Muscle fiber types of women after resistance training ? Quantitative ultrastructure and enzyme activity

Abstract

Muscle biopsies of the vastus lateralis muscle taken before and after 18 weeks of resistance training were compared by preparing frozen cross sections for electron microscopy and using adjacent sections for fiber typing by myosin ATPase activity. Quantitative ultrastructural changes were observed in histochemically-identified muscle fiber types of twelve young women who underwent the training. The percentage of type IIB fibers decreased and IIA fibers increased. The cross-sectional area of all major fiber types increased with training. The absolute volume of myofibrils, intermyofibrillar space, and mitochondria increased with training for most major fiber types (type I, IIA and IIAB), but the relative volume percentages were not significantly changed because of corresponding fiber hypertrophy. Mean mitochondrial size for types I and IIA and myofibril size for types IIC and IIB increased significantly with training. The capillary number per fiber and density did not change with training. Activity levels were measured for selected glycolytic and oxidative enzymes. Cytochrome oxidase and hexokinase increased significantly with training, while creatine kinase, citrate synthase, phosphofructokinase, glyceraldehyde phosphate dehydrogenase and hydroxyacyl CoA dehydrogenase enzymes were not significantly altered. The results suggest that this type of high-repetition resistance training causes the intracellular components of all fiber types to increase proportionally with an increase in fiber size. In addition, the enzyme analysis indicates the muscle as a whole may increase its oxidative phosphorylation capacity in conjunction with the decreased percentage of type IIB fibers.

Impaired free fatty acid utilization by skeletal muscle in non-insulin-dependent diabetes mellitus.

“…HK, PFK, and GAPDH activity reflects the glycolytic capacity of muscle, CK activity is an indicator of capacity for ATP resynthesis from creatine phosphate, CS activity is a marker of Krebs cycle capacity, while COX activity is an index of oxidative phosphorylation, and HADH activity marks mitochondrial capacity for FFA ,(-oxida- tion. The profile of skeletal muscle for these five metabolic capacities was entirely similar between NIDDM and nondiabetic subjects and are somewhat low, consistent with values found in sedentary individuals (23,27). Also, the proportions of types I, Ila, and IIb muscle fibers, as well as the numbers of capillaries per fiber type and the area of the different fibers, were equivalent in NIDDM and nondiabetic subjects.…”

“…Of the seven enzymes assayed in the current study, none was significantly different in NIDDM in comparison with nondiabetic subjects. Both groups had values for enzyme activity, and for fiber type distribution and capillary density, which are consistent with a physically untrained status (23,27, and Simoneau, J.-A., unpublished observations). Although there were no differences in these factors, it remains to be determined whether enzymes more specific to FFA catabolism or proteins involved in FFA transport, such as fatty acid binding proteins (33), are affected by NIDDM, and are potentially important in the mechanism of decreased fasting uptake and oxidation of FFA as found in the current study.…”

Muscular adaptations in response to three different resistance-training regimens: specificity of repetition maximum training zones

“…Results from resistance-training studies investigating capillary changes are equivocal, with reports of increases, decreases and no changes (e.g., Schantz 1982;Tesch et al 1984Tesch et al , 1990Hather et al 1991;Wang et al 1993;McCall et al 1996;Hagerman et al 2000). In the present study, there was a tendency for the number of capillaries per fiber to increase with training, indicating the formation of new capillaries within the muscle (Table 6).…”

Analysis of muscle adaptations to terrestrial stepping in the Urodelan amphibian Pleurodeles waltlii

“…Many muscle parameters are modified following training, such as muscle enzyme activity, myosin composition, parvalbumin level, number of mitochondria, lipids and myofibril content [reviewed in [33]). In particular, the muscle adaptations that occur following changes in physical activity are characterized by changes at the level of the myosin heavy chains [10] as well as the myosin light chains [14].…”