Field of Action of Muscles
As will be seen, each muscle acts most energetically in some special direction of the gaze, termed field of action of that particular muscle; thus the external rectus acts most powerfully when the eye is directed outward, and acts little or not at all when the eye is directed inward, except by purely passive traction. Likewise the superior rectus acts mainly when the eye is directed down. Furthermore, its action is limited to the upper and outer field; for in the upper and inner field elevation is performed chiefly by the inferior oblique.
This is also true of all the other muscles.