Associated postural adjustments are impaired by a lesion of the cortex.

A ballistic movement of one arm may be accompanied by contractions of contralateral postural muscles known as "associated postural adjustments." Ballistic movements are considered to involve the motor cortex, but it is not known where associated postural adjustments are generated. We recorded the EMG activity in the deltoid and latissimus dorsi muscles during ballistic abduction of the arm in 10 normal subjects and five subjects with lesions of the motor cortex. When subjects with cortical lesions abducted the unaffected arm, the associated postural adjustment in the contralateral latissimus dorsi was significantly smaller than normal. We argue that postural adjustments, like ballistic movements, require the participation of the motor cortex.