Objective: To address whether speakers with cleft palate exhibit velopharyngeal mechanism fatigue and are more susceptible to muscle fatigue than are speakers without cleft palate. Methods: Six adults with repaired palatal clefts and mild-moderate hypernasality served as subjects. Velopharyngeal closure force and levator veli palatini muscle activity were recorded. Subjects were asked to repeat /si/ 100 times while an external load consisting of air pressure (0, 5, 15, 25, 35 cm H2O) was applied via a mask to the nasal side of the velopharyngeal mechanism. Fatigue was defined as a reduction in velopharyngeal closure force across the series of /si/ productions, as evidenced by a negatively sloped regression line fit to the closure force data. Results: Absolute levels of velopharyngeal closure force were much lower than those observed previously in speakers without palatal clefts. All subjects showed evidence of fatigue. Furthermore, all subjects demonstrated exhaustion, where they were unable to close the velopharyngeal port against the nasal pressure load. This occurred at pressure load levels lower than those successfully completed by speakers without cleft palate. Conclusions: In speakers with a repaired palatal cleft, the velopharyngeal closure muscles may not possess the same strength and/or endurance as in normal speakers. Alternatively, muscles may possess adequate strength, but not be positioned optimally within the velopharynx following cleft palate repair or may be forced to move velopharyngeal structures that are stiffer as a result of surgical scarring.
