In JoVE (1)

Other Publications (85)

Articles by David Rempel in JoVE

Other articles by David Rempel on PubMed

Short Term and Long Term Effects of Enhanced Auditory Feedback on Typing Force, EMG, and Comfort While Typing

Applied Ergonomics. Mar, 2002  |  Pubmed ID: 12009119

Two studies were conducted to determine the effects of enhanced auditory feedback on typing force, electromyography (EMG) and subjective discomfort. The introduction of enhanced auditory feedback caused a 10-20% reduction in 90th percentile typing force, finger flexor EMG, and finger extensor EMG. Adaptation to the enhanced auditory feedback occurred in <3 min. After 1 week of intermittent enhanced auditory feedback there were no differences in typing force or EMG while subjects were typing with or without the enhanced auditory feedback. The continued use of auditory feedback did not further reduce the levels of typing force or EMG after 1 or 2 weeks of exposure.

A Mobile Tool for Accessibility and Usability Testing of Medical Instrumentation

Conference Proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference. 2004  |  Pubmed ID: 17271416

The Mobile Usability Lab (MU-Lab) is a tool developed by the Rehabilitation Engineering Research Center on Accessible Medical Instrumentation (RERC-AMI) to study the accessibility and usability of medical devices by people with diverse abilities. The system includes a suite of data collection hardware components and a custom software interface to help coordinate problem identification and planning as well as data collection and analysis for usability and accessibility research of medical devices. Hardware components include a laptop computer, data acquisition card, video cameras, quad video processor and wireless microphones. Software components include a customized Web-based usability suite, real-time data collection package and several video editing and data analysis tools.

Upper Extremity Pain and Computer Use Among Engineering Graduate Students

American Journal of Industrial Medicine. Sep, 2004  |  Pubmed ID: 15307128

The objective of this study was to investigate risk factors associated with persistent or recurrent upper extremity and neck pain among engineering graduate students.

Entrapment Neuropathies: Pathophysiology and Pathogenesis

Journal of Electromyography and Kinesiology : Official Journal of the International Society of Electrophysiological Kinesiology. Feb, 2004  |  Pubmed ID: 14759752

A number of theories of pathogenesis of entrapment neuropathy, due to repeated loading, have been proposed and these theories are being actively explored with animal models. Tubes placed loosely around peripheral nerves cause delayed onset, chronic pain and changes in nerve morphology including nerve sprouting. Balloons placed around or adjacent to the nerve and inflated to low pressures, rapidly produce endoneurial edema and a persistent increase in intraneural pressure. The same models demonstrate long-term changes such as demyelination and fibrosis. The applied pressure causes a decrement in nerve function and abnormal morphology in a dose-dependent manner that appears to be linked to the amount of endoneurial edema. A new model involving involuntary, repetitive fingertip loading for 6 h per week for 4 weeks has caused slowing of nerve function at the wrist similar to that seen in patients with carpal tunnel syndrome. These models have the potential to reveal the mechanisms of injury at the cellular and biochemical level and address questions about the relative importance of various biomechanical factors (e.g. peak force, mean force, force rate, duty cycle, etc.). In addition, these models will allow us to evaluate various prevention, treatment and rehabilitation protocols.

Upper Extremity Mononeuropathy Among Engineers

Journal of Occupational and Environmental Medicine / American College of Occupational and Environmental Medicine. Dec, 2005  |  Pubmed ID: 16340709

The objectives of this study were to estimate the prevalence of mononeuropathy at the wrist among engineers who use computers and to identify associated risk factors.

In Vivo Forces Generated by Finger Flexor Muscles Do Not Depend on the Rate of Fingertip Loading During an Isometric Task

Journal of Biomechanics. Nov, 2005  |  Pubmed ID: 16154416

Risk factors for activity-related tendon disorders of the hand include applied force, duration, and rate of loading. Understanding the relationship between external loading conditions and internal tendon forces can elucidate their role in injury and rehabilitation. The goal of this investigation is to determine whether the rate of force applied at the fingertip affects in vivo forces in the flexor digitorum profundus (FDP) tendon and the flexor digitorum superficialis (FDS) tendon during an isometric task. Tendon forces, recorded with buckle force transducers, and fingertip forces were simultaneously measured during open carpal tunnel surgery as subjects (N=15) increased their fingertip force from 0 to 15N in 1, 3, and 10s. The rates of 1.5, 5, and 15N/s did not significantly affect FDP or FDS tendon to fingertip force ratios. For the same applied fingertip force, the FDP tendon generated more force than the FDS. The mean FDP to fingertip ratio was 2.4+/-0.7 while the FDS to tip ratio averaged 1.5+/-1.0 (p<0.01). The fine motor control needed to generate isometric force ramps at these specific loading rates probably required similar high activation levels of multiple finger muscles in order to stabilize the finger and control joint torques at the force rates studied. Therefore, for this task, no additional increase in muscle force was observed at higher rates. These findings suggest that for high precision, isometric pinch maneuvers under static finger conditions, tendon forces are independent of loading rate.

Evidence of Tendon Microtears Due to Cyclical Loading in an in Vivo Tendinopathy Model

Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society. Sep, 2005  |  Pubmed ID: 16140201

Tendon injuries at the epicondyle can occur in athletes and workers whose job functions involve repetitive, high force hand activities, but the early pathophysiologic changes of tendon are not well known. The purpose of this study was to evaluate early tendon structural changes, specifically the formation of microtears, caused by cyclical loading. The Flexor Digitorum Profundus (FDP) muscle of nine New Zealand White rabbits was stimulated to contract repetitively for 80 h of cumulative loading over 14 weeks. The contralateral limb served as a control. The tendon at the medial epicondyle insertion site was harvested, sectioned, and stained. Microtears were quantified, using image analysis software, in four regions of the tendon, two regions along the enthesis and two distal to the enthesis. The tear density (loaded: 1329+/-546 tears/mm(2); unloaded: 932+/-474 tears/mm(2)) and mean tear size (loaded: 18.3+/-6.1 microm(2); unloaded: 14.0+/-4.8 microm(2)) were significantly greater in the loaded limb (p<0.0001) across all regions compared to the unloaded contralateral limb. These early microstructural changes in a repetitively loaded tendon may initiate a degenerative process that leads to tendinosis.

Thumb Force and Muscle Loads Are Influenced by the Design of a Mechanical Pipette and by Pipetting Tasks

Human Factors. 2005  |  Pubmed ID: 15960087

Work involving pipetting is associated with elevated rates of musculoskeletal disorders of the hand and wrist. The purpose of this study was to quantify thumb loading and muscle activity and determine if they varied among pipetting tasks. Fourteen experienced participants performed nine pipetting tasks while surface electromyography was measured for the extensor pollicis brevis, abductor pollicis longus, flexor pollicis longus, and abductor pollicis brevis muscles. For five tasks, participants used a pipette instrumented to measure the thumb force applied to the plunger. High-precision tasks significantly increased static muscle activity but reduced peak thumb force on average 5% as compared with low-precision tasks. Pipetting high-viscosity fluids increased peak thumb forces on average 11% as compared with pipetting low-viscosity fluids. Use of a latch pipette increased muscle activity of three muscles. We conclude that pipette design and pipetting tasks can influence applied thumb force and muscle activity. We recommend that pipettes be designed to limit applied peak forces and that pipette users be instructed in use patterns that will reduce applied forces. Actual or potential applications of this research include modifications to pipette designs and worker training in order to reduce hand pain associated with pipetting.

Pathomechanics of Peripheral Nerve Loading. Evidence in Carpal Tunnel Syndrome

Journal of Hand Therapy : Official Journal of the American Society of Hand Therapists. Apr-Jun, 2005  |  Pubmed ID: 15891983

Peripheral nerve injury is a common occurrence, with carpal tunnel syndrome (CTS) receiving the most attention. Nerve dysfunction associated with compression syndromes results from an interruption or localized interference of microvascular function due to structural changes in the nerves or surrounding tissues. This article reviews the physiologic, pathophysiologic, and histologic effects of compressing peripheral nerves in animal models, and then examines the evidence for similar processes in humans using CTS as a model.

