Muscle hypertrophy and fast fiber type conversions in heavy resistance-trained women

Twenty-four women completed a 20-week heavy-resistance weight training program for the lower extremity. Workouts were twice a week and consisted of warm-up exercises followed by three sets each of full squats, vertical leg presses, leg extensions, and leg curls. All exercises were performed to failure using 6-8 RM (repetition maximum). Weight training caused a significant increase in maximal isotonic strength (1 RM) for each exercise. After training, there was a decrease in body fat percentage (p less than 0.05), and an increase in lean body mass (p less than 0.05) with no overall change in thigh girth. Biopsies were obtained before and after training from the superficial portion of the vastus lateralis muscle. Sections were prepared for histological and histochemical examination. Six fiber types (I, IC, IIC, IIA, IIAB, and IIB) were distinguished following routine myofibrillar adenosine triphosphatase histochemistry. Areas were determined for fiber types I, IIA, and IIAB + IIB. The heavy-resistance training resulted in significant hypertrophy of all three groups: I (15%), IIA (45%), and IIAB + IIB (57%). These data are similar to those in men and suggest considerable hypertrophy of all major fiber types is also possible in women if exercise intensity and duration are sufficient. In addition, the training resulted in a significant decrease in the percentage of IIB with a concomitant increase in IIA fibers, suggesting that strength training may lead to fiber conversions.     

Histochemical, biochemical, and ultrastructural analyses of single human muscle fibers, with special reference to the C-fiber population.

A muscle biopsy from the vastus lateralis muscle of a strength-trained woman was found to contain an unusual fiber type composition and was analyzed by histochemical, biochemical, and ultrastructural techniques. Special attention was given to the C-fibers, which comprised over 15% of the total fiber number in the biopsy. The mATPase activity of the C-fibers remained stable to varying degrees over the pH range normally used for routine mATPase histochemistry. Although a continuum existed, the C-fibers were histochemically subdivided into three main fiber types: IC, IIC, and IIAC. The IC fibers were histochemically more similar to the Type I, the IIAC were more similar to the Type IIA, and the IIC were darkly stained throughout the pH range. Biochemical analysis revealed that all C-fibers coexpressed myosin heavy chains (MHC) I and IIa in variable ratios. The histochemical staining intensity correlated with the myosin heavy chain composition such that the Type IC fibers contained a greater ratio of MHCI/MHCIIa, the IIAC contained a greater ratio of MHCIIa/MHCI, and the Type IIC contained equal amounts of these two heavy chains. Ultrastructural data of the C-fiber population revealed an oxidative capacity between fiber Types I and IIA and suggested a range of mitochondrial volume percent from highest to lowest such that I greater than IC greater than IIC greater than IIA-C greater than IIA. Under physiological conditions, it appears that the IC fibers represent Type I fibers that additionally express some fast characteristics, whereas the Type IIAC are Type IIA fibers that additionally express some slow characteristics. Fibers expressing a 50:50 mixture of MHCI and MHCIIa (IIC fibers) were rarely found. It is not known whether C-fibers represent a distinct population between the fast- and slow-twitch fibers that is specifically adapted to a particular usage or whether they are transforming fibers in the process of going from fast to slow or slow to fast.     

The multiplicity of combinations of myosin light chains and heavy chains in histochemically typed single fibres. Rabbit tibialis anterior muscle.

1. Combined histochemical and biochemical single-fibre analyses [Staron & Pette (1987) Biochem. J. 243, 687-693], were used to investigate the rabbit tibialis-anterior fibre population. 2. This muscle is composed of four histochemically defined fibre types (I, IIC, IIA and IIB). 3. Type I fibres contain slow myosin light chains LC1s and LC2 and the slow myosin heavy chain HCI, and types IIA and IIB contain the fast myosin light chains LC1f, LC2f and LC3f and the fast heavy chains HCIIa and HCIIb respectively. 4. A small fraction of fibres (IIAB), histochemically intermediate between types IIA and IIB, contain the fast light myosin chains but display a coexistence of HCIIa and HCIIb. 5. Similarly to the soleus muscle, C fibres in the tibialis anterior muscle contain both fast and slow myosin light chains and heavy chains. The IIC fibres show a predominance of the fast forms and the IC fibres (histochemically intermediate between types I and IIC) a predominance of the slow forms. 6. A total of 60 theoretical isomyosins can be derived from these findings on the distribution of fast and slow myosin light and heavy chains in the fibres of rabbit tibialis anterior muscle.     

