@article{mirka_jin_hoyle_2009, title={An evaluation of arborist handsaws}, volume={40}, ISSN={["0003-6870"]}, DOI={10.1016/j.apergo.2008.02.011}, abstractNote={A review of the scientific literature reveals little research on the ergonomics of handsaws and no literature on the specific challenges of arborist saws (saws for cutting and pruning living trees). This study was designed to provide some insight into the effects of saw design and height of sawing activity on the biomechanical response of the upper extremity. Eighteen participants performed a simple sawing task at three different heights using six different arborist handsaws. As they performed this task, the electromyographic activity of several muscle groups of the forearm (flexor and extensor digitorum), arm (biceps brachii long and short heads) and shoulder girdle (posterior deltoid, infraspinatus and latissimus dorsi) were sampled. Also gathered were the wrist postures in the radial/ulnar plane at the beginning and ending of the sawing stroke, the time to complete the sawing task and a subjective ranking of the six different saws. The results show an interesting mix of biomechanical and subjective responses that provide insight into handsaw design. First, there were tradeoffs among muscle groups as a function of work height. As work height increased the biceps muscles increased their activation levels (∼19%) while the posterior deltoid activity decreased (∼17%) with the higher location. The results also showed the benefits of a bent handle design (average 21% reduction in ulnar deviation). The subjective responses of the participants generally supported the productivity data, with the saws demonstrating the shortest task completion time also being the ones most highly ranked. Understanding the stresses placed on the upper extremity during sawing activities, and design features that can reduce these stresses, may help saw designers to create products that reduce the risk of injury in workers who use handsaws.}, number={1}, journal={APPLIED ERGONOMICS}, author={Mirka, Gary A. and Jin, Sangeun and Hoyle, Jeff}, year={2009}, month={Jan}, pages={8–14} }
 @article{noack-cooper_sommerich_mirka_2009, title={College students and computers: Assessment of usage patterns and musculoskeletal discomfort}, volume={32}, ISSN={["1875-9270"]}, DOI={10.3233/WOR-2009-0827}, abstractNote={A limited number of studies have focused on computer-use-related MSDs in college students, though risk factor exposure may be similar to that of workers who use computers. This study examined computer use patterns of college students, and made comparisons to a group of previously studied computer-using professionals. 234 students completed a web-based questionnaire concerning computer use habits and physical discomfort respondents specifically associated with computer use. As a group, students reported their computer use to be at least 'Somewhat likely' 18 out of 24 h/day, compared to 12 h for the professionals. Students reported more uninterrupted work behaviours than the professionals. Younger graduate students reported 33.7 average weekly computing hours, similar to hours reported by younger professionals. Students generally reported more frequent upper extremity discomfort than the professionals. Frequent assumption of awkward postures was associated with frequent discomfort. The findings signal a need for intervention, including, training and education, prior to entry into the workforce. Students are future workers, and so it is important to determine whether their increasing exposure to computers, prior to entering the workforce, may make it so they enter already injured or do not enter their chosen profession due to upper extremity MSDs.}, number={3}, journal={WORK-A JOURNAL OF PREVENTION ASSESSMENT & REHABILITATION}, author={Noack-Cooper, Karen L. and Sommerich, Carolyn M. and Mirka, Gary A.}, year={2009}, pages={285–298} }
 @article{kucera_loomis_lipscomb_marshall_mirka_daniels_2009, title={Ergonomic Risk Factors for Low Back Pain in North Carolina Crab Pot and Gill Net Commercial Fishermen}, volume={52}, ISSN={["1097-0274"]}, DOI={10.1002/ajim.20676}, abstractNote={Abstract}, number={4}, journal={AMERICAN JOURNAL OF INDUSTRIAL MEDICINE}, author={Kucera, Kristen L. and Loomis, Dana and Lipscomb, Hester J. and Marshall, Stephen W. and Mirka, Gary A. and Daniels, Julie L.}, year={2009}, month={Apr}, pages={311–321} }
 @article{xu_hsiang_mirka_2009, title={The effects of a suspended-load backpack on gait}, volume={29}, ISSN={["1879-2219"]}, DOI={10.1016/j.gaitpost.2008.06.008}, abstractNote={A suspended-load backpack is a device that is designed to capture the mechanical energy created as a suspended backpack load oscillates vertically on the back during gait. The objective of the current study was to evaluate the effect of a suspended-load backpack system on selected temporal and kinetics parameters describing gait. Nine male participants carried a suspended-load backpack as they walked on an instrumented treadmill with varied levels of load (no backpack, 22.5 kg, and 29.3 kg) and walking speed (1.16 m/s, 1.43 m/s, 1.70 m/s). As the participants performed this treadmill task, ground reaction forces were collected from an instrumented treadmill system. From these data, temporal variables (cycle time, single support time, and double support time) and kinetic variables (normalized weight acceptance force, normalized push-off force, and normalized mid-stance force) were derived. The results showed that the response of the temporal variables were consistent with previous studies of conventional (i.e. stable load) backpacks. The response of the normalized push-off force, however, showed that increasing walking speed significantly (p<0.05) decreased the magnitude of this force, a result contrary to the literature concerning conventional backpacks where this force has been shown to significantly increase. Further evaluation revealed that this reduction in force was the result of a phase shift between the movement of the carried load and the movement of the torso. This suggests that the motion of the load in a suspended-load backpack influences the gait biomechanics and should be considered as this technology advances.}, number={1}, journal={GAIT & POSTURE}, author={Xu, Xu and Hsiang, Simon M. and Mirka, Gary A.}, year={2009}, month={Jan}, pages={151–153} }
 @article{kucera_mirka_loomis_marshall_lipscomb_daniels_2008, title={Evaluating ergonomic stresses in North Carolina commercial crab pot and gill net fishermen}, volume={5}, ISSN={["1545-9632"]}, DOI={10.1080/15459620701873514}, abstractNote={There are challenges in evaluating physical demands of commercial fishing, including identifying sources of exposure variability. Low back biomechanical stresses associated with crab pot and gill net fishing were estimated; the variability was partitioned between and within fishing type, crew size, job title, and worker to improve understanding of risk factors for low back injury. The authors observed 162 person-hours of work among 25 North Carolina commercial fishermen on 16 crews. Postures and forces during fishing tasks were measured through direct and indirect observation using two methods to determine the percentage of time fishermen were exposed to high levels of low back stress. A multilevel linear model estimated exposure variability for the dependent variables by four nesting variables: fishing type, crew size, job title, and worker. Fishermen set and pulled crab pots or gill nets for 80% of the workday. Twenty-five percent of that time was spent handling gear. For both fishing types, handling heavy loads produced high peak compression values (3586 N to 5315 N) and high NIOSH lifting index values (3.3 to 5.4), but these tasks represent a small percentage of the overall work time (0 to 14%). The majority of exposure variation in non-neutral trunk posture and/or force > 9 kg, handling materials, NIOSH Lifting Index > 1, and Lumbar Motion Monitor probability of high-risk group membership > 70% was accounted for by fishing type (range 60 to 91%). Crew size was not an important source of variability for these six variables when fishing type and job title were accounted for in the model; but in the model restricted to crab pot fishing, crew size accounted for 51 to 88% of the variability in low back stress. For both models, job title comprised the majority of exposure variability for NIOSH Lifting Index > 3.0 (46 and 65%) and worker comprised the majority of variability for spine compression > 3400 N (54 and 65%). The magnitude and duration of musculoskeletal loads experienced by fishermen vary by the type of fishing and the tasks performed by the worker. Understanding this variability may help researchers target ergonomic interventions for this work population.}, number={3}, journal={JOURNAL OF OCCUPATIONAL AND ENVIRONMENTAL HYGIENE}, author={Kucera, Kristen L. and Mirka, Gary A. and Loomis, Dana and Marshall, Stephen W. and Lipscomb, Hester J. and Daniels, Julie}, year={2008}, pages={182–196} }
 @article{xu_mirka_hsiang_2008, title={The effects of obesity on lifting performance}, volume={39}, ISSN={["0003-6870"]}, DOI={10.1016/j.apergo.2007.02.001}, abstractNote={Obesity in the workforce is a growing problem worldwide. While the implications of this trend for biomechanical loading of the musculoskeletal system seem fairly straightforward, the evidence of a clear link between low back pain (LBP) and body mass index (BMI) (calculated as whole body mass in kilograms divided by the square of stature in meters) has not been shown in the epidemiology literature addressing this topic. The approach pursued in the current study was to evaluate the lifting kinematics and ground reaction forces of a group of 12 subjects -- six with a BMI of less than 25 kg/m(2) (normal weight) and six with a BMI of greater than 30 kg/m(2) (obese). These subjects performed a series of free dynamic lifting tasks with varied levels of load (10% and 25% of capacity) and symmetry (sagittally symmetric and 45 degrees asymmetric). The results showed that BMI had a significant effect (p<0.05) on trunk kinematics with the high BMI group exhibiting higher peak transverse plane (twisting) velocity (59% higher) and acceleration (57% higher), and exhibiting higher peak sagittal plane velocity (30% higher) and acceleration (51% higher). When normalized to body weight, there were no significant differences in the ground reaction forces between the two groups. This study provides quantitative data describing lifting task performance differences between people of differing BMI levels and may help to explain why there is no conclusive epidemiological evidence of a relationship between BMI and LBP.}, number={1}, journal={APPLIED ERGONOMICS}, author={Xu, Xu and Mirka, Gary A. and Hsiang, Simon M.}, year={2008}, month={Jan}, pages={93–98} }
