Publications by authors named "John Z Wu"

70 Publications

Evaluation of the Fall Protection of Type I Industrial Helmets.

Ann Biomed Eng 2022 Feb 5. Epub 2022 Feb 5.

National Institute for Occupational Safety and Health, Morgantown, WV, USA.

The performance of Type I industrial helmets for fall protection is not required to be tested in standardized tests. The current study analyzed the fall protection performance of Type I industrial helmets and evaluated if the use of a chin strap and the suspension system tightness have any effect on protection performance. Head impact tests were performed using an instrumented manikin. There were 12 combinations of test conditions: with or without chin strap usage, three levels of suspension system tightness, and two impact surfaces. Four representative helmet models (two basic and two advanced models) were selected for the study. Impact tests without a helmet under all other applicable test conditions were used as a control group. There were four replicates for each test condition-a total of 192 impact tests with helmets and eight impact tests for the control group. The peak acceleration and the calculated head impact criteria (HIC) were used to evaluate shock absorption performance of the helmets. The results showed that all four helmet models demonstrated excellent performance for fall protection compared to the barehead control group. The fall protection performance of the advanced helmet models was substantially better than the basic helmet models. However, the effects of the use of chin straps and suspension system tightness on the helmets' fall protection performance were statistically not significant.
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http://dx.doi.org/10.1007/s10439-022-02922-3DOI Listing
February 2022

An alternative method for analyzing the slip potential of workers on sloped surfaces.

Saf Sci 2021 Jan;133

Physical Effects Research Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, USA.

Slips and falls on sloped roof surfaces remain an important safety issue among construction workers. The slip potential has been conventionally analyzed and assessed primarily based on ground reaction forces, which cannot differentiate the specific roles of each of the force factors (e.g., workers' motions-induced dynamic forces and slope-induced static forces) contributing to the slip potential. Their differentiation may enhance the understanding of the slip mechanisms on the sloped roof surfaces and help develop effective walking and working strategies/tactics to minimize the dangerous slips on the elevated roofs. Hence, the objective of this study is to develop a biodynamic method as an additional tool for analyzing the slip potential of a worker walking or working on sloped roof surfaces. A whole-body biodynamic model is proposed and used to develop the alternative method, in which the slip potential is expressed as an analytical function of its major controlling factors including coefficient of friction, slope angle, and biodynamic forces. Some experimental data available in the literature are used to demonstrate the application of the proposed method. The results suggest that the slope may not change the basic trends of the biodynamic forces, but the slope may affect their magnitudes, which can be explained using the system's energy equation also derived from the whole-body biodynamic model. The analytical results suggest that reducing the body acceleration in uphill direction or the deceleration in downhill direction can reduce the slip potential. 'Zigging' and 'zagging' walking on a sloped surface may also reduce the slip potential, as it reduces the effective slope angle. The proposed biodynamic theory can be used to enhance the safety guidelines not only for roofers but also for people walking on ramps, inclined walkways, and mountain terrains.
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http://dx.doi.org/10.1016/j.ssci.2020.105026DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8455163PMC
January 2021

A Review of Hand-Arm Vibration Studies Conducted by US NIOSH since 2000.

Vibration 2021 Jun;4(2):482-528

Physical Effects Research Branch, Health Effects Laboratory Division (HELD), National Institute for Occupational Safety and Health (NIOSH), Morgantown, WV 26505, USA.

Studies on hand-transmitted vibration exposure, biodynamic responses, and biological effects were conducted by researchers at the Health Effects Laboratory Division (HELD) of the National Institute for Occupational Safety and Health (NIOSH) during the last 20 years. These studies are systematically reviewed in this report, along with the identification of areas where additional research is needed. The majority of the studies cover the following aspects: (i) the methods and techniques for measuring hand-transmitted vibration exposure; (ii) vibration biodynamics of the hand-arm system and the quantification of vibration exposure; (iii) biological effects of hand-transmitted vibration exposure; (iv) measurements of vibration-induced health effects; (iv) quantification of influencing biomechanical effects; and (v) intervention methods and technologies for controlling hand-transmitted vibration exposure. The major findings of the studies are summarized and discussed.
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http://dx.doi.org/10.3390/vibration4020030DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8371562PMC
June 2021

Fusing imperfect experimental data for risk assessment of musculoskeletal disorders in construction using canonical polyadic decomposition.

Autom Constr 2020 Nov;119

National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, United States of America.

Field or laboratory data collected for work-related musculoskeletal disorder (WMSD) risk assessment in construction often becomes unreliable as a large amount of data go missing due to technology-induced errors, instrument failures or sometimes at random. Missing data can adversely affect the assessment conclusions. This study proposes a method that applies Canonical Polyadic Decomposition (CPD) tensor decomposition to fuse multiple sparse risk-related datasets and fill in missing data by leveraging the correlation among multiple risk indicators within those datasets. Two knee WMSD risk-related datasets-3D knee rotation (kinematics) and electromyography (EMG) of five knee postural muscles-collected from previous studies were used for the validation and demonstration of the proposed method. The analysis results revealed that for a large portion of missing values (40%), the proposed method can generate a fused dataset that provides reliable risk assessment results highly consistent (70%-87%) with those obtained from the original experimental datasets. This signified the usefulness of the proposed method for use in WMSD risk assessment studies when data collection is affected by a significant amount of missing data, which will facilitate reliable assessment of WMSD risks among construction workers. In the future, findings of this study will be implemented to explore whether, and to what extent, the fused dataset outperforms the datasets with missing values by comparing consistencies of the risk assessment results obtained from these datasets for further investigation of the fusion performance.
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http://dx.doi.org/10.1016/j.autcon.2020.103322DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8064735PMC
November 2020

Kneeling trunk kinematics during simulated sloped roof shingle installation.

