You can assay metabolic enzymes (Comparative Biochemistry and Physiology, Part B 121 (1998) 185–194), perform cytoimmunofluorescence studies or immunoblotting (Cell Prolif. 2006, 39, 127–145) to look at specific markers of muscle fiber type. Electrophoresis to quantiy the different types of myosin heavy chain isoforms is the method of choice (Electrophoresis, 2011, 32, 1804–1806). The different markers of fiber types tell you slightly different stories. It depends on your objectives and on the context of your study.