Muscle fiber types: how many and what kind?

Course of denervation atrophy in type I and type II fibres of rat extensor digitorum longus muscle

In the denervated extensor digitorum longus muscle of the rat type I and type II muscle fibres were differentiated histochemically and their course of atrophy was studied. Until 42 days after denervation type I and type II fibres could be identified by means of the myofibrillar ATPase reaction. Up to that time an exclusive atrophy of type II fibres was found. Type I fibres, the smallest of the normal muscle, did not change their diameters and therefore represented the largest fibres 42 days after denervation. Type II fibres of the "white" muscle portion, in which the larger IIB fibres are predominant, showed a higher rate of atrophy than those of the "red" muscle portion, in which the smaller IIA fibres are predominant: by 42 days the diameters of all type II fibres had gone down to equal values. Combined with a further progress of atrophy at later stages, there was a dedifferentiation of the histochemical properties, and the type I fibres exhibited atrophy as well. 120 days after denervation all muscle fibres were found to be highly atrophied.

Capillary supply of skeletal muscle fibers in untrained and endurance-trained women

Muscle fiber diameters and number of capillaries per fiber, per mm2 and around each fiber were determined in needle biopsies from the lateral part of the quadriceps muscles of 11 young women. Six subjects were untrained (UT) and five were endurance-trained athletes (ET). Average values for maximal oxygen uptake were 43.9 (UT) and 62.1 ml/kg X min (ET). Mean fiber diameter was somewhat smaller in the UT than in the ET group (39.1 and 42.7 micrometer), but the difference was not statistically significant. Fibers with the highest content of mitochondria were on the average 9 micrometer thicker than those with the lowest content. The capillary per fiber ratios were 1.11 +/- 0.07 (mean +/- S.E.) and 1.69 +/- 0.13 in the UT and ET groups, respectively. The number of capillaries around each fiber was 3.04 +/- 0.17 (UT) and 4.42 +/- 0.31 (ET). After correction for shrinkage the number of capillaries per mm2 was 301 (UT) and 404 (ET). The capillary per fiber ratio increased with increasing fiber diameter and with the content content of mitochondria.

Electron probe X-ray microanalysis of human muscle biopsies

The elemental composition of human muscle fibres have been determined by electron probe microanalysis. In order to distinguish between different types of fibres, two approaches were used. In one approach individual fibres were isolated, portions of them used for a typing by histochemical methods and the main part used for X-ray microanalysis. In the other approach the muscle biopsy was serial-sectioned, some sections used for a histochemical typing and the others (16 micrometer thick cryosections) used for X-ray microanalysis in th eelectron microscopy. The comparison of the ratios between P, S and K in Study No. 1 and 2 indicates different concentrations of sulphur in the subsarcolemmal zone and in the interior of the fibre. Both routes give information on all elements (except the ten lightest ones) contained in the fibres or in sections of them, provided the concentration is high enough. In order to obtain quantitative data, expressed as mmol/kgw, the spectra of the specimens were compared to those of standards of known composition and the data subjected to a so called ZAF-correction (corrections for the atomic number effect, absorption of X-rays in the specimen and secondary fluorescence). Quantitative data concerning phosphorus, sulphur, chlorine and potassium were obtained in Study No. 2. A significantly higher sulphur concentration was found in type IIA muscle fibres as compared to those of type I.

Activity patterns of human skeletal muscles: relation to muscle fiber type composition

The muscle activity of normal ambulatory individuals was recorded continuously for 8-hour (working day) periods. Parameters of activity patterns were defined and numerical outcomes for these parameters were compared across a diverse population of muscles. Several pattern parameters, such as the average percentage of time active, were highly correlated with the percentage of type I fibers of a muscle.

Histological patterns of muscle in infants with developmental brain abnormalities

The histology of muscle obtained from 23 hypotonic infants without neuromuscular disease is presented. Long-term follow-up neurological examinations were carried out to determine the site of the lesion. 18 cases have strong evidence of cerebral dysfunction, 12 of whom have histologial abnormalities of fiber-type distribution and diameter. Of the remaining five patients without obvious cerebral abnormality, four also had histological changes, but individual circumstances partially explain the cause of the abnormal histological patterns in these four. No single histological abnormality could be identified, but the results indicate that histological abnormalities of muscle in hypotonic infants without clinical or microscopic evidence of neuromuscular disease may be useful in predicting a cerebral cause for the hypotonia.