 @article{anderson_meador_mcclure_makrozahopoulos_brooks_mirka_2007, title={A biomechanical analysis of anterior load carriage}, volume={50}, ISSN={["0014-0139"]}, DOI={10.1080/00140130701450195}, abstractNote={Front load carriage is a common occupational task in some industries (e.g. agriculture, construction), but, as compared to lifting tasks, relatively little research has been conducted on the biomechanical loading during these activities. The focus of this study was to explore the low back biomechanics during these activities and, specifically, to examine the effects of load height and walking speed on trunk muscle activity and trunk posture. Eleven male participants participated in two separate front load-carriage experiments. The first experiment called for carrying a barbell (with weight corresponding to 20% of elbow flexion strength) at three heights (knuckle height, elbow height and shoulder height) at a constant horizontal distance from the spine. The second experiment called for participants to carry a bucket of potatoes weighing 14 kg at the same three heights, but with no further restrictions in technique. In both experiments, the participants performed this task while either standing still or walking at a self-selected speed. As they performed these tasks, the activity levels of the right-side muscle of the rectus abdominis, external oblique, biceps brachii, anterior deltoid and three levels (T9, T12 and L3) of the erector spinae were sampled. Mid-sagittal plane trunk posture was also quantified using three magnetic field-based motion sensors at T9, T12 and L3. The results showed a significant effect of both walking speed and load height on trunk posture and trunk muscle activity levels in both the barbell and bucket experiments. In the barbell experiment, the walking trials generated 43% more trunk muscle activity than the standing trials. Trials at shoulder height produced 11% more muscle activity than trials at elbow height in the T9 erector spinae muscles and 71% more muscle activity in the anterior deltoid. In the bucket experiment, trunk muscle activity responded in a similar fashion, but the key result here was the quantification of the natural hyperextension posture of the spine used to balance the bucket of potatoes. These results provide insight into muscle activation patterns in dynamic settings, especially (load) carrying biomechanics, and have implications in industrial settings that require workers to carry loads in front of their bodies.}, number={12}, journal={ERGONOMICS}, author={Anderson, A. M. and Meador, K. A. and McClure, L. R. and Makrozahopoulos, D. and Brooks, D. J. and Mirka, G. A.}, year={2007}, pages={2104–2117} }
 @article{southard_mirka_2007, title={An evaluation of backpack harness systems in non-neutral torso postures}, volume={38}, ISSN={["1872-9126"]}, DOI={10.1016/j.apergo.2006.08.007}, abstractNote={Much of the research on backpack design has been focused on spinal loading/biomechanics while the wearer is in a neutral/upright trunk posture, such as those employed by outdoor enthusiasts and schoolchildren. This research has led to some important harness design improvements that reduce trunk muscle exertions, fatigue and improve overall comfort. There are number of occupations, however, wherein workers wear back-mounted packs/devices (e.g. air tanks) while working in non-neutral trunk postures. The objective of the current study was to evaluate the effects of these non-neutral postures on biomechanical loading and then reconsider the backpack system design recommendations. Fifteen participants were asked to support a 18.2 kg load on their back while assuming static forward flexed postures of the torso (15°, 30°, 45°, and 60° of sagittal bend). The mass on the back was attached to the participant through two different harness mechanisms: a basic harness design (as seen on college student backpacks) and a more advanced design containing lateral stiffness rods and a weight-bearing hip belt (as seen on backpacks for hikers). While performing these static, posture maintenance tasks, the activation levels of the bilateral trapezius, erector spinae, and rectus abdominis were collected. Participants also provided subjective ratings of comfort. The results showed that there was a significant interaction between harness type and forward flexion angle for the trapezius and the erector spinae muscles. The normalized EMG for the trapezius muscles showed a 14% and 11% reduction in muscle activity at 15° and 30°, respectively, with the advanced design but these positive effects of the advanced design were not found at the greater flexion angles. Likewise the erector spinae muscles showed a 24% and 14% reduction in muscle activity at 15° and 30°, respectively, with the advanced design harness but these effects of the advanced design were not found at the greater forward flexion angles. The level of forward flexion angle affected the rectus abdominis muscle activity, but neither the harness type main effect nor the interaction of harness type and forward flexion angle was significant. The subjective survey results agreed with the EMG results and showed the advanced design harness was generally more comfortable with respect to the shoulder and low back areas. Collectively, the subjective and objective results show a significant improvement with the advanced harness system but also note an interesting interaction with degree of sagittal flexion, indicating a diminished effectiveness of the design improvements at forward flexed postures. Design criteria for harness systems in these forward flexed postures are discussed.}, number={5}, journal={APPLIED ERGONOMICS}, author={Southard, Stephanie A. and Mirka, Gary A.}, year={2007}, month={Sep}, pages={541–547} }
 @article{shin_mirka_2007, title={An in vivo assessment of the low back response to prolonged flexion: Interplay between active and passive tissues}, volume={22}, number={9}, journal={Clinical Biomechanics (Bristol, Avon)}, author={Shin, G. and Mirka, G. A.}, year={2007}, pages={965–971} }
 @article{southard_freeman_drum_mirka_2007, title={Ergonomic interventions for the reduction of back and shoulder biomechanical loading when weighing calves}, volume={37}, ISSN={["0169-8141"]}, DOI={10.1016/j.ergon.2006.10.016}, abstractNote={Workers in the agriculture industry have exposure to many of the recognized risk factors for work-related musculoskeletal disorders. The focus of the current project was to develop and evaluate devices designed to reduce exposure to risk factors during the process of weighing beef calves. Ergonomic task analysis of current techniques used to weigh these calves indicated significant stress in the cervicobrachial and lumbar regions. Two ergonomic interventions—the “Handle Attachment” and the “Lever Arm”—were developed to improve the body posture of the lifter and reduce joint loading. A laboratory study and field evaluations were conducted for each of these designs. In the laboratory, muscle activities were quantified for the major muscles of cervicobrachial region, the lumbar region and knee extensor muscle group during the performance of the lifting task while using the two new interventions and the standard method. In the field evaluations, farmworkers used these devices and biomechanical models of the whole body postures were developed to quantify changes in the joint loading when using the interventions. The results show that both intervention techniques reduce the required muscle activity (8–71.6% reduction for the muscles of the cervicobrachial region, 2–43% reduction for the muscles of the lumbar region) and the joint loading (33–100% reduction in shoulder abduction moment and 42–57% reduction in spine compression) as compared to the standard method. Overall, the farmworkers noted that the “Handle Attachment” design is less cumbersome to move and use than the “Lever Arm” design, but laboratory study and field study revealed that the “Lever Arm” design provides the highest reduction in muscle activity and joint loading. Using either intervention while performing this task should decrease the risk to the low back and shoulders. The ergonomic intervention research described in this report documents a reduction in exposure to risk factors for shoulder and low back injury in an at-risk population in the agriculture industry.}, number={2}, journal={INTERNATIONAL JOURNAL OF INDUSTRIAL ERGONOMICS}, author={Southard, Stephanie A. and Freeman, Jacklyn H. and Drum, Jonathan E. and Mirka, Gary A.}, year={2007}, month={Feb}, pages={103–110} }
