heights. Kinematics, electromyography (EMG), and cutting force data were collected and used to drive a musculoskeletal model of the shoulder girdle. The model predicted the muscle forces exerted during the task. Both the recorded and computed activation of the muscles was then compared by means of cross-correlation and by comparison of muscle activation trends with respect to the workstation parameters, i.e. cutting direction and workbench height. The results indicated that cutting movements involving arm flexion are preferable to movement requiring internal arm rotation and abduction. The optimal bench height for meat cutting tasks should be between 20 and 30 cm below the worker's elbow height. The present study underlines a beneficial use of musculoskeletal models for adjusting workstation parameters.

The strain index and TLV for HAL: risk of lateral epicondylitis in a prospective cohort

BACKGROUND

This study's objective was to quantify exposure-response relationships between job physical exposure (JPE) and incidence of lateral epicondylitis (LE).

METHODS

A cohort of 536 workers was enrolled from 10 manufacturing facilities and followed monthly for 6 years to ascertain changes in JPE and health status. JPE was individually measured and quantified using the Strain Index (SI) and TLV for HAL. Worker demographics, medical history, psychosocial factors, and current musculoskeletal disorders were obtained.

RESULTS

Fifty-six workers developed LE. In multivariate models JPE, age, family problems, and swimming were associated with increased risk of LE. SI showed an exposure-response relationship with maximum hazard ratio (HR) of 4.5(P = 0.04). TLV for HAL showed a non-statistically significant trend for increased risk of LE (P = 0.19).

CONCLUSION

JPE is associated with increased risk of LE. The SI and TLV for HAL are useful metrics for estimating JPE.

The Strain Index and ACGIH TLV for HAL: risk of trigger digit in the WISTAH prospective cohort

OBJECTIVE

The objective of this study was to investigate the association between job physical exposure (JPE) and incidence of flexor tendon entrapment of the digits (FTED).

BACKGROUND

FTED, commonly known as trigger digit, is associated with age, gender, and certain health disorders. Although JPE has been suggested as a risk factor for FTED, there are no prospective cohort studies.

METHOD

A cohort of 516 workers was enrolled from 10 diverse manufacturing facilities and followed monthly for 6 years. Worker demographics, medical history, and symptoms of FTED were assessed. JPE was individually measured using the Strain Index (SI) and American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value for hand activity level (TLV for HAL). Changes in JPE (assessed quarterly) and symptoms (assessed monthly) were recorded during follow-up. FTED was defined as demonstrated triggering on examination.

RESULTS

Point prevalence of FTED at baseline was 3.6%. During follow-up there were 23 incident FTED cases (left and/or right hands). The incident rate for first occurrence of FTED from enrollment was 1.38 per 100 person-years. Risk factors were JPE, age, gender, diabetes mellitus, carpometacarpal osteoarthrosis, and rheumatoid arthritis. In multivariate models, the SI showed strong association with risk of FTED when treated as a continuous variable and marginal association when dichotomized (SI > 6.1). TLV for HAL showed a statistical trend of increasing risk of FTED using the ACGIH limits, but no association as a continuous variable.

CONCLUSIONS

Both JPE and personal risk factors are associated with FTED development. The SI and TLV for HAL are useful tools for estimating JPE.

The NIOSH lifting equation and low-back pain, Part 1: Association with low-back pain in the backworks prospective cohort study

OBJECTIVE

The aim of this study was to evaluate relationships between the revised NIOSH lifting equation (RNLE) and risk of low-back pain (LBP).

BACKGROUND

The RNLE is commonly used to quantify job physical stressors to the low back from lifting and/or lowering of loads. There is no prospective study on the relationship between RNLE and LBP that includes accounting for relevant covariates.

METHOD

A cohort of 258 incident-eligible workers from 30 diverse facilities was followed for up to 4.5 years. Job physical exposures were individually measured. Worker demographics, medical history, psychosocial factors, hobbies, and current LBP were obtained at baseline. The cohort was followed monthly to ascertain development of LBP and quarterly to determine changes in job physical exposure. The relationship between LBP and peak lifting index (PLI) and peak composite lifting index (PCLI) were tested in multivariate models using proportional hazards regression.

