BIOMECHANICAL RELATIONSHIP BETWEEN STRUCTURE AND MOTION IN THE HUMAN UPPER EXTREMITY

  • ROKUUMA Nobuyuki
    Depertment of Orthopedic Surgery, Scool of Medicine, Tokai University
  • YAMAZAKI Nobutoshi
    Department of Mechanical Engineering, Fuculty of Science and Technology, Keio University

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Other Title
  • 上肢の構造と動作との関係

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Abstract

Most daily motions of the upper extremity are performed to minimize internal energy expenditure. However, around the human joint there are many soft tissues, one of the sources of energy expenditure. The human upper extremity has over degrees of freedom and many muscles to control them, and there are some diarthric muscles. This complex structure of the upper extremity is incomprehensible from the standpoint of the biomechanical criteria of motion. However, the structure is considered to be in involved the smoothness and skill of upper extremity motion. To clarify the relationship, it is effective to use computer simulation, which generates the upper extremity motion automatically. In this paper, we assume that the motions of the upper extremity are performed to minimize the internal power loss at all times, and their aim can be described by the terminal position and posture of the hand. The mathematical model of the upper extremity was constructed of four rigid segments, and the model of the musculo-skeletal system was developed to consider the dynamics by five segments and thirty-six muscles. Seven power modules were defined based on the physiological characteristics of muscles and soft tissues. By using the minimization strategy of a potential function, we can simulate upper extremity motion. The potential function was defined as the weighted sum of the power modules and the weighted sum of reciprocals of the difference between the current situation of the hand and the terminal one. The weights of the power modules involved in the potential function were determined to suit the actual human upper extremity motion, and the weights of the aim of motion were determined to minimize the internal energy expenditure through the motion. For the actual human upper extremity's parameters and some hypothetical parameters, some basic ordinary motions were simulated. Consequently, it was found that there are optimum values for the joint viscosity and segmental proportion for both energy efficiency and the smoothness of motion. But for joint elasticity, there is an optimum value only for the energy efficiency. By working with monarticular muscles cooperatively, diarthric muscle works to decrease not only the muscular work but also the energy expended by the joint viscosity. Applying these results to the musculo-skeletal system of the human upper extremity, the segmental proportion and the muscular arrangement of the upper extremity are suited for the basic ordinary motions. However, the visco-elastic properties of the human upper extremity joints do not always suit the motions, because of the existence of more important purposes of joint visco-elasticity, such as connecting segments or absorbing impacts.

Journal

  • Biomechanisms

    Biomechanisms 10 (0), 129-138, 1990

    Society of Biomechanisms

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