• Journal of the Ergonomics Society of Korea
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• v.15 no.2
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• pp.177-184
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• 1996

In light-weight hand tools, static posture may result in postural fatigue. Psotural tremor of the upper extremity in a static posture was measured to provide guidelines for hand tool weight. Postural tremor was measured on five levels of tool weitht : no weight, 400g, 800g, 1200g, and 1600g. Three types of camcorder recording postures were selected. For each condition, postural tremor was measured together with ENG of biceps, deltoid and pectoralis major, and Borg's CR-20 ratings of perceved exertion. Results of the experiment are as follows : frequency analysis of tremor revealed increased amplitude of frequency bands of 2-4Hz and 10-14Hz. Postural tremor of the upper extremeity maintained the initial level until fatigue developed. After the development of fatigue, the rate of change of postural tremor significantly increased. Different tool weights and hand postures showed different rates of tremor increase. Time tp fatigue and corresaponding endurance time were positively correlated with Borg's RPE scores.

• Journal of the Ergonomics Society of Korea
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• v.33 no.6
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• pp.565-575
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• 2014

Objective: The aim of this study is to evaluate the effect of weight of load and time on the physical workload of repetitive upper-limb tasks with handling light weight loads using EMG and perceived discomfort, and to investigate the relationship between EMG and perceived discomfort for those repetitive tasks of moving light weight loads. Background: Repetitive upper-limb motion is known as one of the main risk factors of musculoskeletal disorders, and a lot of repetitive tasks are carried out while handling light weight loads in the industry. In evaluating the workload of repetitive tasks handling light weight loads, EMG and perceived discomfort can be used, though their relationship in those work conditions are not much investigated. Method: A laboratory experiment with 18 healthy males were conducted to record EMG signals from 5 muscle sites of the right arm and shoulder and rate perceived discomforts for the body parts and the whole body while carrying out repetitive materials-handling tasks for 52min. The subjects were divided into 3 groups which handled the loads of 1kg, 2kg and 3kg, respectively. ANOVAs were conducted to analyze the effects of the weight and time on RMS of EMG amplitude (normalized RMS: NRMS), median frequency of power spectrum of EMG (normalized MDF: NMDF) and perceived discomfort. The correlations between NRMS and NMDF and perceived discomfort were also analyzed. Results: Statistically significant muscular fatigue effects were not found from NRMS and NMDF in most muscles, while there were significant increases of discomfort as the task time elapsed. It was shown that there were an increasing trend of the muscular activity as the weight of load increased and a decreasing trend of median frequency of EMG of upper and lower arms as time elapsed. It was found that there were significant negative correlations between NMDFs from the lower arm and discomfort ratings, though the relationships were weak. Conclusion: It can be concluded that the working conditions adopted in this study were not enough to induce muscular fatigue, while there was significant increase in perceived discomfort. A further study is necessary to integrate the objective and subjective measures for more reliable and sensitive evaluation of workload of repetitive tasks of handling light weight loads. Application: This study can be used as a basic study for the evaluation of workload of repetitive tasks handling light weight loads.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.16 no.2
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• pp.129-134
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• 2005

Background and Objectives : Artecoll(R) is an injectable soft tissue filler, which is a suspension of polymethylmethacrylate microspheres in $3.5\%$ bovine collagen solution. The authors aimed to determine the clinical of Artecoll of Artecoll(R) as an injection material into the vocal fold to correct the glottal insufficiency caused by unilateral vocal cord paralysis. Materials and Methods : Forty-one consecutive patients with unilateral vocal cord paralysis received percutaneous Artecoll injections under local anesthesia. Acoustic, aerodynamic and stroboscopic analyses were prospectively provided before, 1 week and 3 months after injection. Perceptual GRBAS grading by speech language pathologists and subjective ratings of the hoarseness and aspiration by the patients were also obtained. Results : Aerodynamic parameter(maximal phonation time) were significantly improved after the injection (p<0.05). Acoustic parameters (jitter and shimmer) were improved at the 3rd month follow-up. GRBAS uading and patients own subjective scaling of hoarseness and aspiration also showed significant improvement (p<0.05). Early or delayed significant side effects were not observed. Conclusion : Vocal fold injection with Artecoll is a convenient, safe and useful method of temporarily correcting the glottal insufficiency. Further long-term follow-up studies will answer the usefulness and safety of the Artecoll injection laryngoplasty.

• Journal of the Ergonomics Society of Korea
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• v.35 no.2
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• pp.67-74
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• 2016

Objective: The aim of this study is to develop a farming shovel to reduce workload, which helps farmers lower the risk of musculoskeletal disease. Background: Most of work using farming tools including shovels requires repetitive works and awkward postures on body parts, and it could possibly cause work-related musculoskeletal disorders. It is necessary to develop and distribute farm equipment and tools in order to reduce physical workload. Method: To improve the most uncomfortable task perceived by ten farmers during the work with a shovel, the improved shovel was designed and made as a prototype for experiment for the comparison of the existing and improved shovels. Twenty males were recruited for this experiment, and muscle activity (%MVC) of six body parts and subjective discomfort ratings by body parts while working with a shovel were measured. A paired t-test was performed to compare physical workload between the existing shovel and the developed one. Results: A shovel applying foothold tied between shaft and blade was designed, which can help workers reduce repetitive bending of back and pressures for upper limbs while digging soil. According to compared evaluation of the developed shovel and the existing shovel, the developed shovel's %MVCs in all experimental muscles were significantly lower than those of the existing shovel. The developed shovel showed the biggest drop in perceived subjective discomfort rating of back, followed by arm and neck, compared to the existing shovel. Conclusion: It was confirmed that attaching a foothold to a shovel was an effective way of reducing workload in back and upper limbs during digging. Application: In the near future, if we put the prototype of developed shovel to practical use after making up for defects, it will help farm work environment be healthier and safer.