Int J Ind Ergon 2020 May;77

National Institute for Occupational Safety & Health, Centers for Disease Control and Prevention, Health Effects Laboratory Division, 1095 Willowdale Rd, Morgantown, WV, 26505, USA.

Trunk musculoskeletal disorders are common among residential roofers. Addressing this problem requires a better understanding of the movements required to complete working tasks, such as affixing shingles on a sloped residential roof. We analyzed the extent to which the trunk kinematics during a shingling process are altered due to different angles of roof slope. Eight male subjects completed a kneeling shingle installation process on three differently sloped roof surfaces. The magnitude of the trunk kinematics was significantly influenced by both slope and task phase of the shingling process, depending on the metric. The results unequivocally point to roof slope and task phase as significant factors altering trunk kinematics. However, extension of the results to roofing workers should be done carefully, depending on the degree to which the study protocol represents the natural setting. Future studies on shingle installation in residential roofing should absolutely consider capturing a wider array of shingling procedures in order to encapsulate all the possible methods that are used due to the lack of a standardized procedure.
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http://dx.doi.org/10.1016/j.ergon.2020.102945DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8064732PMC
May 2020

Evaluation and Test Methods of Industrial Exoskeletons In Vitro, In Vivo, and In Silico: A Critical Review.

Crit Rev Biomed Eng 2021 ;49(4):1-13

Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV.

Industrial exoskeletons have been used to assist workers during occupational activities, such as overhead work, tool-use, mobility, stooping/squatting, and/or load carrying in various industries. Despite the promise of reducing the risk of work-related musculoskeletal disorders, there is a lack of sufficient evidence to support the safe and effective use of industrial exoskeletons. To assess the merits and residual risks of various types of exoskeletons in different work settings, more comprehensive evaluation procedures are needed. This review study aims to provide an overview of the existing viable and promising methods for evaluating the effectiveness of industrial exoskeletons. The different evaluation methods are organized into three categories-in vitro, in vivo, and in silico studies. The limitations and challenges in different types of evaluation approaches are also discussed. In summary, this review sheds light on choosing appropriate evaluation approaches and may help with decision-making during the development, evaluation, and application of industrial exoskeletons.
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http://dx.doi.org/10.1615/CritRevBiomedEng.2022041509DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC9199587PMC
June 2022

Application of polyethylene air-bubble cushions to improve the shock absorption performance of Type I construction helmets for repeated impacts.

Biomed Mater Eng 2021 ;32(1):1-14

Boise State University, Boise, ID, USA.

Background: The use of helmets was considered to be one of the important prevention strategies employed on construction sites. The shock absorption performance of a construction (or industrial) helmet is its most important performance parameter. Industrial helmets will experience cumulative structural damage when being impacted repeatedly with impact magnitudes greater than its endurance limit.

Objective: The current study is to test if the shock absorption performance of Type I construction helmets subjected to repeated impacts can be improved by applying polyethylene air-bubble cushions to the helmet suspension system.

Methods: Drop impact tests were performed using a commercial drop tower test machine following the ANSI Z89.1 Type I drop impact protocol. Typical off-the-shelf Type I construction helmets were evaluated in the study. A 5 mm thick air-bubble cushioning liner was placed between the headform and the helmet to be tested. Helmets were impacted ten times at different drop heights from 0.61 to 1.73 m. The effects of the air-bubble cushioning liner on the helmets' shock absorption performance were evaluated by comparing the peak transmitted forces collected from the original off-the-shelf helmet samples to the helmets equipped with air-bubble cushioning liners.

Results: Our results showed that a typical Type I construction helmet can be subjected to repeated impacts with a magnitude less than 22 J (corresponding to a drop height 0.61 m) without compromising its shock absorption performance. In comparison, the same construction helmet, when equipped with an air-bubble cushioning liner, can be subjected to repeated impacts of a magnitude of 54 J (corresponding to a drop height 1.52 m) without compromising its shock absorption performance.

Conclusions: The results indicate that the helmet's shock absorbing endurance limit has been increased by 145% with addition of an air-bubble cushioning liner.
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http://dx.doi.org/10.3233/BME-201132DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8006905PMC
August 2021

An Approach to Characterize the Impact Absorption Performance of Construction Helmets in Top Impact.

J Test Eval 2020 Oct;49(3)

Health Effects Laboratory, National Institute for Occupational Safety and Health, 1095 Willowdale Rd., Morgantown, WV 26505, USA.

The helmets used by construction site workers are mainly designed for head protection when objects are dropped from heights. Construction helmets are also casually called "hard hats" in industries. Common construction helmets are mostly categorized as type 1 according to different standards. All type 1 helmets have to pass type 1 standard impact tests, which are top impact tests-the helmet is fixed and is impacted by a free falling impactor on the top crown of the helmet shell. The purpose of this study was to develop an approach that can determine the performance characterization of a helmet. A total of 31 drop impact tests using a representative type 1 helmet model were performed at drop heights from 0.30 to 2.23 m, which were estimated to result in impact speeds from 2.4 to 6.6 m/s. Based on our results, we identified a critical drop height that was used to evaluate the performance of helmets. The peak impact forces and peak accelerations varied nonproportionally with the drop height. When the drop height is less than the critical height, the peak force and peak acceleration increase gradually and slowly with increasing drop height. When the drop height is greater than the critical height, the peak force and peak acceleration increase steeply with even a slight increase in drop height. Based on the critical drop height, we proposed an approach to determine the safety margin of a helmet. The proposed approach would make it possible to determine the performance characteristics of a helmet and to estimate the safety margin afforded by the helmet, if the helmet first passes the existing standardized tests. The proposed test approach would provide supplementary information for consumers to make knowledgeable decisions when selecting construction helmets.
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http://dx.doi.org/10.1520/jte20180604DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC9345406PMC
October 2020

Effects of working posture and roof slope on activation of lower limb muscles during shingle installation.