 @article{reid_mirka_2007, title={Learning curve analysis of a patient lift-assist device}, volume={38}, ISSN={["0003-6870"]}, DOI={10.1016/j.apergo.2006.10.006}, abstractNote={One of the challenges facing ergonomists in the implementation of an ergonomic solution is addressing the concerns related to their impact on productivity. The focus of the current study was to (1) apply standard learning curve analysis to the learning that takes place as an individual works with a patient handling device and (2) compare the effects of two different training protocols on measures of learning. Eighteen subjects completed 11 replications of a patient transfer task after participating in either an "interactive" training protocol or "see-one-do-one" training protocol. The results show that the learning rate for this task was 83% with no difference as a function of training protocol. The results do indicate that the effect of Training Method was significant (p<0.05) for time to complete the first patient lift task (370s for the interactive training vs. 475s for see-one-do-one training). The results of the analysis of the survey data supported the objective results in that the only measure that was responsive to training type (p<0.05) was related to comfort level in performing the patient lift task for the first time. The results emphasize the importance in considering learning when introducing an intervention in the workplace, and showed that in this instance, training type had an immediate impact on productivity, but that this effect diminished over time.}, number={6}, journal={APPLIED ERGONOMICS}, author={Reid, Stephanie A. and Mirka, Gary A.}, year={2007}, month={Nov}, pages={765–771} }
 @article{shu_jiang_xu_mirka_2007, title={The effect of a knee support on the biomechanical response of the low back}, volume={23}, ISSN={["1065-8483"]}, DOI={10.1123/jab.23.4.275}, abstractNote={Stooping and squatting postures are seen in a number of industries (e.g., agriculture, construction) where workers must work near ground level for extended periods of time. The focus of the current research was to evaluate a knee support device designed to reduce the biomechanical loading of these postures. Ten participants performed a series of sudden loading tasks while in a semisquat posture under two conditions of knee support (no support and fully supported) and two conditions of torso flexion (45 and 60°). A weight was released into the hands of the participants who then came to steady state while maintaining the designated posture. As they performed this task, the EMG responses of the trunk extensors (multifidus and erector spinae) were collected, both during the “sudden loading” phase of the trial as well as the steady weight-holding phase of the trial. As expected, the effects of torso flexion angle showed significant decreases in the activation of the multifidus muscles with greater torso angle (indicating the initiation of the flexion–relaxation response). Interestingly, the results showed that the knee support device had no effect on the activation levels of the sampled muscles, indicating that the loss of the degree of freedom from the ankle joint during the knee support condition had no impact on trunk extensor muscle response. The a priori concern with regard to these supports was that they would tend to focus loading on the low back and therefore would not serve as a potential ergonomic solution for these stooping/semisquatting tasks. Because the results of this study did not support this concern, further development of such an intervention is underway.}, number={4}, journal={JOURNAL OF APPLIED BIOMECHANICS}, author={Shu, Yu and Jiang, Zongliang and Xu, Xu and Mirka, Gary A.}, year={2007}, month={Nov}, pages={275–281} }
 @article{shu_mirka_2006, title={A laboratory study of the effects of wrist splint orthoses on forearm muscle activity and upper extremity posture}, volume={48}, ISSN={["0018-7208"]}, DOI={10.1518/001872006778606859}, abstractNote={ Objective: To evaluate the effects of wrist splint orthoses (WSOs) on forearm muscle activity and upper extremity/torso postures. Background: WSOs are ubiquitous in industry, but the literature as to their biomechanical effects is limited. Method: Study 1: Participants performed single-plane wrist exertions with or without a WSO while the electromyographic (EMG) activity of the flexor carpi radialis, flexor carpi ulnaris, and extensor carpi ulnaris was captured. Study 2: Participants performed simple computer jumper installation tasks with or without a WSO while upper extremity/torso postures were recorded. Results: Study 1: A significant interaction between WSOs and wrist angle was observed in the response of forearm muscles (e.g., normalized EMG of the flexor carpi radial is increased from 4.2% to 15.9% as flexion increased from 0° to 36° in the orthosis conditions, whereas in the no-orthosis condition it remained 5% at all wrist flexion angles). Study 2: WSOs were found to effect wrist, torso, and shoulder postures, with the orthoses creating a 48% decrease (36° vs. 18.6°) in wrist flexion and 80% decrease (15° vs. -3°) in ulnar deviation but at a cost of increased shoulder abduction of 22% (36.5° vs. 44.5°) and increased lateral bend of torso of 30% (6° vs. 7.8°). Conclusions: WSOs increased forearm muscle activity at large wrist deviation angles and induced awkward shoulder postures in tasks requiring significant wrist deviation. Application: Use of WSOs in occupational settings should be carefully considered relative to task requirements, as orthoses may do more harm than good. }, number={3}, journal={HUMAN FACTORS}, author={Shu, Yu and Mirka, Gary A.}, year={2006}, pages={499–510} }
 @article{lawrence_buckner_mirka_2006, title={An adaptive system identification model of the biomechanical response of the human trunk during sudden loading}, volume={128}, ISSN={["0148-0731"]}, DOI={10.1115/1.2165696}, abstractNote={Sudden loading injuries to the low back are a concern. Current models are limited in their ability to quantify the time-varying nature of the sudden loading event. The method of approach used six males who were subjected to sudden loads. Response data (EMG and kinematics) were input into a system identification model to yield time-varying torso stiffness estimates. The results show estimates of system stiffness in good agreement with values in the literature. The average root mean square error of the model’s predictions of sagittal motion was equal to 0.1deg. In conclusion, system identification can be implemented with minimal error and used to gain more insight into the time-dependent trunk response to sudden loads.}, number={2}, journal={JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME}, author={Lawrence, BM and Buckner, GD and Mirka, GA}, year={2006}, month={Apr}, pages={235–241} }
 @article{shin_nance_mirka_2006, title={Differences in trunk kinematics and ground reaction forces between older and younger adults during lifting}, volume={36}, ISSN={["0169-8141"]}, DOI={10.1016/j.ergon.2006.05.008}, abstractNote={Age-related changes in trunk kinematics in lifting have received little attention despite a documented increased risk of musculoskeletal injury with age. This study examined the responses in trunk kinematics and ground reaction forces of older and younger subjects during lifting. Ten older (55–63 years) and ten younger (19–29 years) adults performed lifting tasks in six different conditions. A lumbar motion monitor was used to measure the subjects’ trunk kinematics and a force platform was used to measure the ground reaction forces during the lifting motion. The results of this study showed that age had a significant (p<0.05) effect on the transverse plane (axial twisting) trunk kinematics variables (peak velocity and peak acceleration) but did not affect ground reaction forces or other trunk kinematics variables. The peak transverse velocity was 40% lower and peak transverse acceleration was 30% lower in the older subjects as compared to the younger subjects. This study presents the postural adaptation of older subjects to dynamic lifting tasks. Results can be used to understand the risks of older work population in manual material handling tasks.}, number={9}, journal={INTERNATIONAL JOURNAL OF INDUSTRIAL ERGONOMICS}, author={Shin, Gwanseob and Nance, Mack L. and Mirka, Gary A.}, year={2006}, month={Sep}, pages={767–772} }
 @article{jiang_shu_drum_reid_mirka_2006, title={Effects of age on muscle activity and upper body kinematics during a repetitive forearm supination task}, volume={36}, ISSN={["1872-8219"]}, DOI={10.1016/j.ergon.2006.07.008}, abstractNote={The principal objective of this study was to assess the effects of age on upper extremity muscle activation patterns and upper body kinematics during a forearm supination task. Age-related physiological and biomechanical changes in the musculoskeletal system have been documented in the literature. It was hypothesized that these changes may have an impact on muscle recruitment and work technique (postural/kinematic) employed during work tasks. A simple repetitive forearm supination task was used to evaluate these hypotheses. Twenty subjects (ten in each age group 19–29 and 55–65) performed a series of static and dynamic forearm supination tasks on a work simulator. These exertions were performed at eight different levels of supination torque: 5–40 lb-in in 5 lb-in increments. As the subjects performed the static exertions the activation levels of several key muscles of the upper extremity were captured using surface electromyography. As the subjects performed the dynamic exertions, the motions of the upper body and upper extremity were captured using a magnetic field-based motion analysis system. The results of the static exertions showed that older subjects generated 135% greater trapezius muscle activity (significant at p<0.05 level) but no other muscle group sampled showed a significant difference between the age groups. In the dynamic exertions, age had no effect on upper limb/torso kinematic responses. In both the static and dynamic exertions, supination torque level had a significant impact on muscle activity and kinematics. These results provide empirical evidence that age alone does not have a consistent impact on biomechanical responses during physically demanding work tasks.}, number={11}, journal={INTERNATIONAL JOURNAL OF INDUSTRIAL ERGONOMICS}, author={Jiang, Zongliang and Shu, Yu and Drum, Jonathan and Reid, Stephanie and Mirka, Gary A.}, year={2006}, month={Nov}, pages={951–957} }
