Motor control for bilateral muscular contractions in humans.

This article briefly reviews neural mechanisms responsible for bilateral simultaneous muscular contractions by analyzing force outputs and their underlying electromyogram (EMG) and electroencephalographic (EEG) activities. Two major issues were addressed from a series of studies concerning maximal and submaximal (20% of maximal voluntary contraction) bilateral contractions (i.e., mechanisms for the bilateral strength deficit and common drive). It is suggested that: (1) during maximal bilateral contractions there exists a common drive from the central nervous system to the right and left muscles and the bilateral strength deficit is due to the decreased neural activations of the precentral motor cortex of both hemispheres; and (2) during bilateral contractions at submaximal level, a common drive also exists for simultaneous use of homologous muscles and the submaximal bilateral contraction is coordinated mainly under the control of the left hemisphere for right-handed people.