Evidence for three fast myosin heavy chain isoforms in type II skeletal muscle fibers in the adult llama (Lama glama).

Skeletal muscle fiber types classified on the basis of their content of different myosin heavy chain (MHC) isoforms were analyzed in samples from hindlimb muscles of adult sedentary llamas (Lama glama) by correlating immunohistochemistry with specific anti-MHC monoclonal antibodies, myofibrillar ATPase (mATPase) histochemistry, and quantitative histochemistry of fiber metabolic and size properties. The immunohistochemical technique allowed the separation of four pure (i.e., expressing a unique MHC isoform) muscle fiber types: one slow-twitch (Type I) and three fast-twitch (Type II) phenotypes. The same four major fiber types could be objectively discriminated with two serial sections stained for mATPase after acid (pH 4.5) and alkaline (pH 10.5) preincubations. The three fast-twitch fiber types were tentatively designated as IIA, IIX, and IIB on the basis of the homologies of their immunoreactivities, acid denaturation of their mATPase activity, size, and metabolic properties expressed at the cellular level with the corresponding isoforms of rat and horse muscles. Acid stability of their mATPase activity increased in the rank order IIA>IIX>IIB. The same was true for size and glycolytic capacity, whereas oxidative capacity decreased in the same rank order IIA>IIX>IIB. In addition to these four pure fibers (I, IIA, IIX, and IIB), four other fiber types with hybrid phenotypes containing two (I+IIA, IIAX, and IIXB) or three (IIAXB) MHCs were immunohistochemically delineated. These frequent phenotypes (40% of the semitendinosus muscle fiber composition) had overlapped mATPase staining intensities with their corresponding pure fiber types, so they could not be delineated by mATPase histochemistry. Expression of the three fast adult MHC isoforms was spatially regulated around islets of Type I fibers, with concentric circles of fibers expressing MHC-IIA, then MHC-IIX, and peripherally MHC-IIB. This study demonstrates that three adult fast Type II MHC isoproteins are expressed in skeletal muscle fibers of the llama. The general assumption that the very fast MHC-IIB isoform is expressed only in small mammals can be rejected.     

Muscle fiber characteristics and performance correlates of male Olympic-style weightlifters

Biopsies fro the vastus lateralis muscle of male weightlifters (WL; n=6; X +/- SE, age=27.0 +/- 2.1 years), and non-weight-trained men (CON; n=7; age=27.0 +/- 2.0 years) were compared for fiber types, myosin heavy chain (MHC) and titin content, and fiber type-specific capillary density. Differences (p<0.05) were observed for percent fiber types IIC (WL=0.4 +/- 0.2, CON=2.4 +/- 0.8); IIA (WL=50.5 +/- 3.2, CON=26.9 +/- 3.7); and IIB (WL=1.7 +/- 1.4, CON=21.0 +/- 5.3), as well as percent MHC IIa (WL=65.3 +/- 2.4, CON=52.1 +/- 4.2) and percent MHC IIB (WL=0.9 +/- 0.9; CON=18.2 +/- 6.1). All WL exhibited only the titin-1 isoform. Capillary density (caps.mm(-2)) for all fiber types combined was greater for the CON subjects (WL=192.7 +/- 17.3; CON=262.9 +/- 26.3), due primarily to a greater capillary density in the IIA fibers. Weightlifting performances and vertical jump power were correlated with type II fiber characteristics. These results suggest that successful weightlifting performance is not dependent on IIB fibers, and that weightlifters exhibit large percentages of type IIA muscle fibers and MHC IIa isoform content.     

Correlation between myofibrillar ATPase activity and myosin heavy chain composition in single human muscle fibers

Summary Single human muscle fibers were analysed using a combination of histochemical and biochemical techniques. Routine myofibrillar adenosine triphosphatase (mATPase) histochemistry revealed a continuum of staining intensities between the fast fiber types IIA and IIB (type IIAB fibers) after preincubation at pH 4.6. Electrophoretic analysis of single, histochemically-identified fibers demonstrated a correlation between the staining intensity and the myosin heavy chain (MHC) composition. All fibers classified as type I contained exclusively MHCI and all type IIA fibers contained only MHCIIa. Type IIAB fibers displayed variable amounts of both MHCIIa and MHCIIb; the greater the staining intensity of these fibers after preincubation at pH 4.6, the greater the percentage of MHCIIb. Those fibers histochemically classified as type IIB contained either entirely MHCIIb or, in addition to MHCIIb, a small amount of MHCIIa. These data establish a correlation between the mATPase activity and MHC content in single human muscle fibers.     