Histoenzymatic characterization of sub-types of type I fibres in fast muscles of rats

The histochemical activities of succinic dehydrogenase (SDH), myofibrillar Adenosine triphosphatase (ATPase) and alpha glycerophosphate dehydrogenase were studied in serial sections of rat vastus lateralis (red) (RVL), gastrocnemius and diaphragm muscles. Three main fibre-types were distinguished. The "Type I" fibres of RVL and gastrocnemius muscles fell into two distinct groups: one category--"Type IA" showed very low ATPase activity. The second category of "Type IB" fibres displayed moderate ATPase reaction. The "Type IA" fibres were divisible into two sub-groups when tested for SDH reaction. "Type IA1" fibres possessed a homogenous distribution of diformazan granules throughout the fibre: "Type IA2" fibres displayed characteristic "moth-eaten" pattern of diformazan localization. The diaphragm muscle did not show either "Type IB" or "Type IA2" varieties. The great majority of TypeI fibres were sub-type IA1 in the three fast muscles studied. It is also demonstrated here that an inherent heterogeneity exists between Type I filores of diaphragm and leg muscles in regard to alpha-GPD localization. This histochemical data emphasizes the fact that subdivision of TypeI striated muscle fibres of mammalian animals into two sub-types is only approximate and that a further subcategorization is possible.

Postnatal differentiation and growth of skeletal muscle fibres in normal and undernourished rats. A histochemical and morphometric study

The postnatal differentiation and growth patterns of the different histochemical muscle fibre types were studied at frequent age intervals in the extensor digitorum longus (EDL) muscle of normal rats and animals subjected to pre- and postnatal protein-calorie undernutrition. Three stepwise changes were seen in the fibre type composition of the EDL muscle during maturation. In newborn normal rats 2 histochemically and morphometrically distinct fibre populations occurred: small foetal type (type F) fibres or myotubes (about 90%), with the staining characteristics of the so-called type 2C fibres, and larger type 1 fibres (10%). At 5 days of age the percentage of type F fibres had dropped to 50 simultaneously with the emergence of a new population (40%) of type 2B fibres, intermediate in cross-sectional area between the remaining type F fibres and type 1 fibres. Between 15 and 20 days the small type F fibres practically disappeared with the emergence of a corresponding percentage (40%) of type 2A fibres, smaller than both type 1 and type 2B fibres; Between 20 and 60 days the percentage of type 1 rose from 10 to almost 30, type 2B fibres correspondingly diminishing in number but growing at a faster rate than either type 1 or type 2A fibres. In the undernourished rats the histochemical differentiation was retarded at birth, all fibres or myotubes being of the foetal type; However, large type 1 and type 2B fibres were seen at the age of 5 days and the histochemical maturation proceeded almost normally at later stages. On the other hand, at all ages there was a proportional reduction in the cross-sectional area of all fibre types, amounting to about 50% at 180 dyas, and not fully restituted by nutritional rehabilitation. These observations suggest that type F (type 2C) fibres are the undifferentiated precursors of all mature muscle fibres, their stepwise histochemical transformation raising the question of maturational differences in the different types of motoneurones.

Actomyosin ATPase activity of human laryngeal muscles

The muscles from seven human larynxes removed by laryngectomy have been examined for actomyosin ATPase by histochemical methods. The various muscles contained a mixture of ATPase low (type I) and ATPase high (type II) muscle fibres. The thyreoarytenoid muscle had the highest proportion of type II fibres (65%) and the posterior cricoarytenoid muscle had the highest proportion of type I fibres (67%). The other laryngeal muscles had intermediate valves. All human laryngeal muscles had a higher percetage of type I fibres than the corresponding muscles in animals so far examined, a finding which may be related to the development of speech.

Disuse atrophy of skeletal muscle. A morphometric study using image analysis

A morphometric study of disuse atrophy was done on the rat anterior tibilalis muscle over a 13-day period after immobilization of the hind leg by pinning the knee and ankle joints. Cross-sectional areas of individual muscle fibers were measured using image analysis, a new and precise technique. Three types of muscle fibers, light, medium and dark, were defined using a modified myosin-ATPase reaction on cryostat-cut sections. Each of the 3 fiber types was found to show a degree and time course of atrophy unique to itself. At the 0.01 confidence level, the dark fibers (with strongest ATPase reaction) did not shrink significantly. Both the light (ATPase negative) and medium fiber did show significant atrophy at that level; the light shrinking more than the medium. Simple visualization of the light microscopic images was often found to be misleading. Thus, the need was documented for a precise technique for analysis of fiber size distribution.

Myofibril content of histochemical fibre types in rat skeletal muscle

A modification of the histochemical method for myosin ATPase was used to determine the myofibril complement, mean myofibril size and myofibrillar packing of defined muscle fibre types in rat skeletal muscle. Fast muscle fibres (Types IIA and IIB) were found to have smaller myofibrils and a lower packing density than slower (Type I) fibres. These findings were discussed with respect to their relevance in estimations of muscle strength from histological and histochemical preparations of muscle cross-sections.