The Effects of Finger Rest Positions on Hand Muscle Load and Pinch Force in Simulated Dental Hygiene Work

Journal of Dental Education. Apr, 2005  |  Pubmed ID: 15800259

One of the techniques taught in dental and dental hygiene programs is to use finger rests to stabilize the instrument while performing dental scaling or other types of dental work. It is believed that finger rests may also reduce muscle stress and prevent injury due to muscle fatigue. In this study the effects of three different finger rest positions on hand muscle activity and thumb pinch force were compared. Twelve predental students performed simulated dental scaling tasks on a manikin using three different finger rest positions: 1) no finger rest, 2) one finger rest, and 3) two finger rests. Muscle activity and thumb pinch force were measured by surface electromyography and a pressure sensor, respectively. Using two finger rests was always associated with reduced thumb pinch force and muscle activity, as compared to not using any finger rests (p<0.05), while using one finger rest reduced thumb pinch force and muscle activity in most cases. Hence, using finger rests plays an important role in reducing the muscle load of the hand in students performing simulated dental hygiene work. It is concluded that dental and dental hygiene students may benefit from instructions for using finger rests at an early stage of their clinical training. Including biomechanical and ergonomic principles in dental and dental hygiene curricula will raise awareness of ergonomics among dental practitioners and help them incorporate these principles into daily practice.

Carpal Tunnel Pressure Alters Median Nerve Function in a Dose-dependent Manner: a Rabbit Model for Carpal Tunnel Syndrome

Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society. Jan, 2005  |  Pubmed ID: 15607896

An in vivo animal model for carpal tunnel syndrome (CTS) is presented which allows for graded application of pressure to the median nerve within the carpal canal. We hypothesized that such pressure would cause electrophysiologic changes in the median nerve in a dose-related manner, with NCS/EMG changes consistent with CTS in humans.

Long-term Cyclical in Vivo Loading Increases Cartilage Proteoglycan Content in a Spatially Specific Manner: an Infrared Microspectroscopic Imaging and Polarized Light Microscopy Study

Arthritis Research & Therapy. 2006  |  Pubmed ID: 16956418

Understanding the changes in collagen and proteoglycan content of cartilage due to physical forces is necessary for progress in treating joint disorders, including those due to overuse. Physical forces in the chondrocyte environment can affect the cellular processes involved in the biosynthesis of extracellular matrix. In turn, the biomechanical properties of cartilage depend on its collagen and proteoglycan content. To understand changes due to physical forces, this study examined the effect of 80 cumulative hours of in vivo cyclical joint loading on the cartilage content of proteoglycan and collagen in the rabbit metacarpophalangeal joint. The forepaw digits of six anesthetized New Zealand White adult female rabbits were repetitively flexed at 1 Hz with an estimated joint contact pressure of 1 to 2 MPa. Joints were collected from loaded and contralateral control specimens, fixed, decalcified, embedded, and thin-sectioned. Sections were examined under polarized light microscopy to identify and measure superficial and mid zone thicknesses of cartilage. Fourier Transform Infrared microspectroscopy was used to measure proteoglycan and collagen contents in the superficial, mid, and deep zones. Loading led to an increase in proteoglycan in the cartilage of all six rabbits. Specifically, there was a 46% increase in the cartilage deep zone (p = 0.003). The collagen content did not change with loading. Joint loading did not change the superficial and mid zone mean thicknesses. We conclude that long-term (80 cumulative hours) cyclical in vivo joint loading stimulates proteoglycan synthesis. Furthermore, stimulation is localized to cartilage regions of high hydrostatic pressure. These data may be useful in developing interventions to prevent overuse injuries or in developing therapies to improve joint function.

Workplace Interventions to Prevent Musculoskeletal and Visual Symptoms and Disorders Among Computer Users: a Systematic Review

Journal of Occupational Rehabilitation. Sep, 2006  |  Pubmed ID: 16933148

The literature examining the effects of workstation, eyewear and behavioral interventions on musculoskeletal and visual symptoms among computer users is large and heterogeneous.

The Effects of Periodontal Instrument Handle Design on Hand Muscle Load and Pinch Force

Journal of the American Dental Association (1939). Aug, 2006  |  Pubmed ID: 16873329

In comparison with people in other occupations, dentists and dental hygienists are at increased risk of developing work-related musculoskeletal disorders, including carpal tunnel syndrome. An important risk factor in dental practice is forceful pinching, which occurs during dental scaling. Ergonomically designed dental instruments may help reduce the prevalence of MSDs among dental practitioners.

In Vivo Flexor Tendon Forces Increase with Finger and Wrist Flexion During Active Finger Flexion and Extension

Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society. Apr, 2006  |  Pubmed ID: 16514639

The effects of different hand motions and positions used during early protected motion rehabilitation on tendon forces are not well understood. The goal of this study was to determine in vivo forces in human flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) tendons of the index finger during active unresisted finger flexion and extension. During open carpal tunnel surgery (n = 12), flexor tendon forces were acquired with buckle force transducers, and finger positions were recorded on video while subjects actively flexed and extended the fingers at two different wrist angles. Mean in vivo FDP tendon forces varied between 1.3N +/- 0.9 N and 4.0 N +/- 2.9 N while mean FDS tendon forces ranged from 1.3N +/- 0.5 N to 8.5 N +/- 10.7 N. FDP force increased with active finger flexion at both wrist angles of 0 degrees or 30 degrees flexion. FDS force increased with finger flexion when the wrist was in 30 degrees flexion, but was unchanged when the wrist was in 0 degrees of flexion. Tendon forces were similar regardless of whether the fingers were moving in the flexion or extension direction. Active finger flexion and extension with the wrist at 0 degrees and 30 degrees flexion may be used during early rehabilitation protocols with limited risk of repair rupture. This risk can be further decreased for a FDS tendon repair by reducing wrist flexion angle.

VEGF, VEGFR-1, and CTGF Cell Densities in Tendon Are Increased with Cyclical Loading: An in Vivo Tendinopathy Model

Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society. Mar, 2006  |  Pubmed ID: 16479573

Tendon injuries can occur in athletes and workers whose tasks involve repetitive, high-force hand activities, but the early pathophysiologic processes of tendinopathy are not well known. The purpose of this animal study was to evaluate the effects of cyclical tendon loading on the densities of cells producing growth factors such as vascular endothelial growth factor (VEGF), its receptor, vascular endothelial growth factor receptor 1 (VEGFR-1), and connective tissue growth factor (CTGF) in the Flexor Digitorum Profundus (FDP) tendon at the epicondyle. The FDP muscles of nine New Zealand rabbits were electrically stimulated to contract repetitively for 80 h of cumulative loading over 14 weeks. The contralateral limbs served as controls. The tendons at the medial epicondyle insertion sites were harvested, and sections were immunostained with antibodies directed against VEGF, VEGFR-1, or CTGF. Positive-staining cells were counted in six regions of interest: three along the enthesis, and three corresponding regions 1500 microns distal to the enthesis. VEGF (p = 0.0001), VEGFR-1 (p = 0.046), and CTGF (p = 0.0001) cell densities were increased in the tendon of the loaded limb compared to the nonloaded limb. In addition, regional differences in VEGF, VEGFR-1, and CTGF cell densities were found. VEGF, VEGFR-1, and CTGF are increased in tendon experiencing cyclical loading and may play a role in the early vascular changes in the progression to tendinosis.

