• The Journal of Korean Physical Therapy
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• v.30 no.3
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• pp.96-99
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• 2018

Purpose: The purpose of this study was to determine the effects of a chair backrest on respiratory function after prolonged sitting. Methods: Twenty-four young healthy subjects (12 males and 12 females) volunteered to participate in this study, and were equally allocated to a backrest (n=12) or a without backrest group (n=12). A spirometer was used to measure the respiratory functions of all subjects. Results: The chair with backrest group were significant difference in forced vital capacity (FVC), Forced expiratory volume in 1 second (FEV1), and peak expiratory flow (PEF) after sitting for 1 hour, compared with chair without backrest group (p<0.05). The chair with backrest group showed a significantly decreased in FVC, FEV1, and PEF. Conclusion: Using a chair without a backrest may help to reduce lung function deterioration as compared with a chair with a backrest.

• Korean Journal of Applied Biomechanics
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• v.33 no.1
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• pp.1-9
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• 2023

Objective: This study identifies the difference among the heights of a chair's backrest (High, Mid, No), the biomechanical changes chair users undergo over time, and the variables that can measure musculoskeletal disorders, eventually providing information on the appropriate type of backrest. Method: Eleven healthy subjects in their 20s and 30s who had no experience with musculoskeletal disorders or surgical operations within the last 6 months participated in this study. Computer typing tasks were randomly designated and performed according to the type of chair backrest, and evaluation was performed for Flexion-Relaxation Ratio (FRR) analysis after the computer typing tasks. This study used eight infrared cameras (sampling rate: 100 Hz) and nine-channel electromyography (sampling rate: 1,000 Hz). ANOVA with repeated measures was conducted to verify the results, with the statistical significance level being α = .05. Results: Although there was no significant difference in craniovertebral angle (CVA), this study showed time and interaction effects depending on the height of the backrest (p<.05). When working without the backrest, the head-spine angle was lower compared to the chairs with backrest, based on the computer work. As for the head angle, the higher the back of the chair was, the less the head flexion and the body angle became, whereas the body flexion became less when there was a backrest. In addition, the body flexion increased over time in all types of backrests (p<.05). The muscle activity of the upper body tended to be high in the high backrest chair. On the other hand, a lower muscle activity was found with a low backrest. Conclusion: These results show that a chair is more ergonomic when the body angle is correctly set without bending and when it is supported by a low backrest. Accordingly, this study determines that the backrest affects shoulder and neck musculoskeletal disorders during typing and that medium-height backrest chairs can help prevent musculoskeletal disorders, contrary to the expectation that high-backrest chairs are preferable.

• Journal of Korean Physical Therapy Science
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• v.13 no.3
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• pp.15-25
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• 2006

The purpose of this study was to investigate effects of different chair type (with backrest chair and without backrest chair) and pelvic position (anterior pelvic tilting and posterior pelvic tilting) on three abdominal muscles (upper rectus abdominis, external oblique, internal oblique) and back extensor activation during lower extremity exercise. The four different conditions during bilateral knee extension exercise were: (1) leaning on backrest chair with anterior pelvic tilting, (2) leaning on backrest chair with posterior pelvic tilting, (3) anterior pelvic tilting without backrest chair, and (4) posterior pelvic tilting without backrest chair. Fifteen healthy male subjects with no history of neuromusculoskeletal disease voluntarily participated in this study. Electromyography (EMG) was used to collect muscle activation data, and muscle activation data was expressed as a percentage of maximal voluntary isometric contraction (%MVIC). One-way repeated analysis of variance (ANOVA) was used to determine the statistical significance, and Bonferroni comparison was used as a post hoc test. The results of this study were the following: (1) Erector spinae activation was significantly lower in posterior pelvic tilting without backrest compared with that in leaning on backrest chair with anterior pelvic tilting. (2) Upper rectus abdominis activation was significantly lower than erector spinae in all four different chair type and pelvic tilting conditions.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.376-380
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• 2000

All chairs are uncomfortable in the long run, but some chairs become uncomfortable more rapidly than others, and in any particular chair, some people will be more uncomfortable than others. Comfort will depend upon the interaction of chair characteristics, user characteristics, and task characteristics. In this study, we intend to design the comfortable office chair by investigating the anthropometric and biomechanical aspects for Korean. Therefore, we determine the design dimensions using the analysis of anthropometric data. With these dimensions, we design the chair mechanism of which backrest reclines with increasing chair pan declination. This mechanism allows the back to get adequate support at the correct level for any backrest declination. Also, the lumbar support in the backrest descends with increasing backrest reclining. By using this chair, a considerably better sitting posture can be obtained, and uncomfortable feeling and back pain may be prevented.

