Repetitive Lifting Research Articles

Detecting subject-specific fatigue-related changes in lifting kinematics using a machine learning approach

Individual responses to fatigue have been observed in lifting kinematics, suggesting a subject-specific approach is necessary for fatigue identification. One-class support vector machines (OCSVM) may provide an objective method to classify fatigue-related kinematic changes during repetitive lifting. Participants completed a repetitive lifting protocol while motion capture recorded lifting motions. Subject-specific kinematics from participants’ first 35% of lifts trained OCSVM decision boundaries. The remaining lifts were separated into test sets and classified against the decision boundary to identify the percentage of outlier lifts within each test set. Spearman’s correlation assessed if the test sets' percentage of outlier lifts increased concurrently with participants’ rating of perceived exertion (RPE). Significant positive associations were found for participants who demonstrated evidence of fatigue, while no significant associations were found for participants who did not demonstrate evidence of fatigue. These results demonstrate the prospective efficacy of an outlier detection tool for fatigue detection during repetitive lifting. Practitioner Summary: An objective subject-specific fatigue detection method is desired for workplace tasks, such as lifting. An outlier detection machine learning approach was identified when lifting movement patterns changed from baseline throughout a repetitive lifting protocol. Participants who demonstrated an increase in outlier movement patterns had a concurrent increase in self-reported fatigue.

THE STUDY OF A JIB CRANE FROM A CARGO SHIP

This paper presents the study of a jib crane from a general cargo ship. There are numerous different types of vessels operating today in the various markets worldwide. Besides, thousands of cargo vessel ply the world’s oceans and seas each year, handling the bulk of international trade. The cranes from cargo ship is required to be adequate stability and strength for each load. All cranes from vessel are mounted on deck of the ship. Having regard in particular to the stress induced at its mounting or fixing points, adequately ballasted, securely anchored and supported by outriggers as necessary to ensure its stability when lifting. A jib from a crane from cargo ship is a type of overhead lifting device that is often used in a smaller work cell area for repetitive and unique lifting tasks. The extreme values of the stresses and reaction forces are determined by the finite element method. In this manuscript, the design of the cargo ship and the study of a jib crane are made using NX software from Siemens.

An Integrated Dynamic Closed Loop Simulation Platform for Elbow Flexion Augmentation Using an Upper Limb Exosuit Model

Wearable robotic devices are designed to assist, enhance or restore human muscle performance. Understanding how a wearable robotic device changes human biomechanics through complex interaction is important to guide its proper design, parametric optimization and functional success. The present work develops a human-machine-interaction simulation platform for closed loop dynamic analysis with feedback control and to study the effect of soft-robotic wearables on human physiology. The proposed simulation platform incorporates Computed Muscle Control (CMC) algorithm and is implemented using the MATLAB -OpenSim interface. The framework is generic and will allow incorporation of any advanced control strategy for the wearable devices. As a demonstration, a Gravity Compensation (GC) controller has been implemented on the wearable device and the resulting decrease in the joint moments, muscle activations and metabolic costs during a simple repetitive load lifting task with two different speeds is investigated.

Effect of Ultrasound Therapy in the management of Chronic Nonspecific Low Back Pain

Background: Chronic non-specific low-back pain (NSLBP) has become one of the main causes of disability in the adult population around the world. Therapeutic ultrasound is frequently used by physiatrists in the treatment of LBP and is one of the most widely used electro-physical agents in clinical practice.
 Objective: To see the effects of ultrasound therapy (UST) in the patients with chronic nonspecific low back pain.
 Methodology: This randomized control trial was performed in the Department of Physical Medicine & Rehabilitation of Dhaka Medical College Hospital during the period from December 2014 to May 2015. Patients presented with chronic nonspecific LBP in an age between 18 and 55 years of both sexes attending in the Department of Physical Medicine & Rehabilitation at Dhaka Medical College Hospital, Dhaka were included as study population. A total of 80 patients presented with chronic nonspecific LBP who had fulfilled the selection criteria were taken as study population. They were divided into two groups named as treatment group (Group A) and control group (Group B). Each group had 40 patients. During follow up 8 patients (4 patients from each group) were lost. Final analysis was done with data collected from 72 patients. Patients of group A were given UST, NSAIDS, exercises and ADL instructions whereas patients of group B were given same treatment except UST.
 Result: In both groups female were predominant than male. Most of the patients were in 31 – 40 years age group. Mostly housewives suffered from NSLBP. All patients were from either poor or middle-class family. Mean (±SD) duration of pain was 11.3 (±12.5) months and 11.7 (±8.7) months in group A and group B respectively. Sedentary life style and repetitive lifting are the major risk factors in both groups. Character of pain was mostly dull in both groups, severity of pain was mostly moderate and relieving factor was mostly rest in both groups. Prolonged standing and prolonged sitting were the major aggravating factors in both groups. VAS and ODI were reduced gradually in both groups.
 Conclusion: Ultrasound therapy has a significant role in the management of chronic nonspecific low back pain.
 Journal of National Institute of Neurosciences Bangladesh, July 2021, Vol. 7, No. 2, pp. 122-125

