• Journal of the Korean Society of Safety
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• v.16 no.1
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• pp.79-83
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• 2001

Posture of the upper limbs in field works is known to be an important risk factor associated with CTD(Cumulative Trauma Disorders). In particular, uncomfortable posture and highly repetitive works in shipbuilding industry(for instance, sand blasting, grinding and blast painting, etc) made workers exposed to a great risk of injuries. The purpose of this paper is to analyze recruitment pattern of the muscles according to posture(joint angle displacement) during grinding. In this study, EMG signals of pectoralis major, latissimus dorsi, and posterior deltoid muscle were measured and analyzed from FlexComp EMG solution. And subjective ratings of perceived exertion were made using Borg's CR-10 rating scale.

• Journal of Korean Academy of Medicine & Therapy Science
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• v.10 no.2
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• pp.73-80
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• 2018

Objective: We developed an ergonomic pruning shears that allows the user to freely adjust the width of the grip and conducted this study to examine the effects of the pruning shears on grip strength and the fatigue of the fingers. Method: The maximum grip strength was first measured with an digital dynamometer, and the maximum grip strength was measured again after the subjects repeated scissoring 100 times using general pruning shears or ergonomic pruning shears. Borg's CR-10 scale was used to measure subjective fatigue after using the two pruning shears. Results: When the grip strength values after using the two pruning shears were compared with each other the mean grip strength after using ergonomic pruning shears was 27.69 kg, which was higher than that after using general pruning shears, 25.73 kg (p<.05). The subjective fatigue when the two pruning shears were used was shown to be 3.6 points for general pruning shears and 1.73 points for ergonomic pruning shears (p<.05). Conclusion: After repeating scissoring 100 times, the fatigue of the fingers was lower when ergonomic pruning shears were used than when general pruning shears were used and grip strength was higher when ergonomic pruning shears were used than when general pruning shears were used.

• Journal of the Korean Society of Safety
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• v.23 no.2
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• pp.30-36
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• 2008

This paper suggests the best work conditions, including short break time and number of mouse clicks on a computer, to prevent MSDs(Musculoskeletal Disorders) on VDT(Visual Display Terminal) work. Discomfort measures are calculated according to the Borg's CR-10 Scale. The short break time conditions are grouped into 7, 15, and 30 seconds after every 10-minute work period and the number of mouse clicks are divided into 10 clicks/min, 20clicks/min, and 30clicks/min. The result of the ANOVA on the shift value of subjective discomfort shows the following: 1) Regarding the break time and the number of mouse clicks, there are statistical differences between the measured values for the neck and the wrist(p<0.05). 2) Regarding the number of mouse clicks, there are statistical differences between the measured values for the shoulder and the forearm(p<0.1). 3) Regarding the break time and the number of mouse clicks, there are no statistical differences between the measures values for the eyes, upper arms and back(p<0.1).

• Journal of the Ergonomics Society of Korea
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• v.25 no.4
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• pp.145-151
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• 2006

The objective of this study is to investigate the perceived discomfort for postures combined with shoulder flexion/extension and elbow flexion, and external load. 12 healthy male undergraduate and graduate students participated in this experiment. Experimental variables were the shoulder flexion/extension angle(-20°, 0°, 45°, 90°, 135°), the elbow flexion angle (0°, 45°, 120°), and the external load(0, 1.5Kg, 3Kg) as independent variables and a whole body perceived discomfort using Borg's CR10 as a dependent variable. The subjects maintained the given posture for 60 seconds and then rated the perceived discomfort. The ANOVA results showed that all main factors and two-way interactions were statistically significant at α=0.05. As a result of regression analysis to examine the effect of external load on the perceived discomfort, the perceived discomfort linearly increased as the level of external load increased. Then, the effect of external load on the perceived discomfort was quantitatively classified into three levels based on the result of regression analysis.

• Journal of the Korean Society of Safety
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• v.28 no.1
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• pp.81-87
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• 2013

Crane operators usually work with their necks bent forward in a seating position for a long period. They have complained of their musculoskeletal stress at their necks. The objective of this study was to find the level of stress at the neck when crane operators bend their neck forward during their work. Experiments were conducted in the laboratory where subjects bent their necks forward for 1 minute and took a rest for 0.5 minute and repeated this performance for 60 minutes. Subjective evaluation using Borg's CR-10 scale and electromyography (EMG) were used to check the level of the stress at the neck. Subjects reported that the level of pain at the end of 60 min. experiment was close to the extreme pain(level 8.95). The EMG level(amplitude) increased 80% on the average and the center frequency of EMG shifted to the lower frequency level which indicated fatigue of neck muscles. Thus, it was found that there is quite much neck stress for crane operators when they maintain their neck posture of bending forward for a long time during their work. This information will be a basis in searching for an intervention measure for the crane operators' neck stress.

• Journal of the Ergonomics Society of Korea
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• v.18 no.2
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• pp.103-120
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• 1999

The purpose of this study was to evaluate the manual workload in repetitive wrist and finger motion. To evaluate manual workload, angular displacement of the joint, EMG of the muscle and subjective rating were studied. Both wrist motion and finger motion were studied. A screw-driving task was used for the wrist motion experiment. A keyboard typing task was used for the finger motion experiment. All finger joint angles and wrist angles were measured by an angle-measuring glove($CyberGlove^{TM}$, Virtual Technologies, Inc.). Surface EMG was recorded from FCU muscle and FDS muscle simultaneously with the angle measurement. Subjective ratings of exertion were also recorded using the modified Borg's CR-10 scale. Repetition rates of 0.5, 1, 2 motions per second were used with each task. As a result, manual workload increased with increasing repetitiveness. Peak spectral magnitude and frequency components corresponded closely with joint angular displacement amplitudes and repetition rates. Results of the correlation analysis showed that there were significant correlation among EMG, frequency-weighted motion and subjective measurement. Both EMG and frequency-weighted filtering showed consistent workload estimation with increasing task frequency. Subjective ratings showed slight over-estimation of the workload as the task frequency is increased.

