The Human Machine in Three Dimensions: Implications for Measurement and Analysis

Abstract

Scientists and laymen have a favorite analogy: the human body as machine. In this context, machine is “...a structure consisting of a framework and various fixed and moving parts, for doing some kind of work” (Webster’s New World Dictionary, 1974). The human skeletal system is the “framework”, while the neuromuscular system generates forces and controls movements for performing work. Modeled as a machine, the body’s skeletal linkage system acts as mechanical levers (Tichauer, 1978). Dempster (1955) defined skeletal links as straight-line distances between joint centers of rotation; for computer simulations, his interpretation suggests a stick-man model as a reasonable, straight-forward approximation. Unlike present-day machinery, however, there is poor “quality control” in the linkage system of our human machines; that is, the length of the links varies among individuals with respect to body size and even in the same individual with respect to position. Thus, the potential range of variation in body position and mobility may be maximized by behavioral and cultural variables (Maule and Weiner, 1975). Consequently, anthropometrists measuring the body are concerned with standardization of instruments, landmarks, and body configuration. These three technical areas have largely determined the parametric definition of the human machine in current models.