Muscle fiber type distribution in the normal human levator veli palatini muscle.

OBJECTIVE: This study examined the muscle fiber type distribution within the normal adult levator veli palatini muscle.
METHODS: Levator veli palatini muscle tissue was harvested from the palates of 12 (seven female, five male) adult noncleft cadavers. Adjacent sections were stained for adenosine triphosphatase at pH 10.4 or 4.2. After mounting, magnifying, and photographing, Type I versus Type II fiber types were differentiated by the intensity of, or by the inhibition of, staining of matched fibers at each pH level. Type I fibers stained light at pH 10.4 and dark at pH 4.2, while Type II fibers stained light at pH 4.2 and dark at pH 10.4. MAIN OUTCOME MEASURES: The number of fibers counted for each specimen ranged from 60 to 616. The numbers of Type I and Type II stained fibers appearing in each muscle tissue sample were determined and expressed as a percentage of the total number of fibers identified. A few identified fibers could not be labelled as either Type I or Type II.
RESULTS: The overall proportion of Type I fibers, averaged across all specimens, was 59.8%. Male specimens had 67.4% Type I fibers and 31.8% Type II fibers, while female specimens had 54.4% Type I fibers and 44.4% Type II fibers.
CONCLUSIONS: Observed fiber type distributions were similar to those reported for other articulatory muscles, but differed slightly from previously reported distributions for normal levator veli palatini. The distributions observed in this study provide a baseline against which to relate fiber type data from the levator veli palatini of cleft palates to the functional status of the velopharyngeal mechanism.