• 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 the Institute of Convergence Signal Processing
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• v.16 no.2
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• pp.56-62
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• 2015

In this study, we implemented an unconstraint ECG monitoring system on a chair. Nowadays, modern people spend most of their time sitting on the chair. Therefore, it is necessary to have an unconstraint ECG monitoring system that can be used for a long time. The implemented system can perform measurement even with clothes on and it has great advantage on motion artifacts. A pair of unconstraint electrodes are placed on the back of the chair. Amplifier and filters are designed to remove motion artifacts, The baseline noise and power line noise are filtered and very low level of bio-signal is amplified to give a final measurement. Control unit and wireless transmission unit are implemented. Analog signal is converted into digital signal and transmits biological signal to the PC and the smart phone. Therefore continuous ECG monitoring in daily life is made possible. A comparison experiment between Ag / AgCl electrode and unconstraint electrode is conducted to evaluate the performance of the implemented system. As a result, we confirm our unconstraint system can be used for daily life ECG monitoring.

• The Journal of Korean Physical Therapy
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• v.26 no.6
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• pp.449-452
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• 2014

Purpose: The purpose of this study was to analyze the coordination between trunk flexion and lower limb extension contributing to vertical propulsion during sit-to-stand (STS) at different chair heights in the elderly. Methods: Ten elderly subjects were asked to stand up at their natural speed from different chair heights : (1) $90^{\circ}$ knee flexion; (2) $100^{\circ}$ knee flexion; (3) $110^{\circ}$ knee flexion; and (4) $120^{\circ}$ knee flexion. A standard chair without a backrest or armrests was used in this study. To remove inertial effects of upper limb movements, subjects were asked to stand up from a chair with their arms crossed at the chest. Mean of results of three trials were used in the analysis at different knee flexion angles. Distances moved by the shoulder for compensatory trunk movement was recorded by motion analysis and vertical force was recorded under foot using force plates. Distances moved by the shoulder and vertical ground reaction force measurements were analyzed using repeated ANOVA. Results: Distances moved by the shoulder significantly decreased with higher chair (p<0.05). Vertical forces were not significant difference on chair heights (p>0.05), but results of pairwise comparisons for vertical force revealed significant difference between $90^{\circ}$ knee flexion and $120^{\circ}$ knee flexion (p<0.05). Conclusion: Trunk movement is probably used as a compensatory mechanism at low chair heights to increase lift-off from sitting by the elderly.

• Journal of the Ergonomics Society of Korea
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• v.33 no.2
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• pp.143-153
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• 2014

Objective: The aim of this study is to investigate the effects of trunk-forearm supported sitting on trunk flexion angle, trunk extensor fatigue and seat contact pressure. Background: The relationship between sitting posture and musculoskeletal disorders of the trunk extensor fatigue and seat contact pressure has been documented. The trunk-forearm support type ergonomic chair was devised from the fact that trunk-forearm support has been reported to reduce trunk extensor activity and discomfort. Method: Using three different sitting postures, upright ($P_1$), trunk-forearm supported ($P_2$) and normal sitting ($P_3$), six healthy subjects participated in the study. Motion capture system was used to collect head and trunk flexion angle, and surface electromyography (sEMG) was used to collect myoelectric signal of upper trapezius, lower trapezius, erector spinae, multifidus, and pressure mat system was used to measure seat contact pressure. Results: When trunk and forearm were supported by the ergonomic chair, higher head flexion angle showed upright > trunk-forearm supported > normal in order, and muscle fatigue showed less than upright and normal sitting. Mean seat contact pressure decreased 19% than upright sitting. But muscle fatigue was not affected by each condition. Conclusion: Trunk-forearm supported sitting of the ergonomic chair showed positive effect in respect of trunk and head flexion angle, trunk extensor fatigue, seat contact pressure. To acquire comprehensive understanding of the effectiveness of the ergonomic chair, further studies such as anatomical effects from measurement of external applied loading effect to the body from interface pressure analysis are required. Application: The results of the publishing trend analysis might help physiological effects of trunk-forearm support type chair.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.7
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• pp.667-667
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• 2015

• Proceedings of the KIEE Conference
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• 2002.07d
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• pp.2046-2048
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• 2002

In this paper, I designed the inverter pendulum controller to controll the position of a wheel-chair. I used coefficient diagram method (CDM) to design the controller. The CDM is available, because it can make an engineer know all about the characteristic, stability, response time and robustness, of closed loop system. Writing this paper, I simulated the controller to know wheather is can controll the position of wheel-chair using the theorem of inverter pandulum controll, and I identified the usefulness of it.

