AN ANALYSIS OF LOAD TRANSMISSION WITHIN THE HUMAN BODY DURING PUSHING AND PULLING Krystyna Gielo-Perczak 1 , John Rassmussen 2 , and Søren Tørholm Christensen 2 1 Liberty Mutual Research Institute for Safety, Hopkinton, MA, U.S.A. 2 Institute of Mechanical Engineering, Aalborg University, Denmark E-mail: Krystyna.Gielo-Perczak@LibertyMutual.com Central to the study was an investigation of the influence of the three groups of muscles representing and surrounding the joints: (1) arm and the shoulder, (2) trunk muscles and the spine, (3) lower extremity and the pelvis, on the maximum acceptable force applied to the hand during pushing and pulling when an arm was elevated at 5 degrees in a frontal plane. In this paper we report a detailed numerical simulation model that allowed us to quantify the limiting factors in each joint. The calculations were carried out for different arm positions during the right hand pushing and pulling. The computer model of the experiment was built with the AnyBody Modeling System (www.anybodytech.com) and comprised 456 individual muscle units with a detailed description of the human musculoskeletal system. From the results of this approach we can conclude that for all positions of an elevated arm during pushing and pulling, the most critical areas are the shoulder joint and lower back. The force applied at the hand is a critical element of the assessment of individual force limitations during different activities. Therefore, a linked-system analysis of a human body and development of this model can assist during designing of the workplace. INTRODUCTION During manual materials handling human movement typically involves the motion of more than one body segment or one joint. It is a cumulative motion that combines interplay of the joints. Furthermore, the multi- articular muscles transfer moment between joints, and closed chains such as double standing posture introduce statical indeterminacies in the system. A loading analysis therefore requires a linked-system analysis, in which we can calculate the distribution of forces and moments at each joint and in each muscle, and in which forces can flow through the complex mechanical structure. The opportunity to perform such analyses by computer has recently become available with the advent of powerful inverse dynamics modeling techniques and software, and this presents the opportunity of significantly furthering our understanding of the force flow in the working human body. Central to the study is an investigation of the influence of particular joints on the maximum acceptable force applied to the right hand during pulling and pushing when an arm is elevated at 5 degrees in planar plane. The most interesting question is how the strength of muscles surrounding the individual joints influences the other joints. In this paper we report a detailed numerical simulation model that allows us to quantify the limiting factors in each joint. This furthers our understanding of the complex nature of the musculoskeletal system with respect to the dynamic requirements of daily life activities and workplace. METHODOLOGY Description of the Musculoskeletal Model The computer model of the experiment is built with the AnyBody Modeling System (www.anybodytech.com) and is based on models in the public domain AnyScript model repository (www.anybody.aau.dk/repository). The model comprises an arm and shoulder complex with morphology according to van der Helm (1994) with 114 muscle units on each side, a spine model comprising sacrum, all lumbar vertebrae, a rigid thoracic section, and a total of 158 muscles, and a pelvis and lower extremity model with a total of 70 muscles. Totally, the model comprises 456 individual muscle units, and as such it is a very detailed description of the human musculoskeletal system. The model is based on inverse dynamics where the posture and external forces are specified, and the system computes internal muscle forces and joint reactions by means of equilibrium and an