Determination of Muscle Fiber Type in Rodents

Abstract Skeletal muscles consist of muscle fibers that can differ in both composition and functional characteristics. These three types of muscle fibers, broadly categorized as slow, fast IIa, and fast IIb muscle fibers, express characteristic myosin heavy chain proteins and have different metabolic and enzymatic activities, which can be used as surrogate markers to identify the different fiber types. Pathological changes affecting the muscle, such as denervation, muscle disuse, and atrophy not only manifest on a functional level, but also as marked changes in the composition of muscle fiber type of individual muscles. In this unit we describe three methods for histological identification of slow/type I, fast fatigue resistant/type IIa, and fast fatigable/type IIb fibers by staining for either myosin ATPases or oxidative enzyme capacity (succinate dehydrogenase, SDH)—or, alternatively, immunostaining for specific myosin heavy chain isoforms in muscles of mouse hindlimbs. Curr. Protoc. Mouse Biol . 2:231‐243 © 2012 by John Wiley & Sons, Inc.