Muscle fibre types in the suprahyoid muscles of the rat

Five muscle fibre types (I, IIc, IIa, IIx and IIb) were found in the suprahyoid muscles (mylohyoid, geniohyoid, and the anterior and posterior bellies of the digastric) of the rat using immuno and enzyme histochemical techniques. More than 90% of fibres in the muscles examined were fast contracting fibres (types IIa, IIx and IIb). The geniohyoid and the anterior belly of the digastric had the greatest number of IIb fibres, whilst the mylohyoid was almost exclusively formed by aerobic fibres. The posterior belly of the digastric contained a greater percentage of aerobic fibres (83.4%) than the anterior belly (67.8%). With the exception of the geniohyoid, the percentage of type I and IIc fibres, which have slow myosin heavy chain (MHCβ), was relatively high and greater than has been previously reported in the jaw-closing muscles of the rat, such as the superficial masseter. The geniohyoid and mylohyoid exhibited a mosaic fibre type distribution, without any apparent regionalisation, although in the later MHCβ-containing fibres (types I and IIc) were primarily located in the rostral 2/3 region. In contrast, the anterior and posterior bellies of the digastric revealed a clear regionalisation. In the anterior belly of the digastric 2 regions were observed: both a central region, which was almost exclusively formed by aerobic fibres and where all of the type I and IIc fibres were located, and a peripheral region, where type IIb fibres predominated. The posterior belly of the digastric showed a deep aerobic region which was greater in size and where type I and IIc fibres were confined, and a superficial region, where primarily type IIx and IIb fibres were observed.     

Muscle fibre types in the suprahyoid muscles of the rat

Five muscle fibre types (I, IIc, IIa, IIx and IIb) were found in the suprahyoid muscles (mylohyoid, geniohyoid, and the anterior and posterior bellies of the digastric) of the rat using immuno and enzyme histochemical techniques. More than 90% of fibres in the muscles examined were fast contracting fibres (types IIa, IIx and IIb). The geniohyoid and the anterior belly of the digastric had the greatest number of IIb fibres, whilst the mylohyoid was almost exclusively formed by aerobic fibres. The posterior belly of the digastric contained a greater percentage of aerobic fibres (83.4%) than the anterior belly (67.8%). With the exception of the geniohyoid, the percentage of type I and IIc fibres, which have slow myosin heavy chain (MHCβ), was relatively high and greater than has been previously reported in the jaw‐closing muscles of the rat, such as the superficial masseter. The geniohyoid and mylohyoid exhibited a mosaic fibre type distribution, without any apparent regionalisation, although in the later MHCβ‐containing fibres (types I and IIc) were primarily located in the rostral 2/3 region. In contrast, the anterior and posterior bellies of the digastric revealed a clear regionalisation. In the anterior belly of the digastric 2 regions were observed: both a central region, which was almost exclusively formed by aerobic fibres and where all of the type I and IIc fibres were located, and a peripheral region, where type IIb fibres predominated. The posterior belly of the digastric showed a deep aerobic region which was greater in size and where type I and IIc fibres were confined, and a superficial region, where primarily type IIx and IIb fibres were observed.     

Muscle architecture of biceps brachii, triceps brachii and supraspinatus in the horse

Three muscles from the proximal equine forelimb were dissected in order to investigate their potential to contribute to proximal limb mechanics. Muscle mass, fibre length, tendon mass and tendon length were measured from biceps brachii, triceps brachii, supraspinatus and lacertus fibrosus (biceps lateral head mass 171-343.4 g and fibre length 0.5-0.8 cm; biceps medial head mass 283-500 g and fibre length 2.2-4 cm; biceps tendon mass 121.8-260 g and tendon length 35-44 cm; triceps long head mass 3200-6663 g and fibre length 19-26.3 cm; triceps lateral head mass 513.8-1240 g and fibre length 17.5-24 cm; triceps medial head mass 85.2-270.6 g and fibre length 9-16.8 cm; supraspinatus mass 793-1546 g and fibre length 4.7-12.4 cm; lacertus fibrosus mass 4.6-12.4 g and length 10-16 cm). Physiological cross-sectional area (PCSA) and maximum isometric force were estimated for each muscle, and moment arm measurements were taken at the shoulder and elbow joints. Biceps has a greater isometric force-generating capacity than supraspinatus. It also appears to have a larger shoulder moment arm, so could therefore have the potential to make a greater contribution to the shoulder moment than supraspinatus. Supraspinatus is likely to function primarily as a shoulder stabilizer rather than a shoulder extensor. Biceps also functions as an elbow flexor and data here indicate that it has a greater PCSA and isometric force-generating capacity than its antagonist triceps brachii. Calculation of tendon forces showed that the biceps tendon can withstand much greater forces than lacertus fibrosus. This study will enable further investigation into the interaction between energy recycling in elastic tissues and the generation and absorption of mechanical work by adjacent muscle groups in the equine forelimb.     