Fiber type population in limb muscles ofMicrocebus murinus

Populations and distributions of fiber types were studied in 19 limb muscles ofMicrocebus murinus. Proportions and cross-sectional areas of muscles fiber types were compared with data from the literature for other prosimians (Galago, Lemur, andNycticebus), another primate (Macaca cynomolgus), and the rat. Most muscles are heterogenous, with type I fibers (slow oxidative) localized in the deeper part, near the bone. Type IIA fibers (fast oxidative glycolytic) are more evenly distributed than type I and type IIB (fast glycolytic). The combination of large number and large size of type I fibers results in enhanced slow-twitch and oxidative properties as required for antigravity function of postural muscles. Compared with other primates,Microcebus shows relatively small cross-sectional areas of fibers and less numerous type I fibers, in every muscle, which is probably related to small body mass. The fiber type population of the different components of the quadriceps femoris is also related to the particular mode of locomotion of the mouse-lemur: running and leaping, climbing and hopping. M. vastus medialis and m. vastus lateralis are made up only of fast twitch fibers, IIA and IIB. A possible repercussion of hypothyroidism during the rest season and a decrease in locomotor activity was the subject of investigation of the fiber type proportion and section areas. No difference were found between individuals euthanized during the active period and those at rest period. Either a very low level of thyroxine associated with reduced activity is sufficient to maintain the processes controlling myosin expression, or the effects on muscles fibers of natural hypothyroidism and hypokinesia neutralize each other during the rest season.     

Correlation between myofibrillar ATPase activity and myosin heavy chain composition in single human muscle fibers.

Single human muscle fibers were analysed using a combination of histochemical and biochemical techniques. Routine myofibrillar adenosine triphosphatase (mATPase) histochemistry revealed a continuum of staining intensities between the fast fiber types IIA and IIB (type IIAB fibers) after preincubation at pH 4.6. Electrophoretic analysis of single, histochemically-identified fibers demonstrated a correlation between the staining intensity and the myosin heavy chain (MHC) composition. All fibers classified as type I contained exclusively MHCI and all type IIA fibers contained only MHCIIa. Type IIAB fibers displayed variable amounts of both MHCIIa and MHCIIb; the greater the staining intensity of these fibers after preincubation at pH 4.6, the greater the percentage of MHCIIb. Those fibers histochemically classified as type IIB contained either entirely MHCIIb or, in addition to MHCIIb, a small amount of MHCIIa. These data establish a correlation between the mATPase activity and MHC content in single human muscle fibers.     

Type IIC fibres in certain muscles of the adult rat (sedentary and exercised)

Samples were taken, at fixed levels, of the vastus lateralis, the caput lateralis of the gastrocnemius muscle and the longissimus lumbaris of 72 Wistar rats which were either sedentary or subjected to various exercise schedules. The samples were analyzed using the histochemical technique of myosin ATPase (m-ATPase) after preincubation at pH 4.2, and the fibre-types I, II (IIA and IIB) and IIC were identified, calculating the percentage of type IIC fibres as well as their minimum diameter. The percentages of these IIC fibres found in the red and mixed parts of the gastrocnemius (caput lateralis) and the longissimus lumbaris were between 0.7% and 2.6%. However, their presence was not detected in the vastus lateralis or in the white part of the gastrocnemius (caput lateralis). The lack of differences in this fibre type between the males and females of the population was shown statistically. Likewise, no significant modification of the IIC fibres between sedentary and exercised animals was seen. With regard to fibrillar size, females showed a smaller minimum diameter than males, the results showing a small increase in the size of these fibres in both sexes after exercise, although in most cases this was not statistically significant.     

