• 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 KSNVE
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• v.10 no.2
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• pp.269-279
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• 2000

This paper deals with the development of biomechanical model on a seat with backrest support in the vertical direction. Four kinds of biomechanical models are discussed to depict human motion. One DOF model mainly describes z-axis motion of hip, two and three DOF models describe z-axis of hip and head, and while nine DOF model suggested in this study represents more motion than the otehr model. Three kinds of experiments were executed to validate these models. The first one was to measure the acceleration of the floor and hip surface in z-axis, the back surface in x-axis, and the head in z-axis under exciter. From this measurement, the transmissiblities of each subject were obtained. The second one was the measurement of the joint position by the device having pointer and the measurement of contact position between the human body and the seat by body pressure distribution. The third one was the measurement of the seat and back cushion by dummy. The biomechanical model parameters were obtained by matching the simulated to the experimental transmissiblities at the hip, back, and head.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.3
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• pp.171-180
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• 2000

This paper deals with the whole-body vibration and ride quality evaluation in the vertical direction. The responses of the floor, hip, back, and head in four subjects were measured for various seats when the floor was excited by random vibration with r.m.s of 1.2m/s2 in the vertical direction. In the transmissibility between the hip and floor, the fundamental mode is observed at 4.4 Hz. In the transmissibility between the head and floor, the fundamental mode at 4.4Hz and the second mode at 7.6Hz are observed. It is shown that the head motion is 41% larger than the hip motion and the response of female subject is larger than that of male subject. The response without backrest also was compared with that with backrest. From these human responses ride quality of five seats were evaluated by the ride value such as transfer ration having frequency weighting function is the statistical sense. It is observed that the seat having high damping property can reduce the most acceleration exposed to hip in the statistical sense for all ride valves, while the seat having different seat spring doesn't show statistical difference.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.7 s.166
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• pp.1155-1163
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• 1999

This study deals with the vibration ride quality for passenger car when running on straight highway at the speed of 70km/h. Ten accelerations were measured at four positions, three axes each at the feet, hip, and head, and one axis at the back. Five seats that have different static sponge stiffness were used, and two subjects were participated. These accelerations were analyzed to produce the ride values such as component ride value and overall ride value. It was hard to see the difference of ride value by the change of sponge stiffness. However we could rank the ride quality by the total vibration exposed to passengers. From the transfer function between the hip and the foot, the fundamental mode was observed to be around 5.8Hz. Also the transfer function between the head and hip was studied. The optimal damping ratio of the seat was calculated according to the seat natural frequency with human weighting filter which makes the optimal damping ratio different from that without weighting filter.

• Journal of Korean Institute of Industrial Engineers
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• v.39 no.2
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• pp.105-108
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• 2013

Drivers' sitting strategies are considered in car seat design. Existing research has identified representative sitting strategies by visual inspection of seating pressure measurements collected from a small sample size of drivers. The present study recruited 20 female and 20 male participants, measured seating pressure, and classified sitting strategies by cluster analysis. The participants' sitting postures were classified based on seating pressure distribution into mid-back and scapular, mid-back and lumbar, and lumbar sitting strategies for the upper body and hip concentrated, hip and mid-thigh concentrated, and hip and mid-thigh distributed sitting strategies for the lower body. The effects of gender and occupant package layout (OPL) on sitting strategy were nout found significant. The identified sitting strategies would be of use for the design and evaluation of an OPL and a seat.

• Journal of the Ergonomics Society of Korea
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• v.30 no.5
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• pp.605-611
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• 2011

Objective: The aim of this study was to investigate the influence of seat heights for optimizing the ingress/egress performance in the elderly people. Background: Recently elderly users have been increasing in number and the ease of ingress/egress of the vehicle becomes an important issue. Method: Seven elderly subjects participated in this study(age: 71.7${\pm}$3.6yr, height: 167.7${\pm}$5.4cm, weight: 68.1${\pm}$11.5kg). Each subject performed the sitting and rising task from comfortable seated position on the chair under the following conditions: (1) with a lumbar support and (2) without a lumbar support. We measured EMG activities of seven muscles(tibialis anterior, soleus, gastrocnemius, vastus lateralis, rectus femoris, biceps femoris and erector supinae) and ranges of motion in lower limb during sitting and standing from three different heights (400mm, 500mm and 600mm from ground) of slide-up seat. Results: Muscle activities and angular movements of hip and knee joints during standing-up and sitting-down with a high seat height(600mm) were reduced mean 30.4% in extensor muscles, 57.11% in flexor muscle, 18.74% in erector muscle and 31.0% in joints compared with a low seat height(400mm). Conclusion: Muscle activities and joint movements in hip and knee were reduced when rising/sitting from a high seat height(600mm) compared with a low seat height(400mm). Application: This study can be used to design vehicle that are easy to get in and out of by older peoples with or without impairments.

