1. Bvmwc h”n;cs. Vol. 2, pp. 429-44 I Pergamon Press. 1969 Printed in Great Britain zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGF A COMPUTERIZED BIOMECHANICAL MODEL- DEVELOPMENT OF AND USE IN STUDYING GROSS BODY ACTIONS”? DON B. CHAFFIN Department of Industrial Engineering, The University of Michigan. Ann Arbor, Mich. 48104. U.S.A. Abstract-Gross body actions involved in heavy industry. e.g. lifting and carrying materials. are often the cause of injury to the musculoskeletal system. A computer model is developed which treats the human body as a series of seven links from which reactive forces and torques are computed at each articulation during various simulated materials handling tasks. In addition, an analysis of shearing and compressing forces at the lower lumbar spine is included. The assumptions of the present model are presented, along with a discussion of future models. IT zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA HAS been reported by Troup (1965) that a relatively large portion of industrial injuries (as great as 12 per cent) are back disorders resulting from a lifting task. It is also evident from papers by Tichauer (1965), Raof et al. (1960) and Davis zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA et al. (1965) that the estimation of stresses on various parts of the musculoskeletal system during lifting activities will require a complex methodology which takes account of such factors as (1) instan- taneous positions of the extremities and trunk, (2) curvature changes in the spine, (3) strength variations within different muscle groups and people, and (4) abdominal pressure effects. WHOLE-BODY COMPUTERIZED BIOMECHANICAL MODELS - BACKGROUND It has been nearly 80 years since Braune and Fischer ( 1890) published their data re- garding the mass distribution for the various body segments. Since then, fundamental extentions by Dempster ( 1955) and Drillis and Contini ( 1966) have resulted in better estimates of (1) the location of the mass centers-of- gravity, (2) the link lengths, and (3) the magni- tudes of the moments-of-inertia of the various body segments. It is the intent of this paper to describe a computerized biomechanical model which can be used to estimate the forces and torques that are created at six major articulations of the body, (i.e. wrist. elbow, shoulder, hip, knee, and ankle) as well as at the fourth lumbar through the first sacral spinal vertebrae of a person who is performing a weight handling task. This particular model is used as an example of the types of models that are now practical due to the relative ease of use and computational speed of today’s digital computers. However, it was not until the widespread use of the commercial high speed digital computer that this type of data could be easily used in developing analytical models to study the mechanics of the human body. The digital computer has provided a com- putational capacity which. in turn. has fostered the development of several different types of biomechanical models. Some of these models have been formulated to determine the whole- body center-of-gravity location when the body is placed in various configurations (Hanovan, 1964). This type of model is used in deter- mining body movements if mechanically unrestrained and acted upon by changing *Received I4 Junuary 1969. *Presented at the ASME Third Biomechanical and Human Factors Division Conference at the University of Michigan, Ann Arbor, June I2- 13,1969. 429