Type II fast- (A) and type I slow twitch fibers (B), and p27 expression (C) in levator ani muscle of an asymptomatic patient (age 38). A) Fast twitch fibers (f, dark color) alternate with slow twitch fibers (s). B) Parallel section to (A) shows staining of slow twitch fibers. C) Protein p27 is strongly expressed in plasma membrane and adjacent nuclei (arrowheads). Note a lack of cytoplasmic staining.