Measuring the Physical Demands of Work in Hospital Settings: Design and Implementation of an Ergonomics Assessment

Applied Ergonomics. Sep, 2006  |  Pubmed ID: 16226213

Assessing the physical demands of the heterogeneous jobs in hospitals requires appropriate and validated assessment methodologies.

DEVELOPMENT AND EVALUATION OF A NEW DEVICE FOR OVERHEAD DRILLING

Professional Safety. Nov, 2007  |  Pubmed ID: 19079737

Drilling overhead into concrete is a strenuous task that is associated with shoulder, arm, neck and back musculoskeletal disorders due to the forceful and awkward aspects of the work. This common task is done to hang pipes, ducts and trays and is performed by construction workers in the electrical, pipe fitting, sheet metal, ironwork and carpentry trades. In this project, alternative devices for overhead drilling were developed in order to reduce the high shoulder loads. The design premise for the alternative devices was adopted from interventions developed on construction sites. These devices were evaluated for usability, productivity, and fatigue in two rounds of testing by 30 construction workers performing their usual overhead drilling. After each round of testing the device designs were modified based on feedback. The final design was associated with much less arm fatigue but similar productivity compared to the usual method for overhead drilling. The feedback, design suggestions and field testing by experienced construction workers was vital to the successful development of these devices. Field testing were done with real tasks, in diverse field settings, with subjects familiar with the task. Multiple rounds of field testing and redesign can significantly improve the safety and usability of new tools. Having experienced workers accessing the new tools can help with determining if and how a new tool is compatible and beneficial to current work practices.

The Effects of Visual Display Distance on Eye Accommodation, Head Posture, and Vision and Neck Symptoms

Human Factors. Oct, 2007  |  Pubmed ID: 17915601

Determine the effects of display viewing distance on both the visual and musculoskeletal systems while the text height is held constant across viewing distances.

Evaluation of a Dynamic Arm Support for Seated and Standing Tasks: a Laboratory Study of Electromyography and Subjective Feedback

Ergonomics. Apr, 2007  |  Pubmed ID: 17575713

The goal of this study was to determine whether a new dynamic arm support system reduced shoulder and arm muscle load for seated and standing hand/ arm tasks. The new system provides support for both horizontal and vertical arm motion. A total of 11 participants performed ten tasks (five seated and five standing) both with and without the arm support. Outcomes were assessed with electromyography and subjective feedback. Muscle activity was measured over the dominant side supraspinatus, triceps and forearm extensor muscles. Significant (p < 0.01) reductions in static muscle activity were observed in one of ten tasks performed with the support device for the supraspinatus muscle, in five tasks for the triceps and in one task for forearm extensor muscles. Likewise, a significant improvement in subjective measures was reported with the support device for 'ease of task' for two of ten tasks, for 'forearm comfort' for three of ten tasks and for 'shoulder effort' for six of ten tasks. The results suggest that a dynamic forearm support may improve subjective comfort and reduce static muscle loads in the upper extremity for tasks that involve horizontal movement of the arms. For rapid motions, the value of the support is limited due to internal inertia and friction.

A Multi-method Study Evaluating Computing-related Risk Factors Among College Students

Work (Reading, Mass.). 2007  |  Pubmed ID: 17522450

To characterize undergraduate computer use using different data collection methods, emphasizing computing-related postures, use patterns and upper extremity musculoskeletal symptoms.

Work-organizational and Personal Factors Associated with Upper Body Musculoskeletal Disorders Among Sewing Machine Operators

Occupational and Environmental Medicine. May, 2007  |  Pubmed ID: 17522131

OBJECTIVE: To assess the contribution of work-organizational and personal factors to the prevalence of work-related musculoskeletal disorders (WMSDs) among garment workers in Los Angeles. METHODS: This is a cross-sectional study of self-reported musculoskeletal symptoms among 520 sewing machine operators from 13 garment industry sewing shops. Detailed information on work-organizational factors, personal factors, and musculoskeletal symptoms were obtained in face-to-face interviews. The outcome of interest, upper body WMSD, was defined as a worker experiencing moderate or severe musculoskeletal pain. Unconditional logistic regression models were adopted to assess the association between both work-organizational factors and personal factors and the prevalence of musculoskeletal pain. RESULTS: The prevalence of moderate or severe musculoskeletal pain in the neck/shoulder region was 24.0% and for distal upper extremity it was 15.8%. Elevated prevalence of upper body pain was associated with age less than 30 years, female gender, Hispanic ethnicity, being single, having a diagnosis of a MSD or a systemic illness, working more than 10 years as a sewing machine operator, using a single sewing machine, work in large shops, higher work-rest ratios, high physical exertion, high physical isometric loads, high job demand, and low job satisfaction. CONCLUSION: Work-organizational and personal factors were associated with increased prevalence of moderate or severe upper body musculoskeletal pain among garment workers. Owners of sewing companies may be able to reduce or prevent WMSDs among employees by adopting rotations between different types of workstations thus, increasing task variety; by either shortening work periods or increasing rest periods to reduce the work-rest ratio; and by improving the work organization to control psychosocial stressors. The findings may guide prevention efforts in the garment sector and have important public health implications for this workforce of largely immigrant laborers.

Effect of Repetition Rate on the Formation of Microtears in Tendon in an in Vivo Cyclical Loading Model

Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society. Sep, 2007  |  Pubmed ID: 17516500

We reported previously the formation of microtears in an in vivo loaded Flexor Digitorum Profundus (FDP) rabbit tendon with a repetition rate of 60 repetitions per minute and a peak force of 15% of maximum peak tetanic force for 80 cumulative hours. Tear area as a percent of tendon area, tear density (tears/mm(2)), and mean tear size (microm(2)) were higher in tendons from the loaded limb compared to the unloaded control limb. The purpose of the present study was to compare those results to results obtained with a repetition rate of 10 while maintaining the same peak force and force-time integral (n = 8). Due to a strain gradient between the inner and outer sides of the FDP tendon, microtears were quantified in four regions, two regions each along the inner and outer sides of the tendon. The tear area as a percent of total tendon area and the mean tear size were significantly greater in the loaded limb compared to the unloaded limb (p < 0.03). However, the effects were less than those observed at 60 repetitions/min. The higher repetition loading pattern resulted in an increase in tear measures in all four regions, while the lower rate produced changes only in the outer regions of the tendon. This finding may establish where the initial sites of damage occur in tendons that insert into bone in a similar arrangement as the FDP. The results suggest that repetition rate or number of loading cycles is associated with increased tendon microtears or fragility in a dose-response pattern.

A Randomized Controlled Trial Evaluating the Effects of New Task Chairs on Shoulder and Neck Pain Among Sewing Machine Operators: the Los Angeles Garment Study

Spine. Apr, 2007  |  Pubmed ID: 17450065

This is a 4-month randomized controlled trial to evaluate the effect of chair design on neck/shoulder pain among sewing machine operators.

In Vitro System for Applying Cyclic Loads to Connective Tissues Under Displacement or Force Control

Annals of Biomedical Engineering. Jul, 2007  |  Pubmed ID: 17385043

Overuse is thought to be the primary cause of chronic tendon injuries, in which forceful or repetitive loading results in an accumulation of micro-tears leading to a maladaptive repair response. In vitro organ culture models provide a useful method for examining how specific loading patterns affect the cellular response to load which may explain the early mechanisms of tissue injury associated with tendinopathies and ligament injuries. We designed a novel tissue loading system which employs closed-loop force feedback, capable of loading six tissue samples independently under force or displacement control. The system was capable of applying loads up to 40 N at rates of 100 N s(-1) and frequencies of 2 Hz, well above loads and rates measured in rabbit tendons in vivo. Loading parameters such as amplitude, rate, and frequency can be controlled while biomechanical factors such as creep, force relaxation, tangent modulus and Young's modulus can be assessed. The system can be used to examine the relationship between each loading parameter and biomechanical factors of connective tissues maintained in culture which may provide useful information regarding the etiology of overuse injuries.