Ergonomics 2020 Sep 2;63(9):1182-1193. Epub 2020 Jun 2.

National Institute for Occupational Safety and Health, Morgantown, WV, USA.

Awkward and extreme kneeling during roofing generates high muscular tension which can lead to knee musculoskeletal disorders (MSDs) among roofers. However, the combined impact of roof slope and kneeling posture on the activation of the knee postural muscles and their association to potential knee MSD risks among roofers have not been studied. The current study evaluated the effects of kneeling posture and roof slope on the activation of major knee postural muscles during shingle installation via a laboratory assessment. Maximum normalized electromyography (EMG) data were collected from knee flexor and extensor muscles of seven subjects, who mimicked the shingle installation process on a slope-configurable wooden platform. The results revealed a significant increase in knee muscle activation during simulated shingle installation on sloped rooftops. Given the fact that increased muscle activation of knee postural muscles has been associated with knee MSDs, roof slope and awkward kneeling posture can be considered as potential knee MSD risk factors. This study demonstrated significant effects of roof slope and kneeling posture on the peak activation of knee postural muscles. The findings of this study suggested that residential roofers could be exposed to a greater risk of developing knee MSDs with the increase of roof slope during shingle installation due to increased muscle loading. MSDs: musculoskeletal disorders; EMG: electromyography; ANOVA: analysis of variance; MNMA: maximum normalized muscle activation; RF: rectus femoris; VL: vastus lateralis; VM: vastus medialis; BF: biceps femoris; S: semitendinosus.
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http://dx.doi.org/10.1080/00140139.2020.1772378DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7483978PMC
September 2020

Are knee savers and knee pads a viable intervention to reduce lower extremity musculoskeletal disorder risk in residential roofers?

Int J Ind Ergon 2019 Nov;74

National Institute for Occupational Safety & Health, Centers for Disease Control and Prevention, 1095 Willowdale Rd., Morgantown, WV 26505.

One factor commonly associated with musculoskeletal disorder risk is extreme postures. To lessen this risk, individuals must be in an as neutral posture as possible while working. We analyzed how the inclusion of different combinations of two interventions-knee pads and knee savers-can alter lower extremity kinematics during deep or near full flexion kneeling occurs while on different sloped surfaces. Nine male subjects were requested to keep a typical resting posture while kneeling on sloped roofing simulator. We observed that the introduction of a wearable third party device considerably altered lower extremity full flexion kneeling kinematics compared to level deep kneeling. This study provided a sound base for the use of third party devices to reduce musculoskeletal disorder risk on a sloped surface, however further testing with other musculoskeletal disorder risk factors is needed prior to conclusive recommendation.
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http://dx.doi.org/10.1016/j.ergon.2019.102868DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7179875PMC
November 2019

Biomechanical modeling of deep squatting: Effects of the interface contact between posterior thigh and shank.

J Biomech 2019 Nov 13;96:109333. Epub 2019 Sep 13.

National Institute for Occupational Safety and Health, Morgantown, WV, USA.

Epidemiological studies indicate that occupational activities that require extended deep knee flexion or kneeling are associated with a higher prevalence of knee osteoarthritis. In many sport activities, such as a catcher in a baseball or a softball game, athletes have to make repetitive deep squatting motions, which have been associated with the development of osteochondritis dissecans. Excessive deep knee flexion postures may cause excessive loading in the knee joint. In deep knee flexion postures, the posterior aspect of the shank will contact the posterior thigh, resulting in a compressive force within the soft tissues. The current study was aimed at analyzing the effects of the posterior thigh/shank contact on the joint loading during deep knee flexion in a natural knee. An existing, whole body model with detailed anatomical components of the knee (AnyBody) has been adopted and modified for this study. The effects of the posterior thigh/shank contact were evaluated by comparing the results of the inverse dynamic analysis for two scenarios: with and without the posterior thigh/shank contact force. Our results showed that, in a deep squatting posture (knee flexion 120+ degrees), the posterior thigh/shank contact helps reduce the patellofemoral (PF) and tibiofemoral (TF) normal contact forces by 42% and 57%, respectively.
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http://dx.doi.org/10.1016/j.jbiomech.2019.109333DOI Listing
November 2019

Evaluation of the shock absorption performance of construction helmets under repeated top impacts.

Eng Fail Anal 2019 Feb 26;96:330-339. Epub 2018 Oct 26.

National Institute for Occupational Safety and Health, Morgantown, West Virginia, USA.