Four-headed biceps and triceps brachii muscles,with neurovascular variation

Anatomical variations of the biceps brachii and triceps brachii have been described by various authors, but the occurrence of four-headed biceps brachii and triceps brachii in an ipsilateral arm is rare and has not been reported before in the literature. During routine cadaveric dissection in the department of anatomy, Kasturba Medical College, Mangalore, India, various unusual variants were noted in the left arm of a cadaver of a 67-year-old man. The variants include a four-headed biceps, a four-headed triceps, communication between the musculocutaneous and median nerves, and a high origin of deep brachial artery from the axillary artery. The occurrence of these anomalies and the clinical and morphological significance are discussed.     

Cell size and oxidative enzyme activity of rat biceps brachii and triceps brachii muscles

Fiber-type distributions, cross-sectional areas, and oxidative enzyme activities of type-identified fibers in the biceps brachii and triceps brachii muscles of 10-week-old male Wistar rats were determined and compared with those in the soleus and plantaris muscles. The soleus and plantaris muscles consisted of two (I and IIA) and three (I, IIA, and IIB) types of fibers, respectively. The deep regions of the biceps brachii and triceps brachii muscles consisted of three types of fibers, while the surface regions of those muscles consisted only of type IIB fibers. The cross-sectional areas of fibers in the deep and surface regions of the plantaris muscle and in the deep regions of the biceps brachii and triceps brachii muscles were in the rank order of type I = type IIA < type IIB, while the oxidative enzyme activities of fibers in the deep and surface regions of the plantaris muscle and in the deep region of the triceps brachii muscle were in the rank order of type IIB < type I = type IIA. These results indicate that fiber-type distributions, cross-sectional areas, and oxidative enzyme activities are muscle type- and region-specific. Therefore, the metabolic and functional significance of the biceps brachii and triceps brachii muscles, especially in the surface regions, where only type IIB fibers are located, in those muscles, appears to be determined by their fibers having larger cells and lower oxidative enzyme activity.     

Laryngeal muscle fibre types

The internal laryngeal muscles have evolved to subserve the highly specialized functions of airways protection, respiration, and phonation. Their contractile properties, histochemistry, biochemical properties, myosin heavy chain (MyHC) expression and their regulation by nerves and hormones are reviewed and compared with limb muscle fibres. Cricothyroid, the vocal cord tensor, is limb‐like in MyHC composition and fibre type properties, while the vocal fold abductor and adductors are allotypically different, with capacity for expressing an isoform of MyHC that is kinetically faster than the fastest limb MyHC. In rats and rabbits the faster isoform is the extraocular (EO) MyHC, while in carnivores, it is the IIB MyHC. These adaptations enable the abductor and adductor muscles to remain always faster than the cricothyroid as the latter changes in speed during evolution to match changing metabolic and respiratory rates in relation to scaling with body mass. Such phylogenetic plasticity is vital to the airways protection and respiratory functions of these muscles. The posterior cricoarythenoid, the abductor muscle, is tonically driven during expiration, and consequently has a slower fibre type profile than the principal adductor, the thyroarythenoid. The human thyroarythenoid appears not to express EO or IIB MyHC significantly, but is unique in expressing the slow‐tonic MyHC. The concepts of allotype and phylogenetic plasticity help to explain differences in fibre type between limb and laryngeal muscles and between homologous laryngeal muscles in different species. Laryngeal muscle fibres exhibit physiological plasticity as do limb muscles, being subject to neural and hormonal modulation.     

