The cross-sectional diameter of individual fibers may vary depending on the specific muscle and its functional status. In addition, the morphology and diameter of skeletal muscle fibers may change significantly depending on physiological or disease state. Consequently, it may be necessary to measure fiber diameters in clinical as well as in experimental laboratory settings. Altered muscle fiber diameters may be observed in the following conditions:
- Denervation
- Statin-induced rhabdomyolysis
- Noninflammatory myopathies
- Congential myopathies
- Sports physiology
Two main types of skeletal muscle fibers have been identified based on histochemistry and physiological function. Type 1 fibers are high in myoglobin and oxidative enzymes and have many mitochondria. These slow twitch postural muscles are characterized by dark staining for ATPase at pH 4.2, but have light staining at pH 9.4. Type 2 fibers have an abundance of glycolytic enzymes and are fast twitch in contraction response. They stain dark with ATPase at pH 9.4 and light at ph 4.2. Since either Type 1 or Type 2 fibers may be preferentially affected in certain disease or toxicity states, it would be advantageous to measure fiber populations as to prevalence of fiber type or diameter.
In a typical H&E section, muscle fiber is poorly demarcated as shown below.
It is best to use an immunohistochemistry stain like laminin that will clearly demarkate the muscle fibers to allow for image analysis.
After each fiber has been automatically identified with the Flagship algorithm, statistics like area and perimeter on each fiber can then be calculated.