Guidelines for Wrist Posture Based on Carpal Tunnel Pressure Thresholds

Human Factors. Feb, 2007  |  Pubmed ID: 17315846

To develop work guidelines for wrist posture based on carpal tunnel pressure. Background: Wrist posture is considered a risk factor for distal upper extremity musculoskeletal disorders, and sustained wrist deviation from neutral at work may be associated with carpal tunnel syndrome. However, the physiologic basis for wrist posture guidelines at work is limited.

Pinch Forces and Instrument Tip Forces During Periodontal Scaling

Journal of Periodontology. Jan, 2007  |  Pubmed ID: 17199545

The prevalence of upper-extremity musculoskeletal disorders, such as tendinitis, is elevated among dental practitioners. An important risk factor for these disorders is forceful pinching; however, the pinch forces and instrument forces during scaling are unknown.

Finger Flexor Motor Control Patterns During Active Flexion: an in Vivo Tendon Force Study

Human Movement Science. Feb, 2007  |  Pubmed ID: 17173995

An in vivo tendon force measurement system was used to evaluate index finger flexor motor control patterns during active finger flexion. During open carpal tunnel release surgery (N=12) the flexor digitorum profundus (FDP) and flexor digitorum superficilias (FDS) tendons were instrumented with buckle force transducers and participants performed finger flexion at two different wrist angles (0 degrees or 30 degrees ). During finger flexion, there was concurrent change of metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joint angles, but the FDP and FDS tendon force changes were not concurrent. For the FDS tendon, no consistent changes in force were observed across participants at either wrist angle. For the FDP tendon, there were two force patterns. With the wrist in a neutral posture, the movement was initiated without force from the finger flexors, and further flexion (after the first 0.5s) was carried out with force from the FDP. With the wrist in a flexed posture, the motion was generally both initiated and continued using FDP force. At some wrist postures, finger flexion was initiated by passive forces which were replaced by FDP force to complete the motion.

The Effect of Tool Handle Shape on Hand Muscle Load and Pinch Force in a Simulated Dental Scaling Task

Applied Ergonomics. Sep, 2007  |  Pubmed ID: 17156742

Work-related upper extremity musculoskeletal disorders, including carpal tunnel syndrome, are prevalent among dentists and dental hygienists. An important risk factor for developing these disorders is forceful pinching which occurs during periodontal work such as dental scaling. Ergonomically designed dental scaling instruments may help reduce the prevalence of carpal tunnel syndrome among dental practitioners. In this study, eight custom-designed dental scaling instruments with different handle shapes were used by 24 dentists and dental hygienists to perform a simulated tooth scaling task. The muscle activity of two extensors and two flexors in the forearm was recorded with electromyography while thumb pinch force was measured by pressure sensors. The results demonstrated that the instrument handle with a tapered, round shape and a 10 mm diameter required the least muscle load and pinch force when performing simulated periodontal work. The results from this study can guide dentists and dental hygienists in selection of dental scaling instruments.

A Biomechanical Analysis of Applied Pinch Force During Periodontal Scaling

Journal of Biomechanics. 2007  |  Pubmed ID: 17052721

One of the factors associated with the high prevalence of upper extremity musculoskeletal disorders, such as carpal tunnel syndrome, among dental practitioners is the repeated high pinch force applied during periodontal scaling. The goal of this study was to determine the relationship between the pinch force applied during periodontal scaling and the forces generated at the tip of the tool. A linear biomechanical model that incorporated tool reaction forces and a calculated safety margin was created to predict the pinch force applied by experienced and inexperienced dentists during periodontal scaling. Six dentists and six dental students used an instrumented scaling tool while performing periodontal scaling on patients. Thumb pinch force was measured by a pressure sensor, while the forces developed at the instrument tip were measured by a six-axis load cell. A biomechanical model was used to calculate a safety factor and to predict the applied pinch force. For experienced dentists, the model was moderately successful in predicting pinch force (R(2)=0.59). For inexperienced dentists, the model failed to predict peak pinch force (R(2)=0.01). The mean safety margin was higher for inexperienced (4.88+/-1.58) than experienced (3.35+/-0.55) dentists, suggesting that students apply excessive force during scaling.

The Effect of Six Keyboard Designs on Wrist and Forearm Postures

Applied Ergonomics. May, 2007  |  Pubmed ID: 16806042

There is increasing evidence that alternative geometry keyboards may prevent or reduce arm pain or disorders, and presumably the mechanism is by reducing awkward arm postures. However, the effect of alternative keyboards, especially the new designs, on wrist and arm postures are not well known. In this laboratory study, the wrist and forearm postures of 100 subjects were measured with a motion analysis system while they typed on 6 different keyboard configurations. There were significant differences in wrist extension, ulnar deviation, and forearm pronation between keyboards. When considering all 6 wrists and forearm postures together, the keyboard with an opening angle of 12 degrees , a gable angle of 14 degrees , and a slope of 0 degrees appears to provide the most neutral posture among the keyboards tested. Subjects most preferred this keyboard or a similar keyboard with a gable angle of 8 degrees and they least preferred the keyboard on a conventional laptop computer. These findings may assist in recommendations regarding the selection of keyboards for computer usage.

Effect of Dental Tool Surface Texture and Material on Static Friction with a Wet Gloved Fingertip

Journal of Biomechanics. 2007  |  Pubmed ID: 16524584

Hand injuries are an important cause of pain and disability among dentists and dental hygienists and may be due to the high pinch forces involved in periodontal work. The pinch forces required to perform scaling may be reduced by increasing the friction between the tool and fingers. The purpose of this study was to determine whether modifying the tool material, surface texture, or glove type altered the coefficient of static friction for a wet gloved finger. Seven tools with varying surface topography were machined from 13 mm diameter stainless steel and Delrin and mounted to a 6-component force plate. The textures tested were a fine, medium and coarse diamond knurled pattern and a medium and fine annular pattern (concentric rings). Thirteen subjects pulled their gloved, wet thumb pad along the long axis of the tool while maintaining a normal force of 40 N. Latex and nitrile gloves were tested. The coefficient of static friction was calculated from the shear force history. The mean coefficients of static friction ranged from 0.20 to 0.65. The coefficient of static friction was higher for a smooth tool of Delrin than one of stainless steel. Differences in the coefficient of static friction were observed between the coarse and medium knurled patterns and the fine knurled and annular patterns. Coefficients of static friction were higher for the nitrile glove than the latex glove for tools with texture. These findings may be applied to the design of hand tools that require fine motor control with a wet, gloved hand.

Accessibility of Radiology Equipment for Patients with Mobility Disabilities

Human Factors. Oct, 2008  |  Pubmed ID: 19110840

The purpose was to evaluate accessibility of typical radiology platforms by participants with mobility disabilities.

The Split Keyboard: an Ergonomics Success Story

Human Factors. Jun, 2008  |  Pubmed ID: 18689043

The author reviews the paper by Kroemer (1972) on the design of the split geometry keyboard and the subsequent 35 years of research on the topic.

Intensive Keyboard Use and Carpal Tunnel Syndrome: Comment on the Article by Atroshi Et Al

Arthritis and Rheumatism. Jun, 2008  |  Pubmed ID: 18512800

Effect of Wrist Posture on Carpal Tunnel Pressure While Typing

Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society. Sep, 2008  |  Pubmed ID: 18383144

Long weekly hours of keyboard use may lead to or aggravate carpal tunnel syndrome. The effects of typing on fluid pressure in the carpal tunnel, a possible mediator of carpal tunnel syndrome, are unknown. Twenty healthy subjects participated in a laboratory study to investigate the effects of typing at different wrist postures on carpal tunnel pressure of the right hand. Changes in wrist flexion/extension angle (p = 0.01) and radial/ulnar deviation angle (p = 0.03) independently altered carpal tunnel pressure; wrist deviations in extension or radial deviation were associated with an increase in pressure. The activity of typing independently elevated carpal tunnel pressure (p = 0.001) relative to the static hand held in the same posture. This information can guide the design and use of keyboards and workstations in order to minimize carpal tunnel pressure while typing. The findings may also be useful to clinicians and ergonomists in the management of patients with carpal tunnel syndrome who use a keyboard.