RESULTS

Point and lifetime prevalences of LBP at baseline were 7.1% and 75.1%, respectively. During follow-up, there were 123 incident LBP cases. Factors predicting development of LBP included job physical exposure (PLI and PCLI), history of LBP, psychosocial factors, and housework. In adjusted models, risk (hazard ratio [HR]) increased per-unit increase in PLI and PCLI (p = .05 and .02; maximum HR = 4.3 and 4.2, respectively). PLI suggested a continuous increase in risk with an increase in PLI, whereas the PCLI showed elevated, but somewhat reduced, risk at higher exposures.

CONCLUSION

Job physical stressors are associated with increased risk of LBP. Data suggest that the PLI and PCLI are useful metrics for estimating exposure to job physical stressors.

An evaluation of classification algorithms for manual material handling tasks based on data obtained using wearable technologies

With recent progress in wearable measurement systems, physical exposures can be feasibly assessed at high precision in the workplace. Such systems, however, generally lack contextual information for a given job (e.g., task type, duration). To extract such information, we explored three classification algorithms to classify manual material handling (MMH) tasks during a simulated job in a laboratory, using several combinations of outputs from commercially available inertial motion capture and in-shoe pressure measurement systems. A total of 10 participants completed three replications of four cycles of a simulated job. Precision and recall values of ≥ ∼90% and 80%, respectively, and errors in estimated task duration of < ∼14%, could be achieved across the MMH task examined. Classification performance, however, varied between classification algorithms, input data sets and task types. Overall, combining wearable technology with task classification could be an effective approach for field-based exposure assessment, though field-testing is needed to demonstrate the applicability of this method.

PRACTITIONER SUMMARY

Combining wearable technologies with task classification was explored to extract exposure context, specifically task type and duration. Results supported that task classification can facilitate the use of wearable technologies in field-based exposure assessment, specifically by aiding in task identification from within the rather large data sets obtained from these technologies.

Kinetic changes in gait during low magnitude military load carriage

Indian infantry soldiers carry smaller magnitudes of loads for operational requirements. The ground reaction forces (GRFs) and impulse responses of 10 healthy male Indian infantry soldiers were collected while they walked carrying operational loads between 4.2 and 17.5 kg (6.5-27.2% of mean body weight (BW)) and a control condition of no external load (NL). The GRF and impulse components were normalised for BW, and data for each load condition were compared with NL in each side applying one-way analysis of variance followed by Dunnett's post hoc test. Right foot data were compared with corresponding left foot GRF data for all load conditions and NL. There were significant increases in vertical and anteroposterior GRFs with increase in load. Left and right feet GRF data in corresponding load conditions were significantly different in anteroposterior plane. No significant change was observed in the temporal components of support phase of gait. Changes in impulse parameter were observed in the anteroposterior and vertical planes while carrying load greater than 23 and 16.6% of BW for the right foot and left foot, respectively. Result indicates that smaller magnitudes of loads produced kinetic changes proportional to system weight, similar to heavier loads with the possibility of increased injury risk. Observed smaller asymmetric changes in gait may be considered as postural adjustment due to load. Unique physical characteristics of Indian soldiers and the probable design shortcomings of the existing backpack might have caused significant changes in GRF and peak impulse during smaller load carriage.

Biomechanical loading of the shoulder complex and lumbosacral joints during dynamic cart pushing task

The primary objective of this study was to quantify the effect of dynamic cart pushing exertions on the biomechanical loading of shoulder and low back. Ten participants performed cart pushing tasks on flat (0°), 5°, and 10° ramped walkways at 20 kg, 30 kg, and 40 kg weight conditions. An optoelectronic motion capturing system configured with two force plates was used for the kinematic and ground reaction force data collection. The experimental data was modeled using AnyBody modeling system to compute three-dimensional peak reaction forces at the shoulder complex (sternoclavicular, acromioclavicular, and glenohumeral) and low back (lumbosacral) joints. The main effect of walkway gradient and cart weight, and gradient by weight interaction on the biomechanical loading of shoulder complex and low back joints was statistically significant (all p < 0.001). At the lumbosacral joint, negligible loading in the mediolateral direction was observed compared to the anterioposterior and compression directions. Among the shoulder complex joints, the peak reaction forces at the acromioclavicular and glenohumeral joints were comparable and much higher than the sternoclavicular joint. Increased shear loading of the lumbosacral joint, distraction loading of glenohumeral joint and inferosuperior loading of the acromioclavicular joint may contribute to the risk of work-related low back and shoulder musculoskeletal disorder with prolonged and repetitive use of carts.

