Fiber Types in Human Intrinsic Laryngeal Muscles: A Literature Review

The study of muscle fibers allows the composition of muscles and their functional characteristics to be understood in greater detail. In addition, it makes it possible to apply training and rehabilitation programs based on the energy pathways that regulate muscle contraction. Studying muscle fibers is generally associated with the analysis of myosin heavy chains (MHC) which provide information on the functional characteristics and properties of muscles. The objective of this study was to synthesize the available scientific evidence on the distribution of muscle fibers and myosin heavy chain isoforms present in the intrinsic laryngeal muscles of human beings. A systematic review of the literature was carried out and articles found on PubMed, EBSCOHost, and SciELO were analyzed. The findings show the presence of slow-tonic, type I, type II, type IIA, and type IIX/IIB fibers. Additionally, isoforms MHC-I, MHC-IIA, MHC-IIX, MHC-Fetal, MHC-L, and MHC-IIB can be found. In conclusion, intrinsic laryngeal muscles are composed of a combination of slow and fast fibers and MHC isoforms, derived from evolutionary adaptations and changes which have given way, among other things, to the phonetic characteristics of the human voice.