• Journal of the Ergonomics Society of Korea
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• v.24 no.3
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• pp.11-27
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• 2005

The objectives of this study are to analyze representative wrist postures while using hand tools and parts at general assembly processes, to evaluate perceived discomfort on the wrist when external loads are present, and to suggest an evaluation and prediction model of perceived discomfort. Sixteen subjects participated in an experiment to appraise perceived discomfort. Three types of the wrist postures with five levels of non-neutralities were analyzed when five levels of external load were applied to each posture. The ANOVA results showed that the perceived discomfort of wrist postures was significantly affected by both the wrist posture and external load (p$<$0.001). It was also shown that some of the interactions between external loads and the wrist postures(Flexion/$Extension^*$Load, Flexion/$Extension^*$supination/pronation, ulnar/radial $deviation^*$supination/pronation) were significant(p$<$0.001). The result implies that a new posture classification scheme for workload assessment methods may be needed to reflect such effects of external load and wrist posture. A regression model of perceived discomfort was developed with respect to wrist posture and external load from the experimental data. A subsequent experiment revealed that the correlation coefficient between the predicted values of perceived discomfort from the model and the actual values obtained from the experiment was about 0.98. It is expected that the results help to properly estimate the body stress resulting from worker's postures and external loads and can be used as a valuable design guideline to analyze potential hazard of musculoskeletal diseases in industry.

• Journal of the Ergonomics Society of Korea
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• v.28 no.3
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• pp.81-85
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• 2009

Work related musculoskeletal disorders(WMSDs) was a leading cause of sick leave and injuries in the industries of our country. Posture was an important consideration in the design of work method and workplaces, because it affected the ability of workers to use various equipments and influenced how long they could perform their job without feeling discomfort, fatigue, and musculoskeletal disorders. Imbalanced lower limb postures such as a squatting posture were awkward working postures common to the shipbuilding shops, farms, automobiles assembly lines in our country. Different awkward working postures were known to be associated with specific musculoskeletal disorders. Eight postures in lower limb postures divided into balanced and imbalanced postures were evaluated by electromyographic(EMG) activity for lower limb muscles. Twelve male subjects participated in this study. This paper was to analyze the effects of lower limb muscles workload according to lower limb postures(knee angle) and working time. The ANOVA results showed that most EMG root mean square(RMS) values were statistically significant effect according to lower limb postures(knee angle) and working time. Therefore, the results of this study will provide the basis to evaluate workload of lower limb postures correctly adopted by workers in various jobs and the ergonomic reference to prevent WMSDs.

• 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 Korean Biological Nursing Science
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• v.24 no.2
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• pp.131-139
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• 2022

Purpose: This study aimed to examine the changes in stress, occupational stress, and subjective health problems of novice female nurses within the first 18 months of work. Methods: This was a longitudinal study conducted with a secondary data analysis based on the Shift Work Nurse's Health and Turnover (SWNHT) study. The participants were 178 female novice nurses who participated in all 3 data collection activities (on the first day of orientation before ward placement [T0], 6 months after work [T1], and 18 months after work [T2]). The stress, occupational stress, 8 subjective health problems (upper musculoskeletal pain, leg/foot discomfort, depression, anxiety or emotional disorder, sleep disturbance, headache, gastrointestinal disorder, menstrual disorder, and others), and the greatest health problem during the study period were measured, respectively. Data were analyzed using SPSS 26.0 to obtain descriptive statistics. Results: The subjective health of novice female nurses were found to be poor at T1 compared to T0 on both physical (upper musculoskeletal pain, leg/foot discomfort, and sleep disturbance) and psychological health problems (depression and stress). However, the psychological health problems of the participants were alleviated at T2 whereas; physical health problems persisted until T2. Conclusion: Novice nurses had poor health problems 6 months after work. Sleep disturbance and musculoskeletal pain persisted although other health problems such as depression and stress were alleviated over the period. Strategies to prevent and manage different health problems of novice female nurses at different work duration are urgently needed.

• Journal of Korean Institute of Industrial Engineers
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• v.27 no.4
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• pp.413-423
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• 2001

Low back disorders (LBDs) are one of the most common and costly work-related musculoskeletal disorders. One of the major possible risk factors of LBDs is to work with static and awkward trunk postures, especially in a complex trunk posture involving flexion, twisting and lateral bending simultaneously. This study is to examine the effect of complex trunk postures on the postural stresses using a psychophysical method. Twelve healthy male students participated in an experiment, in which 29 different trunk postures were evaluated using the magnitude estimation method. The results showed that subjective discomfort significantly increased as the levels of trunk flexion, lateral bending and rotation increased. Significant interaction effects were found between rotation and lateral bending or flexion when the severe lateral bending or rotation were assumed, indicating that simultaneous occurrence of trunk flexion, lateral bending and rotation increases discomfort ratings synergistically. A postural workload evaluation scheme of trunk postures was proposed based on the angular deviation levels from the neutral position. Each trunk posture was assigned numerical stress index depending upon its discomfort rating, which was defined as the ratio of discomfort of a posture to that of its neutral posture. Four qualitative action categories for the stress index were also provided in order to enable practitioners to apply corrective actions appropriately. The proposed scheme is expected to be applied to several field areas for evaluating trunk postural stresses.