Skeletal Muscle Metabolism and Body Fat Content in Men and Women

The purpose of the present study was to verify the relationships between indicators of body Eat content and specific characteristics of skeletal muscle in a large sample of men and women. Six skinfold thicknesses (σ6S) and maximal oxygen uptake (VO₂ max) were measured in 348 Caucasian subjects (149 women and 199 men). Fiber type proportions (type I, type IIA, and type IIB) and activity levels of marker enzymes for the Krebs cycle (malate dehydrogenase, MDH) and for the fatty acid oxidation (3-hydroxya-cyl CoA dehydrogenase, HADH) pathways were determined in vastus lateralis muscle samples. No significant correlation was found between fiber type proportions and σ6S. Significant and negative correlations were, however, obtained in both genders between the σ6S and MDH enzyme activity (r = ?0.23; p<0.01), but not between the σ6S and HADH enzyme activity. When individuals with low and high amount of subcutaneous fat but paired for VO₂max were compared, vastus lateralis of fat men exhibited the same proportion of type I fiber (38.6 ± 10.3 vs 38.5 ± 13.4 %) and HADH activity level (3.43 ± 1.05 vs. 334 ± 0.81 U/g), but had about 20% less MDH enzyme activity than vastus lateralis of leaner men (158 ± 35 vs. 198 ± 43 U/g;p<0.05). No difference was found in any of these muscle phenotypes when comparisons were made between women with low and high amount of subcutaneous fat but also paired for VO₂max. Moreover, no relations were observed between skeletal muscle fiber type proportion or metabolic markers with relative subcutaneous fat distribution. In conclusion, these results indicate that the proportion of fiber type of skeletal muscle is not a determinant of body fat content or fat distribution in men and women. However, the results of the present study suggest, at least in men, that a low oxidative capacity of skeletal muscle, undetected by muscle fiber typing, is associated with an augmented body fat content.     

Neuromuscular partitioning, architectural design, and myosin fiber types of the M. vastus lateralis of the llama (Lama glama)

The llama (Lama glama) is one of the few mammals of relatively large body size in which three fast myosin heavy chain isoforms (i.e., IIA, IIX, IIB) are extensively expressed in their locomotory muscles. This study was designed to gain insight into the morphological and functional organization of skeletal musculature in this peculiar animal model. The neuromuscular partitioning, architectural design, and myosin fiber types were systematically studied in the M. vastus lateralis of adult llamas (n = 15). Four nonoverlapping neuromuscular partitions or compartments were identified macroscopically (using a modified Sihler's technique for muscle depigmentation), although they did not conform strictly to the definitions of "neuromuscular compartments." Each neuromuscular partition was innervated by primary branches of the femoral nerve and was arranged within the muscle as paired partitions, two in parallel (deep-superficial compartmentalization) and the other two in-series (proximo-distal compartmentalization). These neuromuscular partitions of the muscle varied in their respective architectural designs (studied after partial digestion with diluted nitric acid) and myosin fiber type characteristics (identified immunohistochemically with specific anti-myosin monoclonal antibodies, then examined by quantitative histochemistry and image analysis). The deep partitions of the muscle had longer fibers, with lower angles of pinnation, and higher percentages of fast-glycolytic fibers than the superficial partitions of the muscle. These differences clearly suggest a division of labor in the whole M. vastus lateralis of llamas, with deep partitions exhibiting features well adapted for dynamic activities in the extension of stifle, whereas superficial portions seem to be related to the antigravitational role of the muscle in preserving the extension of the stifle during standing and stance phase of the stride. This peculiar structural and functional organization of the llama M. vastus lateralis does not confirm the generalized idea that deep muscles or the deepest portions within the same muscles somehow develop postural and/or low-intensity isometric functions. Rather, it suggests a primacy of architecture over intramuscular location in determining fiber type composition and hence division of labor within the muscle. A compartmentalization in the distribution of the three fast-subtype fibers (IIA, IIX, and IIB) also occurred, and this could also be relevant functionally, since these fiber types differed significantly in size (IIA < IIX < IIB), oxidative capacity (IIA > IIX > IIB), and capillarization (IIA = IIX > IIB). Furthermore, a typical spatial pattern in fiber type distribution was encountered in llama muscle (i.e., fiber types were consistently ranked in the order I --> IIA --> IIX --> IIB from the center to the periphery of fascicles), suggesting again peculiar and not well understood functional adaptations in these species.     

Downregulation in muscle Na(+)-K(+)-ATPase following a 21-day expedition to 6,194 m.

