Kari Babski-Reeves

Effects of psychosocial and individual factors on physiological risk factors for upper extremity musculoskeletal disorders while typing

Psychosocial factors are hypothesized to contribute to work-related musculoskeletal disorder (WMSD) development, although previous research has been largely epidemiological or has focused primarily on the shoulders, back and neck. The objective of this study was to quantify the effects of mental workload and time pressure on perceived workload and physiological responses of the distal upper extremity. A total of 18 typists completed nine 5-min typing sessions representing three levels of time pressure and mental workload. Levels were manipulated by adjusting typing speed and by requiring participants to perform arithmetic tasks while typing. Outcomes were measured in muscle activation levels, wrist postures and movements, key strike force and subjective assessments of workload. In general, increased time pressure increased muscle activation, key strike force and wrist deviations; and increased mental workload increased key strike force. Mental workload and time pressure mediated physical risk factors during typing to increase WMSD risk for the distal upper extremity.

Infrared imaging of the anterior deltoid during overhead static exertions

Infrared imaging has been used to detect the presence of neuromuscular disorders of the cervical spine and upper extremities. Despite diagnostic uses, evaluative or prognostic uses of thermography are limited. The objective of this study was to quantify surface temperature changes over the anterior deltoid and evaluate efficacy of thermography as an assessment tool. Surface temperature, discomfort ratings and endurance time were quantified during overhead static exertions until exhaustion at two work loads (15 and 30% maximum voluntary contraction) and shoulder angles (90° and 115°). Ten participants free of confounding conditions participated in the study. The 90° shoulder angle and 30% exertion level resulted in significantly faster thermal image rates of change, shorter endurance times and faster perceived discomfort increases. Thermography readings were more sensitive to changes in shoulder posture than load changes. This study provides preliminary evidence that thermography may be a useful exposure assessment tool. There is a need for new evaluation tools to quantify risk factor exposure for injury. Thermography was sensitive to changes in task loadings, illustrating its potential use for risk assessment. Specifically, changes in observed blood flow patterns during task performance are likely to conform to known physiological responses to injury.

Effects of portable computing devices on posture, muscle activation levels and efficiency

Very little research exists on ergonomic exposures when using portable computing devices. This study quantified muscle activity (forearm and neck), posture (wrist, forearm and neck), and performance (gross typing speed and error rates) differences across three portable computing devices (laptop, netbook, and slate computer) and two work settings (desk and computer) during data entry tasks. Twelve participants completed test sessions on a single computer using a test-rest-test protocol (30min of work at one work setting, 15min of rest, 30min of work at the other work setting). The slate computer resulted in significantly more non-neutral wrist, elbow and neck postures, particularly when working on the sofa. Performance on the slate computer was four times less than that of the other computers, though lower muscle activity levels were also found. Potential or injury or illness may be elevated when working on smaller, portable computers in non-traditional work settings.

The use of continuous exposure data for predicting CTS in fish processing operators

Carpal tunnel syndrome (CTS) remains one of the most commonly reported and studied work related musculoskeletal disorders. Categorical representations of exposures has been critical in identifying associations between risk factors and CTS, however, quantification of exposure—response relationships require using continuous exposure data. Also, few interactions between risk factors, especially between risk factor categories, have been investigated. The objectives of this study were to investigate the utility of using continuous exposure data and to identify interaction effects of risk factors, both within and between risk factor categories, for predicting CTS. A cross sectional study was performed at a fish processing facility in which 53 participants were evaluated during normal task performance. Due to task asymmetry, each hand was considered separately, providing 106 hands for analysis. Direct measurement and a questionnaire were used to quantify exposures to common occupational and personal risk factors. Stepwise logistic regression analysis was performed to identify three models for predicting CTS and assess predictive ability using: occupational risk factors only (three-way interactions considered), personal risk factors only (two-way interactions considered), and a mixed model considering two-way interactions across risk factor categories and previously identified significant interactions. Models including only occupational or personal risk factors were moderately accurate overall (73% and 77% respectively), but were not sensitive in differentiating between CTS cases and non-cases (39% and 33% respectively). The mixed model was found to be accurate (88%) and sensitive (78%), though only one interaction effect was included. The results of this study illustrate the importance of using continuous exposure data, especially in job tasks where exposures to occupational risk factors is similar, when differentiating between high and low risk job tasks.

Reverse 911 as a Complementary Evacuation Warning System

This study investigates the effectiveness of Reverse 911 warning systems compared with other evacuation warning sources. This study also investigates the impact of individual differences on evacuation behavior, and presents a regression model of evacuation behavior on the basis of empirical data. A 57 question survey was administered by telephone to people who had been affected by the 2007 San Diego wildfires, with 1020 usable responses (8.4% response rate). By signal detection theory, Reverse 911 warnings had the best performance compared with other evacuation warning sources, as indicated by the high influence rating (0.66) and hit rate (1.00). People who received the Reverse 911 warning also had a significantly higher rate of evacuation (0.80), as did those who received warnings from more than one source (0.78). Regression analysis shows that the Reverse 911 warning was critical in predicting whether an individual evacuated. Demographic factors, including knowledge and experience with previous wildfires, also played a significant role in evacuation rates, and therefore must be considered when designing a warning system.