Study protocol title: a prospective cohort study of low back pain

BACKGROUND

Few prospective cohort studies of workplace low back pain (LBP) with quantified job physical exposure have been performed. There are few prospective epidemiological studies for LBP occupational risk factors and reported data generally have few adjustments for many personal and psychosocial factors.

METHODS/DESIGN

A multi-center prospective cohort study has been incepted to quantify risk factors for LBP and potentially develop improved methods for designing and analyzing jobs. Due to the subjectivity of LBP, six measures of LBP are captured: 1) any LBP, 2) LBP ≥ 5/10 pain rating, 3) LBP with medication use, 4) LBP with healthcare provider visits, 5) LBP necessitating modified work duties and 6) LBP with lost work time. Workers have thus far been enrolled from 30 different employment settings in 4 diverse US states and performed widely varying work. At baseline, workers undergo laptop-administered questionnaires, structured interviews, and two standardized physical examinations to ascertain demographics, medical history, psychosocial factors, hobbies and physical activities, and current musculoskeletal disorders. All workers' jobs are individually measured for physical factors and are videotaped. Workers are followed monthly for the development of low back pain. Changes in jobs necessitate re-measure and re-videotaping of job physical factors. The lifetime cumulative incidence of low back pain will also include those with a past history of low back pain. Incident cases will exclude prevalent cases at baseline. Statistical methods planned include survival analyses and logistic regression.

DISCUSSION

Data analysis of a prospective cohort study of low back pain is underway and has successfully enrolled over 800 workers to date.

Performance evaluation of a wearable inertial motion capture system for capturing physical exposures during manual material handling tasks

With a long-term goal of improving quantification of physical exposures in the workplace, this study examined the ability of a commercially available inertial motion capture (IMC) system in quantifying exposures during five different simulated manual material handling tasks. Fourteen participants repeated all these tasks in three 20 min sequential time blocks. Performance of the IMC system was compared against an optical motion capture (OMC) system ('gold standard') in terms of joint angles, angular velocities and moments at selected body parts. Though several significant changes in performance over time were found, the magnitudes of these were relatively small and may have limited practical relevance. The IMC system yielded peak kinematic values that differed by up to 28% from the OMC system. The IMC system, in some cases, incorrectly reflected the actual extremity positions of a participant, and which can cause relatively large errors in joint moment estimation. Given the potential limitations, practical recommendations are offered and discussed.

PRACTITIONER SUMMARY

Use of an inertial motion capture system can advance the quantification of physical exposures in situ. Results indicate a good potential capacity for capturing physical exposure data in the field for an extended period, while highlighting potential limitations. Future system application can help provide better understandings of dose-exposure relationships.

The effect of posture category salience on decision times and errors when using observation-based posture assessment methods

Observation-based posture assessment methods (e.g. RULA, 3DMatch) require classification of body postures into categories. This study investigated the effect of improving posture category salience (adding borders, shading and colour to the posture categories) on posture selection error rates and decision times of novice analysts. Ninety university students with normal or corrected normal visual acuity and who were not colourblind, were instructed to select posture categories as quickly and accurately as possible, in five salience conditions (Plain (no border, no shading, no colour); Grey Border; Red Border; Grey Shading (GS) and Red Shading (RS)) for images presented in randomised blocks (240 classifications made by each participant) on a computer interface. Participants responded quickest in the Border conditions, classifying postures about 5% faster than in the Plain condition. Coloured diagrams significantly reduced posture classification errors by approximately 1.5%. Overall, the best performance, based on both error rate and decision time combined, resulted from incorporating a Grey Border to the posture category diagrams; a simple enhancement that could be made to most current observation-based posture assessment tools.

PRACTITIONER SUMMARY

The salience of posture diagrams used in observation-based posture assessment tools was evaluated with respect to analyst error rates and decision times. The best performance resulted from incorporating a grey border to the posture diagrams; a simple enhancement that can be made to most current observation-based posture assessment tools.