 @article{bajaj_mirka_sommerich_khachatoorian_2006, title={Evaluation of a redesigned self-checkout station for wheelchair users}, volume={18}, ISSN={["1040-0435"]}, DOI={10.1080/10400435.2006.10131903}, abstractNote={Self-checkout is the emergent/emerging retail technology wherein users (shoppers) check out their own items using an interactive kiosk. A dramatic growth is anticipated in the prevalence of self-checkout systems in retail environments. A study was conducted to develop and evaluate a redesign of a self-checkout system with a focus on issues related to physical accessibility for wheelchair users. Two checkout station prototypes were built: a full-scale model of an existing system and a full-scale model of a system with design modifications (e.g., inclusion of appropriate wheelchair clearance under the workstation, reduced vertical position of the credit card reader, etc.). Five wheelchair users and 10 non–wheelchair users performed simulated self-checkout activities using both workstations. The principal independent variable was workstation type (standard design vs. modified design). The dependent measures were productivity (time to complete a transaction), shoulder flexion angle, torso flexion angle, and the user's subjective assessment of the experience. The results of this study indicate that workstation type did not influence productivity levels in either participant group (wheelchair users or non–wheelchair users). Posture, on the other hand, was significantly improved: the peak shoulder angle was reduced by 64% in wheelchair users and by 69% in the non–wheelchair user group. Peak flexion angle of the torso was also reduced by 67% for wheelchair users. Subjective feedback from the wheelchair user group supported the postural data by showing an overall preference for the redesigned workstation, whereas the non–wheelchair group showed no preference between the two. These results indicate that design for populations with specific limitations does not need to come at a cost of reduced accessibility for persons without these limitations; universal design is achievable.}, number={1}, journal={ASSISTIVE TECHNOLOGY}, author={Bajaj, K and Mirka, GA and Sommerich, CM and Khachatoorian, H}, year={2006}, pages={15–24} }
 @article{joines_sommerich_mirka_wilson_moon_2006, title={Low-level exertions of the neck musculature: A study of research methods}, volume={16}, ISSN={1050-6411}, url={http://dx.doi.org/10.1016/j.jelekin.2005.09.007}, DOI={10.1016/j.jelekin.2005.09.007}, abstractNote={Musculoskeletal neck discomfort is prevalent in many occupations and has been the focus of much research employing surface electromyography (sEMG). Significant differences in experimental methods among researchers make comparisons across studies difficult. The goal of the current research was to use empirical methods to answer specific methodological questions concerning use of sEMG in evaluation of the neck extensor system. This was accomplished in two studies. In Experiment 1, ultrasound technology was used to: (a) determine accessibility of m. splenius and semispinalis capitis with surface electrodes, (b) identify appropriate electrode locations for these muscles/muscle groups, and (c) illustrate potential benefits of using ultrasound in locating muscles/placing electrodes. Experiment 2 sought to assess effects of posture when normalizing sEMG data. Results from Experiment 1 showed no direct access to semispinalis capitis for surface electrodes; their activity can only be sampled as part of a group of muscles. In most subjects, m. splenius was found to be accessible to surface electrodes. Electrode placement recommendations are provided. Results of Experiment 2 showed significant differences in normalized EMG data between a posture-specific technique and a reference posture technique. Posture-specific normalization is recommended for accurately assessing the relative intensity of contractions of these muscles.}, number={5}, journal={Journal of Electromyography and Kinesiology}, publisher={Elsevier BV}, author={Joines, Sharon M.B. and Sommerich, Carolyn M. and Mirka, Gary A. and Wilson, James R. and Moon, Samuel D.}, year={2006}, month={Oct}, pages={485–497} }
 @article{sudhakaran_mirka_2005, title={A laboratory investigation of personality type and break-taking behavior}, volume={35}, ISSN={["1872-8219"]}, DOI={10.1016/j.ergon.2004.09.003}, abstractNote={Abstract The Type A personality trait is characterized by time urgency and competitiveness and has been shown to have an impact on human performance in a variety of settings. A laboratory study was conducted to assess the effect of personality type on the break-taking behavior of participants asked to perform a fatiguing overhead work task. Sixteen subjects (eight classified as Type A individuals and eight classified as Type B individuals) performed 40 repetitions of a simple assembly task in an overhead position and were allowed to take breaks as needed. The dependent measures included the time to complete the experiment, the average cycle time, the number of breaks taken, the total amount of break time, and the average pain level experienced during the whole experiment. The results of this study showed a wide range in the work–rest strategies employed by the participants. Some chose regularly scheduled breaks, others seemed to identify a specific pain threshold at which they would take a break, while still others adopted a strategy of taking a small number of longer breaks. Interestingly, personality type did not have a significant effect on the break-taking behavior of the participants as defined by our dependent measures. Further, an analysis of a cadre of additional potential covariates (upper extremity anthropometric characteristics, pain level at break time, etc.) did not provide any additional predictive ability in the analysis of the break-taking behavior. The results do show that these intra-individual “strategies” that the participants employed in performing this fatiguing task appear to be stable over the duration of the experiment, indicating that there are probably additional individual characteristics that may be driving the response, providing an interesting direction for future research. Relevance to industry Work-related musculoskeletal disorders continue to be a considerable problem in many industries. Personal characteristics of the worker may influence their exposures to recognized risk factors, and the evaluation of personality type relative to one component of work style (break-taking behaviors) is the focus of this work.}, number={3}, journal={INTERNATIONAL JOURNAL OF INDUSTRIAL ERGONOMICS}, author={Sudhakaran, S and Mirka, GA}, year={2005}, month={Mar}, pages={237–246} }
 @article{jiang_shin_freeman_reid_mirka_2005, title={A study of lifting tasks performed on laterally slanted ground surfaces}, volume={48}, ISSN={["0014-0139"]}, DOI={10.1080/00140130500123761}, abstractNote={Lifting in most industrial environments is performed on a smooth, level ground surface. There are, however, many outdoor work environments (e.g. agriculture and construction) that require manual material handling activities on variable grade ground surfaces. Quantifying the biomechanical response while lifting under these conditions may provide insight into the aetiology of lifting-related injury. The aim of the current study was to quantify the effect of laterally slanted ground surfaces on the biomechanical response. Ten subjects performed both isometric weight-holding tasks and dynamic lifting exertions (both using a 40% of max load) while standing on a platform that was laterally tilted at 0, 10, 20 and 30° from horizontal. As the subject performed the isometric exertions, the electromyographic (EMG) activity of trunk extensors and knee extensors were collected and during the dynamic lifting tasks the whole body kinematics were collected. The whole body kinematics data were used in a dynamic biomechanical model to calculate the time-dependent moment about L5/S1 and the time-dependent lateral forces acting on the body segments. The results of the isometric weight-holding task show a significant (p < 0.05) effect of slant angle on the normalized integrated EMG values in both the left (increase by 26%) and right (increase by 70%) trunk extensors, indicating a significant increase in the protective co-contraction response. The results of the dynamic lifting tasks revealed a consistent reduction in the peak dynamic L5/S1 moment (decreased by 9%) and an increase in the instability producing lateral forces (increased by 111%) with increasing slant angle. These results provide quantitative insight into the response of the human lifter under these adverse lifting conditions.}, number={7}, journal={ERGONOMICS}, author={Jiang, ZL and Shin, G and Freeman, J and Reid, S and Mirka, GA}, year={2005}, month={Jun}, pages={782–795} }
 @article{lawrence_mirka_buckner_2005, title={Adaptive system identification applied to the biomechanical response of the human trunk during sudden loading}, volume={38}, ISSN={["1873-2380"]}, DOI={10.1016/j.jbiomech.2004.09.038}, abstractNote={Epidemiological evidence indicates that sudden loading of the torso is a risk factor for low back injury. Accurately quantifying the time-varying loading of the spine during sudden loading events and how these loading profiles are affected by workplace factors such as fatigue, expectation, and training can potentially lead to intervention strategies that can reduce these risks. Electromyographic and trunk motion data were collected from six male participants who performed a series of sudden loading trials with varying levels of expectation (no preview, 300-ms audible preview), fatigue (no fatiguing exertion preceding sudden load, short duration/high intensity fatiguing exertion preceding sudden load), and training (untrained, trained). These data were used as inputs to an adaptive system identification model wherein time-varying lower back stiffness, torque, work, and impulse magnitudes were calculated. Results indicated that expectation significantly increased peak and average stiffness by 70% and 113%, respectively, and significantly decreased peak torque, work, and impulse magnitudes by 36%, 50%, and 45%, respectively. Training significantly decreased peak torque and work by 25% and 34%, respectively. The results also showed a significant interaction between expectation and training wherein training had a positive effect during the trials with preview but no effect during the trials with no preview (increased peak stiffness by 17% and decreased impulse magnitude by 43%).}, number={12}, journal={JOURNAL OF BIOMECHANICS}, author={Lawrence, BM and Mirka, GA and Buckner, GD}, year={2005}, month={Dec}, pages={2472–2479} }
