Is frontalis activity a reliable indicator of the activity in other skeletal muscles?

Multichannel integrated action-potential recordings (called electromyometrograms of EMMGs) from 10 individuals with various functional symptoms and disorders were selected for statistical examination to obtain evidence bearing on the topic in question. Each EMMG recorded the action-potential levels from four regions simultaneously via four channels of integrating differential amplifiers. The subjects sat quietly, awake and alert, with eyes open and head erect. Electrodes were placed over antagonistic muscle groups in the following regions: (1) forehead, (2) jaw-throat, (3) right forearm, (4) left leg. Successive 1-minute action-potential levels from each of these regions were sued to calculate within-subject correlations (r) and predictabilities (r 2 and R2) among the different regions. Mean and median correlations (r) and predictabilities (r 2 and R 2) for each of the following pairs of regions were found to be weak: (1) forehead and jaw-throat, (2) forehead and forearm, (3) forehead and leg, (4) jaw-throat and forearm, (5) jaw-throat and leg, (6) forearm and leg. The findings support the statement that the frontalis or any of the other regions measured are poor indicators of the amount of activity elsewhere in the skeletal musculature of awake and alert individuals. When combined with basic principles of neuroanatomy and neurophysiology, the findings also support the statement that there is probably no portion of the skeletal musculature that can be used to quantify the activity in other portions.