An Electromyographic Study of Coactivity of Human Extraocular Muscles in Following Movements

Abstract

Cocontraction is defined as the simultaneous increased contraction of extraocular muscles which are normally antagonistic in their primary field of action. It has been hypothesized that cocontraction occurs when the eye moves from its primary position to any secondary or tertiary position.¹ According to this hypothesis, as the lateral rectus abducts an eye, the vertical recti as well as the obliques cocontract to steady the eye in its horizontal path. At the same time, the cocontraction prevents undue torsion of the globe and helps maintain abduction as the lateral rectus loses its mechanical advantage as the movement progresses. The same reasoning would apply to adduction, supraduction, and infraduction. It is the purpose of this paper to report the results of testing this hypothesis by multiplechannel electromyography. The steadying effect and reinforcement of eye movement by cocontraction of auxiliary muscles* was postulated as early as 1897 by Duane.² By