To investigate the hypothesis that acclimatization to altitude would result in a downregulation in muscle Na(+)-K(+)-ATPase pump concentration, tissue samples were obtained from the vastus lateralis muscle of six volunteers (5 males and 1 female), ranging in age from 24 to 35 yr, both before and within 3 days after a 21-day expedition to the summit of Mount Denali, Alaska (6,194 m). Na(+)-K(+)-ATPase, measured by the [(3)H]ouabain-binding technique, decreased by 13.8% [348 +/- 12 vs. 300 +/- 7.6 (SE) pmol/g wet wt; P < 0.05]. No changes were found in the maximal activities (mol. kg protein(-1). h(-1)) of the mitochondrial enzymes, succinic dehydrogenase (3.63 +/- 0.20 vs. 3.25 +/- 0.23), citrate synthase (4. 76 +/- 0.44 vs. 4.94 +/- 0.44), and malate dehydrogenase (12.6 +/- 1. 8 vs. 12.7 +/- 1.2). Similarly, the expedition had no effect on any of the histochemical properties examined, namely fiber-type distribution (types I, IIA, IIB, IC, IIC, IIAB), area, capillarization, and succinic dehydrogenase activity. Peak aerobic power (52.3 +/- 2.1 vs. 50.6 +/- 1.9 ml. kg(-1). min(-1)) and body mass (76.9 +/- 3.7 vs. 75.5 +/- 2.9 kg) were also unaffected. We concluded that acclimatization to altitude results in a downregulation in muscle Na(+)-K(+)-ATPase pump concentration, which occurs without changes in oxidative potential and other fiber-type histochemical properties.     

Misclassification of hybrid fast fibers in resistance-trained human skeletal muscle using histochemical and immunohistochemical methods

ABSTRACT: Staron, 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 groups: traditional 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 methods: myosin 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.     

Skeletal muscle morphology in power-lifters with and without anabolic steroids

The morphological appearance of the vastus lateralis (VL) muscle from high-level power-lifters on long-term anabolic steroid supplementation (PAS) and power-lifters never taking anabolic steroids (P) was compared. The effects of long- and short-term supplementation were compared. Enzyme-immunohistochemical investigations were performed to assess muscle fiber type composition, fiber area, number of myonuclei per fiber, internal myonuclei, myonuclear domains and proportion of satellite cells. The PAS group had larger type I, IIA, IIAB and IIC fiber areas (p<0.05). The number of myonuclei/fiber and the proportion of central nuclei were significantly higher in the PAS group (p<0.05). Similar results were seen in the trapezius muscle (T) but additionally, in T the proportion of fibers expressing developmental myosin isoforms was higher in the PAS group compared to the P group. Further, in VL, the PAS group had significantly larger nuclear domains in fibers containing ≥5 myonuclei. The results of AS on VL morphology in this study were similar to previously reported short-term effects of AS on VL. The initial effects from AS appear to be maintained for several years.     

Myosin types in human skeletal muscle fibers

By combining enzyme histochemistry for fiber typing with immunohistochemistry for slow and fast myosin a correlation between fiber type and myosin type was sought in human skeletal muscle. Fiber typing was done by staining for myofibrillar ATPases after preincubation at discriminating pH values. Myosin types were discriminated using type specific anti-rabbit myosin antibodies shown to cross-react with human myosin and were visualized by a protein A-peroxidase method. Type I fibers were shown to contain slow myosin only, type IIA and IIB fibers fast myosin only, and type IIC fibers both myosins in various proportions. When muscle biopsies from well-trained athletes were investigated essentially the same staining pattern was observed. However, rarely occurring type I fibers with high glycolytic activity were detected containing additional small amounts of fast myosin and occasional type IIA fibers had small amounts of slow myosin. Based on the observation of various fiber types in which slow and fast myosin coexist we propose a dynamic continuum of fibers encompassing all fiber types.     

Myosin types in human skeletal muscle fibers

Summary By combining enzyme histochemistry for fiber typing with immunohistochemistry for slow and fast myosin a correlation between fiber type and myosin type was sought in human skeletal muscle. Fiber typing was done by staining for myofibrillar ATPases after preincubation at discriminating pH values. Myosin types were discriminated using type specific anti-rabbit myosin antibodies shown to cross-react with human myosin and were visualized by a protein A-peroxidase method. Type I fibers were shown to contain slow myosin only, type IIA and IIB fibers fast myosin only, and type IIC fibers both myosins in various proportions. When muscle biopsies from well-trained athletes were investigated essentially the same staining pattern was observed. However, rarely occurring type I fibers with high glycolytic activity were detected containing additional small amounts of fast myosin and occasional type IIA fibers had small amounts of slow myosin. Based on the observation of various fiber types in which slow and fast myosin coexist we propose a dynamic continuum of fibers encompassing all fiber types.     

