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Background. Researchers employing a variety of training methods have demonstrated a fast-to-slow fibre transformation in animal skeletal muscle. The observation as to whether this occurs in exercise trained humans is limited and equivocal.
Methods. Experimental design: to examine this issue, skeletal muscle from seven subjects who had participated in a decade or more of high intensity aerobic training (DT) and six nontrained (NT) subjects was obtained by muscle biopsy from the vastus lateralis muscle (VL) and subjected to a modified myofibrillar ATPase technique to identify muscle fibre types. Muscle tissue was histochemically treated by exposure to an alkaline preincubation (pH 9.9), an acid preincubation (pH 4.3 or 4.6) and the formate-KCl preincubation buffer (pH 4.54), previously employed in animal studies.
Results. The formate-KCl preincubation medium identified all major fibre types at a single pH in human subjects. The percentage of type I fibres in DT was 70.9% vs 37.7% in NT (p<0.01), while the type Ila fibres in DT (25.3%) was much lower (p<0.01) than NT (51.8%). Surprisingly, type Ila fibres in the DT group displayed lesser oxidative staining intensity (p<0.01) than type Ila fibres from the NT group. Mean crosssectional area of type I fibres for DT (6233.9+/-1421.7 (mu)m^sup 2^) was greater (p<0.05) than either type I (5746.8+/-1135.2 (mu)m^sup 2^) or II (5693.5+/-1214.6 (mu)m^sup 2^) from NT.
Conclusions. The results revealed that endurance training may promote a transition from type II to type I muscle fibre types and occurs at the expense of the type II fibre population.
KEY WORDs: Muscle biopsy - Adenosine triphosphatase metabolism - Muscle fibre metabolism - Cross sectional area - Oxidative and glycolytic stain.
Several investigators have confirmed that mammalian skeletal muscle could be differentiated into type I and type II fibres using the myofibrillar actomyosin adenosine triphosphatase (ATPase) staining procedure as originally proposed by Brooke and Kaiser.1 Gollnick et al.2 utilizing animal tissue developed a method to identify fibre types of skeletal muscle on the basis of the sequential activation-inactivation of myofibrillar actomyosin ATPase during acid preincubation. Morever modifications in histochemical procedures3 4 advancement in biochemicals 6 and immunohistochemical7 techniques have led to identification of a continuum of fibre types between type I and type IIb.
Researchers have confirmed the plasticity of skeletal muscle utilizing techniques such...