Congenital fiber type disproportion in identical twins

Eighteen-month-old identical twins with the muscle histological characteristics of congenital fiber type disproportion are reported. The fiber typing system of pH-dependent adenosine triphosphatase was used to analyze the size and percentage of type 1, 2A, and 2B fibers in muscle tissue obtained by needle biopsy. Both twins had significantly larger type 2 than type 1 fibers, with 2B fibers representing the largest type. One patient also had type 1 predominance at the expense of a reduction in 2B (2B deficiency). The probands as well as other family members had transient delayed motor development, macrocephaly, and normal intelligence. A biopsy obtained from 1 of these family members failed to demonstrate a similar histological abnormality. The disorder is nonprogressive in this family, as evidenced by minimal disability in the older members and gradual improvement in the probands.

Low intensity training, inactivity and resumed training in sedentary men

The effects of a low intensity training regimen, consisting of two 7-week periods with an interspersed 8-week inactivity period were investigated in 16 sedentary men. A follow-up was made on 7 subjects after 38 additional weeks' training. Systemic as well as local effects were studied using exercise tests and leg muscle biopsies. The two 7-week training periods both resulted in a 6% increase in Vo2 max and a lowered heart rate during submaximal work. No persisting training effects were detected by exercise tests after inactivity. In skeletal muscle, however, striking differences in enzyme activity pattern and ultrastructure were observed between the two periods, indicating that some training effect of importance for muscle metabolic adaptation might have persisted during inactivity. It is suggested that such an effect might be associated with the local oxygen supply. During the 38-week training period there was a large increase in muscle metabolic capacity, but no change in maximal oxygen uptake. This separation of systemic and local training effects indicates a lack of a direct causal relationship between muscle metabolic potential and max imal oxygen uptake. It is suggested that the elevated muscle oxidative capacity is of importance for an increased endurance capacity.

Myosin light chain patterns of individual fast and slow-twitch fibres of rabbit muscles

Single muscle fibres were isolated by microdissection from freeze-dried samples of rabbit psoas and soleus muscles. The individual fibres were typed according to qualitative histochemical reactions for succinate dehydrogenase or NADH-tetrazolium reductase and for alkaline Ca2+-activated myofibrilla myosin ATPase after acid or alkaline preincubation. Methods are described for electrophoretic analysis by means of polyacrylamide disc electrophoresis in the presence of SDS of total myofibrilla proteins in single fibres after pre-extraction of soluble proteins. Fast-twitch white fibres revealed a myosin light chain pattern characteristic of "fast- type" myosin with three light chains of apparent molecular weights of 22,300 (LC1) 18,400 (LC2) and 16,000 (LC3). Fast-twitch red fibres were indistinguishable in this respect from fast-twist white fibres and showed an identical pattern of myosin light chains. Slow-twitch fibres could be characterized by a myosin light chain pattern typical of myosin of slow-twitch muscles with peptides of the apparent molecular weights of 23,500 (LC1Sa), 23,000 (LC1Sb) and 18,500 (LS2S). Slow-twitch fibres isolated from soleus as well as from psoas muscle were indistinguishable with regard to their myosin light chain patterns, thus suggesting that fibres of the same histochemical type correspond in their myosin light chain patterns irrespective of their origin from different muscles.

A method for correlating ultrastructural and histochemical data from individual muscle fibers

The present study describes a new method making possible correlation of histochemical and ultrastructural data from identical muscle fibers. The method appears a valuable tool in studies where both light and electron microsocopy are required to obtain all necessary information.

Fiber types and metabolic potentials of skeletal muscles in sedentary man and endurance runners

This description of some of the present knowledge on skeletal muscle fibers, their metabolic potentials, and their interplay with the degree of physical activity has revealed that skeletal muscle of man has a very large capacity for adaptation. Moreover, this adaptability appears to be of utmost importance for the metabolic response as well as for performance. Although all this is true, it should not distract us from the fact that we are lacking the most important information. The questions that need to be answered are: What triggers the changes to take place? Which are the regulatory mechanisms?

Post-tetanic mechanical tension and evoked action potentials in McArdle's disease

The tension produced by the cramp evoked in the adductor pollicis muscle by repetitive stimuli to the nerve (20/s for 50 s) and by full voluntary effort in the brachial biceps was measured in a patient with McArdle's disease. The contracture was 17% of the peaktetanic tension, and was not associated with action potentials. Twitches superimposed on the contracture were at most diminished to half, as were their action potentials. Both slow and fast muscle fibres participated in the contracture. The contraction time of the twitches elicited after the tetanus was prolonged more in the patient than in a normal subject of the same age. There was evidence of delayed firing, first observed 90 seconds after the peak of the contracture. The patient had electromyographic and histological signs of myopathy.