It is accepted in industries that an industrial helmet should be disposed of when it is subjected to a significant impact. There is no scientific evidence that supports this well-accepted belief. The current study was intended to evaluate the shock absorption performance of industrial helmets under repeated impacts. Common industrial or construction helmets are categorized as Type I according to ANSI Z89.1 and they are designed to mainly protect top impacts. A representative basic Type I construction helmet model was selected in the study. Helmets were repeatedly impacted ten times using a commercial drop tower tester with an impactor (mass 3.6 kg) at different drop heights from 0.30 to 2.03 m. A total of 80 impact trials were performed in the study. The relationships of the transmitted force with the drop height and with impact number were analyzed. A new parameter - the endurance limit - was proposed to evaluate the shock absorption performance of a helmet. The helmets were observed to experience cumulative structural damage with increasing impact number, resulting in a degrading shock absorption performance, when being impacted repeatedly with magnitudes greater than the endurance limit. Repeated impacts with magnitudes smaller than the endurance limit did not cause measurable cumulative structural damage to the helmets in our study.
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http://dx.doi.org/10.1016/j.engfailanal.2018.10.015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6760905PMC
February 2019

Assessing work-related risk factors for musculoskeletal knee disorders in construction roofing tasks.

Appl Ergon 2019 Nov 17;81:102901. Epub 2019 Jul 17.

National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV, 26505, USA. Electronic address:

Roofers often suffer from musculoskeletal disorders (MSDs) to their knees due to spending a large amount of time kneeling while performing work-related roofing activities on sloped rooftops. Several ergonomic studies have identified kneeling as a potential risk factor for knee injuries and disorders. Existing biomechanical models and sensor technologies used to assess work-related risk factors for different construction trades are not applicable in roof work settings especially on slanted rooftop surfaces. This work assesses the impacts of work-related factors, namely working posture and roof slope, on the potential risk of developing knee MSDs due to residential roofing tasks in a laboratory setting. Nine human subjects participated in the experiment and mimicked shingle installation on a slope-configurable wooden platform. Maximum angles of right and left knee flexion, abduction, adduction, and axial rotation (internal and external) were measured as risk indicators using a motion capture system under different roof slope settings. The results demonstrated that roof slope, working posture and their interaction may have significant impacts on developing knee MSDs during roofing activities. Knees are likely to be exposed to increased risk of MSDs due to working in a dynamic kneeling posture during shingle installation. In our study, flexion in both knees and adduction in the right knee were found lower in high-pitched rooftops; however, abduction in the left knee and internal rotation in the right knee were found higher during shingle installation. Hence proper attention is needed for these situations. This study provides useful information about the impact of roof work settings on knee MSDs development, which may facilitate effective interventions such as education, training, and tools to prevent knee injuries in construction roofing tasks.
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http://dx.doi.org/10.1016/j.apergo.2019.102901DOI Listing
November 2019

An evaluation of the contact forces on the fingers when squeezing a spherical rehabilitation ball.

Biomed Mater Eng 2018 ;29(5):629-639

National Institute for Occupational Safety and Health, Morgantown, WV, USA.

The rehabilitation squeeze ball is a popular device to help strengthen the hand, fingers and forearm muscles. The distributions of the contact pressure in the interface between the therapy ball and hand/fingers can affect the joint moment of each of the individual fingers, thereby affecting rehabilitation effects. In the current study, we evaluated the contact force distributions on the fingers when gripping a spherical object. Eight female adults [age 29 (9.1) years, mass 64.6 (7.1) kg, height 163.5 (1.9) cm, hand length 17.2 (0.7) cm] participated in the study. Contact force sensors were attached to the middle of the palmar surfaces of the distal, middle, and proximal phalanges of the four fingers in the longitudinal direction. In order to evaluate the effects of the ball stiffness on the contact force distributions on the fingers, subjects were requested to perform quasi-static gripping on a standard tennis ball and on a rehabilitation ball. The tennis ball is much stiffer and experiences smaller deformation under compression compared to the rehabilitation ball. We analyzed the force share among the distal, middle, and proximal finger segments, when subjects gripping balls of different stiffnesses (tennis ball vs. rehabilitation ball) and at three different grip efforts. Our results indicated that the grip force is contributed about 60% and 40% by the middle/ring fingers and by the index/little fingers, respectively. These characteristics are independent of the grip force levels and stiffness of the contact surface.
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http://dx.doi.org/10.3233/BME-181013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6388416PMC
February 2019

Vibrations transmitted from human hands to upper arm, shoulder, back, neck, and head.

Int J Ind Ergon 2017 Dec 22;62:1-12. Epub 2016 Jul 22.

Engineering & Control Technology Branch, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, USA.

Some powered hand tools can generate significant vibration at frequencies below 25 Hz. It is not clear whether such vibration can be effectively transmitted to the upper arm, shoulder, neck, and head and cause adverse effects in these substructures. The objective of this study is to investigate the vibration transmission from the human hands to these substructures. Eight human subjects participated in the experiment, which was conducted on a 1-D vibration test system. Unlike many vibration transmission studies, both the right and left hand-arm systems were simultaneously exposed to the vibration to simulate a working posture in the experiment. A laser vibrometer and three accelerometers were used to measure the vibration transmitted to the substructures. The apparent mass at the palm of each hand was also measured to help in understanding the transmitted vibration and biodynamic response. This study found that the upper arm resonance frequency was 7-12 Hz, the shoulder resonance was 7-9 Hz, and the back and neck resonances were 6-7 Hz. The responses were affected by the hand-arm posture, applied hand force, and vibration magnitude. The transmissibility measured on the upper arm had a trend similar to that of the apparent mass measured at the palm in their major resonant frequency ranges. The implications of the results are discussed.

Relevance To Industry: Musculoskeletal disorders (MSDs) of the shoulder and neck are important issues among many workers. Many of these workers use heavy-duty powered hand tools. The combined mechanical loads and vibration exposures are among the major factors contributing to the development of MSDs. The vibration characteristics of the body segments examined in this study can be used to help understand MSDs and to help develop more effective intervention methods.
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http://dx.doi.org/10.1016/j.ergon.2016.07.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5672949PMC
December 2017

Assessing Work-Related Risk Factors on Low Back Disorders among Roofing Workers.