A Three-dimensional Anthropometric Solid Model of the Hand Based on Landmark Measurements

Ergonomics. Apr, 2008  |  Pubmed ID: 18357538

Hand anthropometry data are largely based on measurements of the hand in an outstretched hand posture and are, therefore, difficult to apply to tool gripping hand postures. The purpose of this project was to develop a representative, scalable hand model to be used with 3-D software drawing packages to aid in the ergonomic design of hand tools. Landmarks (66) on the palmar surface of the right hand of 100 subjects were digitised in four functional hand postures and, from these, 3-D surface models of a mean, 25th and 75th% hand were developed. The root mean square differences in hand length between the hand model and the digitised data for the 25th, 50th and 75th percentile hand were 11.4, 3.2 and 8.9 mm, respectively. The corresponding values for hand breadth were 2.0, 0.4 and 1.4 mm. There was good agreement between distances on the digitised hand and the hand model. The application of this research includes improved ergonomic hand tool design through the use of hand anthropometry reference values developed from the general population using grasping hand postures.

A Randomized Controlled Trial of Chair Interventions on Back and Hip Pain Among Sewing Machine Operators: the Los Angeles Garment Study

Journal of Occupational and Environmental Medicine / American College of Occupational and Environmental Medicine. Mar, 2008  |  Pubmed ID: 18332775

Determine whether an adjustable chair with a curved or a flat seat pan improved monthly back and hip pain scores in sewing machine operators.

MMP-1, IL-1beta, and COX-2 MRNA Expression is Modulated by Static Load in Rabbit Flexor Tendons

Annals of Biomedical Engineering. Feb, 2008  |  Pubmed ID: 18172766

Tendon cells respond to their mechanical environment by synthesizing and degrading the surrounding matrix. This study examined how expression of genes associated with tendon degeneration is affected by static loads. Forty flexor tendons from 10 New Zealand White rabbits were harvested and secured in a tissue loading system. A static load of 0, 2, 4, or 6 MPa was applied to tendons for 20 h. MMP-1, IL-1beta, COX-2, GAPDH, and 18s mRNA expression was measured by qRT-PCR. MMP-1 expression in tendons loaded to 6 MPa was significantly increased 259% compared to tendons loaded to 4 MPa. Relative to a 0 MPa load, IL-1beta expression was inhibited with load at 4 MPa (48%) while COX-2 expression was increased at 6 MPa (219%). A polynomial regression analysis found a significant positive correlation between creep and expression of MMP-1 (R(2) = 0.53, p < 0.001) and IL-1beta (R(2) = 0.55, p < 0.001). The results of this study indicate that moderate load inhibits IL-1beta and high load stimulates COX-2 relative to stress shielding. MMP-1 expression is up-regulated with high loads compared to moderate loads. The correlation between creep and expression suggests that the pathway for MMP-1 and IL-1beta expression, leading eventually to tendon degeneration, may be regulated by the biomechanical factor creep.

Evaluation of Gene Expression Through QRT-PCR in Cyclically Loaded Tendons: an in Vivo Model

European Journal of Applied Physiology. Feb, 2008  |  Pubmed ID: 17922137

An in vivo rabbit animal model for the tendinopathy, epicondylitis, was used to examine the effects of repetitive load on the expression of various genes associated with matrix remodeling. Following 80 h of cumulative load, tissue from the distal and proximal regions of the flexor digitorum profundus tendon was collected. Quantitative RT-PCR was used to asses mRNA levels of collagenase-1 (MMP-1), stromelysin (MMP-3), vascular endothelial growth factor (VEGF), connective tissue growth factor (CTGF), cyclooxygenase-2 (COX-2), interleukin-1beta (IL-1beta), type III collagen (COL-III) and fibronectin (FBRN). No significant differences in expression levels were found between loaded and unloaded limbs at either region of the tendon. The findings were unexpected as the same model has already demonstrated an increase in the density of cells staining for VEGF and CTGF. Different regulatory mechanisms between mRNA and protein expression or localized changes missed due to homogenization of the tissue samples, may explain the discrepancy in findings.

Cyclic Loading Inhibits Expression of MMP-3 but Not MMP-1 in an in Vitro Rabbit Flexor Tendon Model

Clinical Biomechanics (Bristol, Avon). Jan, 2008  |  Pubmed ID: 17892905

Gene expression analysis is useful for assessing cellular behavior and may improve our understanding of the initial cellular response to mechanical load leading to tendon degeneration. This study assessed gene expression of MMP-1 and MMP-3, genes associated with matrix degradation, in tendons exposed to cyclic loads within physiologic range.

Evaluation of Two Posture Survey Instruments for Assessing Computing Postures Among College Students

Work (Reading, Mass.). 2009  |  Pubmed ID: 20075519

To determine agreement between two posture assessment survey instruments and which, if any, were correlated with experiencing upper extremity musculoskeletal symptoms.

A New Method for Overhead Drilling

Ergonomics. Dec, 2009  |  Pubmed ID: 19941190

In the construction sector, overhead drilling into concrete or metal ceilings is a strenuous task associated with shoulder, neck and back musculoskeletal disorders due to the large applied forces and awkward arm postures. Two intervention devices, an inverted drill press and a foot lever design, were developed then compared to the usual method by construction workers performing their normal overhead drilling activities (n = 14). While the intervention devices were rated as less fatiguing than the usual method, their ratings on usability measures were worse than the usual method. The study demonstrates that the intervention devices can reduce fatigue; however, additional modifications are necessary in order to improve usability and productivity. Devices designed to improve workplace safety may need to undergo several rounds of field testing and modification prior to implementation.

Self-reported Pain and Physical Signs for Musculoskeletal Disorders in the Upper Body Region Among Los Angeles Garment Workers

Work (Reading, Mass.). 2009  |  Pubmed ID: 19923678

Reports of pain and physical exam findings for musculoskeletal disorders (MSDs) are two common outcome measures independently used to assess work-related MSDs in the scientific literature. How these measures correlate with each other, however, is largely unknown. We recruited 520 sewing machine operators to describe the correlation between subjective self-reported pain and physical findings of MSDs in three upper body regions including the neck/shoulder, elbow/forearm, and hand/wrist. Self-reports of pain and physical findings resulted in different and partly non-overlapping classifications of subjects as MSD cases in our study. Both outcome measures were found to be consistently associated with 'having a medical history of MSDs', 'perceived physical exertion', 'perceived job insecurity' (neck/shoulder), being of older age (arm/forearm), and female gender (arm/forearm and hand/wrist); however, we observed inconsistency for the measures for a number of other job related factors such as 'operating a single machine' and 'number of work hours per week'. Because to date no agreed upon "gold standard" for diagnosing MSDs exists, our findings suggest that research results can be very different when using self-reported measures versus physical exam findings. Also, in order to evaluate the success of an intervention, screening, or surveillance program for work related MSDs, it is important to define clearly which outcome measure best to employ.