 @article{brandenburg_mirka_2005, title={Assessing the effects of positive feedback and reinforcement in the introduction phase of an ergonomic intervention}, volume={47}, ISSN={["1547-8181"]}, DOI={10.1518/001872005774860078}, abstractNote={ Resistance to change is common in ergonomic interventions, often resulting in negative consequences when the intervention's effectiveness is studied. A lab-based study assessed the effects of positive reinforcement during the intervention process. On Day 1 all participants performed a simple screw-driving task that placed stress on the cervicobrachial region through static loading. On Day 2 a control group received basic information about ergonomics and then performed the task using an ergonomic intervention that has been shown to reduce loading on these muscle groups. The experimental group received the same basic information but also received positive reinforcement while performing the task with the ergonomic intervention. Subjective task assessment surveys and body-part discomfort surveys were administered, and these, along with speed of performance, were assessed in both groups. The results showed a significantly (p < .05) more positive subjective impression of the intervention for the feedback group than for the control group (29%-57% improvement) with no real changes in either the performance or discomfort levels. Applications of this research include improving workers' acceptance of ergonomic interventions in industrial and other settings. The reinforcement technique evaluated in this paper has yielded consistently positive effects in our ongoing ergonomic intervention research. }, number={3}, journal={HUMAN FACTORS}, author={Brandenburg, DL and Mirka, GA}, year={2005}, pages={526–535} }
 @article{mirka_2005, title={Development of an ergonomics guideline for the furniture manufacturing industry}, volume={36}, ISSN={["0003-6870"]}, DOI={10.1016/j.apergo.2004.10.003}, abstractNote={Industry-specific ergonomics guidelines are an important component in the four-pronged approach to workplace ergonomics currently pursued by the United States Occupational Safety and Health Administration. The American Furniture Manufacturers Association has taken the initiative of developing such a guideline for its members. The result of this effort is the “AFMA Voluntary Ergonomics Guideline for the Furniture Manufacturing Industry”, a document that includes basic information about ergonomics program components as well as a compilation of work-proven, ergonomics best practices as submitted by members of the furniture manufacturing community. This guideline was developed through an industry-research-government partnership and made strategic use of the unique attributes that each sector brought to this effort. Outlined in this paper are some of the characteristics of this partnership including, the roles played by each, the different motivations for pursuing the guideline, the challenges faced during the development of the document, the successes experienced in this process, as well as a proposed outline for measuring the effectiveness of this effort. The hope is that this summary, and some of the lessons learned contained herein, would be helpful to others considering the prospect of developing such a guideline for their industry.}, number={2}, journal={APPLIED ERGONOMICS}, author={Mirka, GA}, year={2005}, month={Mar}, pages={241–247} }
 @article{shu_drum_southard_shin_mirka_2005, title={The effect of a repetitive, fatiguing lifting task on horizontal ground reaction forces}, volume={21}, ISSN={["1065-8483"]}, DOI={10.1123/jab.21.3.260}, abstractNote={There are many outdoor work environments that involve the combination of repetitive, fatiguing lifting tasks and less-than-optimal footing (muddy/slippery ground surfaces). The focus of the current research was to evaluate the effects of lifting-induced fatigue of the low back extensors on lifting kinematics and ground reaction forces. Ten participants performed a repetitive lifting task over a period of 8 minutes. As they performed this task, the ground reaction forces and whole body kinematics were captured using a force platform and magnetic motion tracking system, respectively. Fatigue was verified in this experiment by documenting a decrease in the median frequency of the bilateral erector spinae muscles (pretest-posttest). Results indicate significant (p < 0.05) increases in the magnitude of the peak anterior/posterior (increased by an average of 18.3%) and peak lateral shear forces (increased by an average of 24.3%) with increasing time into the lifting bout. These results have implications for work environments such as agriculture and construction, where poor footing conditions and requirements for considerable manual materials handling may interact to create an occupational scenario with an exceptionally high risk of a slip and fall.}, number={3}, journal={JOURNAL OF APPLIED BIOMECHANICS}, author={Shu, Y and Drum, J and Southard, S and Shin, G and Mirka, GA}, year={2005}, month={Aug}, pages={260–270} }
 @article{mirka_shin_kucera_loomis_2005, title={Use of the CABS methodology to assess biomechanical stress in commercial crab fishermen}, volume={36}, ISSN={["1872-9126"]}, DOI={10.1016/j.apergo.2004.08.001}, abstractNote={Commercial fishing is a job characterized by long hours in an unpredictable, dynamic natural environment and variable demands placed on the musculoskeletal system, requiring strength, coordination, and endurance. The focus of this project was in the quantification of the biomechanical stresses placed on the lumbar spine during the work activities of commercial crab fishermen. The continuous assessment of back stress (CABS) methodology was used to develop distributions describing the amount of time that each of the crew members on a two- or three-man crabbing crew spend at various levels of low back stress. The results of this analysis, expressed in terms of time-weighted histograms, show significant inter and intra-crewmember variability in the stress measures during regular daily work activities. For the three man crew, the captain has relatively low stress levels throughout the work day, while the mate performs high force (up to 30 kg), dynamic exertions while pulling the crab pots from the water up into the boat and high loads (20-40 kg) during the loading and unloading of the boat in the morning and evening, respectively. The third man of the crew experiences static awkward postures (forward flexed postures held for up to 5 min at a time) as he sorts and packs the crabs. For the two-man crew, the results show a more even distribution of the high stress activities between the crewmembers. The application of the results of this analysis for prioritization of work tasks for ergonomic intervention is discussed.}, number={1}, journal={APPLIED ERGONOMICS}, author={Mirka, GA and Shin, G and Kucera, K and Loomis, D}, year={2005}, month={Jan}, pages={61–70} }
 @article{leyman_mirka_kaber_sommerich_2004, title={Cervicobrachial muscle response to cognitive load in a dual-task scenario}, volume={47}, ISSN={["1366-5847"]}, DOI={10.1080/00140130310001629766}, abstractNote={People working in an office environment often have to deal with significant cognitive workload due to the coordination of multiple, simultaneous tasks. The objective of this research was to examine the impact of cognitive load in office-type tasks on physical-stress response, using a dual-task paradigm involving a primary cognitive task and secondary typing task. The central hypothesis of this research was that altering the demands of the cognitive task would lead to a difference in physical stress-level and performance. Cognitive load was manipulated by presenting participants with three different types of cognitive tasks described in Rasmussen's (1983) taxonomy, including skill-, rule-, and knowledge-based tasks. Dependent variables examined in the study included: (1) electromyographic activity of the upper trapezius (pars descendens) and cervical erector spinae muscles, (2) performance in a secondary typing task, and (3) subjective measures of stress and cognitive workload. The results of this study revealed that the primary task causing the highest level of perceived workload also produced 61% higher muscle activity in the right trapezius, and 6 and 11% higher activity in the left and right cervical erector spinae, respectively, in comparison to muscle activity associated with the cognitive task causing the lowest perceived workload. With respect to performance, a 23% decrease was observed in typing productivity when the rule-based task was completed simultaneously vs. typing in the absence of any additional cognitive task (the baseline condition). This information may be used to better organize work activities in office environments to increase performance and reduce stress.}, number={6}, journal={ERGONOMICS}, author={Leyman, ELC and Mirka, GA and Kaber, DB and Sommerich, CM}, year={2004}, month={May}, pages={625–645} }