Ergonomic exposures and control measures associated with mass fatality decedent handling in morgues and body collection points in a New York healthcare system during COVID-19: A case series

IntroductionIn April 2020, novel coronavirus SARS-CoV-2 (COVID-19) produced an ongoing mass fatality event in New York. This overwhelmed hospital morgues necessitating emergent expansion of capacity in the form of refrigerated trucks, trailers, and shipping containers referred to as body collection points (BCPs). The risks for musculoskeletal injury during routine and mass fatality mortuary operations and experiences of decedent handlers throughout the "first wave" of COVID-19 are presented along with mitigation strategies MethodsAwareness of the high rates of musculoskeletal injury among health care workers due to ergonomic exposures from patient handling, including heavy and repetitive manual lifting, prompted safety walkthroughs of mortuary operations at multiple hospitals within a health system in New York State by workforce safety specialists. Site visits sought to identify ergonomic exposures and ameliorate risk for injury associated with decedent handling by implementing engineering, work practice, and administrative controls. ResultsMusculoskeletal exposures included manual lifting of decedents to high and low surfaces, non-neutral postures, maneuvering of heavy equipment, and push/pull forces associated with the transport of decedents DiscussionRisk mitigation strategies through participatory ergonomics, education on body mechanics, development of novel handling techniques implementing friction-reducing aides, procurement of specialized equipment, optimizing BCP design, and facilitation of communication between hospital and system-wide departments are presented along with lessons learned. After-action review of health system workers' compensation data found over four thousand lost workdays due to decedent handling related incidents, which illuminates the magnitude of musculoskeletal injury risk to decedent handlers.

Modeling the metabolic reductions of a passive back-support exoskeleton.

Despite several attempts to quantify the metabolic savings resulting from the use of passive back-support exoskeletons (BSEs), no study has modeled the metabolic change while wearing an exoskeleton during lifting. The objectives of this study were to: 1) quantify the metabolic reductions due to the VT-Lowe's exoskeleton during lifting; and 2) provide a comprehensive model to estimate the metabolic reductions from using a passive BSE. In this study, 15 healthy adults (13 males, 2 females) of ages 20-34 yr (mean = 25.33, SD = 4.43) performed repeated freestyle lifting and lowering of an empty box and a box with 20% of their bodyweight. Oxygen consumption and metabolic expenditure data were collected. A model for metabolic expenditure was developed and fitted with the experimental data of two prior studies and the without-exoskeleton experimental results. The metabolic cost model was then modified to reflect the effect of the exoskeleton. The experimental results revealed that VT-Lowe's exoskeleton significantly lowered the oxygen consumption by ∼9% for an empty box and 8% for a 20% bodyweight box, which corresponds to a net metabolic cost reduction of ∼12% and ∼9%, respectively. The mean metabolic difference (i.e., without-exo minus with-exo) and the 95% confidence interval were 0.36 and (0.2-0.52) W/kg for 0% body weight and 0.43 and (0.18-0.69) W/kg for 20% body weight. Our modeling predictions for with-exoskeleton conditions were precise, with absolute freestyle prediction errors of <2.1%. The model developed in this study can be modified based on different study designs, and can assist researchers in enhancing designs of future lifting exoskeletons.NEW & NOTEWORTHY We present a new model of the metabolic cost of repetitive lifting, and how that is affected by wearing a passive back support exoskeleton. We compute the effective biomechanical efficiencies of moving the body and a carried load during lifting, and determine the effect of an exoskeleton's efficiency on its metabolic reduction. This model is useful for understanding the effects of exoskeletons on the body and for designing future exoskeletons.

