Relationship between muscle activity of the frontalis and the associated brow displacement

Although the relationship between regional facial muscle activity and resul tant displacement of the face is important to the refinement of many of the treatments of facial paralysis and palsy, this relationship has not been a dequately explored. Wie analyzed the relationship between frontalis muscle activity as measured with surface electromyography and the associated eyebr ow displacement as measured with the maximal static response assay in 16 hu man volunteers. We hypothesized that graded, sustained muscle activity woul d correlate with graded, sustained elevation of the eyebrow. We found that (1) the relationship between the muscle activity and the corresponding disp lacements was best described by activity versus displacement squared (r(2) = 0.993); (2) there was a wide variation between individual brews for the r elationship between muscle activity and displacement; (3) there was a norma l amount of asymmetry of the relationship between muscle activity and displ acement between the two brews of a subject; (4) left and right frontalis ge nerated the same amount of muscle activity, but left brews elevated signifi cantly higher; (5) the method of simultaneous measurement of muscle activit y and displacement used in this study yielded results similar to those prev iously reported; and (6) the methods used in this study are useful to furth er investigate the relationship between muscle activity and displacement.