Quantification of fibre type regionalisation: an analysis of lower hindlimb muscles in the rat

Newly developed concepts and methods for the quantification of fibre type regionalisation were used for comparison between all muscles traversing the ankle of the rat lower hindlimb (n = 12). For each muscle, cross‐sections from the proximodistal midlevel were stained for myofibrillar ATPase and classified as type I (‘slow’) or II (‘fast’). For the 11 ‘fast’ muscles (i.e. all except soleus), the muscle outline and the position of each type I fibre were digitised for further computer processing. Two potentially independent aspects of type I fibre regionalisation were evaluated quantitatively: (1) the degree to which type I fibres were restricted to a limited portion of the total cross‐sectional area (‘area‐regionalisation’) ; (2) the extent and direction of the difference (if any) between the centre of the muscle cross‐section and the calculated centre for the type I fibre cluster (‘vector regionalisation’). Statistical analysis showed that type I fibres were vector regionalised in practically all investigated muscles and area regionalised within most of them, the only consistent exceptions being peroneus brevis and peroneus digitorum 4, 5. In muscles with a high degree of area regionalisation the population of type I fibres also had a markedly eccentric intramuscular position (i.e. high vector regionalisation). A significant relationship was observed between the relative position of a muscle within the hindlimb (transverse plane) and the direction and degree of its type I fibre eccentricity. On average, the degree of type I fibre eccentricity was greater for muscles remote from the limb centre than for those situated more centrally. In addition, the intramuscular concentration of type I fibres was typically greatest towards the centre of the limb, the most striking exception being tibialis posterior. For the slow soleus muscle, which is centrally placed within the limb, our analysis concerned the type II fibres, which were found to be weakly vector regionalised but not significantly area regionalised. It is concluded that, within muscles of the rat's lower hindlimb, fibre type regionalisation is a general and graded phenomenon which may reflect differentiating (embryological?) mechanisms of a transmuscular significance. Furthermore, the analysis demonstrated the usefulness of our new methods and concepts for the quantification of fibre type regionalisation.     

Anticipation of elbow joint perturbation shortens the onset time of the reflex EMG response in biceps brachii and triceps brachii

This study aimed to investigate the influence of the anticipation of a perturbation torque applied to extend the elbow joint on the onset time of reflex electromyogram (EMG) responses. A perturbation torque generated by an electromagnetic torque motor system was applied to the forearm of eleven subjects during trials. The trials were divided into an anticipated (AN) condition - perturbation torque applied after the auditory signal - and an unanticipated (UAN) condition - suddenly applied perturbation. To detect the reflex EMG response in the biceps brachii (Bb) and triceps brachii (Tb) muscles, a new method involving the discrete wavelet transform and outlier tests was used. We found that the onset time of the reflex response in both the muscles in the AN condition was significantly shorter than that in the UAN condition. The angle of transition from flexion to extension, which was induced by the reflex response of Bb, was also significantly smaller in the AN condition than in the UAN condition. The results indicate that the anticipation of an applied perturbation torque decreases the onset time of the reflex response in the Bb and Tb.     

Muscle fibre composition of ratvastus intermedius following immobilisation at different muscle lengths

The knee joints of one hind limb of male Wistar rats (250–300 g) were immobilised in a plaster cast for up to 3 weeks with the limb in either the fully extended or flexed position Serial frozen sections ofvastus intermedius muscle were stained histochemically for myosin ATPase, succinic dehydrogenase, phosphorylase and capillaries. Muscle fibres were classified as either slow twitch oxidative (SO), fast twitch oxidative glycolytic (FOG) or fast twitch glycolytic (FG).Fibre area of SO fibres (3019 ²) decreased by 50% following 3 weeks' immobilisation in the stretched (1532 ²) and shortened (1517 ²) positions. Atrophy of FOG fibres (2456 ²) was greater in muscles immobilised in the stretched (750 ²) than shortened (1185 ²) positions. Evidence has been obtained that muscle fibre number remained unchanged following immobilisation. Control muscles contained 70.4% SO fibres, 29.6% FOG fibres and >0.5% FG fibres. Immobilisation produced an increased proportion of high myosin ATPase staining fibres. The percentage occurrence of FOG fibres increased to 65% and 83% respectively, in muscles immobilised for 3 weeks in the stretched and shortened positions. Mechanisms for the transformation of muscle fibre types and the influence of muscle length on the properties of immobilised muscle are discussed.     

