Background: This study evaluated the activity of the frontalis muscle, the corrugator supercilii muscle, and the orbicularis oculi muscle according to eyebrow movement and aging.
Methods: Two random cohorts of women aged 20 to 30 years (young group, n = 20; mean age, 24.8 years) and 50 to 70 years (old group, n = 20; mean age, 55.8 years) were recruited prospectively. Surface electromyography was used to evaluate motor unit action potential for each muscle in each of six eyebrow movements. Details on statistical analysis are described in the text.
Results: In both age groups, corrugator supercilii muscle activity was the highest for all six movements. Frontalis muscle activity was highest with maximal frowning but not with maximal eye opening. Orbicularis oculi muscle activity was significantly greater in the older age group than in the younger age group for most actions. When the motion proportion of each muscle was compared, the respective orbicularis oculi muscle and corrugator supercilii muscle indices were higher in the older age group than in the young group.
Conclusions: Eyebrows are maintained by the dynamic balance of frontalis, corrugator supercilii, and orbicularis oculi muscles, and various combinations of motor recruitment of these muscles determine the eyebrow position and shape. For youthful eyebrows, attenuation of the depressor muscle may restore the muscle balance in treatments for eyebrow rejuvenation.