Development and testing of the aerial porter exoskeleton.

Back pain is one of the largest drivers of workplace injury and lost productivity in industries around the world. Back injuries were one of the leading reasons in resulting in days away from work at 38.5% across all occupations, increasing for manual laborers to 43%. While the cause of the back pain can vary across occupations, for materiel movers it is often caused from repetitive poor lifting. To reduce the issues, the Aerial Porter Exoskeleton (APEx) was created. The APEx uses a hip-mounted, powered exoskeleton attached to an adjustable vest. An onboard computer calculates the configuration of the user to determine when to activate. Lift form is assisted by using a novel lumbar brace mounted on the sides of the hips. Properly worn, the APEx holds the user upright while providing additional hip torque through a lift. This was tested by having participants complete a lifting test with the exoskeleton worn in the "on" configuration compared with the exoskeleton not worn. The APEx has been shown to deliver 30Nm of torque in lab testing. The activity recognition algorithm has also been shown to be accurate in 95% of tested conditions. When worn by subjects, testing has shown average peak reductions of 14.9% BPM, 8% in VO2 consumption, and an 8% change in perceived effort favoring the APEx.

SEMG-Triggered Fast Assistance Strategy for a Pneumatic Back Support Exoskeleton.

To prevent lower back pain (LBP) in the industrial workplace, various powered back support exoskeletons (BSEs) have been developed. However, conventional kinematics-triggered assistance (KA) strategies induce latency, degrading assistance efficiency. Therefore, we proposed and experimentally evaluated a surface electromyography (sEMG)-triggered assistance (EA) strategy. Nine healthy subjects participated in the lifting experiments: 1) external loads test, 2) extra latency test, and 3) repetitive lifting test. In the external loads test, subject performed lifting with four different external loads (0 kg, 7.5 kg, 15 kg, and 22.5 kg). The assistance was triggered earlier by EA compared to KA from 114 ms to 202 ms, 163 ms to 269 ms for squat and stoop lifting respectively, as external loads increased from 0 kg to 22.5 kg. In the extra latency test, the effects of extra latency (manual switch, 0 ms, 100 ms and 200 ms) in EA on muscle activities were investigated. Muscle activities were minimized in the fast assistance (0 ms and 100 ms) condition and increased with extra latency. In the repetitive lifting test, the EA strategy significantly reduced L1 muscle fatigue by 70.4% in stoop lifting, compared to KA strategy. Based on the experimental results, we concluded that fast assistance triggered by sEMG improved assistance efficiency in BSE and was particularly beneficial in heavy external loads situations. The proposed assistive strategy can be used to prevent LBP by reducing back muscle fatigue and is easily applicable to various industrial exoskeleton applications.

Exploring the role of task constraints on motor variability and assessing consistency in individual responses during repetitive lifting using linear variability of kinematics

To better understand the assessment of motor variability (MV) in an occupational context, this study determined the role of task constraints on MV and consistency in individual MV responses. Twenty participants performed repetitive lifting under four constraints differing in restriction of foot movement and load weight. MV was assessed for three body regions and for the whole-body using linear variability of three-dimensional joint angles. Foot movement caused significant increases of lower body (11–17%), low back (318–439%) and a reduction in upper body variability (4%), whereas no effects of weight nor interaction of foot restriction and weight were found. Good individual consistency (ICC = 0.71–0.84) was demonstrated across constraints. Even though MV is affected by constraints, this study supports that MV is largely an individual trait independent of constraints. Future work should evaluate if MV remains an individual trait across different tasks, and if MV is confounded by other task constraints.