• Journal of the Korean Society of Safety
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• v.23 no.5
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• pp.119-124
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• 2008

Many automobile assembly workers often do several cycles of tasks continuously, i.e., without breaks, to get a longer break. This is not recommended since the dose of fatigue increases exponetially with time and it takes much longer time to recover. In this study, a laboratory experiment was conducted to investigate the effect of work/rest schedules on workload of a repetitive upper-limb task. Eleven male subjects participated in the experiment, in which simulated screw driving tasks were carried out repetitively with 3 different work/rest schedules: standard breaks(1 cycle of work at a time, 60 20-s breaks), medium breaks(5 cycles of work at a time, 12 100-s breaks), and long breaks(10 cycles of work at a time, 6 200-s breaks). The result showed that medium- and long-breaks schedules significantly increased the level of perceived discomfort and %HRR as compared to the standard-break schedule. The subjects' preference was not statistically different among work/rest schedules, which might be caused from the absolutely low level of workload of the experimental tasks. From the results, it is recommended to have frequent and shorter breaks rather than infrequent and longer breaks to decrease the level of physical workload. A more expanded studies, however, should be carried out to provide more practical safety guidelines on the work practice of continuous working without breaks among automobile assembly workers.

• Fashion & Textile Research Journal
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• v.19 no.4
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• pp.504-514
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• 2017

Discomfort as well as muscular pain and musculoskeletal diseases occur in cases of stressed posture due to prolonged pressure. Therefore, the American Academy of Orthopaedic Surgeons (AAOS) and Pediatric Orthopaedic Society of North America (POSNA) recommend that bags that weigh no more than 15 - 20% of the wearer's weight. However, despite the prolonged pressure from using baby carriers, there are no recommendations and limited studies on how to protect wearers. Therefore, this study investigates subjective fatigue according to the usage of waist support and hip seat. Based on this, muscle fatigue and secondary subjective fatigue according to three types of currently commercial baby carriers (X-type, H-type, and H-hip type) were measured. Subjective comfortability was evaluated on a 5 point Likert-scale and subjective fatigue was evaluated on Borg's CR-10 scale. Objective muscle fatigue was also compared by measuring and analyzing electromyogram (EMG). The results of primary subjective fatigue showed statistically significant changes in the shoulders, waist, calves, and soles of the feet according to the usage of hip seats and waist support. Electromyogram measurements also showed less muscle fatigue at the upper trapezius muscle and thoracic erector spine muscle for the H-hip seat baby carrier, which has both waist support and hip seat, compared to an X-type baby carrier, which has neither. However, results of subjective fatigue showed opposite results at the waist despite having same results at the shoulders and beneath the shoulders. This show discrepancies between objective muscle fatigue and subjective fatigue; therefore, that both aspects must be taken into consideration when developing ergonomic baby carriers.

• Journal of the Ergonomics Society of Korea
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• v.28 no.4
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• pp.35-49
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• 2009

This study investigated perceived discomforts and those reasons of the young and middle-aged, the aged, the disabled and the pregnant in various daily activities, and elicited universal design factors based on human capacities (physical, sensory, cognitive and affective). A total of eighty people (twenty subjects for each user group) participated in one-to-one interviews about thirty six items of daily activities. A degree of discomfort of the daily activities was measured using Borg's CR10 scale. As a result, the disabled and the pregnant complained about almost all of the daily activities, and their degrees of discomforts were significantly higher than those of the youth and middle-aged and the aged. However, the youth and middle-aged and the aged only complained about some specific items. The major reasons of discomforts were related to physical and affective capabilities in general, where the detailed reasons of each user group were comparatively different. Finally, the universal design factors were elicited for each daily activity item based on the results of each user group. This study can be used to understand the discomforts and characteristics of the aged, the disabled and the pregnant in the various daily activities. The universal design factors elicited can also be applied to design related products and facilities universally.

• PNF and Movement
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• v.17 no.3
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• pp.379-389
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• 2019

Purpose: This study examined the effects of wheelchair handle directions on the trunk muscle activity of adult males when climbing ramps. It also evaluated the wheelchair attendant's physical discomfort during tasks. Methods: Healthy males aged over 20 years were chosen and the direction of wheelchair handle grip was randomly selected. The grips included a general grip with ulnar deviation, a medial grip with wrist pronation, and a neutral grip with a neutral wrist. The trunk muscle activity was measured using surface electromyography. Furthermore, the physical discomfort of wheelchair attendants was subjectively evaluated using the Borg CR-10 Scale, which rates the perceived exertion. In addition, the SPSS 18.0 program was used perform repeated measure ANOVA to compare muscle activity and subjective discomfort during the interventions. The contrast test was also conducted with a significance level (α) of 0.05. Results: There was significant difference between the general grip and the medial grip in the rhomboid major muscle and the lumbar erector spinae muscle (p<0.05). In addition, there was significant difference between the general grip and the neutral grip in the rhomboid major muscle and the lumbar erector spinae muscle (p<0.05). Further, there was significant difference between the general grip and the neutral grip in subjective discomfort (p<0.05). Conclusion: In this study, adult male trunk muscle activity and subjective discomfort were lowest when using the neutral grip while climbing ramps. Accordingly, we suggest that neutral grips will help improve the function of the musculoskeletal system and reduce the subjective discomfort by putting less strain on the trunk muscles and maximizing efficiency with less force.