Some Requirements and Fundamental Issues in Digital Human Modeling Don Chaffin Chapter 2 in Handbook of Digital Human Modeling, ed. V. Duffy, CRC Press, 2009. The use of digital human models to improve certain ergonomic attributes in a proposed design is not a new concept. Ryan and Springer at Boeing Aircraft in the late 1960s developed a digital human model that could be used to assess pilot reach requirements for people of varied anthropometry (Ryan & Springer, 1969). It had an exertion optimization method for predicting reach postures. About the same time, Chaffin, Kilpatrick, and Hancock (1970) described the development of a seated digital human model. It accepted data about the locations and orientations of objects that needed to be manipulated, and when combined with a list of tasks to be performed by a person, it produced an MTM prediction of performance times. It also provided a graphical illustration of a simple 3D avatar that contained an empirically driven optimization IK that displayed various predicted postures required to reach the objects and tools being used. The University of Michigan’s 3D Static Strength Prediction Program was developed in the 1970s to run in batch mode on a mainframe computer. It was later released in 1984 to run on early PCs, and it included a 3D stick figure avatar that could be manipulated by the users to allow them to simulate people of varied anthropometry, when performing high exertion tasks. Evan and Chaffin (1985) described how workplace and task information could be integrated into the UM 3DSSPP along with a wire mesh 3D avatar to perform ergonomics assessments. In a similar development at the University of Pennsylvania, starting in the late 1970s, Jack was being created, and by the late 1980s it had an enfleshed 3D avatar and a sophisticated set of inverse kinematics routines to allow a user to easily manipulate simple movements and object-grasping tasks (Badler et al., 1993). Also, by the late 1980s the U.S. Air Force was using derivatives of the earlier Boeing model, entitled COMBIMAN and CREWCHIEF, to evaluate pilot and maintenance tasks. These programs included a simple 3D avatar (McDaniel, 1990), and provided access to a database of anthropometric and human strength attributes related to the tasks of interest. Similarly, in the United Kingdom during the 1980s, Case, Porter, and Bonney (1990) were developing a sophisticated 3D avatar and workplace/vehicle CAD system, referred to as SAMMIE, which allowed reach and sight lone evaluations. The point of this brief summary describing some of the early DHM models is to remind the reader that various types of digital human models have been around for over 35 years. Unfortunately, their acceptance and use have not been rapidly assimilated into organizations to improve the ergonomic design of most of the hardware and software systems used today. This is despite the fact that the benefits when using such a technology have been well acknowledged over the last decade in books by Badler et al. (1993), Peacock and Karwowski (1993), and Chaffin (2001). abs2009_02