Ergonomics and GI Endoscopy

Gastrointestinal Endoscopy. Jul, 2009  |  Pubmed ID: 19559836

The Effects of Split Keyboard Geometry on Upper Body Postures

Ergonomics. Jan, 2009  |  Pubmed ID: 19308823

Split, gabled keyboard designs can prevent or improve upper extremity pain among computer users; the mechanism appears to involve the reduction of awkward wrist and forearm postures. This study evaluated the effects of changes in opening angle, slope and height (independent variables) of a gabled (14 degrees) keyboard on typing performance and upper extremity postures. Twenty-four experienced touch typists typed on seven keyboard conditions while typing speed and right and left wrist extension, ulnar deviation, forearm pronation and elbow position were measured using a motion tracking system. The lower keyboard height led to a lower elbow height (i.e. less shoulder elevation) and less wrist ulnar deviation and forearm pronation. Keyboard slope and opening angle had mixed effects on wrist extension and ulnar deviation, forearm pronation and elbow height and separation. The findings suggest that in order to optimise wrist, forearm and upper arm postures on a split, gabled keyboard, the keyboard should be set to the lowest height of the two heights tested. Keyboard slopes in the mid-range of those tested, 0 degrees to -4 degrees, provided the least wrist extension, forearm pronation and the lowest elbow height. A keyboard opening angle in the mid-range of those tested, 15 degrees, may provide the best balance between reducing ulnar deviation while not increasing forearm pronation or elbow separation. These findings may be useful in the design of computer workstations and split keyboards. The geometry of a split keyboard can influence wrist and forearm postures. The findings of this study are relevant to the positioning and adjustment of split keyboards. The findings will also be useful for engineers who design split keyboards.

A Randomized Controlled Trial Evaluating an Alternative Mouse or Forearm Support on Change in Median and Ulnar Nerve Motor Latency at the Wrist

American Journal of Industrial Medicine. Apr, 2009  |  Pubmed ID: 19142961

The purpose of this study was to determine the effects of an alternative mouse and/or a forearm support board on nerve function at the wrist among engineers.

Pinch Force and Forearm-muscle Load During Routine Colonoscopy: a Pilot Study

Gastrointestinal Endoscopy. Jan, 2009  |  Pubmed ID: 19111694

Overuse injuries of the hand, wrist, forearm, and shoulder are common among endoscopists and may be from repetitive pinching and gripping forces or awkward posturing. In this pilot study, we evaluated distal upper-extremity musculoskeletal load during colonoscopy (1) to confirm the feasibility of performing ergonomic measurements in endoscopists and (2) to identify tasks that may contribute to overuse injuries.

The Booster Break Program: Description and Feasibility Test of a Worksite Physical Activity Daily Practice

Work (Reading, Mass.). 2010  |  Pubmed ID: 21099018

Work breaks are underutilized opportunities to promote health. The Booster Break program is a co-worker led physical activity group session devoted exclusively to standard 15-minute work breaks. The purpose of this study was to report the fidelity, attendance, feasibility, and sustainability of the Booster Break program and to explore its potential impact.

Development of a Method for Evaluating Accessibility of Medical Equipment for Patients with Disabilities

Applied Ergonomics. Dec, 2010  |  Pubmed ID: 20723883

The purpose of this study was to develop a method for evaluating accessibility of medical equipment for patients with disabilities.

Overhead Drilling: Comparing Three Bases for Aligning a Drilling Jig to Vertical

Journal of Safety Research. Jun, 2010  |  Pubmed ID: 20630276

Drilling overhead into concrete or metal ceilings is a strenuous task done by construction workers to hang ductwork, piping, and electrical equipment. The task is associated with upper body pain and musculoskeletal disorders. Previously, we described a field usability evaluation of a foot lever and inverted drill press intervention devices that were compared to the usual method for overhead drilling. Both interventions were rated as inferior to the usual method based on poor setup time and mobility.

Field Evaluation of a Modified Intervention for Overhead Drilling

Journal of Occupational and Environmental Hygiene. Apr, 2010  |  Pubmed ID: 20094939

Drilling holes into concrete or metal ceilings is one of the most physically demanding tasks performed in construction. The work is done overhead with rotary impact hammer drills that weigh up to 40 N. The task is associated with pain and musculoskeletal disorders at the wrist, forearm, shoulder, and back. The mechanism of injury is thought to be the high forces and non-neutral shoulder and wrist postures applied during drilling. Previously, we described a field study of a foot lever and inverted drill press intervention devices that received poor usability ratings compared with the usual method for overhead drilling based on problems with mobility and productivity. Using a participatory intervention model, feedback from construction workers (N = 13) was used to develop a new intervention design that incorporated a wheeled tripod base and a unique method of aligning the drilling column to vertical. A different group of construction workers (N = 23) evaluated usability and fatigue of the new device during their regular overhead drilling in comparison with the usual method. Four of 12 usability ratings were significantly better with the intervention device compared with the usual method. Subjective shoulder fatigue was less with the new intervention (1.1 vs. 3.3; scale 0 to 5; p < 0.001). This difference was supported by objective outcome measures; the mean hand forces during drilling were 26 N with the intervention compared with 245 N with the usual method. The percentage of time with the shoulder flexed or abducted to more than 60 degrees was less with the intervention compared with the usual method (21 vs. 40%; p = 0.007). There was significantly less head extension with the intervention compared with the usual method. There were no significant differences in overall productivity between the two methods. This study demonstrates that a new intervention device for overhead drilling has improved usability and subjective fatigue ratings compared with the usual method. These improvements are most likely due to the reduced hand forces, reduced shoulder abduction and flexion, and reduced drilling time.

Follow-up of Neck and Shoulder Pain Among Sewing Machine Operators: The Los Angeles Garment Study

American Journal of Industrial Medicine. Apr, 2010  |  Pubmed ID: 20017187

The aim of the present study is to explore factors affecting or modifying self-reported neck/shoulder pain in sewing machine operators.

Effort-reward Imbalance and One-year Change in Neck-shoulder and Upper Extremity Pain Among Call Center Computer Operators

Scandinavian Journal of Work, Environment & Health. Jan, 2010  |  Pubmed ID: 19967325

The literature on psychosocial job factors and musculoskeletal pain is inconclusive in part due to insufficient control for confounding by biomechanical factors. The aim of this study was to investigate prospectively the independent effects of effort-reward imbalance (ERI) at work on regional musculoskeletal pain of the neck and upper extremities of call center operators after controlling for (i) duration of computer use both at work and at home, (ii) ergonomic workstation design, (iii) physical activities during leisure time, and (iv) other individual worker characteristics.

Systematic Review of the Role of Occupational Health and Safety Interventions in the Prevention of Upper Extremity Musculoskeletal Symptoms, Signs, Disorders, Injuries, Claims and Lost Time

Journal of Occupational Rehabilitation. Jun, 2010  |  Pubmed ID: 19885644

Little is known about the most effective occupational health and safety (OHS) interventions to reduce upper extremity musculoskeletal disorders (MSDs) and injuries.

The Effect of Two Alternative Arm Supports on Shoulder and Upper Back Muscle Loading During Pipetting

Work (Reading, Mass.). 2011  |  Pubmed ID: 21673447

Pipetting involves static upper arm positions with the pipette held away from the body for sustained periods of time, putting increased musculoskeletal load on the shoulder and upper back. This study explores the effect of using two alternative arm supports while pipetting on muscle loading in the shoulder/neck region.

Ergonomic Evaluation of Ten Single-channel Pipettes

Work (Reading, Mass.). 2011  |  Pubmed ID: 21673445

Repetitive pipetting is a task that is associated with work-related musculoskeletal disorders of the hand and arm.

1st Place, PREMUS Best Paper Competition: Workplace and Individual Factors in Wrist Tendinosis Among Blue-collar Workers--the San Francisco Study

Scandinavian Journal of Work, Environment & Health. Mar, 2011  |  Pubmed ID: 21298225

Workplace studies have linked hand/wrist tendinosis to forceful and repetitive hand exertions, but the associations are not consistent. We report findings from a prospective study of right wrist tendinosis among blue-collar workers.