J Constr Eng Manag 2017 07 7;143(7). Epub 2017 Mar 7.

National Institute for Occupational Safety and Health, 1095 Willowdale Rd., Morgantown, WV 26505.

Roofers have long suffered from low back disorders (LBDs), which are a primary nonfatal injury in construction. Ergonomic studies have identified several risk factors associated with LBDs in workplaces and developed biomechanical models for general LBD risk assessments. However, these models cannot be directly used for assessments in roof workplaces because they are designed for general tasks without considering roofers' posture variance and effects of working on slanted roof surfaces. This paper examined the relationship between roofing work-related factors and LBD risk among roofers using a laboratory assessment. A pitch-configurable wood platform was built to mimic the rooftop. The maximum trunk flexion angle and normalized electromyography (EMG) signals were measured as indicators using a motion capture system and a skeletal muscle signal recording system under different settings, i.e., different roof slopes, postures, facing directions, and working paces. The results indicated the measured factors with significant effects on the LBD development and revealed unfavorable conditions (e.g., using a stooped posture to work on low-pitch rooftops at a fast pace) where the work on rooftops needs particular attention. Such information is useful for systematic understanding of roofing nonfatal LBD developments among construction professionals and may enable development of interventions and guidelines for reducing the prevalence of LBDs at roofing jobsites.
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http://dx.doi.org/10.1061/(ASCE)CO.1943-7862.0001320DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6444369PMC
July 2017

Modeling of the interaction between grip force and vibration transmissibility of a finger.

Med Eng Phys 2017 07 9;45:61-70. Epub 2017 May 9.

Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, USA.

It is known that the vibration characteristics of the fingers and hand and the level of grip action interacts when operating a power tool. In the current study, we developed a hybrid finger model to simulate the vibrations of the hand-finger system when gripping a vibrating handle covered with soft materials. The hybrid finger model combines the characteristics of conventional finite element (FE) models, multi-body musculoskeletal models, and lumped mass models. The distal, middle, and proximal finger segments were constructed using FE models, the finger segments were connected via three flexible joint linkages (i.e., distal interphalangeal joint (DIP), proximal interphalangeal joint (PIP), and metacarpophalangeal (MCP) joint), and the MCP joint was connected to the ground and handle via lumped parameter elements. The effects of the active muscle forces were accounted for via the joint moments. The bone, nail, and hard connective tissues were assumed to be linearly elastic whereas the soft tissues, which include the skin and subcutaneous tissues, were considered as hyperelastic and viscoelastic. The general trends of the model predictions agree well with the previous experimental measurements in that the resonant frequency increased from proximal to the middle and to the distal finger segments for the same grip force, that the resonant frequency tends to increase with increasing grip force for the same finger segment, especially for the distal segment, and that the magnitude of vibration transmissibility tends to increase with increasing grip force, especially for the proximal segment. The advantage of the proposed model over the traditional vibration models is that it can predict the local vibration behavior of the finger to a tissue level, while taking into account the effects of the active musculoskeletal force, the effects of the contact conditions on vibrations, the global vibration characteristics.
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http://dx.doi.org/10.1016/j.medengphy.2017.04.008DOI Listing
July 2017

An improved finite element modeling of the cerebrospinal fluid layer in the head impact analysis.

Biomed Mater Eng 2017 ;28(2):187-199

Department of Neurosurgery, West Virginia University, Morgantown, West Virginia, USA.

The finite element (FE) method has been widely used to investigate the mechanism of traumatic brain injuries (TBIs), because it is technically difficult to quantify the responses of the brain tissues to the impact in experiments. One of technical challenges to build a FE model of a human head is the modeling of the cerebrospinal fluid (CSF) of the brain. In the current study, we propose to use membrane elements to construct the CSF layer. Using the proposed approach, we demonstrate that a head model can be built by using existing meshes available in commercial databases, without using any advanced meshing software tool, and with the sole use of native functions of the FE package Abaqus. The calculated time histories of the intracranial pressures at frontal, posterior fossa, parietal, and occipital positions agree well with the experimental data and the simulations in the literature, indicating that the physical effects of the CSF layer have been accounted for in the proposed modeling approach. The proposed modeling approach would be useful for bioengineers to solve practical problems.
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http://dx.doi.org/10.3233/BME-171666DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6388415PMC
July 2017

Finite element simulations of the head-brain responses to the top impacts of a construction helmet: Effects of the neck and body mass.

Proc Inst Mech Eng H 2017 Jan 21;231(1):58-68. Epub 2016 Dec 21.

2 Department of Neurosurgery, West Virginia University, Morgantown, WV, USA.

Traumatic brain injuries are among the most common severely disabling injuries in the United States. Construction helmets are considered essential personal protective equipment for reducing traumatic brain injury risks at work sites. In this study, we proposed a practical finite element modeling approach that would be suitable for engineers to optimize construction helmet design. The finite element model includes all essential anatomical structures of a human head (i.e. skin, scalp, skull, cerebrospinal fluid, brain, medulla, spinal cord, cervical vertebrae, and discs) and all major engineering components of a construction helmet (i.e. shell and suspension system). The head finite element model has been calibrated using the experimental data in the literature. It is technically difficult to precisely account for the effects of the neck and body mass on the dynamic responses, because the finite element model does not include the entire human body. An approximation approach has been developed to account for the effects of the neck and body mass on the dynamic responses of the head-brain. Using the proposed model, we have calculated the responses of the head-brain during a top impact when wearing a construction helmet. The proposed modeling approach would provide a tool to improve the helmet design on a biomechanical basis.
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http://dx.doi.org/10.1177/0954411916678017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5308880PMC
January 2017

Finite element modeling of finite deformable, biphasic biological tissues with transversely isotropic statistically distributed fibers: toward a practical solution.

