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

Objective: This study examined the muscle fiber type distribution within th e normal adult levator veil 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 mountin g, magnifying, and photographing, Type I versus Type II fiber types were di fferentiated by the intensity of, or by the inhibition of, staining of matc hed fibers at each pH level. Type I fibers stained light at pH 10.4 and dar k 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 range d from 60 to 616, The numbers of Type I and Type II stained fibers appearin g in each muscle tissue sample were determined and expressed as a percentag e of the total number of fibers identified. A few identified fibers could n ot be labelled as either Type I or Type II. Results: The overall proportion of Type I fibers, averaged across all speci mens, was 59.8%, Male specimens had 67.4% Type I fibers and 31.8% Type II f ibers, while female specimens had 54.4% Type I fibers and 44.4% Type II fib ers. Conclusions: Observed fiber type distributions were similar to those report ed for other articulatory muscles, but differed slightly from previously re ported distributions for normal levator veli palatini. The distributions ob served in this study provide a baseline against which to relate fiber type data from the levator veil palatini of cleft palates to the functional stat us of the velopharyngeal mechanism.