Effects of negatively sloped keyboard wedges on risk factors for upper extremity work-related musculoskeletal disorders and user performance

Several changes to computer peripherals have been developed to reduce exposure to identified risk factors for musculoskeletal injury, notably in keyboard designs. Negative keyboard angles and their resulting effects on objective physiological measures, subjective measures and performance have been studied, although few angles have been investigated despite the benefits associated with their use. The objective of this study was to quantify the effects of negative keyboard angles on forearm muscle activity, wrist posture, key strike force, perceived discomfort and performance and to identify a negative keyboard angle or range of keyboard angles that minimizes exposure to risk factors for hand/wrist injuries. Ten experienced typists (four males and six females) participated in a laboratory study to compare keyboard angles ranging from 0° to −30°, at 10° increments, and a keyboard with a 7° slope, using a wedge designed for use with standard QWERTY keyboards. Repeatability of exposures was examined by requiring participants to complete two test sessions 1 week apart. Dependent variable data were collected during 10 min basic data entry tasks. Wrist posture data favoured negative keyboard angles of 0° (horizontal) or greater, compared to a positive keyboard angle of 7°, especially for the flexion/extension direction. In general, the percentage of wrist movements within a neutral zone and the percentages of wrist movements within ±5° and ±10° increased as keyboard angle became more negative. Electromyography results were mixed, with some variables supporting negative keyboard angles whilst other results favoured the standard keyboard configuration. Net typing speed supported the −10° keyboard angle, whilst other negative typing angles were comparable, if not better than, with the standard keyboard. Therefore, angles ranging from 0° to −30° in general provide significant reductions in exposure to deviated wrist postures and muscle activity and comparable performance.

Comparisons of measures for quantifying repetition in predicting carpal tunnel syndrome

Abstract Carpal tunnel syndrome (CTS) is the most commonly reported work-related musculoskeletal disorder of the upper extremity. While a causal relationship has been found between the repetitiveness of job tasks and CTS development, no studies have compared the predictive accuracy of various measures used to quantify repetition. The objective of this study was to compare the accuracy of measures commonly used to quantify repetition (cycle time (CT), number of hand movements (HM), and exposure classification (EC)) (i.e. high and low repetition), in predicting CTS and positive findings for CTS. Participant exposure to repetition was quantified through direct and video observation of operators within a fish processing facility. Logistic regression results indicate that for diagnosed CTS, HM were the only repetition measure to have a significant relationship, and was tentatively concluded to be the best predictor. Three interactions were also found to have significant relationships with diagnosed CTS (HM×Age, HM×Gender×Age, EC×Gender×Age). No statistically significant results were found for positive findings for CTS. The accuracy measures (percent correct, sensitivity, specificity, false positive, and false negative) did not differ for each repetition measure or interactions with the covariates considered for either dependent variable. Relevance to industry This research provides guidance on accurate assessment of exposure to repetition for prioritizing job tasks relative to risk of developing carpal tunnel syndrome.

Efficacy of Using Thermography to Assess Shoulder Loads during Overhead Intermittent Work

Upper extremity work related musculoskeletal disorders remain a priority research area due to their prevalence and cost despite efforts to mitigate their presence in the workplace. A laboratory study was conducted to investigate the effects of task parameters on surface temperature patterns, which have been previously linked to musculoskeletal injury, of the middle deltoid and trapezius while performing overhead tasks. Twelve participants (6 males and 6 females) completed one hour test sessions of an automotive assembly task simulation. Independent variables included duty cycle (33%, 50%, and 67%) and work height (two overhead positions). Results showed that thermography readings are sensitive to task demands on the musculature during dynamic tasks. Duty cycle and the interaction of duty cycle and work height were found to affect temporal and spatial thermal patterns, with lower duty cycles and lower work heights resulting in higher temperatures and faster rates of change.

Interaction Effects of Wrist and Forearm Posture on the Prediction of Carpal Tunnel Syndrome Cases Within a Fish-Processing Facility

Deviated wrist posture has been implicated as a risk factor for carpal tunnel syndrome (CTS), although alone it has not been found to have a causal relationship with CTS. Studies investigating deviated wrist posture have quantified posture in a single plane of motion and not interactions of wrist postures in multiple planes. The objective of this cross-sectional study was to investigate the ability of wrist and forearm posture interaction effects to predict CTS among a population of fish processing operators. A total of 53 participants performing five job tasks were evaluated using electrogoniometers. Due to task asymmetry, each hand was evaluated separately and treated independently, providing 106 hands as data observations. Using logistic regression analysis it was found that a model including flexed (F); extended (E), the interaction of length of employment (LE) by FE, and the interaction of LE by FE by pronation/supination (PS) accurately classified 78% of all hands as cases or non-cases. The sensitivity of the final model was approximately 48%. The developed model was found to have superior predictive ability when compared to models not considering interaction terms, indicating that posture interactions may in fact have a significant effect on CTS alone.

Assessing Posture While Typing on Portable Computing Devices in Traditional Work Environments and at Home

Mobile computers are becoming increasingly popular for many user populations, since they allow owners to perform computing activities in a number of settings (e.g., home, office). However, little research exists that quantifies ergonomic exposures associated with using mobile computing devices, particularly in non-traditional environments or for newer, compact mobile computers (e.g., slate computers). Therefore, the objective of this study was to quantify posture differences between mobile computing devices when performing data entry tasks at a traditional workstation and on a sofa. Wrist and neck flexion/extension (FE) and wrist radial/ulnar deviation (RU) were measured using electrogoniometers. When working at the non-traditional work station (i.e., sofa), postures were found to be degraded particularly when typing on the slate computer. These findings indicate that the potential or injury or illness may be elevated when working on smaller computers in non-traditional work settings.