Misclassification of Hybrid Fast Fibers in Resistance-Trained Human Skeletal Muscle Using Histochemical and Immunohistochemical Methods

• Published in: Journal of strength and conditioning research 2012-10, Vol.26 (10), p.2616-2622
• Main Authors: Staron, Robert S., Herman, Jennifer R., Schuenke, Mark D.
• Format: Article
• Language: English
• Subjects: Analysis; Biopsy; Dietary fiber; Evaluation; Exercise (intensity); Female; Histocytochemistry; Humans; Immunohistochemistry; Legs; Muscle Fibers, Fast-Twitch - classification; Muscle Fibers, Fast-Twitch - cytology; Muscle Fibers, Fast-Twitch - enzymology; Muscle Fibers, Fast-Twitch - physiology; Muscles (histochemistry); Muscles (type); Musculoskeletal system; Myosin Heavy Chains - analysis; Myosins - analysis; Physical fitness; Proteins; Quadriceps Muscle - cytology; Quadriceps Muscle - enzymology; Quadriceps Muscle - physiology; Resistance exercise; Resistance Training; Strength (training); Women; Young Adult
• ISSN: 1064-8011; 1533-4287
• DOI: 10.1519/JSC.0b013e3182667095

ABSTRACTStaron, RS, Herman, JR, and Schuenke, MD. Misclassification of hybrid fast fibers in resistance-trained human skeletal muscle using histochemical and immunohistochemical methods. J Strength Cond Res 26(10)2616–2622, 2012—Sixteen healthy untrained women participated in a 6-week progressive resistance training program to compare 2 common methods of classifying fiber types. The women were a subset from a previous study and were randomly divided into 2 groupstraditional strength training (TS, n = 9) and non-exercising control (C, n = 7). The TS group performed 3 lower limb exercises (leg press, squat, and knee extension) using 6–10 repetitions maximum 2 days per week for the first week and 3 days per week for the remaining 5 weeks (17 total workouts). Pre- and posttraining vastus lateralis muscle biopsies were analyzed for fiber type composition using 2 popular methodsmyosin adenosine triphosphatase (mATPase) histochemistry and myosin heavy chain (MHC) immunohistochemistry. Six fiber types (I, IC, IIC, IIA, IIAX, and IIX) were delineated using each method separately and in combination. Because of the subjective nature of each method (visual assessment of staining intensities), IIAX fibers expressing a small amount of MHCIIa were misclassified as type IIX using mATPase histochemistry, whereas those expressing a small amount of MHCIIx were misclassified as type IIA using MHC immunohistochemistry. As such, either method used separately resulted in an underestimation of the type IIAX fiber population. In addition, the use of mATPase histochemistry alone resulted in an overestimation of type IIX, whereas there was an overestimation of type IIA using MHC immunohistochemistry. These fiber typing errors were most evident after 6 weeks of resistance training when fibers were in transition from type IIX to IIA. These data suggest that the best approach to more accurately determine muscle fiber type composition (especially after training) is the combination of mATPase histochemical and MHC immunohistochemical methods.