Z Angew Math Phys 2016 Apr 5;67. Epub 2016 Apr 5.

Department of Mechanical and Manufacturing Engineering The University of Calgary Calgary, AB, Canada

The distribution of collagen fibers across articular cartilage layers is statistical in nature. Based on the concepts proposed in previous models, we developed a methodology to include the statistically distributed fibers across the cartilage thickness in the commercial FE software COMSOL which avoids extensive routine programming. The model includes many properties that are observed in real cartilage: finite hyperelastic deformation, depth-dependent collagen fiber concentration, depth- and deformation-dependent permeability, and statistically distributed collagen fiber orientation distribution across the cartilage thickness. Numerical tests were performed using confined and unconfined compressions. The model predictions on the depth-dependent strain distributions across the cartilage layer are consistent with the experimental data in the literature.
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http://dx.doi.org/10.1007/s00033-015-0598-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4908457PMC
April 2016

Review and Evaluation of Hand-Arm Coordinate Systems for Measuring Vibration Exposure, Biodynamic Responses, and Hand Forces.

Saf Health Work 2015 Sep 19;6(3):159-73. Epub 2015 Jun 19.

Engineering & Control Technology Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV, USA.

The hand coordinate systems for measuring vibration exposures and biodynamic responses have been standardized, but they are not actually used in many studies. This contradicts the purpose of the standardization. The objectives of this study were to identify the major sources of this problem, and to help define or identify better coordinate systems for the standardization. This study systematically reviewed the principles and definition methods, and evaluated typical hand coordinate systems. This study confirms that, as accelerometers remain the major technology for vibration measurement, it is reasonable to standardize two types of coordinate systems: a tool-based basicentric (BC) system and an anatomically based biodynamic (BD) system. However, these coordinate systems are not well defined in the current standard. Definition of the standard BC system is confusing, and it can be interpreted differently; as a result, it has been inconsistently applied in various standards and studies. The standard hand BD system is defined using the orientation of the third metacarpal bone. It is neither convenient nor defined based on important biological or biodynamic features. This explains why it is rarely used in practice. To resolve these inconsistencies and deficiencies, we proposed a revised method for defining the realistic handle BC system and an alternative method for defining the hand BD system. A fingertip-based BD system for measuring the principal grip force is also proposed based on an important feature of the grip force confirmed in this study.
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http://dx.doi.org/10.1016/j.shaw.2015.05.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4674512PMC
September 2015

Theoretical foundation, methods, and criteria for calibrating human vibration models using frequency response functions.

J Sound Vib 2015 Nov;356:195-216

Engineering & Control Technology Branch, National Institute for Occupational Safety and Health, Morgantown, WV 26505, USA.

While simulations of the measured biodynamic responses of the whole human body or body segments to vibration are conventionally interpreted as summaries of biodynamic measurements, and the resulting models are considered quantitative, this study looked at these simulations from a different angle: model calibration. The specific aims of this study are to review and clarify the theoretical basis for model calibration, to help formulate the criteria for calibration validation, and to help appropriately select and apply calibration methods. In addition to established vibration theory, a novel theorem of mechanical vibration is also used to enhance the understanding of the mathematical and physical principles of the calibration. Based on this enhanced understanding, a set of criteria was proposed and used to systematically examine the calibration methods. Besides theoretical analyses, a numerical testing method is also used in the examination. This study identified the basic requirements for each calibration method to obtain a unique calibration solution. This study also confirmed that the solution becomes more robust if more than sufficient calibration references are provided. Practically, however, as more references are used, more inconsistencies can arise among the measured data for representing the biodynamic properties. To help account for the relative reliabilities of the references, a baseline weighting scheme is proposed. The analyses suggest that the best choice of calibration method depends on the modeling purpose, the model structure, and the availability and reliability of representative reference data.
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http://dx.doi.org/10.1016/j.jsv.2015.06.047DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4699322PMC
November 2015

Automated pressure map segmentation for quantifying phalangeal kinetics during cylindrical gripping.

Med Eng Phys 2016 Feb 18;38(2):72-9. Epub 2015 Dec 18.

National Institute for Occupational Safety and Health (NIOSH), 1095 Willowdale Road MS 2027, Morgantown, WV 26505, USA; Present address: Lake Erie College of Osteopathic Medicine (LECOM), 1858 West Grandview Blvd, Erie, PA 16509, USA.

Inverse dynamics models used to investigate musculoskeletal disorders associated with handle gripping require accurate phalangeal kinetics. Cylindrical handles wrapped with pressure film grids have been used in studies of gripping kinetics. We present a method fusing six degree-of-freedom hand kinematics and a kinematic calibration of a cylinder-wrapped pressure film. Phalanges are modeled as conic frusta and projected onto the pressure grid, automatically segmenting the pressure map into regions of interest (ROIs). To demonstrate the method, segmented pressure maps are presented from two subjects with substantially different hand length and body mass, gripping cylinders 50 and 70 mm in diameter. For each ROI, surface-normal force vectors were summed to create a reaction force vector and center of pressure location. Phalangeal force magnitudes for a data sample were similar to that reported in previous studies. To evaluate our method, a surrogate was designed for each handle such that when modeled as a phalanx it would generate a ROI around the cells under its supports; the classification F-score was above 0.95 for both handles. Both the human subject results and the surrogate evaluation suggest that the approach can be used to automatically segment the pressure map for quantifying phalangeal kinetics of the fingers during cylindrical gripping.
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http://dx.doi.org/10.1016/j.medengphy.2015.11.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4830423PMC
February 2016

An examination of the vibration transmissibility of the hand-arm system in three orthogonal directions.

