Measurement of facial muscle strength in normal subjects

Muscle strength is a fundamental measure of function for neuromuscular systems; however, mimetic facial muscle strength has never been recorded. The objective of the present feasibility project was to measure facial muscle strength.

The study design was a prospective experimental trial in 10 normal subjects. Descriptive statistics, tests, and analysis of variance were used to summarize and compare data.

Subjects were selected by convenience following submission and approval of a prospectively designed protocol and consent form to the Human Studies Committee. Application of a force transducer to the central eyebrow and commissure during eyebrow raising, eyelid closing, smiling, and puckering was performed by two methods: surface adhesion method (n = 5) and direct probe application method (n = 5). Data were recorded in pounds. Three repetitions of each movement were made.

Rank order of muscle strengths (in pounds) by the surface adhesion technique was as follows: brow, 0.758; eye, 0.549; pucker, 0.387; and smile, 0.307. By direct probe application the rank order of muscle strengths was as follows: eye, 0.880; brow, 0.773; and smile, 0.730.

Objective measures of facial motion are crucial for quantitative investigations of preventative, therapeutic, reconstructive, and rehabilitative interventions for facial nerve and muscle lesions. Until the present, objective measures required cross-correlations with current standards that were subjective. This is the first time an actual physical measure of facial muscle function has been performed. The purpose of presenting this preliminary work is to stimulate advancement along this line of research.