Blood flow and uptake of glucose and amino acids in ischemic muscle

In order to examine muscle ischemia, muscle blood flow in the rat hindlimb was decreased by vessel ligation. Amino acid uptake, studied with [14C]alpha-aminoisobutyric acid, was decreased in ischemic Type I (soleus) muscle. Glucose uptake, studied with [14C]deoxyglucose, was increased in Type I muscle. These changes were temporally associated with histologic changes of ischemia in soleus muscle. Denervation, atrophy, and hypertrophy also produced uptake changes with these techniques, and although more prominent in soleus, the changes were also seen in Type II muscle.

Muscle adaptation to extreme endurance training in man

To evaluate the effect of extreme endurance training on muscle fibre composition and activities of oxidative enzymes in different fibre types biopsies were taken from vastus lateralis, gastrocnemius and deltoideus of elite orienteers. Comparisons were made between the (trained) leg muscles and the (relatively untrained) arm muscles, and with leg muscles of 16--18 years old boys. The orienteers had the same percentage type I fibres and vastus lateralis and gastrocnemius as in deltoideus, but higher percentage type I fibres in vastus lateralis compared with the controls. The similarity between trained and untrained muscle in the orienteers suggests that training had not caused the high percentage type I fibres which rather might be the result of selection of individuals with the best prerequisites for high oxidative capacity. However, the distribution of type II subgroups in the leg muscles of the orienteers differed from both their own deltoideus and leg muscles of the controls, the relationship IIA/IIB being altered in favour of the more oxidative IIA. The leg muscles of the orienteers also showed an increased occurrence of the normally IIC fibre. These latter findings point at the possibility of a training induced alteration in the subgroup pattern. Unlike in the controls there was no significant difference in succinate dehydrogenase activity, measured in single fibres, between type I and II fibres in gastrocnemius of the orienteers. Thus, type II fibres have the ability metabolically to adapt to high oxidative demands. This might to some extent be mediated by a conversion from IIB to IIA form.

Differentiation of fibres in human masseter, temporal and biceps brachii muscles. A histochemical study

Masseter, temporal and biceps brachii muscles were histochemically evaluated for fibre type differentiation on 19 aborted fetuses (gestational ages 15-23 weeks), in 2 premature infants of 34 and 36 weeks gestation and in 2 fullterm stillborn infants. There was no convincing evidence of fibre type differentiation in the masticatory muscles before 22 weeks' gestation while a fairly distinct differentiation was seen in biceps brachii specimens at 16 weeks' gestation with ATPase at pH 4.35. Around 22 weeks two types of fibre were found in all specimens with ATPase at pH 4.35. With regular ATPase (pH 9.4) there was a relatively weak difference in staining between different types of fibre in the masticatory muscles. In biceps brachii Type I and Type II were demonstrated. Neonatally 3 levels of staining were seen in biceps brachii with regular ATPase (pH 9.4); while ATPase pH 4.35 and 4.6 demonstrated the subtypes IIB and IIC. In the masticatory mucles only 2 levels were recognized with regular ATPase and all type II fibres had the characteristics of Type IIC as seen with with ATPase at pH 4.35.

The value of enzyme histochemical techniques in the classification of fibre types of human skeletal muscle. 2. The histochemical demonstration of myosin adenosine triphosphatase in skeletal muscles from adult patients with or with no diseases of the neuromuscular system. A comparison between results obtained by calcium salt and lead salt techniques

In the present investigation the results of a lead salt technique and two calcium salt techniques for the deomonstration of the activity of myosin adenosine triphosphatase in sections of both normal and pathological human skeletal muscle specimens are compared. It was seen that the histochemical results obtained by the different techniques are similar, especially with regard to the identification of fibre-types. It can be clearly stated, that the alkaline phosphatase activity present in muscle fibers of diseased skeletal msucles revealed only a very slight activity with the substrate ATP, so the alkaline phosphatase activity in general did not disturb the reliability of the different myosin ATPase techniques. Moreover it was found that the presence of the mitochondrial Ca2+ -ion activated ATPase with a high pH-optimum in muscle fibers did not give rise to faulty results. From studies with dinitrophenol it can be concluded that this substance activates the myosin ATPase present in type I fibres especially.

Fingerprint inclusions. Ultrastructural demonstration of muscle fiber type specificity

Fingerprint inclusions were identified in the skeletal muscle of a child with severe hypotonia. The mean Z-line and M-line widths from each of 19 muscle fibers containing the fingerprint inclusions were calculated. The mean Z-line widths were 85-99 nm, and the mean M-line widths were 75-101 nm. According to out present system of fiber typing, all of these fibers would be classified as Type I. The possible pathogenesis and fiber type specificity of the fingerprint inclusion is discussed.