 @article{shin_shu_li_jiang_mirka_2004, title={Influence of knee angle and individual flexibility on the flexion-relaxation response of the low back musculature}, volume={14}, ISSN={["1050-6411"]}, DOI={10.1016/j.jelekin.2003.12.001}, abstractNote={In many occupational settings (e.g. agriculture and construction) workers are asked to maintain static flexed postures of the low back for extended periods of time. Recent research indicates that the resulting strain in the viscoelastic, ligamentous tissues may have a deleterious effect on the stability of the spine and the normal reflex response of spinal tissues. The purpose of this study was to evaluate the previously described flexion–relaxation response in terms of the interactive effect of trunk flexion angle (30°, 50°, 70°, 90°), knee flexion angle (0° (straight knees), 20°, 40°) and individual flexibiliteky (low, medium, and high). These conditions were tested under two levels of loading: no load (just supporting the weight of the torso) and trunk extension moment equal to 50% of the subject’s posture-specific maximum voluntary trunk extension capacity. Surface electromyographic (EMG) data were collected from the multifidus, the longissimus, the iliocostalis, the vastus medialis, the rectus femoris, the vastus lateralis, the biceps femoris, and the gastrocnemius-soleus group from a sample of eight male participants as they performed isometric weight holding tasks in the postures defined by the combinations of trunk angle and knee angle. The results of this study showed that knee angle did have a significant effect on the lumbar extensor muscle activity but only consistently at the 90° trunk angle. Participant flexibility showed a consistent trend of decreasing lumbar extensor muscle activity with decreased flexibility across all trunk angle values. Most interesting was the interactive response of flexibility and knee angle, wherein the flexibility of the participant influenced the trunk angles at which the knee flexion angle affected the flexion–relaxation response. Highly flexible subjects showed an effect of knee angle on the flexion–relaxation response only at the 90° trunk angle; subjects in the medium flexibility category showed a similar response in both the 70° and 90° trunk angles; subject in the low flexibility group showed no knee angle effect on the flexion–relaxation response. Overall the results confirm previous results with regard to the contribution of the passive tissues to the overall trunk extension moment but also show that the tension in the bi-articular biceps femoris, which was influenced by knee flexion angle and flexibility, affects the ratio of active extensor moment contributions of the lumbar extensor musculature to passive extensor moment contributions from the muscular and ligamentous tissues. The results of this study provide empirical data describing this complicated, interactive response.}, number={4}, journal={JOURNAL OF ELECTROMYOGRAPHY AND KINESIOLOGY}, author={Shin, G and Shu, Y and Li, Z and Jiang, ZL and Mirka, G}, year={2004}, month={Aug}, pages={485–494} }
 @article{duke_mirka_sommerich_2004, title={Productivity and ergonomic investigation of bent-handle pliers}, volume={46}, ISSN={["1547-8181"]}, DOI={10.1518/hfes.46.2.234.37341}, abstractNote={ Awkward wrist posture is generally considered an occupational risk factor for hand/wrist disorders, leading to the ergonomic design principle of “bend the tool, not the wrist.” Sixteen participants performed a computer jumper installation task and a simple assembly task while productivity, wrist posture, and shoulder posture were measured. The work surface orientation (vertical and 45°) and the level of constraint placed on the user (constrained grip and unconstrained grip) were also varied. The results indicate that the beneficial effects of the bent-handle pliers are task dependent. In the computer jumper task the bent-handle pliers resulted in 5.3% faster task performance, whereas in the assembly task performance was 4.9% faster with the straight-handle pliers. The bent-handle pliers reduced shoulder deviations by 50% in the jumper installation task, and ulnar deviation was reduced by 12% and 22% for the jumper installation task and the assembly task, respectively (all significant at p < .05). However, allowing participants to hold the pliers in a grip configuration of their choosing (unconstrained technique) often reduced these postural benefits. In applying these results to work place design activities, one should recognize that the ergonomic utility of benthandle pliers can be considerable but that the 3-D kinematics characteristics of the task must be considered. }, number={2}, journal={HUMAN FACTORS}, author={Duke, K and Mirka, GA and Sommerich, CM}, year={2004}, pages={234–243} }
 @article{shin_mirka_2004, title={The effects of a sloped ground surface on trunk kinematics and L5/S1 moment during lifting}, volume={47}, ISSN={["1366-5847"]}, DOI={10.1080/00140130310001653066}, abstractNote={There are many work environments that require workers to perform manual materials handling tasks on ground surfaces that are not perfectly flat (e.g. in agriculture, construction, and maritime workplaces). These sloped ground surfaces may have an impact on the lifting strategy/technique employed by the lifter, which may, in turn, alter the biomechanical loading of the spine. Describing the changes in kinematics and kinetics of the torso is the first step in assessing the impact of these changes and is the focus of the current research. Subjects' whole-body motions were recorded as they lifted a 10 kg box while standing on two inclined surfaces (facing an upward slope: 10° and 20°), two declined surfaces (facing a downward slope: − 10° and − 20°), and a flat surface (0°) using three lifting techniques (leg lift, back lift and freestyle lift). These data were then used in a two-dimensional, five-segment dynamic biomechanical model (top-down) to evaluate the effect of these slopes on the net moment about the L5/S1 joint. The results of this study showed an interesting interaction effect wherein the net L5/S1 moment was relatively insensitive to changes in slope angle under the back lift condition, but showed a significant effect during the leg lift and freestyle lifting conditions. The results show that under the freestyle lifting condition the peak L5/S1 moment was significantly higher for the inclined surfaces as compared to the flat surfaces (6.8% greater) or declined surfaces (10.0% greater). Subsequent component analysis revealed that both trunk flexion angle and angular trunk acceleration were driving this response. Collectively, the results of this study indicate that ground slope angle does influence the lifting kinematics and kinetics and therefore needs to be considered when evaluating risk of low back injury in these working conditions.}, number={6}, journal={ERGONOMICS}, author={Shin, G and Mirka, G}, year={2004}, month={May}, pages={646–659} }
 @article{mirka_monroe_nay_lipscomb_kelaher_2003, title={Ergonomic interventions for the reduction of low back stress in framing carpenters in the home building industry}, volume={31}, ISSN={["0169-8141"]}, DOI={10.1016/S0169-8141(03)00025-8}, abstractNote={Framing carpenters in the residential sector of the construction industry have exposure to many of the documented risk factors for low back disorders. On-site exposure data were collected from a sample of residential framing carpentry subcontractors and these were summarized using the continuous assessment of back stress (CABS) methodology. From these analyses those tasks placing the greatest stress on the low back were identified and prototype interventions were developed that reduced exposures to the specific risk factors. These prototypes were then evaluated in the field and their effects on the low back stress and productivity were quantified. The results of this analysis for three of these prototypes (a pneumatic wall lift, an extension handle for a pneumatic nail gun and a vertical lumber handling system) are presented in this paper. The pneumatic wall lift reduced peak spine compression by 63% and had mixed effects on productivity depending on the characteristics of the wall being erected. The extension handle for the pneumatic nail gun had a marked decrease in the average spine compression (73%) and also had mixed effects on the productivity depending on the characteristics of the support structures under the subflooring. The vertical lumber handling system created significant reductions in both the peak (70%) and average (32%) spine compression forces as well as a significant improvement in productivity (increase of up to 77%). Several of these interventions had positive effects in other body regions (primarily shoulder loading) but these were not quantified in the rigorous way that the low back stress was evaluated. Finally, subjective assessments by the workers varied across the interventions and were heavily weighted by their effects on productivity. Engineering controls are the most effective methods for controlling work-related musculoskeletal disorders. This study evaluates the effectiveness of a set of engineering controls for the prevention of back injury/illness in framing carpenters.}, number={6}, journal={INTERNATIONAL JOURNAL OF INDUSTRIAL ERGONOMICS}, author={Mirka, GA and Monroe, M and Nay, T and Lipscomb, H and Kelaher, D}, year={2003}, month={Jun}, pages={397–409} }
 @article{smith_sommerich_mirka_george_2002, title={An investigation of ergonomic interventions in dental hygiene work}, volume={33}, number={2}, journal={Applied Ergonomics}, author={Smith, C. A. and Sommerich, C. M. and Mirka, G. A. and George, M. C.}, year={2002}, pages={175–184} }
 @article{shivers_mirka_kaber_2002, title={Effect of grip span on lateral pinch grip strength}, volume={44}, ISSN={["1547-8181"]}, DOI={10.1518/0018720024496999}, abstractNote={ Repetitive, high-force pinch grip exertions are common in many occupational activities. The goal of the current study was to quantify the relationship between lateral pinch grip span (distance between thumb and index finger) and lateral pinch grip strength. An experiment was conducted in which 40 participants performed maximal lateral pinch grip exertions at 11 levels of grip span distances (0, 10%, ... 100% of maximum functional lateral pinch grip span distance). The results show a significant effect of lateral pinch grip span, with strength at the maximum functional lateral pinch grip span 40% higher than that found at the smallest lateral pinch grip span considered. Between these two endpoints, strength increased monotonically with increasing pinch grip span. The application of these results in pinch grip design criteria for both high-force and long-duration exertions is discussed. Potential applications of this research include the design of hand tools and controls for which significant force is applied by the user. }, number={4}, journal={HUMAN FACTORS}, author={Shivers, CL and Mirka, GA and Kaber, DB}, year={2002}, pages={569–577} }
