Objective: The purpose of this study was to explore the expression of facial muscle fatigue in individuals without impaired muscle function using surface electromyography (EMG).
Design: Descriptive study of the expression of facial muscle fatigue in individuals without impaired muscle function.
Participants: Convenience sample. Twenty individuals, 5 men and 15 women, between 20 and 50 years of age who volunteered to participate.
Outcome measures: Two tests of fatigue, a 10-second sustained contraction test, and a 25 repeated 3-second contractions test, were conducted on three facial expressions: brow raise, smile, and pucker. Surface EMG quantification of the muscle activity of the voluntary maximal facial muscle contractions was recorded during the fatigue tests.
Results: For the sustained fatigue test, all three expressions had a significant decline in activity (brow raise 34.51%, smile 22.96%, and pucker 29.05%); confirmed by a one-way ANOVA with repeated measures (brow raise df = 2, 38; f = 53.28; p = 0.00; smile df = 2, 38; f = 39.913; p = 0.00; pucker df = 2, 38; f = 76.002; p = 0.00). For the repeated fatigue test, percent fatigue was significant for smile (11.62%; df = 1, 19; f = 13.823; p = 0.001) but not for brow raise (7.27%; df = 1, 19; f = 1.945; p = 0.179) or pucker (4.22%; df = 1, 19; f = 2.508; p = 1.30).
Conclusions: The muscle activity of sustained maximal voluntary muscle contractions of facial muscles fatigues significantly with time for brow raise, smile, and pucker expressions. The same facial muscles are more resistant to fatigue of muscle activity with repeated, brief contractions. Knowing the amount of facial muscle fatigue of individuals without impairment can be beneficial in developing outcome measures and goals for rehabilitation of individuals with facial neuromuscular dysfunction. Changes in fatigue tests of an individual with facial neuromuscular dysfunction with rehabilitation is reviewed for comparison.