Terminal innervation ratios and fiber type grouping in normal porcine skeletal muscle

Terminal innervation ratios were determined in normal porcine semiendinosus to test the hypothesis that intramuscular collateral branching of subterminal axons gives rise to fiber type grouping. Innervation ratios were near 1.00 in both the lateral pale portion which exhibits type II predominance and in the medial red portion which exhibits extensive grouping of type I fibers. Type grouping observed in porcine skeletal muscle is not the result of multi-fiber innervation by subterminal axons, but, rather, may be the manifestation of a unique motor unit topography.

A comparative histochemical study of the masseter muscle of the cattle, sheep, swine, dog, guinea pig, and rat

The masseter muscles of different mammals were studied by means of hisotchemical reactions: NADH: Nitro BT oxidoreductase (NADHOX), 3-hydroxybutyrate: NAD+ oxidoreductase (HBOX), glycerol-3-phosphate: menadione oxidoreductase (GPOX), and acid-stable and alkali-stable myosin adenosine triphosphatase (ATPase). The masseter mucles of cattle and sheep consisted only of the fibres that reacted moderately for GPOX and strongly for NADHOX, HBOX, and the acid-stable ATPase. The masseter fibres of rats and guinea pigs reacted uniformly and strongly for GPOX and the alkali-stable ATPase. The fibres of the rats showed a weak to strong reaction for NADHOX and mostly a negative reaction for HBOX, whereas those of the guinea pigs reacted uniformly and strongly for NADHOX and HBOX.The masseter fibres of swine and dogs showed a weak or strong reaction for the alkali-stable and a negative or weak reation for HBOX. The fibres of the swine were weak to strong in NADHOX activity and those of the dogs uniformly strong; the fibres of the two species gave a moderate to strong reaction for GPOX. The masseter fibres of the ruminant differed from those of the other species in histochemical properties, and appeared to have the histochemical characteristics that meed functional demands for slow, long-term exercise.

The effects of experimental denervation and reinnervation on skeletal muscle fiber type and intramuscular innervation

Porcine muscle has a unique grouped arrangement with 3-70 Type I fibers occurring in clusters surrounded by Type II fibers. The deep medial portion of the porcine semitendinosus exhibits a regular pattern of extensive Type I grouping whereas the superficial or lateral portion of the muscle exhibits Type II predominance. Mean values for terminal innervation ratios were 1.00 +/- 0.01 and 1.02 +/- 0.01 in normal superficial and deep semitendinosus respectively. Subterminal axons, therefore, do not branch intramuscularly and innervate only one muscle fiber in normal porcine muscle. Following nerve crush and subsequent reinnervation, fiber type conversion occurred which resulted in a fiber type grouping pattern dissimilar to the normal grouped arrangement. Significantly (P less than 0.01) elevated terminal innervation ratios (1.45-2.15) were measured in reinnervated muscle as a result of extensive branching of subterminal axons, but the percentage of Type I and Type II muscle fibers was unchanged. It was concluded that: (1) nerve crush causes distal nerve degeneration, loss of the normal fiber type pattern, and extensive collateral ramification of subterminal axons; (2) collateral reinnervation imposes a neuronal influence on muscle fibers which dictates transformation of all muscle fibers innervated by a single subterminal axon to a uniform histochemical profile; and (3) the type grouping observed in normal porcine muscle is not a result of neuronal influence mediated by collateral branching of subterminal axons.

[Histochemical, quantitative and ultrastructural maturation of human fetal muscle]

Histochemical studies of muscle specimens from human fetuses showed: (a) a uniform fiber type population having the properties of Type IIC fibres up to 19 weeks of development; (b) a progressive appearance of Type I fibres after that age; (c) a decrease in number of Type IIC fibres during the last 3 months of pregnancy, accompanied by the appearance of Type IIB and Type IIA fibres; (d) the presence after the myotube stage of fibers with a light peripheral halo in sections stained for mitochondrial dehydrogenases. Electron-microscopic examination of the muscle fibres confirmed the existence of a peripheral halo devoid of myofibrils and mitochondria and showed: (a) scarcity of myofibrils in comparison with mature muscle fibres and (b) irregularity in shape of the myofibrils. In addition, quantitative studies demonstrated an important variation of the fibre diameters up to 21 weeks and the increase of the mean diameter after this age. It is suggested that the persistence after birth of some features of immaturity identical to those described in this work may be considered as a pathological finding.

Electrical and mechanical responses in the platysma and in the adductor pollicis muscle: in normal subjects

In the platysma of 34 normal subjects the amplitude of the action potential and twitch tension and tetanic tension were lower, the contraction time of the isometric twitch was 1.4 times shorter, and the potentiation of twitch tension in a staircase and after tetanus was two to four times greater than in m. adductor pollicis. Differences in twitch kinetics and potentiation were related to the four times higher incidence of fast fibres in the platysma than in the adductor pollicis muscle, as determined by histochemistry. Ninety-five per cent confidence limits were established for comparison with patients with myasthenia gravis.