Adaptive Control Method for Dynamic Synchronization of Wearable Robotic Assistance to Discrete Movements: Validation for Use Case of Lifting Tasks

Dynamic control of robotic exoskeletons is paramount to ensuring safe, synergistic assistive action of functional benefit to users. To date, exoskeleton controllers have excelled in rhythmic and quasi-rhythmic tasks, whereas control methods for assisting discrete movements remain limited by their task-specificity. Inspired by neurophysiological dynamic movement primitives (DMPs), we formulated a novel controller that facilitated a variety of lifting movements using a single <i>adaptive</i> DMP (aDMP), for wearable robotic assistance of discrete movements. For a variety of load lifting tasks, we first benchmarked our method&#x0027;s trajectory prediction accuracy against the state-of-the-art DMP using passively recorded exoskeleton sensor data (offline), followed by a functional validation of online aDMP trajectory estimates. Finally, we assessed the functional effects of aDMP-based exoskeletal assistance on joint kinematics and muscular activity during repetitive lifting. The new aDMP method accurately predicted and smoothly synchronized robotic assistance with variable movement trajectories, resulting in reduced muscular activation of the erector spinae muscles (up to 47.6&#x0025;) while preserving lower-limb joint kinematics and reducing the extension time by 15.5&#x0025; compared to unassisted conditions. This method holds promise for use in a wide range of wearable robotic applications, including both clinical rehabilitation and user assistance in activities of daily living and&#x002F;or manual labor.

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.

Effects of passive exoskeleton support on EMG measures of the neck, shoulder and trunk muscles while holding simulated surgical postures and performing a simulated surgical procedure

Exoskeletons have shown significant impact at reducing the biomechanical demand on muscles during repetitive lifting and overhead tasks in non-healthcare industries. However, the benefits of exoskeletons are yet to be realized in the operating room, particularly as work-related musculoskeletal disorders continue to be a concern for surgeons. This study quantified the effect of using neck, arm, and trunk exoskeletons on muscle activity while assuming typical postures held in the operating room. Fourteen participants were recruited to participate in this study. In this two-part experiment participants were asked to 1) hold a series of neck flexion, arm abduction and trunk flexion postures seen in surgical procedures, and 2) perform a simulated surgical task requiring five different trunk flexion posture levels. Participants were required to complete these tasks with and without passive exoskeleton(s). This study showed that even for postures held short time periods, exoskeletons are beneficial at reducing the demand on muscles; however, the reduction in muscle demand depends on body segment and postural angle, as intended with these passive exoskeletons. Furthermore, for the simulated surgical task with awkward trunk flexion postures (10–65°), the trunk exoskeletons showed a significant reduction in the rate of rise in back muscle sEMG (+1.365%MVC/min vs. +0.769%MVC/min for non-dominant lumbar extensor muscles, p = 0.0108; +1.377%MVC/min vs. +0.770%MVC/min for the dominant lumbar extensor muscles, p = 0.0196) over 25 min, consequently resulting in improved trunk subjective discomfort scores (7.34 vs. 4.30, p < 0.05), with no impact on the neck and shoulder biomechanical demand. The results from this study indicate that exoskeletons may be a potential intervention to reduce biomechanical loading during surgery.

A Passive Back-Support Exoskeleton for Manual Materials Handling: Reduction of Low Back Loading and Metabolic Effort during Repetitive Lifting

OCCUPATIONAL APPLICATIONS Globalization and eCommerce continue to fuel unprecedented growth in the logistics and warehousing markets. Simultaneously, the biggest bottleneck for these industries is their human capital. Where automation and robotic solutions fail to deliver a return on investment, humans frequently take over handling tasks that place harmful loads and strains on the body. Occupational exoskeletons can reduce fatigue and strain by supporting the lower spine and are designed to prevent work-related musculoskeletal disorders and other injuries. They are a mid- to long-term investment for industries to improve ergonomic conditions in workplaces, with the potential for reducing absences from work, sick days logged, and workers compensation claims. To examine the effectiveness of the newly introduced Paexo Back exoskeleton, a study was completed with 10 participants who completed manual load handling tasks with and without the exoskeleton. Key findings include significant reductions in metabolic effort and low back loading when the exoskeleton is worn.