Int J Ind Ergon 2015 Feb;45:21-34

Engineering & Control Technology Branch, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, USA.

The objective of this study is to enhance the understanding of the vibration transmission in the hand-arm system in three orthogonal directions (, and ). For the first time, the transmitted vibrations distributed on the entire hand-arm system exposed in the three orthogonal directions via a 3-D vibration test system were measured using a 3-D laser vibrometer. Seven adult male subjects participated in the experiment. This study confirms that the vibration transmissibility generally decreased with the increase in distance from the hand and it varied with the vibration direction. Specifically, to the upper arm and shoulder, only moderate vibration transmission was measured in the test frequency range (16 to 500 Hz), and virtually no transmission was measured in the frequency range higher than 50 Hz. The resonance vibration on the forearm was primarily in the range of 16-30 Hz with the peak amplitude of approximately 1.5 times of the input vibration amplitude. The major resonance on the dorsal surfaces of the hand and wrist occurred at around 30-40 Hz and, in the direction, with peak amplitude of more than 2.5 times of the input amplitude. At higher than 50 Hz, vibration transmission was effectively limited to the hand and fingers. A major finger resonance was observed at around 100 Hz in the and directions and around 200 Hz in the direction. In the fingers, the resonance magnitude in the direction was generally the lowest, and the resonance magnitude in the direction was generally the highest with the resonance amplitude of 3 times the input vibration, which was similar to the transmissibility at the wrist and hand dorsum. The implications of the results are discussed.

Relevance To Industry: Prolonged, intensive exposure to hand-transmitted vibration could result in hand-arm vibration syndrome. While the syndrome's precise mechanisms remain unclear, the characterization of the vibration transmissibility of the system in the three orthogonal dimensions performed in this study can help understand the syndrome and help develop improved frequency weightings for assessing the risk of the exposure for developing various components of the syndrome.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4666322PMC
http://dx.doi.org/10.1016/j.ergon.2014.11.001DOI Listing
February 2015

Analysis of the Constraint Joint Loading in the Thumb During Pipetting.

J Biomech Eng 2015 Aug 9;137(8):084501. Epub 2015 Jun 9.

Dynamic loading on articular joints is essential for the evaluation of the risk of the articulation degeneration associated with occupational activities. In the current study, we analyzed the dynamic constraint loading for the thumb during pipetting. The constraint loading is considered as the loading that has to be carried by the connective tissues of the joints (i.e., the cartilage layer and the ligaments) to maintain the kinematic constraints of the system. The joint loadings are solved using a classic free-body approach, using the external loading and muscle forces, which were obtained in an inverse dynamic approach combined with an optimization procedure in anybody. The constraint forces in the thumb joint obtained in the current study are compared with those obtained in the pinch and grasp tests in a previous study (Cooney and Chao, 1977, "Biomechanical Analysis of Static Forces in the Thumb During Hand Function," J. Bone Joint Surg. Am., 59(1), pp. 27-36). The maximal compression force during pipetting is approximately 83% and 60% greater than those obtained in the tip pinch and key pinch, respectively, while substantially smaller than that obtained during grasping. The maximal lateral shear force is approximately six times, 32 times, and 90% greater than those obtained in the tip pinch, key pinch, and grasp, respectively. The maximal dorsal shear force during pipetting is approximately 3.2 and 1.4 times greater than those obtained in the tip pinch and key pinch, respectively, while substantially smaller than that obtained during grasping. Our analysis indicated that the thumb joints are subjected to repetitive, intensive loading during pipetting, compared to other daily activities.
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http://dx.doi.org/10.1115/1.4030311DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4782612PMC
August 2015

Analysis of the effects of surface stiffness on the contact interaction between a finger and a cylindrical handle using a three-dimensional hybrid model.

Med Eng Phys 2014 Jul 13;36(7):831-41. Epub 2014 Apr 13.

National Institute for Occupational Safety and Health, Morgantown, WV, USA.

Contact interactions between the hand and handle, such as the contact surface softness and contact surface curvature, will affect both physical effort and musculoskeletal fatigue, thereby the comfort and safety of power tool operations. Previous models of hand gripping can be categorized into two groups: multi-body dynamic models and finite element (FE) models. The goal of the current study is to develop a hybrid FE hand gripping model, which combines the features of conventional FE models and multi-body dynamic models. The proposed model is applied to simulate hand-gripping on a cylindrical handle with covering materials of different softness levels. The model included three finger segments (distal, middle, and proximal phalanxes), three finger joints (the distal interphalangeal (DIP), proximal interphalangeal (PIP), and metacarpophalangeal (MCP) joint), and major anatomical substructures. The model was driven by joint moments, which are the net effects of all passive and active muscular forces acting about the joints. The finger model was first calibrated by using experimental data of human subject tests, and then applied to investigate the effects of surface softness on contact interactions between a finger and a cylindrical handle. Our results show that the maximal compressive stress and strain in the soft tissues of the fingers can be effectively reduced by reducing the stiffness of the covering material.
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http://dx.doi.org/10.1016/j.medengphy.2014.03.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4573534PMC
July 2014

Analysis of the musculoskeletal loading of the thumb during pipetting--a pilot study.