Contractile and histochemical properties of the inferior oblique muscle in the rat and in the cat

Mechanical and histochemical properties of inferior oblique muscles(IO) were compared in adult albino rat and pigmented cat. The twitch contraction times and the fusion frequencies were about the same in both species indicating similar contractile properties of the fast contracting fibers. Rat IO seemed to contain fewer slowly contracting fibers than cat IO; half-decay time of the twitch was shorter in rat than in cat muscles and fusion started at higher stimulus frequencies. Fatique resistance was lower in rat than in rat than in cat. Post-tetanic potentiation occurred in the cat but not in the rat IO. Almost all fibers of rat IO were rich in myofibrillar ATPase. In cat IO most fibers showed high myofibrillar ATPase activity, but some fibers in the global layer had moderate to small amounts of this enzyme. This correlates well with the physiological differencies between cat and rat IO.

Muscle structure and function in the goose, quail, pheasant, guinea hen, and chicken

1. Metabolic functions, fiber composition and, in some cases, mitochondrial morphology have been investigated in the pectoralis major and sartorius of the goose, quail, pheasant, guinea-hen, broiler chicken and laying hen. 2. In the pectoralis only two types of fibers, red and white twitch fibers, are found in all birds studied except in the quail, where a third twitch fiber also occurs. Red fibers form the main part in the quail and goose, white fibers in the rest. In the sartorius at least three types of fibers, two twitch and one tonus are found in all birds except in the guinea-hen where only two fibers can be found. 3. The metabolic pattern of the muscles, based on determination of specific activities of metabolic key enzymes, varies greatly among the birds. Three groups can be discerned from the ratio between aerobic and anaerobic activities or between fatty acid oxidation and carbohydrate metabolism. The metabolic patterns are reflected in the fiber combinations of the muscles. 4. The size and number of the mitochondria vary among different animals and different fiber types. The metabolism of red and white fibers is discussed.

Histochemical sub-types of three fibre-types of avian skeletal muscle

The soleus muscle of adult chicken was studied histochemically. Succinic dehydrogenase (SDH) and myofibrillar ATPase reactions, with or without preincubation in K2-EDTA salt, were compared in serial frozen sections. Based upon the distributions of the above reactions, the three major fibre types distinguished were "Type I red", "Type II red" and "Type II white". On the basis of non preincubated ATPase reaction alone two sub-types of type I red fibres could be distinguished. However, following preincubation in a "Cold" solution of K2-EDTA, Type II red fibres fell into two sub-types and Type II white fibres fell into three sub-types. Amalgamating the two already existing classifications, a more elaborate classification is presented for characterizing these different sub-types. The presence of two different or a spectrum of staining variations in a seemingly homogeneous population of muscle fibres in a given fibre-type emphasizes the possible correlation between this histochemical data and the heterogeneity of contraction times of the different motor units.

Spinal muscle in scoliosis. Part 2. The proportion and size of type 1 and type 2 skeletal muscle fibres measured using a computer-controlled microscope

The development of the computer-controlled microscope system described has made it possible to estimate accurately the contribution made to the muscle fibre population by both Type 1 and Type 2 fibres. This method is more convenient, and at least as accurate as manual methods. It is also possible to measure the size of the individual fibres using this system. The system has been applied to this study of the spinal muscles in scoliosis. The results show that there is a difference in the ratio of Type 1 to Type 2 fibres in the spinal muscles on the 2 sides of the curve. The difference is found only at the apex of the curve. The results demonstrate that there are more Type 2 fibres on the concavity of the curve at the level of the apex. This difference is due to a disparity in the number of each fibre type rather than a difference in their relative sizes. The imbalance of Type 1 fibres at the apex of the curve may provide a sustained muscle pull on the spine so causing a curve convex to that side.

The histochemical profile of the human masseter. An autopsy and biopsy study

A histochemical study has been carried out upon samples of muscle obtained from the human masseter. Sixteen specimens obtained either at autopsy or biopsy have shown that the middle and deep portions of the muscle contain fibres which in their size, histochemical staining properties and number correspond to the appearances noted in most human limb skeletal muscles. By contrast, samples taken from the superficial portion of the masseter demonstrated several unusual characteristics: these included a striking inequality of muscle fibre size in that the Type II fibres were much smaller than those of Type I but exceeded the latter in total number. This part of the muscle also contained, in 6 out of 10 samples, substantial numbers of intermediate fibres identified by myofibrillar ATPase staining. This study has confirmed that the superficial part of the human masseter is different morphologically and presumably functionally from the middle and deep parts of the muscle.

