Hueseok Choi

Biomechanical Evaluation for Washing Machine Design Suggested Newly for Prevention of Musculoskeletal Disorders

Recently, many studies have reported the fact that an excessively accumulated psychological and physical burden induced from physical labor conducted routinely in home and industry can be one of main reasons of musculoskeletal disorders in the working population. This fact makes increase interests in studies to reduce a risk of musculoskeletal disorders through grafting ergonomic considerations on working environment. However, there are currently limited methodologies in quantitative evaluations of new ergonomic suggestions to reduce a risk of musculoskeletal disorders. The current study is therefore performed to evaluate quantitatively effects of a design of washing machine as a new ergonomic suggestion onto prevention of musculoskeletal disorders, through application of a biomechanical evaluation methodology. For this, three-dimensional motion analysis by using musculoskeletal models with Rapid Entire Body Assessment (REBA), which has been generally used for a simple evaluation of a degree of harmfulness of the human body at specific working postures to be considered, was performed. The results of REBA did not give us enough information and their results were somewhat simple and inaccurate, but the results of the three-dimensional motion analysis give us enough information such as alteration of main muscle forces and joint moments required during washing work. All results showed that the main muscle strengths and joint moments were decreased effectively for reduction of a risk of musculoskeletal disorders during the washing work with newly designed washing machine evaluated in the current study, compared with those generated during the washing work with general washing machine. From these results, it can be concluded that a risk of the musculoskeletal disorders, which may be induced by a repetitive washing work, may be reduced through using the washing machine designed ergonomically and newly. Also, it is thought that if our ergonomic design can be applied for improvement of working environment in lifting and laying works conducted repeatedly for a treatment work of goods, which have a strong resemblance to the behaviors generated * 이 저서(논문·예술연구)는 2001학년도 연세대학교 학술연구비의 (부분적인) 지원에 의하여 이루어진 것임.

Foot/Ankle Roll-Over Characteristics for Different Joint Alignments of the Ankle-Foot Orthosis( AFO) during Level Walking

This study investigated foot/ankle roll-over characteristics for different joint alignments of the ankle-foot orthosis(AFO). Seven volunteers without any musculoskeletal or foot problems participated in motion analyses. To obtain roll-over shape of the ankle-foot complex, we used trajectories of ankle and knee joints and the center of pressure(COP) between initial contact (lC) and opposite initial contact(OIC). After the roll-over shape was determined for each data, it was represented by a circular arc using the least-square method. Results showed that for the more dorsiflexed AFOs, the more distally the roll-over trajectory moved at initial contact. Also, we found that the radius of curvature significantly increased and the center of roll-over shape moved posteriorly and superiorly in dorsiflexed AFOs. Present results might provide a better understanding for the proper alignment of the orthotics as well as a single roll-over shape during walking.

THE BALANCE RECOVERY MECHANISMS AGAINST THE FORWARD PERTURBATION

In this paper, biomechanical aspects of dynamic postural responses against forward perturbations were experimentally determined by simultaneous measurements of joint angles, linear accelerations, EMG activations, CoP movements and ground reaction forces(GRF). The sequence of joint motions due to the forward perturabation was in the order of ankle dorsiflexion, knee flexion and then hip flexion during the second half of the acceleration phase. Forward accerlerations were found both at the heel and the sacrum during the second half of the acceleration phase and the early, constant speed phase. Tibialis anterior(TA) for ankle dorsiflexion and biceps femoris(BF) for knee flexion, the primary muscle to recover balances against the forward perturbation, was activated during the half of acceleration phase. Ankle strategy was used for slow-speed perturbation, but mixed strategy of both ankle and hip used for the fast-speed perturbation. In addition, speed and magnitude of the perturbation influenced the postural response.

Joint moments and center of body mass according to the weight of side loaded carriage in walking

The present study investigated the biomechanical effects of weight variation for side loaded carriage during walking upon joint moments and the center of body mass by using the inverse dynamic analysis. The motion data which were used as input data for inverse dynamic simulation were measured by the 3D motion analysis system. Six infrared cameras and two force plates were utilized and thirty nine reflective markers were attached to the subject to capture the walking motion with side loaded carriage. The healthy male subjects were participated in the experiment, and they walked with side loaded carriage which weighs 0, 5, 10 and 15kg, respectively. For each walking, the weight of side loaded carriage was selected randomly. As a result, the COM(Center Of Mass) was more inclined to the opposite side of side loaded carriage as the weight increased. This is the result of the balance mechanism of human in walking with side load. In other words, the human kept the total balance, leaning to the side of unloading when the human walked with one heavy side loaded. In addition, the ankle plantar-flexion moment of loading side was larger than that of unloading side when the weight increased. In knee joint, the knee extension moment of unloading side was smaller than that of loading side when the weight increased. The magnitude of hip extension moment had no significant difference. The hip extension moment of loading side was larger than that of unloading side. These results showed that the human used the ankle and hip joint of the loading side to support the body and the knee joint of the unloading side to progress the walking with keeping the balance of the body.