The most frequently used classification for adult
human limb muscles includes three fiber types: type I
(slow, oxidative, fatigue-resistant), IIA (fast, oxidative,
intermediate metabolic properties), and IIx (fastest, glycolytic,
fatigable). Humans also express, under various
conditions and in specific muscles, other types of myosin
such as embryonic, neonatal, and extraocular (see Ref. [23]
for a detailed description and discussion).