• Physical Therapy Korea
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• v.25 no.2
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• pp.1-12
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• 2018

Background: It is very difficult for hemiplegic patients to effectively perform the sit-to-stand (STS) movements independently because of several factors. Moreover, the analysis of STS motion in hemiplegic patients has been thus far confined to only muscle strength evaluation with little information available on structural and environmental factors of varying chair height and foot conditions. Objects: This study aimed to analyze the change in biomechanical factors (ground reaction force, center of mass displacement, and the angle and moment of joints) of the joints in the lower extremities with varying chair height and foot conditions in hemiplegic patients while they performed the STS movements. Methods: Nine hemiplegic patients voluntarily participated in this study. Their STS movements was analyzed in a total of nine sessions (one set of three consecutive sessions) with varying chair height and foot conditions. The biomechanical factors of the joints in the lower extremities were measured during the movements. Ground reaction force was measured using a force plate; and the other abovementioned parameters were measured using an infra-red camera. Two-way repeated analysis of variance was performed to determine the changes in biomechanical factors in the lower extremities with varying chair height and foot conditions. Results: No interaction was found between chair height and foot conditions (p>.05). All measured variables with varying chair height showed a significant difference (p<.05). Maximum joint flexion angle, maximum joint moment, and the displacement of the center of mass in foot conditions showed a significant difference (p<.05); however the maximum ground reaction force did not show a significant difference (p>.05). Conclusion: The findings suggest that hemiplegic patients can more stably and efficiently perform the STS movement with increased chair height and while they are bare-foot.

• 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.

• International journal of advanced smart convergence
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• v.9 no.3
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• pp.199-206
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• 2020

A wheelchair is an essential rehabilitation assistant device for the movement of paraplegia patients and generally paralyzed patients who cannot walk normally. In particular, the applicability of the manual/motorized wheelchair is gradually increasing. Until now, decelerators using belt, chain and worm gears, etc have been widely used. However, a decelerator takes a large space although it is a simple device and thus is not ideal for the driving part of manual/motorized wheelchair. For these reasons, in this study we developed a driving part producing a large driving force through a decelerator using planetary gears rather than conventional worm gear-based decelerator. We designed the tooth profile of the planetary gears for decelerator using Kisssoft program, In addition, we designed the driving part so as to apply it to the wheels of conventional wheelchairs, and then optimized the mechanism for the principles of manual/motorized transposition of the driving part and the operational principles. Based on the results of this study, we finally designed and manufactured a driving part for wheelchair decelerator in the form of planetary gears with 1 sun gear, 2 planetary gears and 1 ring gear.

• Journal of the Korean Society of Clothing and Textiles
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• v.17 no.2
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• pp.197-206
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• 1993

We studied relation between the clothing pressure applied by foundations(waist nipper, girdle, body suit) on the waist of bodies and muscular activity, feeling of tightness. The main results were summerized as follows ; 1. Clothing pressure applied by foundations was high in order of girdle>waist nipper>body suit, also clothing pressure was higher back than front and side, sitting on the chair than standing posture, ventral flection than repose. Individual differences, even if size of body was equal, were shown in clothing pressure applied by foundations with subcutaneous fat's amount in measuring region. 2. The muscular activity of rectus abdominis than obliquus externus abdominis was more affected by foundations in all kinds of postures and motions. Amplitude of electromyogram was high sitting on the chair than standing posture, but there was little difference with motion variation. The wearing girdle strongly affected on the muscular activities of rectus abdominis and obliquus externus abdominis as compared with waist nipper and body suit. 3. The value for feeling of tightness by wearing waist nipper was higher than girdle and body suit. Also the case when sitting on the chair and ventral flection, the value for feeling of tightness was high. When the foundations were on the body, most tightened on the region of the body was anterior abdominal region.