Figure 1.

Patterns of normal electromyography (EMG) activity. In trace, the four EMGs shown in order from top to bottom are pectoralis major (PM), anterior deltoid (AD), latissimus dorsi (LD), and infraspinatus (IS). (a) EMG activity during flexion: PM and LD inactive and AD and IS active. (b) EMG activity during abduction: PM and LD inactive and AD and IS active. (c) EMG activity during external rotation: PM, LD, and AD inactive, activity only in IS. (d) EMG activity during flexion/ adduction: Activity in all the muscles. (e) EMG activity in extension with minimal or no activity in PM/AD/LD, but activity in IS