Electromyographic (EMG) recordings from human extraocular and levator muscles were made during fixation, following, vergence, and saccadic movements, and during blinks and lateral head tilting. Motor units that altered activity with one type of movement also did so with eye movements of other types or during fixation at another gaze position. Recordings made from the orbital layers of the muscle (away from the globe) showed activity earlier in recruitment of the muscle, while motor units recorded from layers near the globe became active later in the recruitment pattern. These findings support the notion that various histologic muscle fiber types are functionally differentiated on the basis of the amount of work that they do, rather than on the basis of the type of eye movement to which they contribute.
Scott AB, Collins CC. Division of Labor in Human Extraocular Muscle. Arch Ophthalmol. 1973;90(4):319-322. doi:10.1001/archopht.1973.01000050321017