Use of a passive lumbar back exoskeleton during a repetitive lifting task: effects on physiologic parameters and intersubject variability

Objectives. This study evaluated the effects of wearing the Laevo v2.56 exoskeleton (Laevo, The Netherlands) on physiological parameters related to working load and metabolic cost (MC) during a lifting task, explored the variability in exoskeleton performance among users and determined whether perceived discomfort negatively correlates with a reduction in MC. Methods. Twenty participants completed a 4-min repetitive lifting task with/without the exoskeleton. Respiratory gases, heart rate, blood lactate and ratings of perceived exertion and experienced discomfort were collected, and MC was calculated. Results. Wearing the exoskeleton significantly reduced MC and oxygen uptake during the lifting task by 4.8 and 3.8%, respectively. Workload reduction occurred in 65% of the participants. Conclusion. The Laevo v2.56 exoskeleton reduced MC and workload in a repetitive lifting task in a subject-dependent manner. Future studies should focus on identifying factors that could cause performance variability such as user–robot interaction forces.

Deliberate Practice and Motor Learning Principles to Underpin the Design of Training Interventions for Improving Lifting Movement in the Occupational Sector: A Perspective and a Pilot Study on the Role of Augmented Feedback.

Spine posture during repetitive lifting is one of the main risk factors for low-back injuries in the occupational sector. It is thus critical to design appropriate intervention strategies for training workers to improve their posture, reducing load on the spine during lifting. The main approach to train safe lifting to workers has been educational; however, systematic reviews and meta-analyses have shown that this approach does not improve lifting movement nor reduces the risk of low back injury. One of the main limitations of this approach lies in the amount, quality and context of practice of the lifting movement. In this article, first we argue for integrating psychologically-grounded perspectives of practice design in the development of training interventions for safe lifting. Principles from deliberate practice and motor learning are combined and integrated. Given the complexity of lifting, a training intervention should occur in the workplace and invite workers to repeatedly practice/perform the lifting movement with the clear goal of improving their lifting-related body posture. Augmented feedback has a central role in creating the suitable condition for achieving such intervention. Second, we focus on spine bending as risk factor and present a pilot study examining the benefits and boundary conditions of different feedback modalities for reducing bending during lifting. The results showed how feedback modalities meet differently key requirements of deliberate practice conditions, i.e., feedback has to be informative, individualized and actionable. Following the proposed approach, psychology will gain an active role in the development of training interventions, contributing to finding solutions for a reduction of risk factors for workers.

Detection of muscle fatigue caused by repeated posterior tongue lift movement from neck surface EMG: a pilot study.

Fatigue is an important factor for muscle strengthening in rehabilitation medicine. Frequency analysis has been regarded as the gold standard for muscle fatigue assessment in surface electromyography (EMG). However, there are no experiments quantifying fatigue with grouped discharge (GD), which is one of the historical phenomena observed in patients having fatigue, by using high sampling rate recording of EMG. To investigate the effect of fatigue, which is induced by repeated posterior tongue lift movement (TLM), on the occurrence of GD peaks, thus, to provide possible basis as a parameter for future fatigue evaluation. Nineteen healthy adults (9men and 10 women) participated in this study. The muscle fatigue protocol consisted of repetitive posterior TLM and maximum voluntary contractions (MVC). Bilateral N-EMG (Neck surface EMG for measuring the muscle activity of the posterior tongue) was recorded. Subjective tongue fatigue at the end of the protocol was significantly higher than at beginning throughout the muscle fatigue protocol (p<.01). The frequency of occurrence of GD peaks was 0.9±1.2 (per second) at the baseline in 33 of 38subject sides, and significantly increased depending on fatigue progression (p<.01). It was shown that fatigue due to repetitive posterior tongue lifting resulted in significant increase in the frequency of occurrence of GD peaks. Especially, the nature of GD, showing very few occurrences at non-fatigue condition, might work as an advantageous property for its use in future absolute evaluation of fatigue phenomena.

