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The Skeletomotor System: Surface Electromyography
LOUIS G. TASSINARY, JOHN T. CACIOPPO, AND ERIC J. VANMAN

The brain recalls just what the muscles grope for; no more, no less . . . (Faulkner, 1936, p. 143) The principal function of the nervous system is the coordinated innervation of the musculature. Its fundamental anatomical plan and working principles are understandable only on theseterms. (Sperry, 1952, p. 298)

INTRODUCTION

The sophistication of the skeletomuscular system enables the vast repertoire of adaptive reflexes and skilled actions characteristic of behavior. The electrophysiological signals associated with active muscles have been of interest for centuries due to the complexity of their organization and dynamics, their clinical applications, and their value asindices of and possible contributors to behavioral processes. In this chapter, we provide an introduction specifically to psychophysiological research on the skeletomotor system.1 We begin by reviewing the history of this research and by articulating some of the major issues, limitations, and advantages of surface electromyography (EMG) as a noninvasive measure of muscular activity. We then reviewbriefly the physiological basis of EMG and summarize guidelines for surface EMG recording in humans. We continue with a discussion of the social context for EMG recording and of psychophysiological principles and common paradigms that have emerged from research on the skeletomotor system. For EMG signals to be of theoretical significance, one must consider conjointly the historical, physical,social, and inferential contexts in which these signals are acquired.

The first is the history of the physiology of the muscles, which derives from the writings of the early Greek philosophers, and from the scientific renaissance in the seventeenth century. The second is the history of psychophysiological research, which began in earnest with the work of such figures as Duchenne (1990/1862), Spencer(1870), Darwin (1873/1872), and James (1890), all of whom emphasized relatively subtle patterns of muscular actions as a way of characterizing and understanding human behavior generally.
Muscle physiology

HISTORICAL CONTEXT

In this section we identify two distinct themes in the development of electromyography in psychophysiology.
1

Additional information on electromyography generally canbe found in Basmalian nand DeLuca (1985), Johnson and Pease (1997), Loeb and Gans (1986), or Ludin (1995).

The history of muscle physiology can be traced back to the fourth century B.C.E., when Aristotle provided clear descriptions of coordinated motor acts (e.g., locomotion and the importance of the mechanism of flexion) in his books De Motu Animalium and De Incessu Animalium. The field ofneurophysiology can be traced to Franceso Redi’s deduction in 1666 that the shock of the electric ray fish (Torpedo torpedo) emanated from specialized muscle tissue (Wu, 1984). It was not until the early nineteenth century, however, that a sensitive instrument for measuring small electric currents was invented (i.e., the galvanometer). In 1833, Carlo Matteucci used such a device to demonstrate anelectrical potential between an excised frog’s nerve and its damaged muscle. Du-Bois Reymond, a student of the renowned physiologist Johannes Muller, built ¨ upon Matteucci’s then recent publication, eventually publishing the results of an extensive series of investigations on the electrical basis of muscular contraction as well as providing the first in vivo evidence of electrical activity in humanmuscles during voluntary contraction (Basmajian & De Luca, 1985). The study of the thermodynamics of muscle contraction owes a debt to another of Muller’s students, Hermann Ludwig Ferdinand von Helmholtz. Fueled by the desire to abolish the notion of vital forces underlying muscular actions, von Helmholtz began an investigation into the chemical transformations occurring in frog muscle during...