The Strain Index (SI) and Threshold Limit Value (TLV) for Hand Activity Level (HAL): risk of carpal tunnel syndrome (CTS) in a prospective cohort

A cohort of 536 workers was enrolled from 10 diverse manufacturing facilities and was followed monthly for six years. Job physical exposures were individually measured. Worker demographics, medical history, psychosocial factors, current musculoskeletal disorders (MSDs) and nerve conduction studies (NCS) were obtained. Point and lifetime prevalence of carpal tunnel syndrome (CTS) at baseline (symptoms + abnormal NCS) were 10.3% and 19.8%. During follow-up, there were 35 new CTS cases (left, right or both hands). Factors predicting development of CTS included: job physical exposure (American conference of governmental industrial hygienists Threshold Limit Value (ACGIH TLV) for Hand Activity Level (HAL) and the Strain Index (SI)), age, BMI, other MSDs, inflammatory arthritis, gardening outside of work and feelings of depression. In the adjusted models, the TLV for HAL and the SI were both significant per unit increase in exposure with hazard ratios (HR) increasing up to a maximum of 5.4 (p = 0.05) and 5.3 (p = 0.03), respectively; however, similar to other reports, both suggested lower risk at higher exposures. Data suggest that the TLV for HAL and the SI are useful metrics for estimating exposure to biomechanical stressors.

PRACTITIONER SUMMARY

This study was conducted to determine how well the TLV for HAL and the SI predict risk of CTS using a prospective cohort design with survival analysis. Both the TLV for HAL and the SI were found to predict risk of CTS when adjusted for relevant covariates.

Outcomes of arthroscopic rotator cuff repairs in obese patients

HYPOTHESIS

Rotator cuff tears are common orthopedic injuries and their arthroscopic treatment can be technically challenging. This study evaluated the outcomes of arthroscopic rotator cuff repairs in obese patients. We hypothesized that there would be a direct correlation between worse outcomes of arthroscopic rotator cuff repairs and increasing body mass index (BMI).

MATERIALS AND METHODS

A retrospective review of patients undergoing arthroscopic rotator cuff repair by one orthopedic surgeon between 2005 and 2008 was performed. The study included 149 rotator cuff repairs. Recorded data included age, sex, BMI, size of rotator cuff tear on magnetic resonance imaging and intraoperatively, number of anchors used for repair, functional outcomes (American Shoulder and Elbow Surgeons and University of Pennsylvania scores), surgery time, total time for anesthesia, positioning, and hospital stay. Tears were classified by size. Strict inclusion and exclusion criteria were used. Surgical procedures were performed with general anesthesia, interscalene block, beach chair positioning, and a standardized operative technique. Patients followed a standard postoperative rehabilitation protocol.

RESULTS

Mean patient age was 66 years. Mean follow-up was 16.3 months. Tears were classified as high grade partial (12%), small (23%), medium (29%), large (22%), and massive (14%). Patients were classified as normal weight (38%), overweight (23%), obese (20%), and morbidly obese (19%). A statistically significant correlation was found between obesity and worse functional outcomes, longer operative times, and longer length of hospital stay.

DISCUSSION

This study reports new data concerning the association of BMI and early clinical outcome after arthroscopic rotator cuff repair surgery. Even though the obese group had greater limitations and lower rates of satisfaction at final follow-up than their non-obese counterparts, they still reported significant improvements from the surgery.

CONCLUSION

Obesity has a negative impact on the operative time of arthroscopic rotator cuff repairs, length of hospitalization, and functional outcomes.

Job Analysis Techniques for Distal Upper Extremity Disorders

Distal upper extremity (DUE) work-related musculoskeletal disorders (WMSDs) are among the most costly injuries suffered in industry today. These WMSDs are reported in both office (computer use) and manufacturing environments. Job physical exposure analysis techniques for DUE WMSDs range from simple checklists to quantitative models. A summary of literature review of biomechanical, physiological, psychophysical and epidemiological bases for job physical exposure risk factors for DUE WMSDs is provided. Several job analysis methods suitable for manufacturing environments are reviewed and discussed. A comparative analysis of Rapid Upper Limb Assessment (RULA), Threshold Limit Value for Hand Activity Level (TLV for HAL), and the Strain Index is provided along with results from validation studies and advantages and disadvantages of each method. Three examples from industries are provided to demonstrate applications of RULA, TLV for HAL, and the Strain Index. Last, issues with current job analysis methods when a worker rotates to different jobs and/or when a job consists of several tasks are discussed as well as the need for more robust models to account for these variations in physical exposure in real-world environments.