Evaluation and Control of Respirable Silica Exposure During Lateral Drilling of Concrete

Journal of Occupational and Environmental Hygiene. Feb, 2012  |  Pubmed ID: 22214178

The Effects of Periodontal Curette Handle Weight and Diameter on Arm Pain: a Four-month Randomized Controlled Trial

Journal of the American Dental Association (1939). Oct, 2012  |  Pubmed ID: 23024308

The design of periodontal curette handles may cause or aggravate arm pain in dental practitioners. The authors conducted a four-month randomized controlled trial to evaluate the effects of curette handle diameter and weight on arm pain among dental hygienists and dentists.

Distal Upper Extremity Musculoskeletal Risk Factors Associated with Colonoscopy

Work (Reading, Mass.). 2012  |  Pubmed ID: 22317441

Gastroenterologists are at increased risk for developing recurrent thumb, hand, and elbow pain due to colonoscopy procedures. We evaluated forearm muscle loads and wrist postures during routine colonoscopy (N=12 gastroenterologists) to understand distal upper extremity musculoskeletal risk factors associated with the 4 different subtasks of colonoscopy. Bilateral forearm extensor carpiradialis (ECR) and flexor digitorum superficialis (FDS) surface electromyography and bilateral wrist postures were recorded continuously. The mean duration of colonoscopy was 24.2 (± 12.1) minutes and was dominated by the withdrawal subtask [13.7 (± 8.8) min] followed by right colon insertion [5.8 (± 4.8) min], left colon insertion [3.5 (± 3.1) min], and retroflexion [1.2 (± 2.1) min]. Median (APDF50) and peak (APDF90) left forearm muscle activity was significantly greater than right forearm muscle activity across all subtasks. Median and peak ECR muscle activity was significantly greater during the left and right colon insertion subtasks compared to retroflexion. Both wrists were predominantly in wrist extension during all phases of colonoscopy. The left forearm muscle activity was higher than right forearm activity due to differences in wrist posture and grip force. The risk factors for the left hand may be reduced with alternative designs and support mechanisms for the colonoscope head.

Touch Displays: the Effects of Palm Rejection Technology on Productivity, Comfort, Biomechanics and Positioning

Ergonomics. 2013  |  Pubmed ID: 24134774

Direct touch displays can improve the human-computer experience and productivity; however, the higher hand locations may increase shoulder fatigue. Palm rejection (PR) technology may reduce shoulder loads by allowing the palms to rest on the display and increase productivity by registering the touched content and fingertips through the palms rather than shoulders. The effects of PR were evaluated by having participants perform touch tasks while posture and reaction force on the display were measured. Enabling PR, during which the subjects could place the palms on the display (but were not required to), resulted in increased wrist extension, force applied to the display and productivity, and less discomfort, but had no effect on the self-selected positioning of the display. Participants did not deliberately place their palms on the display; therefore, there was no reduction in shoulder load and the increased productivity was not due to improved hand registration. The increased productivity may have been due to reduced interruptions from palm contacts or reduced motor control demands.

Holding a Tablet Computer with One Hand: Effect of Tablet Design Features on Biomechanics and Subjective Usability Among Users with Small Hands

Ergonomics. 2013  |  Pubmed ID: 23909815

The purpose of this study was to evaluate tablet size (weight), orientation, grip shape, texture and stylus shape on productivity, biomechanics and subjective usability and fatigue when the tablet was held with just the left hand. A total of 15 male and 15 female subjects, ages 16-64 years, tested eight tablets and three styluses. Overall, the usability, fatigue and biomechanical evaluation of tablet design features supported the use of smaller to medium-sized tablets, with a ledge or handle shape on the back and surfaced with a rubberised texture. Larger, heavier tablets had significantly worse usability and biomechanics and their use with one hand should be limited. The stylus with a tapered grip (7.5-9.5 mm) or larger grip (7.6 mm) had better usability and biomechanics than one with a smaller grip (5 mm). There were no significant differences in productivity between design features. These design parameters may be important when designing tablets.

The Effect of Keyboard Key Spacing on Typing Speed, Error, Usability, and Biomechanics: Part 1

Human Factors. Jun, 2013  |  Pubmed ID: 23829030

In this study, we evaluated the effects of key spacing on a conventional computer keyboard on typing speed, percentage error, usability, and forearm muscle activity and wrist posture.

Pooling Job Physical Exposure Data from Multiple Independent Studies in a Consortium Study of Carpal Tunnel Syndrome

Ergonomics. 2013  |  Pubmed ID: 23697792

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

Personal and Workplace Psychosocial Risk Factors for Carpal Tunnel Syndrome: a Pooled Study Cohort

Occupational and Environmental Medicine. Aug, 2013  |  Pubmed ID: 23645610

Between 2001 and 2010, six research groups conducted coordinated multiyear, prospective studies of carpal tunnel syndrome (CTS) incidence in US workers from various industries and collected detailed subject-level exposure information with follow-up symptom, physical examination, electrophysiological measures and job changes.

Booster Breaks in the Workplace: Participants' Perspectives on Health-promoting Work Breaks

Health Education Research. Jun, 2013  |  Pubmed ID: 23466367

Increasing sedentary work has been associated with greater cardiovascular and metabolic risk, as well as premature mortality. Interrupting the sedentary workday with health-promoting work breaks can counter these negative health effects. To examine the potential sustainability of work-break programs, we assessed the acceptance of these breaks among participants in a Booster Break program. We analyzed qualitative responses from 35 participants across five worksites where one 15-min physical activity break was taken each workday. Two worksites completed a 1-year intervention and three worksites completed a 6-month intervention. Responses to two open-ended questions about the acceptance and feasibility of Booster Breaks were obtained from a survey administered after the intervention. Three themes for benefits and two themes for barriers were identified. The benefit themes were (i) reduced stress and promoted enjoyment, (ii) increased health awareness and facilitated behavior change, and (iii) enhanced workplace social interaction. The barrier themes were the need for (iv) greater variety in Booster Break routines and (v) greater management support. This study provides empirical support for the acceptance and feasibility of Booster Breaks during the workday. Emphasizing the benefits and minimizing the barriers are strategies that can be used to implement Booster Breaks in other workplaces.

Prevalence and Incidence of Carpal Tunnel Syndrome in US Working Populations: Pooled Analysis of Six Prospective Studies

Scandinavian Journal of Work, Environment & Health. Sep, 2013  |  Pubmed ID: 23423472

Most studies of carpal tunnel syndrome (CTS) incidence and prevalence among workers have been limited by small sample sizes or restricted to a small subset of jobs. We established a common CTS case definition and then pooled CTS prevalence and incidence data across six prospective studies of musculoskeletal outcomes to measure CTS frequency and allow better studies of etiology.

Exposure-response Relationships for the ACGIH Threshold Limit Value for Hand-activity Level: Results from a Pooled Data Study of Carpal Tunnel Syndrome

Scandinavian Journal of Work, Environment & Health. Nov, 2014  |  Pubmed ID: 25266844

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).

Effects of Varying Case Definition on Carpal Tunnel Syndrome Prevalence Estimates in a Pooled Cohort

Archives of Physical Medicine and Rehabilitation. Dec, 2014  |  Pubmed ID: 25175160

To analyze differences in carpal tunnel syndrome (CTS) prevalence using a combination of electrodiagnostic studies (EDSs) and symptoms using EDS criteria varied across a range of cutpoints and compared with symptoms in both ≥1 and ≥2 median nerve-served digits.

The Effect of Keyboard Key Spacing on Typing Speed, Error, Usability, and Biomechanics, Part 2: Vertical Spacing

Human Factors. Jun, 2014  |  Pubmed ID: 25029899

The objective was to evaluate the effects of vertical key spacing on a conventional computer keyboard on typing speed, percentage error, usability, forearm muscle activity, and wrist posture for both females with small fingers and males with large fingers.

