Surface electromyographic (sEMG) studies were performed on 300 normal adults to estimate normal values of sEMG records of muscle activity in the detection and evaluation of stages of normal swallowing. Our study was a prospective observational study of healthy volunteers. The parameters evaluated during swallowing include the timing, amplitude (voltage), and graphic patterns of activity of the orbicularis oris, masseter, submental, and laryngeal strap muscles covered by the platysma. Three tests were examined: voluntary single swallows of saliva ("dry" swallow), voluntary single water swallows ("normal"), and voluntary single swallows of excessive amounts of water (20 ml, "stress test"). Duration and amplitude of muscle activity in oral, pharyngeal, and initial esophageal stages of swallowing (mean + standard deviation, range + standard deviation) were measured for groups of adults of different ages (18-40, 41-70, 70+ years). Shapes of graphic records were evaluated relative to timing and voltage. The overall normal mean values for stage-by-stage duration of muscle activity during single swallowing were established for healthy adults. The duration of muscle activity in all tests showed insignificant increases with age except for the elderly group (70+) in which it was statistically significant (SPSS, chi(2) criterion, 95% confidence interval, p < 0.05). There were no statistically significant gender-related differences in duration or amplitude of muscle activity during single swallowing for any age group (p greater than or equal to 0.05). We conclude that the rectified and filtered sEMG provides a noninvasive means to assess certain aspects of complex muscle activity in deglutition. Surface EMG of swallowing is a simple and reliable noninvasive screening method for evaluating swallowing with low levels of discomfort. Stage-by-stage evaluation of duration can be very important for diagnosing the etiology of dysphagia. The combined normative timing of events, amplitude, and graphic data can be used for evaluating complaints and symptoms, as well as for comparison purposes in pre- and postoperative stages and in EMG monitoring during otolaryngological or neurological treatment. These parameters represent stages required for normal deglutition and provide a basis for the comparison of swallowing performance both within and between patients.