Concentric laminated bodies. Ultrastructural demonstration of muscle fiber type specificity

Concentric laminated bodies were identified in the skeletal muscle of 3 children affected by muscle weakness and hypotonia with probable cerebral involvement. The mean Z-line and M-line widths from each of 11 muscle fibers containing the concentric laminated bodies were calculated. The mean Z-line widths were 61-81 nm and the mean M-line widths from 7 out of 11 fibers were 54-65 nm. According to our present system of fiber typing, the majority of these fibers would be classified as subtype IIB. The possible pathogenesis and fiber type specificity of the concentric laminated body is discussed.

Muscle pathology of myotonia congenita

We have investigated the muscle biopsies of 8 patients with myotonia congenita. There were 2 families with autosomal recessive inheritance (5 cases), 1 with autosomal dominant inheritance, and 2 sporadic cases. Mild abnormalities were seen with routine pathological preparations which were nondiagnostic. Histochemical studies of fiber subtypes demonstrated a complete absence of Type 2B muscle fibers in all of our patients regardless of the type of inheritance. this is the first reporot of an entity in which there is a consistent absence of a muscle fiber type, and some speculation has been made as to the possible causes.

Skeletal muscle fiber types in the adult mouse

The ATPase reaction and its pH lability demonstrate three fiber types in the adult mouse gastrocnemius; Type I (light staining with alkaline preincubation and dark with acid preincubation), Type IIA (dark after alkaline preincubation), type IIB (dark after alkaline and acid preincubation). The SDH and NADH-tetrazolium reductase reactions also demonstrate three types of fibers; those low (A), intermediate (B) or high (C) in oxidative enzyme activity. However, the use of both procedures in serial sections demonstrates that four different combinations occur; the IIB fibers are high in SDH activity, the I fibers are intermediate in SDH enzyme activity, while the IIA fibers are either low or intermediate in SDH activity. These fiber types are present within the gastrocnemius muscle in a distinct pattern of zones. The predominant fiber type, located in the superficial half of the muscle, is the IIA (A) fiber which is high in ATPase and low in SDH activity. This is consistent with the fact that the gastrocnemius is generally considered a white, fast muscle. The IIB and I fibers are fewer in number and are located deeper in the muscle.

The symptomatology, morphology and biochemistry of glycogenosis type II (Pompe) in the adult

The mild, generalized myopathy (glycogenosis type II) of a 23-year-old male, previously thought to have progressive muscular dystrophy, was studied clinically, electro-myographically, biochemically and with light- and electron microscopes. However, the history and clinical aspects, as well as the registration of high frequency discharges in the electromyogram first made the diagnosis uncertain. This kind of spontaneous activity has been found in nearly all cases reported in the literature. Light microscopic and histochemical examinations show vacular degeneration and glycogen storage in muscle fibres. With the electron microscope we found free dispersed glycogen in the cytoplasm and membrane-bound glycogen, glycogen-filled lysosomes. Biochemical measurements of the muscle enzymes, involved in the glycogen breakdown, were normal except for acid alpha-1,4-glucosidase, which was deficient. The evidence of these findings in this abortive form of glycogenosis type II is discussed and compared with the few cases found in the literature.

Human muscle fiber types in power lifters, distance runners and untrained subjects

Muscle biopsies were taken from the vastus lateralis of 12 males: 5 control subjects, 4 power lifters and 3 distance runners. Three fiber "types" were distinguished by comparing serial sections for alkaline myofibrillar adenosine triphosphatase (ATPase) and succinic dehydrogenase (SDH) activities: 1. high ATPase and low SDH; fast-twitch-glycolytic (FG). 2. High ATPase and high SDH; fast-twitch-oxidative-glycolytic (FOG). 3. Low ATPase and high SDH; slow-twitch-oxidative (SO). In some cases the distinction between the FOG and FG classess was not clear and a group termed "transitional" was employed. A variation in percentage of fiber types and fiber area was found among individuals. The percentage of SO fibers varied from 19.6-60.1% within all 3 groups, with a mean of 40.5%. In the control group approximately 75% of the fibers were oxidative (FOG + SO). The major characteristics of the lifters were a decrease in the percentage of FOG fibers and a hypertrophy of FOG and FG fibers. The distance runners had a high percentage of oxidative fibers with few FG fibers. It is suggested that the fast-twitch fibers are mainly involved in the adaptation of muscle to exercise since the percentage of SO fibers varies greatly among individuals within and between the 3 groups studied.