• Journal of the Ergonomics Society of Korea
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• v.34 no.2
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• pp.151-165
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• 2015

Objective: This study aims to develop and scientifically investigate the efficacy of the Spine S-curve Reactive Backrest that responds to the spine curvature of the user when seated, and maintains and enhances the natural S-curve of the lower back, thereby helping to relieve fatigue, correct posture and prevent spine deformities. Background: The focus of current development, design guidelines and/or standards for office chairs is mainly placed on the chair's dimensions, incline angle, adjusting features and lumbar support. Research and development was called for developing a chair backrest that maintains and improves the S-curve of the full spine. Method: The Spine S-curve Reactive Backrest was ergonomically designed to maintain correct posture and enhance user comfort. When leaned on, the backrest responds to the user's spine line and the whole lower back sits closely against the backrest, thereby aligning the user's lower back and backrest as one to maintain and improve the natural S-curve formation of the spine. In order to evaluate the efficacy of the newly designed chair (new design) and the comparison target (chair), five male college students of standard body type with normal spine curvature were selected as test subjects, and a motion analyzer and electromyography were utilized to measure S-curve and erector spinae muscle activity when seated. Results: The spine S-curve was better maintained and improved when sitting in the new design than in the comparison chair. Particularly notable was the greater displacement gap of the thoracic spine than the cervical spine, and also that of the lumbar more than the thoracic spine, with the increase of the backrest tilting angle. Furthermore, the electromyogram results showed the new design caused a lower fatigue level of the erector spinae muscles compared to the comparison chair, and also earned a higher preference in the subjective opinion results. Conclusion: The newly designed chair in this study responds to the user's spine curvature and maintains and enhances the lower back's natural S-curve, and thereby relieves fatigue, promotes better posture, and helps to prevent spine deformities better than existing office chairs. There is a need to widely introduce and supply this new design. Application: The new design is applicable to office and student chairs, and is expected to improve concentration and work efficiency.

• Journal of the Ergonomics Society of Korea
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• v.32 no.1
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• pp.145-152
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• 2013

Objective: The aim of this study is to develop an ergonomic office chair that has an alarm function for the unbalanced sitting postures. Background: Contrary to expectation, it is reported that office workers sit on their chairs much more in unbalanced postures during daily work. Even though an office worker uses an ergonomically good-designed chair and begins their work in a good sitting posture, his/her posture is likely to shift to the unbalanced bad posture. Therefore, a posture alarm system would be very helpful in keeping office workers' good postures. Method: We developed a prototype chair with four load cells under a seat pan and one load cell beneath a backrest. Through some experiments, we set the criteria for unbalanced bad postures then implemented the criteria into the alarm system of the prototype chair. The chair called e-BASE chair could detect unbalance postures and show alarms for chair users. We also enhanced back support by developing a step-wised folding backrest. Results: The e-BASE chair showed better performance in interface pressure distributions and balanced posture ratio in VDT work. Conclusion: The ergonomic chair with posture alarm function(e-BASE chair) was developed. It showed better performance in seat pressure distribution and in keeping good posture during office work. Application: The posture alarm system and folding backrest can be applied to the new models of office chair.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.167-174
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• 2010

In this study, the optimal position for the backrest pivot of an office chair was investigated by evaluating its performance in terms of the lumbar support and sliding distance of the back from the backrest during tilting motions. The simulation was performed using a mathematical model, which included a human body and a chair. Forty-two backrest pivot points were selected on the sagittal plane around the hip joint of a sitting model. A motion analysis study was also performed using a prototype of an office chair (A-type) with a backrest pivot located on the hip joint of a normal Korean model and a typical office chair (B-type) with its pivot located under the seat. The simulation results showed that both the lordosis angle and the slide distance of the back were minimized when the backrest pivot was positioned close to the hip joint. The experimental results showed that the slide distance and gap between the sitter's lumbar and the backrest was smaller with the A-type than the B-type. Based on the simulation and experimental results, it can be concluded that the backrest can support the sitter's lumbar area more effectively as the pivot position for reclining approaches closer to the hip joint. In this position, the sitter can maintain a comfortable and healthy sitting posture. This paper presents the methods and guidelines for designing an office chair with ergonomic considerations.