• Journal of the Korea Safety Management & Science
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• v.16 no.4
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• pp.371-378
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• 2014

Manual materials handling tasks are the main risk factors for the work-related musculoskeletal disorders. Many assistant tools for manual materials handling are being used in various kind of industries. One of them is a 4-wheeled cart which is widely used in manufacturing factories, hospitals, etc. The major force required to control the 4-wheeled cart is pushing and pulling. There are two types of handles being used for the 4-wheeled cart : vertical type (two vertical handles), and horizontal type (one horizontal handle). This study tried to investigate the pushing forces and subjective discomforts (hand/writst, shoulder, low back, and overall) of the two handle types with different handle height and distance conditions. Twelve healthy male students (mean age = 23.4 years) participated in the experiment. The independent variables were handle angle (horizontal, vertical), handle height (low, medium, high), and handle distance (narrow, medium, wide). The full factorial design was used for the experiment and the maximum pushing forces were measured in 18 different conditions ($2{\times}3{\times}3$). Analysis of variance (ANOVA) procedure was conducted to test the effects of the independent variables on the pushing force and discomfort levels. Handle height and angle were found to be the critical design factors that affect the maximal pushing forces and subjective discomfort. In the middle height, subjects exerted higher pushing forces, and experience lower discomfort levels compared to the high, and low height. There was no statistical influence of the handle distance to the pushing forces and subjective discomfort levels. It was found out that the effects of the handle angle (horizontal and vertical) on both pushing force and subjective discomfort were statistically significant (p < 0.05). The vertical handle revealed higher pushing force and lower discomfort level than the horizontal handle. The reason for that was thought to be the different postures of the hand when grasping the handles. The horizontal handle induced pronaton of the hand and made hand posture more deviated from the neutral position.

• Journal of the Ergonomics Society of Korea
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• v.28 no.1
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• pp.9-19
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• 2009

Repetitive movement, inadequate working posture, overuse of force, physical contact with sharp edge, vibration and temperature were well known risk factors of WMSDs (Work-related Musculoskeletal Disorders). Many researchers have investigated the relationship between inadequate working postures and incidences of WMSDs of the upper extremities, whereas relatively few researchers have tried to evaluate workload associated with the lower-body postures. The effects of lower-limb postures including various knee flexion angles on the subjective discomfort, heart rate and EMG of lower-limb muscles were investigated in this study. Thirty graduate students were asked to maintain thirteen different body postures, and heart rate and EMG data of five muscle groups (electro spine, biceps femoris, vastus medialis, gastrocnemius and tibialis anterior) from each posture were collected during fifteen minutes sustaining tasks. All participants were also asked to report their discomfort ratings of body parts. Results showed that high subjective discomfort ratings and heart rates were reported at the postures of knee angles of $60^{\circ}$ and $90^{\circ}$, whereas low discomfort ratings were founded at the postures of chair heights with 20cm, 40cm, and sitting with crossed legged. The change of median frequency for each muscle group during fifteen minutes tasks was investigated for each body posture to evaluate the relationship between muscle fatigue and body posture. It was found that the trends of changes of median frequency were different based on muscle group as well as lower-limb body posture from this study.

• 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.

• Safety and Health at Work
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• v.7 no.1
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• pp.49-54
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• 2016

Background: Prolonged sitting leads to low back discomfort and lumbopelvic muscle fatigue. This study examined the characteristics of body perceived discomfort and trunk muscle fatigue during 1 hour of sitting in three postures in office workers. Methods: Thirty workers sat for 1 hour in one of three sitting postures (i.e., upright, slumped, and forward leaning postures). Body discomfort was assessed using the Body Perceived Discomfort scale at the beginning and after 1 hour of sitting. Electromyographic (EMG) signals were recorded from superficial lumbar multifidus, iliocostalis lumborum pars thoracis, internal oblique (IO)/transversus abdominis (TrA), and rectus abdominis muscles during 1 hour of sitting. The median frequency (MDF) of the EMG power spectrum was calculated. Results: Regardless of the sitting posture, the Body Perceived Discomfort scores in the neck, shoulder, upper back, low back, and buttock significantly increased after 1 hour of sitting compared with baseline values ($t_{(9)}=-11.97$ to -2.69, p < 0.05). The MDF value of the EMG signal of rectus abdominis, iliocostalis lumborum pars thoracis, and multifidus muscles was unchanged over time in all three sitting postures. Only the right and left IO/TrA in the slumped sitting posture was significantly associated with decreased MDF over time (p = 0.019 to 0.041). Conclusion: Prolonged sitting led to increased body discomfort in the neck, shoulder, upper back, low back, and buttock. No sign of trunk muscle fatigue was detected over 1 hour of sitting in the upright and forward leaning postures. Prolonged slumped sitting may relate to IO/TrA muscle fatigue, which may compromise the stability of the spine, making it susceptible to injury.

• Journal of the Ergonomics Society of Korea
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• v.16 no.2
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• pp.73-82
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• 1997

Daily exposure to constrained body postures and deviations from neutral postures over a long period may result in discomfort as well as pains and aches in the muscles, joints, tendons, and other soft tissues. Furthermore, it was known that poor body postures are a major cause of musculoskeletal disorders in industry. Therefore, in this study, comfort ranges of joint motions were obtained as a criterion for evaluating body postures and designing workplaces ergonomically, which were bases on subjects' perceived discomfort level estimated by magnitude estimation. Nineteen healthy male subjects participated in the laboratory study. They results showed that comfort ranges of joint motions occurred in the wrist, elbow, neck, and ankle were little less than their normal range of joint motions, but those in the back(L5/S1) and hip joint were much less than their normal ones. This fact implies that the back and jip movements are more stressful than the other joints movements. It is expected that comfort ranges of joint motions can be used as a valuable guideline when designing and evaluating workplaces.