Intrafusal fibre types in rat limb muscle spindles: morphological and histochemical characteristics

Morphological, histochemical and ultrastructural characteristics of intrafusal fibre types were studied in rat muscle spindles. The existence of three intrafusal fibre types, namely the typical bag, the intermediate bag and the chain fibres was confirmed. Intrafusal fibres differ in diameter, length and number of nuclei in the equatorial zone. Histochemically, typical bag fibres exhibit both alkali- and acid-stable ATPase activity and low SDH activity. Intermediate bag fibres possess low alkali-stable ATPase activity; after acid-preincubation, however, they have low activity only in the juxtaequatorial region, whereas in the polar zones they exhibit high acid-stable ATPase activity. The SDH activity varies from moderate to high. The chain fibres exhibit high alkali-stable and low acid-stable ATPase and high SDH activity in the extensor digitorum longus muscle, whereas in the soleus muscle the acid-stable ATPase activity varies from a low one to a high one, either among individual chain fibres in one spindle, and/or repeatedly along the fibre length. Since there are regional differences in morphological characteristics and in staining properties of intrafusal fibres, a reliable identification of intrafusal fibre types can only be achieved by an analysis of serial sections.

Adaptive transformation of rat soleus motor units during growth

Soleus motor units of 5 and 34 week-old rats, weighing 150 and 520 g respectively, were examined for contraction time at 36 degrees C, innervation ratio as well as cross-sectional area, ATPase and SDH activity of fibres. The muscle was continuously adjusted to the growth of the animal. Between 5 and 34 weeks the proportion of Type II fibre units with 15-26 msec contraction time decreased from 33% to 10% and Type I fibre units with 27-40 msec contraction time thus increased from 67 to 90%. This was parallelled by approximately the same relative changes in number of Type II and Type I fibres.

Luft's disease. Further biochemical and ultrastructural studies of skeletal muscle in the second case

In the second known case of non-thyroidal hypermetabolism (Luft's disease), there were large areas of mitochondrial aggregates in all fibers. Many mitochondria were abnormally large and contained packed cristae. In isolated mitochondrial fractions, studies of oxidative phosphorylation showed defective respiratory control and normal phosphorylation capacity ("loose coupling"). Spectra and content of cytochromes were normal. Basal ATPase activity was seven times greater than normal and poorly stimulated by 2,4-dinitrophenol. The rate of energy-dependent calcium uptake by isolated mitochondria was normal, but the amount of calcium accumulated was much decreased. Calcium could not be retained and was spontaneously released into the medium within 30 seconds. "Recycling" of calcium between mitochondria and cytosol may take place in vivo and result in sustained stimulation of respiration and loose coupling.

Changes in muscle fibre size and physical performance in patients with rheumatoid arthritis after short-term physical training

Ten patients with rheumatoid arthritis of moderate severity were given 6 weeks' intense physical training. During the investigation period the patients improved their physical performance capacity as well as their rate of perceived exertion. There was an increase in the muscle fibre size, of type I and type II, most pronounced in the latter fibre group. No 'flare-up' of the arthritis could be seen during the training period. Comments are made as to which patients might benefit by a short-term physical training.

Changes in muscle fibre size and physical performance in patients with rheumatoid arthritis after 7 months physical training

Ten patients with rheumatoid arthritis of moderate severity were given 7 months' physical training. During the investigation period the patiens improved their physical performance capacity as well as they lowered their rate of perceived exertion during submaximum exercise. There was a small increase in muscle fibre size and a correlation was found between muscle strength and type II fibre size. Clinical examination and X-ray studies did not reveal any further joint destruction during the investigation period.

Needle biopsies of muscle in infants for diagnosis and research

The results of needle biopsies of muscle in 14 infants (age-range four months to 3 years 3 months) with marked hypotonia are presented. In adults, needle biopsies of muscle have been used to aid in the diagnosis of neuromuscular disorders, with considerable success. The simplicity of the method and the high quality of the samples obtained in the present study suggest that further evaluation of the technique in infants and small children is warranted, and that needle biopsy may in future take precedence over the more commonly used open technique.

Histochemical and histopathological changes in skeletal muscle in late-onset hereditary distal myopathy (Welander)

Histochemical and histopathological staining methods were applied to muscle biopsy material from 13 patients with distal myopathy of late onset. Six cases showed slight to moderate histopathological changes and the normal distinction between Type I and Type II muscle fibres, based on their staining characteristics for myofibrillar ATPase, was well preserved. A selective Type I atrophy and an irregular distribution of oxidative enzyme and fat staining in Type I fibres were evident. In the other 7 cases, with moderate to advanced histopathological changes, there was a marked blurring of the normal difference observed in ATPase activity between Type I and TYpe II fibres. Thus, both types of fibre exhibited a high intensity of staining for myofibrillar ATPase at pH 9.4 without inhibition by acid preincubation (pH 4.3). These changes in phosphatase activity were found not only in atrophic fibres but also in normal-sized fibres without other signs of degeneration. Nuclear proliferation in chains and "ring fibres" were found. The early histopathological and histochemical changes in distal myopathy are strikingly similar to those of myotonic dystrophy.