An unusual origin for the accessory head of biceps brachii muscle

During the superficial dissection of the pectoral region and the arm, an abnormal biceps brachii muscle was observed unilaterally. This muscle had three heads. Whereas the short and long heads had their normal origin, the accessory head originated from the anterior surface of the distal part of the pectoralis major muscle, which formed the anterior axillary fold. To our knowledge, this variation has not been previously described. Innervation and vascular supply of this accessory head was from the musculocutaneous nerve and the brachial artery, respectively. © 1996 Wiley-Liss, Inc.     

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

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. Present address: Department of Medicine, University of California at San Diego, School of Medicine, San Diego, CA, 92103, USA     

Unusual variation of a third head of the biceps brachii muscle

A human cadaver was studied which presented a biceps brachii with three heads of origin in the left arm. The third or humeral head presented an unique area of insertion into the bicipital aponeurosis (lacertus fibrosus).     

Differential activation of regions within the biceps brachii muscle during fatigue

Aim: To examine the occurrence of repeated differential activation between the heads of the biceps brachii muscle and its relation to fatigue prevention during a submaximal contraction. Methods: Thirty‐nine subjects carried out an isometric contraction of elbow flexion at 25% of maximal voluntary contraction (MVC) until exhaustion. A grid of 13 by 10 electrodes was used to record surface electromyographic signals from both heads of the biceps brachii. The root‐mean‐square of signals recorded from electrodes located medially and laterally was used to analyse activation differences. Differential activation was defined as periods of 33% different activation level between the two heads of the biceps brachii muscle. Results: Differential muscle activation was demonstrated in 30 of 33 subjects with appropriate data quality. The frequency of differential activation increased from 4.9 to 6.6 min^?1 at the end of the contractions with no change in duration of the differential activations (about 1.4 s). Moreover, the frequency of differential activation was, in general, negatively correlated with time to exhaustion. Conclusion: The observed differential activation between the heads of the biceps brachii can be explained by an uneven distribution of synaptic input to the motor neurone pool. The findings of this study indicate that differential activation of regions within a muscle does not prevent fatigue at a contraction level of 25% of MVC.     

Nonuniform changes in fibre types in the soleus muscle of the developing rat

Muscle fibre composition among the proximal (25%), middle (50%) and distal (75%) regions of the rat soleus muscle at various ages were compared to investigate whether the region-specific changes in fibre types known to occur under nonphysiological conditions (i.e. electrical stimulation along with immobilization in a lengthened position) also occur in the developing muscle. In addition, we attempted to detect fibres with nonuniform histochemical properties in the different segments, processing with myofibrillar actomyosin adenosine triphosphatase after pre-incubation at pH 10.3 against successive cryosections (200 m apart). Samples were obtained from 66 Wistar rats of both sexes ranging in age from 13 to 85 days and subdivided into age groups of 2, 3, 4, 5 and 12 weeks. The mass and length of the soleus muscle increased most significantly at age 3–4 and 2–4 weeks, respectively. The distal region had a significantly lower percentage of type I fibres than the middle region at age 3 weeks, than the proximal and middle regions at age 4 weeks. In addition, some fibres [0.7 (SD 0.5)% n=19 ± 13] possessing nonuniform histochemical properties in different segments were observed from the middle and distal region at age 4 weeks. These findings would suggest that transformations from type II to type I fibres in the soleus muscle of the developing rat occur from the proximal or middle segments.     