大鼠与家兔生后各年龄阶段跖肌纤维的比较

应用建立在肌球蛋白重链异构体基础上的标准肌动球蛋白ATP酶和琥珀酸脱氢酶组织化学方法,分析大鼠和家兔出生后发育各年龄阶段跖肌纤维型分布。在生后2周至24周龄的大鼠和家兔Ⅰ、ⅡX型肌纤维百分比例减少,而ⅡA、ⅡB型纤维则增加。进行大量单肌纤维的组织化学特征的比较和相关性探讨。结果显示动物平均体重与跖肌的平均湿重随生后发育逐渐增加,Ⅰ、ⅡX、ⅡA及ⅡB型纤维均在生后各年龄组的全部肌肉内被发现,但出生后2日龄组是个例外。在生后发育期间,雄性大鼠和家兔ⅡB型纤维的平均肌纤维型构成要大于雌性大鼠和家兔,而雄性大鼠和家兔Ⅰ、ⅡX、ⅡA型三种氧化组织化学分类的肌纤维型构成均小于雌性大鼠和家兔。大鼠Ⅰ、ⅡX、ⅡA和ⅡB型纤维的平均横切面积显然要比家兔的同类型肌纤维要小。在大鼠和家兔可见明显的性别差异。大鼠和家兔的ⅡX型纤维横切面积是最小的,Ⅰ、ⅡA型纤维呈中等大小,ⅡB型纤维最大。该重要的测试有助于我们深入研究啮齿类动物快肌纤维生理特征的适应。     

Correlation between myofibrillar ATPase activity and myosin heavy chain composition in rabbit muscle fibers

Combined histochemical and biochemical analyses were performed on single fibers of rabbit soleus muscle. Histochemically, four fiber types (I, IC, IIC, IIA) were defined. Of these, types I and IIA were separate, histochemically homogeneous groups. A heterogeneous C fiber population exhibited a continuum of staining intensities between types I and IIA. Microelectrophoretic analyses of specific, histochemically defined fibers revealed that type I fibers contained exclusively HCI, whereas type IIA fibers contained only HCIIa. The C fibers were characterized by the coexistence of both heavy chains in varying ratios, type IC with a predominance of HCI and type IIC with a predominance of HCIIa. A direct correlation existed between the myosin heavy chain composition and the histochemical mATPase staining and was especially evident in the C fiber population with its variable HCI/HCIIa ratio. This correlation did not apply to the myosin light chain complement.     

Skeletal muscle fiber area alterations in two opposing modes of resistance-exercise training in the same individual

The purpose of this study was to observe fiber area changes that might occur in the same subject from two opposing resistance-exercise training regimes isolating the quadriceps muscle group. Twelve college-age men divided into two groups participated in each of two 7.5-week regimens; one performed a muscular strength program (high-resistance, low-repetition) 4 days a week on a resistance-exercise apparatus, while the other performed a muscular endurance (low-resistance, high-repetition) program. After a 5.5-week hiatus, the groups changed regimens for the second 7.5 weeks. Closed-needle biopsies of the dominant vastus lateralis and isokinetic dynamometer evaluations were made before and at the end of each training period. The muscle samples were analyzed for area changes. In both groups the initial exercise stimulus, whether for strength or endurance, increased the area of fibers of all three major types (I, IIA, and IIB). Subjects doing strength exercises as their second treatment showed a further increase in the area of type I and IIB fibers, whereas those doing endurance exercises showed a decrease in all fiber types. From the first to the last biopsy all fiber areas were decreased (P less than 0.05) in the control-strength-endurance group and increased (P less than 0.05) in the control-endurance-strength group. These results suggested that endurance exercise preceding strength exercise in an isolated muscle group maximized fiber area adaptations to exercise stress. Consideration should thus be given in exercise and rehabilitation programs to the muscle cellular adaptations evidenced in different orders of training, particularly if muscular strength is considered important.     

Skeletal muscle characteristics of reindeer (Rangifer tarandus L.)

Fibre type composition, fibre areas, capillaries, enzyme activities and intramuscular substrates were analysed on skeletal muscle samples from reindeer. The muscles contained 10-20% Type I fibres and a higher percentage of Type IIB (40-60%) than Type IIA fibres (20-40%). All fibre types revealed medium or dark staining intensity for oxidative capacity. Glycolytic capacity was greatest in Type IIB fibres. All fibres stained for glycogen, while Type I and IIA fibres stained for lipids. The mean number of capillaries in contact with fibres of each type, relative to fibre type area was high in all muscle types. The metabolic profile of reindeer muscle indicates that energy, to a great extent, is produced through oxidative pathways.