• Journal of Biomedical Engineering Research
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• v.29 no.6
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• pp.484-492
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• 2008

Sit to stand(STS) movement is one of the most common activity in daily life. In addition, Korean traditionally stand up from various sitting heights in one's daily life compared to other foreigners. As Korea enter rapidly to the aging society, needs of the elderly's independent life are increasing. Therefore the importance of research about the analysis of elderly's activity in daily life is rapidly increasing. In this study, we analyzed joint movements and changes of muscle length during STS(sit-to-stand) at various sitting heights(table seat, bath seat, bottom) in the Korean elderly's daily life by using the motion analysis and musculoskeletal modeling. Ten Korean elderly and young were participated in this experiment. Three heights of sitting posture which could represent typical sitting in Korean daily life were chosen as table seat(42cm), bath seat(21cm) and bottom(0cm). As the results, the elderly showed both smaller knee/hip flexion and larger trunk flexion relatively in comparison to the young during table seat STS. The elderly also showed larger dorsiflexion and smaller ROM of knee, hip, trunk compared to the young during bath seat STS. Additionally, the elderly showed larger plantarflexion, hip flexion, smaller knee flexion and trunk flexion during the first half of bottom STS and larger knee flexion, hip flexion and trunk flexion during the second half of bottom STS. In addition, we could know contraction and relaxation characters of major muscles in lower limb during various STS through the analysis of changes in muscle length by musculoskeltal modeling.

• The Journal of the Convergence on Culture Technology
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• v.10 no.3
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• pp.7-11
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• 2024

The bedsore prevention cushion serves to prevent the skin on the buttocks of a wheelchair user from being damaged through friction with the wheelchair seat. This is because it absorbs some of the weight applied to the wheelchair seat and allows the weight to be applied evenly to the entire contact surface. For the impact test, which is part of the performance testing of bedsore prevention cushions, a hip model that represents the sitting posture of a wheelchair user is required. In this study, a hip model was manufactured for impact testing of bedsore prevention cushions for wheelchairs. Performance tests for pressure bedsore prevention cushions for wheelchairs include KSP 0236, a Korean standard, and KS P ISO 16840-2, an ISO international standard. The hip model proposed in KS P ISO 16840-2 was more suitable for impact testing of bedsore prevention cushions for wheelchairs. However, the guidelines for making hip models proposed by international standards need to be modified to reflect the advancement of model making technology and use easier methods. We propose a new hip model production method that produces a hip model out of plastic all at once and additionally attaches SS-41 steel plates processed into the shape of the hip to make the mass of the model similar to the human body.

• Journal of Korean Institute of Industrial Engineers
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• v.41 no.1
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• pp.74-78
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• 2015

A bus seat is required to be ergonomically designed in terms of its shape and physical properties to increase seating comfort. The present study is intended to develop a systematic bus seat evaluation protocol based on seating comfort. A total of 48 participants evaluated 12 parts (seat belt, recliner, armrest, headrest, upper-back support, lumbar support, seatback bolster, seatback overall, hip support, thigh support, seatpan bolster, and seatpan overall) of 12 bus seats with 17 subjective comfort measures (e.g., convenience of control, suitability of size, and overall comfort). Lastly, ergonomic features of shape and physical properties of each seat part were identified based on the subject evaluation analysis results. The developed bus seat evaluation protocol can be applied to evaluate various types of seats.

• Journal of Biomedical Engineering Research
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• v.32 no.3
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• pp.191-197
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• 2011

Lifting chair is a typical assistive product to aid for standing up and sitting down for persons with disability. It is particularly useful for the elderly persons whose muscular system is weakened by degenerative joint disease. This paper describes biomechanical assessments of lifting chair with hip-up function. In experiments we measured 3D motion and electromyographic(EMG) signal on the femoral muscle when subject performs the standing motion on the predetermined seat height. Based on assessment of the standing motion, we select the hip-up angle as 15 degrees to cover the relative femoral angle when EMG peak value is appeared. Using an implemented prototype lifting chair with hip-up function we perform standing experiments with five subjects. The experimental results show that the lifting and hip-up functions are effective to assist for standing up motion with less muscle force.