 @article{mirka_smith_shivers_taylor_2002, title={Ergonomic interventions for the furniture manufacturing industry. Part I - lift assist devices}, volume={29}, ISSN={["0169-8141"]}, DOI={10.1016/S0169-8141(01)00067-1}, abstractNote={The objectives of this intervention research project were to develop and evaluate engineering controls for the reduction of low back injury risk in workers in the furniture manufacturing industry. An analysis of injury/illness records and survey data identified upholsterers and workers in the machine room as two occupations within the industry at elevated risk for low back injury. A detailed ergonomic evaluation of the activities performed by these workers was then performed and the high risk subtasks were identified. The analysis for upholsterers revealed: (1) high forces during the loading and unloading of the furniture to and from the upholstery bucks, (2) static awkward postures (extremeflexion>50°, lateralbending>20°, twisting>20°) during the upholstering of the furniture, and (3) repetitive bending and twisting throughout the operation. For machine room workers, this ergonomic evaluation revealed repetitive bending and twisting (up to 5 lifts/min and sagittal flexion>80°, lateral bending>15°, twisting>45°) when getting wooden components from or moving them to the shop carts that are used to transport these materials. Engineering interventions were then developed and evaluated in the laboratory to document the reduction of exposure to these stressors. The height-adjustable upholstery buck system eliminated the lifting and lowering requirements and affected trunk kinematics during the upholstery operation by reducing peak sagittal angles by up to 79% (average: 52%; range: 27–79%), peak sagittal accelerations by up to 42% (average: 71%; range: 0–74%) and peak lateral position by up to 31% (average: 20%; range: 12–31%), and showed no impact on time to complete the task. The machine room lift reduced peak sagittal angle by up to 90% (average: 76%; range: 64–90%), peak sagittal accelerations by up to 86% (average: 72%; range: 59–86%) and had a positive impact on the time to complete the task (average reduction: 19%). The ergonomic intervention research documented in this report shows the impact of engineering controls for the furniture manufacturing industry on the risk factors for work-related low back injuries.}, number={5}, journal={INTERNATIONAL JOURNAL OF INDUSTRIAL ERGONOMICS}, author={Mirka, GA and Smith, C and Shivers, C and Taylor, J}, year={2002}, month={May}, pages={263–273} }
 @article{mirka_shivers_smith_taylor_2002, title={Ergonomic interventions for the furniture manufacturing industry. Part II - Handtools}, volume={29}, ISSN={["0169-8141"]}, DOI={10.1016/S0169-8141(01)00068-3}, abstractNote={The objectives of this intervention research project were to develop and evaluate engineering controls for the reduction of the upper extremity injury risk in workers in the furniture manufacturing industry. The analysis of OSHA Form 200 logs and surveys of furniture workers revealed that upholsterers, workers who use random orbital sanders and workers who use spray guns are at higher levels of risk of illness than the rest of the working population. An on-site ergonomic analysis of these three jobs was performed and the following risk factors were identified for each of these three work groups: upholsterers—repetitive, high-force pinch grips; sanders—long-duration static grip forces; and sprayers—awkward postures (ulnar wrist deviations and wrist flexion). Engineering interventions in the form of new or modified handtools were then evaluated in the laboratory to assess their effectiveness in reducing exposure to these risk factors. For sanding, an interface was created that secured the hand to the sander with the intention of reducing the need for static grip forces during sanding. A new handtool was created for upholsterers that replaced the repetitive pinch grips with a power grip. Finally, a commercially available spray gun with ergonomic features was evaluated. Each of these modified tools/methods was compared with the standard methods typically used in industry. The results show that most of the intended beneficial effects were realized. The random orbital sander interface reduced extensor muscle activities by an average of 30%. The upholstery handtool reduced the intrinsic hand muscle activities by an average of 51%. The effects of the adapted spray gun were most prominent when working on horizontal surfaces and showed an average reduction of 40° of wrist flexion and 14° of ulnar deviation as compared to the standard pistol grip spray gun in this activity. The ergonomic intervention research described in this report documents a reduction in exposure to risk factors for upper extremity cumulative trauma disorders for three work activities in the furniture manufacturing industry.}, number={5}, journal={INTERNATIONAL JOURNAL OF INDUSTRIAL ERGONOMICS}, author={Mirka, GA and Shivers, C and Smith, C and Taylor, J}, year={2002}, month={May}, pages={275–287} }
 @article{psihogios_sommerich_mirka_moon_2001, title={A field evaluation of monitor placement effects in VDT users}, volume={32}, ISSN={["0003-6870"]}, DOI={10.1016/S0003-6870(01)00014-X}, abstractNote={Appropriate visual display terminal (VDT) location is a subject of ongoing debate. Generally, visual strain is associated with higher placement, and musculoskeletal strain is associated with lower placement. Seeking resolution of the debate, this paper provides a comparison of results from previous lab-based monitor placement studies to recommendations and outcomes from viewing preference and neutral posture studies. The paper then presents results from a field study that addressed two outstanding issues: Does monitor placement in a workplace elicit postures and discomfort responses similar to those seen in laboratory settings? Results showed placements in the workplace elicited postures similar to those in lab studies. Additionally, preferred VDT location generally corresponded to the location in which less neck discomfort was reported, though that trend requires further investigation. Overall, there seems to be consistent evidence to support mid-level or somewhat higher placement, as a rule-of-thumb, considering preferred gaze angle and musculoskeletal concerns. However, optimal placement may be lower for some individuals or tasks.}, number={4}, journal={APPLIED ERGONOMICS}, author={Psihogios, JP and Sommerich, CM and Mirka, GA and Moon, SD}, year={2001}, month={Aug}, pages={313–325} }
 @article{lutz_starr_smith_stewart_monroe_joines_mirka_2001, title={The use of mirrors during an assembly task: a study of ergonomics and productivity}, volume={44}, DOI={10.1080/001401301750048222}, abstractNote={Industrial assembly tasks often require awkward, sustained neck and/or shoulder postures that can lead to increased musculoskeletal discomfort and reduced productivity. The aim of this study was to investigate the effects of mirror and periscope visual aids as ergonomic interventions designed to eliminate awkward postures of the cervicobrachial region during assembly tasks. Participants simulated a simple assembly task by using a cordless screwdriver to drive screws into a pre-tapped aluminium block. Trials of 15 min were run for each of four distinct assembly workstation configurations: industry standard (in-line screwdriver, work at elbow height, no visual aid); pistol grip (pistol grip screwdriver, work at shoulder height, no visual aid); mirror (in-line screwdriver, work at elbow height, single mirror visual aid); and periscope (in-line screwdriver, work at elbow height, two-mirror visual aid system). Muscular activity, discomfort, body posture, productivity and operator subjective assessment were recorded to determine the effects of the visual aid interventions. The results show that when comparing the interventions to the industry standard condition, there was a 45% reduction in average cervical erector spinae activity, a 90% reduction in average neck flexion angle and a 72% reduction in neck discomfort with the interventions. When comparing these interventions to the pistol grip condition there was an 80% reduction in activity of the dominant side deltoid, a 92% reduction in shoulder flexion angle and an 81% decrease in shoulder discomfort with the interventions. Productivity was greatest in the industry standard configuration followed by the pistol grip (9% lower), the periscope (13% lower) and the mirror (23% lower) configurations. A follow-up study that compared the productivity of the periscope configuration with that of the industry standard configuration showed that within a 4-h work period this productivity differential decreased by over 33%.}, number={2}, journal={Ergonomics}, author={Lutz, T. J. and Starr, H. and Smith, C. A. and Stewart, A. M. and Monroe, M. J. and Joines, S. M. B. and Mirka, G. A.}, year={2001}, pages={215–228} }