J Biomech 2014 Jan 15;47(2):392-9. Epub 2013 Nov 15.

National Institute for Occupational Safety & Health, Morgantown, WV 26505, USA.

Previous epidemiological studies indicate that the use of thumb-push mechanical pipettes is associated with musculoskeletal disorders (MSDs) in the hand. The goal of the current study was to analyze the loading in the muscle-tendon units in the thumb during pipetting. The hand is modeled as a multi-body linkage system and includes four fingers (index, long, ring, and little finger), a thumb, and a palm segment. Since the current study is focused on the thumb, the model includes only nine muscles attached to the thumb via tendons. The time-histories of joint angles and push force at the pipette plunger during pipetting were determined experimentally and used as model input; whereas forces in the muscle-tendon units in the thumb were calculated via an inverse dynamic approach combined with an optimization procedure. Results indicate that all nine muscles have force outputs during pipetting, and the maximal force was in the abductor pollicis brevis (APB). The ratio of the mean peak muscle force to the mean peak push force during the dispensing cycle was approximately 2.3, which is comparable to values observed in grasping tasks in the literature. The analysis method and results in the current study provide a mechanistic understanding of MSD risk factors associated with pipetting, and may be useful in guiding ergonomic designs for manual pipettes.
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http://dx.doi.org/10.1016/j.jbiomech.2013.11.015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4782592PMC
January 2014

Theoretical relationship between vibration transmissibility and driving-point response functions of the human body.

J Sound Vib 2013 Nov;332(24):6193-6202

Engineering & Control Technology Branch, National Institute for Occupational Safety and Health, Morgantown, WV 26505, USA.

The relationship between the vibration transmissibility and driving-point response functions (DPRFs) of the human body is important for understanding vibration exposures of the system and for developing valid models. This study identified their theoretical relationship and demonstrated that the sum of the DPRFs can be expressed as a linear combination of the transmissibility functions of the individual mass elements distributed throughout the system. The relationship is verified using several human vibration models. This study also clarified the requirements for reliably quantifying transmissibility values used as references for calibrating the system models. As an example application, this study used the developed theory to perform a preliminary analysis of the method for calibrating models using both vibration transmissibility and DPRFs. The results of the analysis show that the combined method can theoretically result in a unique and valid solution of the model parameters, at least for linear systems. However, the validation of the method itself does not guarantee the validation of the calibrated model, because the validation of the calibration also depends on the model structure and the reliability and appropriate representation of the reference functions. The basic theory developed in this study is also applicable to the vibration analyses of other structures.
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http://dx.doi.org/10.1016/j.jsv.2013.07.017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4671508PMC
November 2013

The musculoskeletal loading profile of the thumb during pipetting based on tendon displacement.

Med Eng Phys 2013 Dec 6;35(12):1801-10. Epub 2013 Sep 6.

National Institute for Occupational Safety & Health, Morgantown, WV 26505, USA. Electronic address:

Strong evidence indicates that highly repetitive manual work is associated with the development of upper extremity musculoskeletal disorders (MSDs). One of the occupational activities that involves highly repetitive and forceful hand work is manual pipetting in chemical or biological laboratories. In the current study, we quantified tendon displacement as a parameter to assess the cumulative loading exposure of the musculoskeletal system in the thumb during pipetting. The maximal tendon displacement was found in the flexor pollicis longus (FPL) tendon. Assuming that subjects' pipetting rates were maintained constant during a period of 1 h, the average accumulated tendon displacement in the FPL reached 29 m, which is in the lower range of those observed in other occupational activities, such as typing and nail gun operations. Our results showed that tendon displacement data contain relatively small standard deviations, despite high variances in thumb kinematics, suggesting that the tendon displacements may be useful in evaluating the musculoskeletal loading profile.
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http://dx.doi.org/10.1016/j.medengphy.2013.08.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5014230PMC
December 2013

Modeling of the biodynamic responses distributed at the fingers and palm of the hand in three orthogonal directions.

J Sound Vib 2013 Feb;232(4):1125-1140

Engineering & Control Technology Branch, National Institute for Occupational Safety and Health Morgantown, WV 26505, USA.

The objectives of this study were to develop models of the hand-arm system in the three orthogonal directions ( , and ) and to enhance the understanding of the hand vibration dynamics. A four-degrees-of-freedom (DOF) model and 5-DOF model were used in the simulation for each direction. The driving-point mechanical impedances distributed at the fingers and palm of the hand reported in a previous study were used to determine the parameters of the models. The 5-DOF models were generally superior to the 4-DOF models for the simulation. Hence, as examples of applications, the 5-DOF models were used to predict the transmissibility of a vibration-reducing glove and the vibration transmissibility on the major substructures of the hand-arm system. The model-predicted results were also compared with the experimental data reported in two other recent studies. Some reasonable agreements were observed in the comparisons, which provided some validation of the developed models. This study concluded that the 5-DOF models are acceptable for helping to design and analyze vibrating tools and anti-vibration devices. This study also confirmed that the 5-DOF model in the direction is acceptable for a coarse estimation of the biodynamic responses distributed throughout the major substructures of the hand-arm system. Some interesting phenomena observed in the experimental study of the biodynamic responses in the three directions were also explained in this study.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4656148PMC
http://dx.doi.org/10.1016/j.jsv.2012.10.003DOI Listing
February 2013
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