Postures and movements in the most common tasks of power line workers

The repair and maintenance of electrical power lines involves awkward postures, which are known risk factors for developing musculoskeletal disorders. The aim of the present study was to quantify postures and movements of upper arm, head, upper back and neck in the main tasks performed by line workers. Posture of twelve right-handed line workers was recorded by inclinometry and presented as percentiles of angular and angular velocity distributions. All tasks involved considerable upper-arm elevation, ranging from 73° to 115° for the 90th percentile. Upper-arm elevation showed significant differences between tasks, but no consistent differences between right and left sides. Regarding velocity, the right arm presented higher levels than the left arm. All tasks required significant extension of head, upper back and neck, ranging from 7° to 67° for head (10th percentile). All tasks, except the one performed with a continuous extension, also involved pronounced flexion, ranging from 33° to 60° for the head (90th percentile). Work which required highly elevated arms also required significant head extension (r(2)=0.56). Awkward postures of upper arms, head, upper back and neck were identified by inclinometry, demonstrating the need for preventative interventions to reduce musculoskeletal disorders among line workers.

Hand-hold location and trunk kinematics during box handling

Trunk kinematics variables have been shown to be related to low back injury risk during lifting tasks and it was hypothesised that changes in hand-hold positions could influence trunk kinematics and thereby risk. Fourteen subjects lifted a 5 or 10 kg box using four different hand placement locations (two symmetric and two asymmetric) while their trunk kinematics (position, velocity and acceleration in the sagittal, coronal and transverse planes) were captured using the lumbar motion monitor (LMM). These kinematics data were then used to calculate the probability of high risk group membership (PHRGM) as defined in the LMM risk assessment model. The results showed significant effects of hand placement on trunk kinematics, resulting in significant changes in the PHRGM variable ranging from a low of 20% in a the symmetric low load condition to a high of 38% under the asymmetric, 10 kg condition. STATEMENT OF RELEVANCE: Manual materials handlers use a variety of hand-hold positions on boxes during lifting. Where a lifter grabs the box can influence the trunk kinematics during the lifting task and these kinematics have been shown to provide some insight into risk of low back injury. This study documents the trunk postures and kinematics as a function of hand-hold position.

Effects of military load carriage on kinematics of gait

Manual load carriage is a universal activity and an inevitable part of the daily schedule of a soldier. Indian Infantry soldiers carry loads on the waist, back, shoulders and in the hands for a marching order. There is no reported study on the effects of load on gait in this population. It is important to evaluate their kinematic responses to existing load carriage operations and to provide guidelines towards the future design of heavy military backpacks (BPs) for optimising soldiers' performance. Kinematic changes of gait parameters in healthy male infantry soldiers whilst carrying no load (NL) and military loads of 4.2-17.5 kg (6.5-27.2% body weight) were investigated. All comparisons were conducted at a self-selected speed. Soldier characteristics were: mean (SD) age 23.3 (2.6) years; height 172.0 (3.8) cm; weight 64.3 (7.4) kg. Walk trials were collected using a 3-D Motion Analysis System. Results were subjected to one-way ANOVA followed by Dunnett post hoc test. There were increases in step length, stride length, cadence and midstance with the addition of a load compared to NL. These findings were resultant of an adaptive phenomenon within the individual to counterbalance load effect along with changes in speed. Ankle and hip ranges of motion (ROM) were significant. The ankle was more dorsiflexed, the knee and hip were more flexed during foot strike and helped in absorption of the load. The trunk showed more forward leaning with the addition of a load to adjust the centre of mass of the body and BP system back to the NL condition. Significant increases in ankle and hip ROM and trunk forward inclination (> or =10 degrees ) with lighter loads, such as a BP (10.7 kg), BP with rifle (14.9 kg) and BP with a light machine gun (17.5 kg), may cause joint injuries. It is concluded that the existing BP needs design improvisation specifically for use in low intensity conflict environments. STATEMENT OF RELEVANCE: The present study evaluates spatial, temporal and angular changes at trunk and limb joints during military load carriage of relatively lighter magnitude. Studies on similar aspects on the specific population are limited. These data can be used for optimising load carriage and designing ensembles, especially a heavy BP, for military operations.