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In this study, biomechanical characteristics during the whole process of gait initiation for twenty normal healthy volunteers were determined by the motion analysis with six near-infrared cameras, four forceplates, and an EMG system. Gait initiation, a transitional movement phenomenon from quiet stance to steady-state walking, involves a series of muscular activities, GRFs, movements of COP and COM, and joint motions. Results showed that the location of the net COP to be most lateral during double limb stance at the beginning of gait initiation. During gait initiation, changes in anteroposterior components of GRFs were first found and then changes in vertical components followed. Hip and knee motions were found before the ankle joint motion. Walking speed, step length, and stride length gradually increased until the second step. The interaction between the COM and COP is tightly regulated to control the trajectory of the COM and thereby control total body balance.

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.

Gait initiation is a transitional process from the balanced upright standing to the beginning of steady-state walking. Steady-state walking represents the start of repeated gait pattern with steady-state walking speed within one gait cycle. Hemiplegic patients’ gait initiation was analyzed using the 3D motion analysis system synchronized with 2 force plates. The first vertex(V1) in the CoP trajectory was placed on the lateral-posterior point from the leading limb side, and the third vertex(V3) was placed on the lateral-anterior point from the trailing limb side in the CoP of the normal gait initiation. However, V1 was not nearly shown and V3 was placed on the posterior from the trailing limb side in the CoP of the hemiplegic gait initiation. The time and distance from the onset to the toe-off(P1) and from the toe-off to the initial contact( P2) were analyzed that the mean time was larger and the mean distance was shorter when the affected limb was leading limb. The net CoP data obtained on gait initiation with hemiplegic patients suggest that they compensated with different strategies with respect to the limb whether it was leading limb or trailing limb for their impairment.

In this paper, we analyzed changes in muscle length of lower limbs during high-heel walking based on the musculoskeletal model. Twenty young healthy women participated in this study. For each subject, the 3D motion analysis was performed for four different cases; walking with flat shoe, 3 cm high-heel, 6 cm high-heel, and 9 cm high-heel. Then the musculoskeletal model, with modified Hill-type muscles, was made from subjects' anthropometric data and 3D motion capture data. Results showed that heel height did not show significant difference in hip joint motion. However, for 6 cm and 9 cm high-heels, knee flexion increased during loading response due to the insufficient extension of biceps femoris short head. Changes in muscle length of soleus and tibialis anterior significantly decreased and the muscle force of soleus decreased. Our results showed that the ankle joint played most important role to adapt high-heel lower than 6 cm, but the contribution of other lower extremity joints, especially knee joint, would be required for the higher heel. Changes in muscle length provided more valuable information to determine gait characteristics in various clinical conditions.

The foot, an exceedingly complicated system, is essential to move the body forward and to keep dynamic stability during gait. In most previous studies on gait analysis, the foot has been defined as a single rigid segment, which results in many problems to understand the foot motion in detail. The purpose of this study is to develop a multi-segment foot model that can help analyze biomechanics of the foot during gait. A 9-segment foot model with 8 major joints was developed in this study. In addition, it was applied to the 3D motion analysis to determine the kinematics and the kinetics of the foot in the normal walking. Understanding the detailed foot motions by the present multi-segment foot model would be very useful to diagnose patients with various foot diseases.