0383 Use of an O*NET Based Job Exposure Matrix to Predict Prevalence of Carpal Tunnel Syndrome in a Large Pooled Cohort

Occupational and Environmental Medicine. Jun, 2014  |  Pubmed ID: 25018376

To determine if job title based physical exposure measures predicted prevalent carpal tunnel syndrome (CTS) in a large pooled cohort of workers.

0323  Workplace Psychosocial Risk Factors for Carpal Tunnel Syndrome: a Pooled Prospective Study0323  Workplace Psychosocial Risk Factors for Carpal Tunnel Syndrome: a Pooled Prospective Study

Occupational and Environmental Medicine. Jun, 2014  |  Pubmed ID: 25018350

Seven research groups conducted coordinated studies of carpal tunnel syndrome (CTS). In this analysis of the pooled cohort, we estimate associations of workplace psychosocial factors and CTS incidence with adjustment for biomechanical factors.

Meta-analysis: Association Between Wrist Posture and Carpal Tunnel Syndrome Among Workers

Safety and Health at Work. Mar, 2014  |  Pubmed ID: 24932417

Carpal tunnel syndrome (CTS) is a common work-related peripheral neuropathy. In addition to grip force and repetitive hand exertions, wrist posture (hyperextension and hyperflexion) may be a risk factor for CTS among workers. However, findings of studies evaluating the relationship between wrist posture and CTS are inconsistent. The purpose of this paper was to conduct a meta-analysis of existing studies to evaluate the evidence of the relationship between wrist posture at work and risk of CTS.

Effect of Font Size and Glare on Computer Tasks in Young and Older Adults

Optometry and Vision Science : Official Publication of the American Academy of Optometry. Jun, 2014  |  Pubmed ID: 24830373

At a fixed viewing distance (VD), reading speed increases with print size. It is not known if this holds for computer tasks when postures are not constrained. Reflective glare on a monitor may reduce productivity. The effects of both may be modified by age. We evaluated effects of age, font size, and glare on performance for visually demanding text-based tasks on a computer.

The Impact of Posture on Wrist Tendinosis Among Blue-collar Workers: the San Francisco Study

Human Factors. Feb, 2014  |  Pubmed ID: 24669549

The objective was to evaluate the effect of wrist posture on incidence of wrist tendinosis in a prospective cohort of blue-collar workers.

Personal and Workplace Psychosocial Risk Factors for Carpal Tunnel Syndrome: a Pooled Study Cohort: Author Response

Occupational and Environmental Medicine. Apr, 2014  |  Pubmed ID: 24503336

Associations Between Workplace Factors and Carpal Tunnel Syndrome: A Multi-site Cross Sectional Study

American Journal of Industrial Medicine. May, 2015  |  Pubmed ID: 25778111

Few large epidemiologic studies have used rigorous case criteria, individual-level exposure measurements, and appropriate control for confounders to examine associations between workplace psychosocial and biomechanical factors and carpal tunnel syndrome (CTS).

General Population Job Exposure Matrix Applied to a Pooled Study of Prevalent Carpal Tunnel Syndrome

American Journal of Epidemiology. Mar, 2015  |  Pubmed ID: 25700886

A job exposure matrix may be useful for the study of biomechanical workplace risk factors when individual-level exposure data are unavailable. We used job title-based exposure data from a public data source to construct a job exposure matrix and test exposure-response relationships with prevalent carpal tunnel syndrome (CTS). Exposures of repetitive motion and force from the Occupational Information Network were assigned to 3,452 active workers from several industries, enrolled between 2001 and 2008 from 6 studies. Repetitive motion and force exposures were combined into high/high, high/low, and low/low exposure groupings in each of 4 multivariable logistic regression models, adjusted for personal factors. Although force measures alone were not independent predictors of CTS in these data, strong associations between combined physical exposures of force and repetition and CTS were observed in all models. Consistent with previous literature, this report shows that workers with high force/high repetition jobs had the highest prevalence of CTS (odds ratio = 2.14-2.95) followed by intermediate values (odds ratio = 1.09-2.27) in mixed exposed jobs relative to the lowest exposed workers. This study supports the use of a general population job exposure matrix to estimate workplace physical exposures in epidemiologic studies of musculoskeletal disorders when measures of individual exposures are unavailable.

Personal and Workplace Factors and Median Nerve Function in a Pooled Study of 2396 US Workers

Journal of Occupational and Environmental Medicine / American College of Occupational and Environmental Medicine. Jan, 2015  |  Pubmed ID: 25563546

Evaluate associations between personal and workplace factors and median nerve conduction latency at the wrist.

Lateral Epicondylitis: New Evidence for Work Relatedness

Joint, Bone, Spine : Revue Du Rhumatisme. Jan, 2015  |  Pubmed ID: 25553834

Developing a Pooled Job Physical Exposure Data Set from Multiple Independent Studies: an Example of a Consortium Study of Carpal Tunnel Syndrome

Occupational and Environmental Medicine. Feb, 2015  |  Pubmed ID: 25504866

Six research groups independently conducted prospective studies of carpal tunnel syndrome (CTS) incidence in 54 US workplaces in 10 US States. Physical exposure variables were collected by all research groups at the individual worker level. Data from these research groups were pooled to increase the exposure spectrum and statistical power.

A Frequency-duty Cycle Equation for the ACGIH Hand Activity Level

Ergonomics. 2015  |  Pubmed ID: 25343340

A new equation for predicting the hand activity level (HAL) used in the American Conference for Government Industrial Hygienists threshold limit value®(TLV®) was based on exertion frequency (F) and percentage duty cycle (D). The TLV® includes a table for estimating HAL from F and D originating from data in Latko et al. (Latko WA, Armstrong TJ, Foulke JA, Herrin GD, Rabourn RA, Ulin SS, Development and evaluation of an observational method for assessing repetition in hand tasks. American Industrial Hygiene Association Journal, 58(4):278-285, 1997) and post hoc adjustments that include extrapolations outside of the data range. Multimedia video task analysis determined D for two additional jobs from Latko's study not in the original data-set, and a new nonlinear regression equation was developed to better fit the data and create a more accurate table. The equation, HAL = 6:56 ln D[F(1:31) /1+3:18 F(1:31), generally matches the TLV® HAL lookup table, and is a substantial improvement over the linear model, particularly for F>1.25 Hz and D>60% jobs. The equation more closely fits the data and applies the TLV® using a continuous function.

A Hand Speed-duty Cycle Equation for Estimating the ACGIH Hand Activity Level Rating

Ergonomics. 2015  |  Pubmed ID: 25343278

An equation was developed for estimating hand activity level (HAL) directly from tracked root mean square (RMS) hand speed (S) and duty cycle (D). Table lookup, equation or marker-less video tracking can estimate HAL from motion/exertion frequency (F) and D. Since automatically estimating F is sometimes complex, HAL may be more readily assessed using S. Hands from 33 videos originally used for the HAL rating were tracked to estimate S, scaled relative to hand breadth (HB), and single-frame analysis was used to measure D. Since HBs were unknown, a Monte Carlo method was employed for iteratively estimating the regression coefficients from US Army anthropometry survey data. The equation: HAL = 10[e(-15:87+0:02D+2:25 ln S)/(1+e(-15:87+0:02D+2:25 ln S)], R(2) = 0.97, had a residual range ± 0.5 HAL. The S equation superiorly fits the Latko et al. ( 1997 ) data and predicted independently observed HAL values (Harris 2011) better (MSE = 0.16) than the F equation (MSE = 1.28).

Biomechanical Risk Factors for Carpal Tunnel Syndrome: a Pooled Study of 2474 Workers

Occupational and Environmental Medicine. Jan, 2015  |  Pubmed ID: 25324489

Between 2001 and 2010, five research groups conducted coordinated prospective studies of carpal tunnel syndrome (CTS) incidence among US workers from various industries and collected detailed subject-level exposure information with follow-up of symptoms, electrophysiological measures and job changes.

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