 @article{mirka_glasscock_stanfield_wilson_2000, title={An empirical approach to characterizing trunk muscle coactivation using simulation input modeling techniques}, volume={33}, ISSN={["0021-9290"]}, DOI={10.1016/s0021-9290(00)00151-2}, abstractNote={Accurately describing trunk muscle coactivation is fundamental to quantifying the spine reaction forces that occur during lifting tasks and has been the focus of a great deal of research in the spine biomechanics literature. One limitation of previous approaches has been a lack of consideration given to the variability in these coactivation strategies. The research presented in this paper is an empirical approach to quantifying and modeling trunk muscle coactivation using simulation input modeling techniques. Electromyographic (EMG) data were collected from 28 human subjects as they performed controlled trunk extension exertions. These exertions included isokinetic (10 and 45°/s) and constant acceleration (50°/s/s) trunk extensions in symmetric and asymmetric (30°) postures at two levels of trunk extension moment (30 and 80 Nm). The EMG data were collected from the right and left pairs of the erector spinae, latissimus dorsi, rectus abdominis, external obliques and internal obliques. Each subject performed nine repetitions of each combination of independent variables. The data collected during these trials were used to develop marginal distributions of trunk muscle activity as well as a 10×10 correlation matrix that described how the muscles cooperated to produce these extension torques. These elements were then combined to generate multivariate distributions describing the coactivation of the trunk musculature. An analysis of these distributions revealed that increases in extension moment, extension velocity and sagittal flexion angle created increases in both the mean and the variance of the distributions of the muscular response, while increases in the rate of trunk extension acceleration decreased both the mean and variance of the distributions of activity across all muscles considered. Increases in trunk asymmetry created a decrease in mean of the ipsi–lateral erector spinae and an increase in the mean of all other muscles considered, but there was little change in the variance of these distributions as a function of asymmetry.}, number={12}, journal={JOURNAL OF BIOMECHANICS}, author={Mirka, GA and Glasscock, NF and Stanfield, PM and Wilson, JR}, year={2000}, month={Dec}, pages={1701–1704} }
 @article{mirka_kelaher_nay_lawrence_2000, title={Continuous assessment of back stress (CABS): A new method to quantify low-back stress in jobs with variable biomechanical demands}, volume={42}, ISSN={["0018-7208"]}, DOI={10.1518/001872000779656525}, abstractNote={ Jobs with a high degree of variability in manual materials handling requirements expose limitations in current low-back injury risk assessment tools and emphasize the need for a probabilistic representation of the biomechanical stress in order to quantify both acute and cumulative trauma risk. We developed a hybrid assessment methodology that employs established assessment tools and then represents their evaluations in a way that emphasizes the distributions of biomechanical stress. Construction work activities in the home building industry were evaluated because of the high degree of variability in the manual material handling requirements. Each task was evaluated using the Revised NIOSH Lifting Equation, The University of Michigan Three- Dimensional Static Strength Prediction Program™, and the Ohio State University Lumbar Motion Monitor Model. The output from each model was presented as time-weighted histograms of low-back stress, and the assessments were compared. The results showed considerable differences in what were considered high-risk activities, indicating that these 3 assessment tools consider the risk of low-back injury from different perspectives. The time-weighted distribution aspect of this methodology also contributed vital information toward the identification of high-risk activities. These results illustrate the necessity for more advanced low-back injury risk assessment techniques for jobs with highly variable manual materials handling requirements. }, number={2}, journal={HUMAN FACTORS}, author={Mirka, GA and Kelaher, DP and Nay, DT and Lawrence, BM}, year={2000}, pages={209–225} }
 @article{kelaher_mirka_dudziak_2000, title={Effects of semi-rigid arch-support orthotics: an investigation with potential ergonomic implications}, volume={31}, ISSN={["0003-6870"]}, DOI={10.1016/S0003-6870(00)00018-1}, abstractNote={For many years, arch-support orthotics have been prescribed for individuals with discomfort and/or abnormal skeletal alignments in the structures of the lower extremity. Recently there has been an increased interest in promoting semi-rigid orthotics as an ergonomic aid for asymptomatic workers who must stand all day at their workplace. A laboratory study was performed to assess the biomechanical impact of prefabricated semi-rigid orthotics on asymptomatic individuals. Ten subjects wore semi-rigid arch-support orthotics (experimental condition) for two months and flexible polyurethane/Sorbothane ® shoe inserts (control condition) for two months. Throughout this 18-week testing period, the subjects returned to the lab to perform a battery of assessment tests at regularly scheduled intervals. These tests examined subject strength, standing posture, stability, fatigue effects, and body part discomfort. The results of this study showed no significant changes in the strength, posture, or stability as a function of insert type. The subjects reported a reduction in low-back discomfort along with an increase in foot discomfort during a fatiguing exertion task while wearing the semi-rigid orthotics as compared to the control condition.}, number={5}, journal={APPLIED ERGONOMICS}, author={Kelaher, D and Mirka, GA and Dudziak, KQ}, year={2000}, month={Oct}, pages={515–522} }
 @article{davis_mirka_2000, title={Transverse-contour modeling of trunk muscle-distributed forces and spinal loads during lifting and twisting}, volume={25}, number={2}, journal={Spine (Philadelphia, Pa. 1976)}, author={Davis, J. R. and Mirka, G. A.}, year={2000}, pages={180–189} }
 @article{glasscock_turville_joines_mirka_1999, title={The Effect of Personality Type on Muscle Coactivation during Elbow Flexion}, volume={41}, ISSN={0018-7208 1547-8181}, url={http://dx.doi.org/10.1518/001872099779577318}, DOI={10.1518/001872099779577318}, abstractNote={ A great deal of interest has been generated recently regarding the influence that psychosocial factors may have on the reporting of and disability associated with work-related musculoskeletal disorders. The current study considers the potential influence of one psychosocial factor - personality type - on basic neuromuscular control strategies and biomechanical loading. The study investigated the hypothesis that Type A people exhibit increased muscular antagonism relative to their Type B counterparts. Volunteers participated in an EMG-based biomechanical study to investigate the co-activation patterns of the major muscles that span the elbow joint during elbow flexion exertions. Results showed that, averaging across all conditions, the antagonist muscle activity was significantly higher for Type A individuals than for their Type B counterparts (10% of maximum for Type A, 5.5% of maximum for Type B). Although the study was somewhat limited in its size and scope, the results indicate that certain psychosocial factors may be more than a filter in postinjury response and may directly influence biomechanical loading. A potential application of this research is an increased awareness that certain individuals may be at greater risk of developing work-related musculoskeletal disorders. }, number={1}, journal={Human Factors: The Journal of the Human Factors and Ergonomics Society}, publisher={SAGE Publications}, author={Glasscock, Naomi F. and Turville, Kristine L. and Joines, Sharon B. and Mirka, Gary A.}, year={1999}, month={Mar}, pages={51–60} }
 @inbook{sommerich_mirka_1998, title={Managing work-related musculoskeletal injuries}, booktitle={Ergonomics in manufacturing: Raising productivity through workplace improvement (Ch. 19)}, publisher={Dearborn, Mich.: Society of Manufacturing Engineers; Norcross, Ga.: Engineering & Management Press}, author={Sommerich, C. M. and Mirka, G. A.}, editor={Karwowski, W. and Salvendy, G.Editors}, year={1998} }
 @article{turville_psihogios_ulmer_mirka_1998, title={The effects of video display terminal height on the operator: a comparison of the 15 degrees and 40 degrees recommendations}, volume={29}, ISSN={["0003-6870"]}, DOI={10.1016/S0003-6870(97)00048-3}, abstractNote={Prolonged use of video display terminals (VDTs) has been shown to be a risk factor for musculoskeletal and visual discomfort. A standard workplace design recommendation is to position the centre of the VDT 15 degrees below horizontal eye level. Recently a viewing angle of 40 degrees below horizontal has been suggested based on studies that have indicated that this is the preferred viewing angle for visually intensive tasks. The goal of this study was to investigate the effects of these two VDT positions on muscular activity, muscular fatigue, head/neck posture, visual acuity, operator performance (productivity and quality), heart rate and operator subjective assessment. The experimental task consisted of reading text from a computer screen and answering reading comprehension questions using a mouse and a keyboard. Each experimental session lasted 2 h. The 40 degree VDT position showed significantly greater head tilt angles and higher muscle activity levels for six of the 10 neck, shoulder and back muscles sampled. No significant differences in visual acuity, operator performance or heart rate were detected as a result of monitor location. Seven of the 12 subjects preferred the 15 degree monitor position.}, number={4}, journal={APPLIED ERGONOMICS}, author={Turville, KL and Psihogios, JP and Ulmer, TR and Mirka, GA}, year={1998}, month={Aug}, pages={239–246} }
 @article{mirka_kelaher_baker_harrison_davis_1997, title={Selective activation of the external oblique musculature during axial torque production}, volume={12}, number={3}, journal={Clinical Biomechanics (Bristol, Avon)}, author={Mirka, G. A. and Kelaher, D. P. and Baker, A. and Harrison, A. and Davis, J. R.}, year={1997}, pages={172–180} }