• The Journal of Korea Robotics Society
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• v.4 no.3
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• pp.243-249
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• 2009

In modern society, people spend most of their time on various types of chairs. However, it is not easy for a designer to design a comfortable chair because satisfaction with the chair depends not only on the quantitative elements such as size, but also on the qualitative element such as the user's feeling. To deal with these problems, there have been many studies on designing ergonomic chairs. This paper proposes the haptic-aided design (HAD) system to design an ergonomic chair. Based on the HAD system, the designer can experience whether the chair is comfortable or not through the haptic device, and also can modify the design parameters instantaneously. The haptic chair capable of controlling the design parameters in real time was proposed as a haptic simulator. The controllable parameters, such as seat height, reclining angle, stiffness of the backrest, and so on were selected based on the previous research related to ergonomic chairs. The proposed methodology will help reduce the development cost and time by replacing the process of making the real mock-ups and prototypes with the haptic chair.

• Physical Therapy Korea
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• v.11 no.1
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• pp.19-25
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• 2004

The purpose of this study was to investigate the effects of backrests of varying degrees ($90^{\circ}$, $100^{\circ}$, $110^{\circ}$) on three abdominal muscles (upper rectus abdominis, external oblique, internal oblique) and back extensor activation during lower extremity exercise. The three different conditions during bilateral knee extention exercise were: (1) leaning on a chair with a $90^{\circ}$ backrest, (2) leaning on a chair with a $100^{\circ}$ backrest, (3) leaning on a chair with a $110^{\circ}$ backrest. Fifteen healthy muscle subjects (mean age=24.2 years [SD=2.96], mean height=175.6 cm [SD=7.46], mean weight=69.1 kg [SD=7.36]) with no history of neuromusculoskeletal disease voluntarily participated in this study. Electromyography was used to collect muscle activation, and the muscle activation was expressed as a percentage of maximal voluntary isometric contraction (%MVIC). Repeated one-way analysis of variance (ANOVA) was used to determine the statistical significance. The results were as follows: (1) upper rectus abdominis, external oblique, internal oblique activation measured significantly lower. (2) measured significantly lower when lower degree.

• Physical Therapy Korea
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• v.19 no.1
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• pp.46-55
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• 2012

The purpose of this study was to investigate the effect of the two different types of chairs on trapezius muscle activation during dictation tasks. Seventeen university students, each of whom were within ${\pm}1$ standard deviation of the mean Korean standard body size, voluntarily participated in this study. Surface electromyography was used to collect electrical signals from both the upper and lower trapezius muscles. Amplitude Probability Distribution Function (APDF) was performed to analyze the muscle activity. The findings of this study were 1) The backrest-point height of the auditorium chair and the height, length and width of the connected desk were shorter than what was suggested by the KS. Another difference was that the auditorium chair had a bigger angle of the backrest compared to the classroom chair. 2) Regarding within-subject effect the sole statistically significant difference was found between activation of the upper trapezius muscle. The upper trapezius muscle's %RVC in the APDF 10th-50th-90th percentile was statistically higher for participants sitting in the auditorium chair than for participants sitting in the classroom chair (p<.05). 3) There was an interaction effect between the 'two chair-types' and the 'two muscle-sides' in the APDF 10th-50th percentile (p<.05). 4) There was an interaction effect between the 'two chair-types' and the 'three gaze-direction' in the APDF 90th percentile (p<.05). The findings of this study indicated that maintaining a writing posture for a prolonged period of time in an auditorium chair significantly increased the left upper trapezius muscle activation compared to a classroom chair.