• Journal of the Ergonomics Society of Korea
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• v.26 no.3
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• pp.59-65
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• 2007

In this study, six grip spans (45mm-65mm) were tested to evaluate the effects of handle grip span and user's hand size on maximum grip strength, individual finger force, and subjective ratings of comfort using a digital dynamometer with individual force sensors. Forty-six males were assigned into three hand size groups according to their hand lengths. Results showed that overall 55mm and 50mm grip spans were the most comfortable sizes and associated with the highest grip strength in the maximum grip force exertions, whereas 65mm grip span was rated as the least comfortable size as well as the lowest grip strength. In the interaction effect of grip span and hand size, small and middle hand sized participants rated the best preference and the least preference grip spans differently with large hand sized participants. With respect to the analysis of individual finger force, the middle finger force was the strongest and the highest contribution to the total finger force, followed by ring, index and little fingers. In addition, it was noted that each finger had a different optimal grip span for exerting maximum force resulting in a bowed contoured shaped handle for two-handle hand tools. Thus, the grip spans for two-handle hand tools might be designed according to the users' hand and finger anthropometrics to maximize performance and subjective perception of comfort.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.6
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• pp.82-88
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• 2006

The study investigated how an adaptive cruise control system induced behavioral adaptation in drivers using a full-scale driving simulator. Forty drivers with different driving styles participated in the study to compare headway-time, vehicle lateral position variation, and head and eye movement when driving with and without the adaptive cruise control system. Results showed that system induced positive behavioral adaptation by drawing consistency in driving speed and headway-time regardless of the driving styles. However, the results also showed that the drivers' reliance on the system induced negative adaptation including reduced lane keeping ability and reduced attention during driving. As a strategy to prevent negative adaptation, the study proposed information service to drivers with the adaptive cruise control system status and driving environment, and investigated effectiveness of the service. Twelve drivers participated in the experiment to compare headway-time, vehicle lateral position variation and subjective ratings when driving with and without the information service. Results showed that the information service assisted the drivers to maintain safer and more comfortable headway-time without impairing drivers' steering ability.

• Journal of Korean Institute of Industrial Engineers
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• v.32 no.3
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• pp.236-241
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• 2006

Monitor height is one of the key factors in the VDT workstation design. Most of the previous studies have focused on traditional VDT workplace where the operators performed data entry or word processing tasks using single monitor. This study aimed to suggest proper monitor height when the main task was monitoring information from different number of information sources. Twelve male students participated in three experiments: single information source (one monitor), two information sources (one monitor and one CCTV), and three information sources (one monitor, one CCTV and a window). Subjects performed monitoring tasks for 10 minutes with 3 different monitor center heights : 89.0 cm (Low), 111.3 cm (Middle), and 124.8 cm (High). Surface EMG signals of five neck muscles, subjective discomfort ratings, preference, and working postures were recorded. Results indicated that the middle height was proper for one monitor condition, but the low monitor height was recommended for more than two information sources.

• Journal of the Korean Society of Safety
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• v.23 no.1
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• pp.46-50
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• 2008

The purpose of the present study was to investigate the mariner's information characteristics in ship-ta-ship collision situation using the full mission ship-handling simulator. Risk levels of ship-to-ship collision were manipulated by whether the target ship complies with the naval regulations and by movement patterns of target ship. Dependent variables reflecting mariner's information characteristics in ship-ta-ship collision situation were measured in terms of radar detection reaction time, free recall performance of past navigation situation, and subjective ratings for the task difficulty. The results showed that, in general, the mariners appeared to be deteriorated in their radar detection reaction time and free recall performance as the risk of ship-ta-ship collision increased. Also, the mariners tended to rate required tasks more difficult in the high risk ship-ta-ship collision situation.

• Journal of Korean Institute of Industrial Engineers
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• v.30 no.2
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• pp.76-83
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• 2004

This study aimed to empirically investigate perceived discomfort depending upon external load, upper limb postures and their holding time. Discomfort was obtained through an experiment, in which external load, wrist flexion/extension, elbow flexion, shoulder flexion and adduction/abduction were used as experimental variables. The subjects were instructed to hold given postures for 60s and to rate their subjective discomfort scores at 5s, 20s, 40s and 60s by using the free modulus method of magnitude estimation. The results showed that while only external load and elbow flexion were statistically significant at the holding time of 5s at ${\alpha}=0.05$ or 0.10, external load and upper limb postures excluding shoulder adduction/abduction significantly affected discomfort ratings at 20s, 40s and 60s at ${\alpha}=0.01$ or 0.05. Discomfort scores were also significantly different between four posture holding times at ${\alpha}=0.01$. The effects of external load and holding time were much larger than those of upper limb postures. Based on the results of this study, it is recommended that external load and holding time as well as working postures betaken into consideration to precisely quantify postural load in industry.

• Journal of the Ergonomics Society of Korea
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• v.29 no.1
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• pp.73-82
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• 2010

The purpose of this study is to understand motion characteristics of older drivers during reaching seat belt compared to young drivers and to provide design guidelines in order to reduce discomfort for the elderly. The whole body kinematics of each subject was captured using 12-camera motion analysis system. Subjective ratings on discomfort levels were obtained simultaneously using a questionnaire. This paper first presents the result of motion characteristics of elderly drivers' reach motion to seat belt. Compared to young drivers, older drivers performed seat belt reach motions less efficiently and moved slower due to mostly the movement error. Older drivers also made use of reduced joint range of motion in cervical left rotation, lumbar left rotation and right shoulder adduction, which can be explained by their reduced active range of motions (AROMs). To compensate for their reduced joint range of motion, older drivers rotated pelvis more.