Inter-individual variability in a repetitive lifting task

Trunk kinematics directly impact the biomechanical loading of the tissues of the low back. Quantifying the variability in trunk kinematics may provide deeper insights into biomechanical loading and low back injury risk. Inter-lifter variability in trunk kinematics was assessed as twenty participants performed a repetitive lifting task at three levels of the NIOSH Lifting Index. Trunk kinematics were captured and Levene’s test of homogeneity of variance was used to test the hypothesis that variance in kinematic parameters increased as a function of level of lifting index. Results showed considerable levels of variability in all kinematics parameters, and for sagittal range of motion, mean sagittal velocity, transverse range of motion, and mean transverse velocity the variance was significantly affected (p&lt;0.05) by level of lifting index. The results of this study demonstrate that variability (both inter- and intra-lifter) should be considered as one considers the relative risk of a lifting task.

Influence of an on-body lifting aid (HAL® for Care Support) on kinematics during repetitive lifting in healthy men

Work-related lower back pain (LBP) leads to socio-economic burden and demands solutions. The hybrid assistive limb (HAL) for Care Support (Cyberdyne Inc., Ibaraki, Japan) is an active on-body lifting aid to assist joint motion according to the wearer’s voluntary motor drive to reduce the lumbar load. A few studies investigated HAL and stated efficacy in terms of enhanced performance and reduced fatigue, yet the question remained if the use of HAL may result in a different execution of movement, for example by influencing the kinematics of the lower extremities. The aim of this study was to determine the influence of HAL on kinematics of the lower limbs and the spinal column during repetitive freestyle symmetrical lifting. Kinematic data was recorded by an inertial measurement unit sensor system in 11 healthy men lifting and lowering a 19.5 kg barbell under three conditions (no HAL, HAL Level 3/5, HAL Level 5/5). Outcome parameters were maximum and minimum angles as well as range of motion (ROM) of thoracic spine, lumbar spine, hip- and knee joint in sagittal plane. We found a significantly decreased ROM of the lumbar spine as well as a significantly reduced maximum and minimum thorax extension when starting lifting and in upright position after lifting, respectively, while using HAL. Influence of HAL on the kinematics of the lower limbs was not significant. Differences between both evaluated HAL conditions were not significant. This study proved limited lumbar spine ROM and reduced thorax extension without alterations of lower limbs kinematics when using HAL. This might potentially decrease the risk of work-related LBP.

A passive back exoskeleton supporting symmetric and asymmetric lifting in stoop and squat posture reduces trunk and hip extensor muscle activity and adjusts body posture – A laboratory study

The influence of a passive exoskeleton was assessed during repetitive lifting with different lifting styles (squat, stoop) and orientations (frontal/symmetric, lateral/asymmetric) on trunk and hip extensor muscle activity (primary outcomes), abdominal, leg, and shoulder muscle activity, joint kinematics, and heart rate (secondary outcomes). Using the exoskeleton significantly and partially clinically relevant reduced median/peak activity of the erector spinae (≤6%), biceps femoris (≤28%), rectus abdominis (≤6%) and increased median/peak activity of the vastus lateralis (≤69%), trapezius descendens (≤19%), and median knee (≤6%) and hip flexion angles (≤11%). Using the exoskeleton had only limited influence on muscular responses. The findings imply the exoskeleton particularly supports hip extension and requires an adjusted body posture during lifting with different styles and orientations. The potential of using exoskeletons for primary/secondary prevention of musculoskeletal disorders should be investigated in future research including a greater diversity of users in terms of age, gender, health status.

Worker Injuries in Southern California's Warehousing Industry: How to Better Protect Workers in This Burgeoning Industry?

Dangerous conditions and worker injuries in the rapidly growing warehousing industry have gained attention in recent years, with accounts typically drawing on worker reports and investigative journalism. We analyzed workers' compensation injury claims and California Division of Occupational Safety and Health (Cal/OSHA) citations in Southern California's large warehousing sector. Claims increased from 2014 to 2018, with a majority of injuries caused by repetitive motion, lifting and other ergonomic risk factors. Cal/OSHA cited employers for violating standards to protect workers from unsafe vehicle operations, dangerous machinery and equipment, and falls; and for failing to implement injury prevention programs. These citations address the causes of some worker injuries; however, no Cal/OSHA citations were issued for violating the state's Repetitive Motion Injuries prevention standard. Nor do enforcement activities address the underlying causes highlighted by workers-high production quotas and a relentless work pace-that characterize the industry. We discuss the value and limitations of our approach and the implications of our results.