Muscle efficiency: the controversial role of elasticity and mechanical energy conversion in stretch-shortening cycles

The analysis of muscle efficiency was performed on a variety of simulated muscle stretch-shortening cycles of in situ rat gastrocnemius muscle. The processes of biochemical energy conversions (phosphorylation and contraction-coupling) and mechanical conversions (internal work to external work) were incorporated in the efficiency calculations. Metabolic cost was determined using a simple linear model. Special attention was drawn to the interacting roles of series elastic compliance and contraction dynamics. The results showed that series elastic compliance affected the efficiency of muscle contraction to a great extent. Stiff muscle was well designed to perform efficient contractions in which muscle merely shortened while active. Compliant muscle performed best in true stretch-shortening contractions utilising the storage and release of series elastic energy effectively. However, both stiff and compliant series elastic elements showed similar optimal muscle efficiency values in shortening contractions and stretch-shortening contractions, respectively. The findings indicate that the storage and re-utilisation of series elastic energy does not enhance overall muscle efficiency, but that optimal efficiency is obtained by a proper design of the muscle with regard to the dynamics of the movement task. Furthermore, it was found that although biochemical efficiency determined the feasible range of muscle efficiency, mechanical work conversions had the strongest influence on the exact value of overall muscle efficiency in stretch-shortening contractions. Electronic Publication     

Spatial distribution of muscle fibers in a lumbrical muscle of the rat

The spatial distributions of two differnt populations of muscle fibers were measured in cross-sections taken from the mid-belly of adult 4DL muscles. Muscle fibers belonging to a single motor unit (identified by glycogen depletion) were distributed randomly in most muscles. Muscle fibers which contained slow myosin (identified immunohistochemically) were distributed nonrandomly, being evenly distributed throughout most of the muscle cross-section, but excluded from the edge of the muscle. Interpreted from a developmental perspective, the results are consistent with the proposals that slow myosin-containing fibers in the adult represent the original population of primary myotubes, and that the adult pattern of motor unit fiber type is achieved by synapse elimination from mismatched fibers rather than by conversion of fiber type. © 1993 Wiley-Liss, Inc.     

A general, computer-based method for study of the spatial distribution of muscle fiber types in skeletal muscle

Summary The present method provides detailed quantitative information on the spatial distribution of the muscle fiber types in skeletal muscle. This is accomplished by comparing the measured spatial distribution of the fiber types with a computer-simulated random pattern. The method is based on a registration of the absolute frequency for six principal categories of fiber contacts (I-I, I-IIA, I-IIB, IIA-IIA, IIA-IIB, IIB-IIB). A computer program was designed tosimulate a random pattern of fibers. The simulations were performed with high accuracy with regard to fiber type proportion and the number of neighbouring fibers. The computer then calculated the frequency for each of the different categories of fiber contacts in the simulated random pattern. The measured distribution of fiber contacts could thus be compared to the simulated random pattern. In three bovine muscles studied, the spatial distribution of the muscle fiber types showed a similar pattern. The muscle fibers had a distinct tendency to be surrounded by fibers of a different type. In all three muscles the difference between the measured and the simulated random pattern was statistically significant (p<10^-3).     

Muscle fibre types and enzyme activities after training with local leg ischaemia in man

Eight healthy men performed supine one-legged training on a bicycle ergometer 45 min per leg four times per week for 4 week. The ergometer and lower body were inside a pressure chamber, the opening of which was sealed at the level of the crotch. One leg trained with impeded leg blood flow (I-leg), induced by an increased (50 mmHg) chamber pressure, at the highest tolerable intensity. The contralateral leg trained at the same power under normal pressure (N-leg). Before and after training biopsies were taken from the vastus lateralis of both legs and maximal one-legged exercise tests were executed with both legs. Biopsies were repeated when the subjects had been back to their habitual physical activity for 3 months. Training increased exercise time to exhaustion, but more in the I-leg than in the N-leg. After training, the I-leg had higher activity of citrate synthase (CS), a marker of oxidative capacity, and lower activity of the M-subunit of lactate dehydrogenase isoenzymes. It also had a higher percentage of type-I fibres and a lower percentage of IIB fibres, larger areas of all fibre types and a greater number of capillaries per fibre. It is concluded that ischaemic training changes the muscle metabolic profile in a direction facilitating aerobic metabolism. An altered fibre-type composition may contribute, but is not enough prerequisite for the change.